inverter - How an Inverter Functions, How to Repair Inverters - General Tips

How an Inverter Functions, How to Repair Inverters – General Tips

In this post we will try to learn how to diagnose and repair an inverter, by comprehensively learning the various stages of an inverter, and how a basic inverter functions.

Before we discuss how to repair an inverter it would be important for you to first get fully informed regarding how does an inverter worka. The following content walks you through both the aspects which can prove very useful to any electronic technician.

Stages of an Inverter

As the name suggests DC to AC inverter is an electronic device which is able to convert a DC potential normally derived from a lead-acid battery into a stepped-up AC potential which may be quite comparable to the voltage that is found in our domestic AC Mains outlets.

Repairing sophisticated inverters are not easy due to their many involved complex stages and requires expertise in the field. Inverters which provide sine wave outputs or the ones which use PWM technology to generate modified sine wave can be difficult to diagnose and troubleshoot for the folks who are relatively new to electronics.

However, simpler inverter designs that involve basic operating principles can be repaired even by a person who is not specifically an expert with electronics.

Before we move into the fault finding details it would be important to discuss how does an inverter work and the different stages normally an inverter may comprise:

An inverter in its most basic form may be divided into three fundamental stages viz. oscillator, driver and the transformer output stage.


This stage is basically responsible for the generation of oscillating pulses either through an IC circuit or a transistorized circuit.

These oscillations are basically the productions of alternate battery positive and negative (ground) voltage peaks with a particular specified frequency (number of positive peaks per second.) Such oscillations are generally in the form of square pillars and are termed as square waves, and the inverters operating with such oscillators are called square wave inverters.

The above generated square wave pulses though are too weak and can never be utilized to drive high current output transformers. Therefore these pulses are fed to the next amplifier stage for the required task.

For info on Inverter oscillators you can also refer to the complete tutorial which explains how to design an Inverter from the scratch


Booster or Amplifier (Driver):

Here the received oscillating frequency is suitably amplified to high current levels using either power transistors or Mosfets.

Though the boosted response is an AC, but is still at the battery supply voltage level and therefore cannot be used to operate electrical appliances which work at higher voltage AC potentials.

The amplified voltage is therefore finally applied to the output transformer secondary winding.

Output Power Transformer:

We all know how a transformer works; in AC/DC power supplies it is normally used to step-down the applied input mains AC to the lower specified AC levels through magnetic induction of its two windings.

In inverters a transformer is used for similar purpose but with just opposite orientation, i.e. here the low level AC from the above discussed electronic stages is applied to the secondary windings resulting in an induced stepped up voltage across the primary winding of the transformer.

This voltage is finally utilized for powering the various household electrical gadgets like lights, fans, mixers, soldering irons etc.

"You may also want to learn how to design an Inverter Transformer"


inverter 1 - How an Inverter Functions, How to Repair Inverters - General Tips


Basic Principle of Operation of an Inverter

The above diagram shows the most fundamental design of an inverter, the working principle becomes the back bone for all conventional inverter designs, from the simplest to the most sophisticated ones.

The functioning of the shown design may be understood from the following points:

1) The positive from the battery powers the oscillator IC (Vcc pin), and also the center tap of the transformer.

2) The oscillator IC when powered starts producing alternately switching Hi/lo pulses across its output pins PinA and PinB, at some given frequency rate, mostly at 50Hz, or 60Hz depending as per the country specs.

3) These pinouts can be seen connected with the relevant power devices #1, and #2, which could be mosfets or power BJTs.

3) At any instant when PinA is high, and PinB is low, the Power Device#1 is in the conducting mode, while Power Device#2 is held switched OFF.

4) This situation connects the upper tap of the transformer to ground via the power device#1, which in turn causes the battery positive to pass through upper half of the transformer, energizing this section of the transformer.

5) Identically, in the next instant when the pinB is high and PinA is low, the lower primary winding of the transformer becomes activated.

6) This cycle repeats continuously causing a push-pull high current conduction across the two halves of the transformer winding.

7) The above action within the transformer secondary causes an equivalent amount of voltage and current to switch across the secondary by means of magnetic induction, resulting in the production of the required 220V or the 120V AC across the secondary winding of the transformer, as indicated in the diagram.


DC to AC Inverter, Repairing Tips

In the above explanation a couple of things become very critical for obtaining correct results from an inverter.

1) First, the generation of the oscillations, due to which the power mosfets are triggered and the process of voltage induction is able to take place across the winding of the transformer.

2) The second important factor is the frequency of the oscillations, which is fixed as per the country’s specifications, for example countries that supply 230 V, generally have a working frequency of 50 Hz, in other countries where 120 V is specified mostly work at 60 Hz frequency.

3) Sophisticated electronic gadgets like TV sets, DVD players, computers etc. are never recommended to be operated with square wave inverters. The sharp rise and fall of the square waves are just not suitable for such applications.

4) However there are ways through more complex electronic circuits for modifying the square waves so that they become more favorable with the above discussed electronic equipment.

Inverters using further complex circuits are able to produce waveforms almost identical to the waveforms available at our domestic mains AC outlets.

How to Repair an Inverter

Once you get well versed with the different stages normally incorporated in an inverter unit as explained above, troubleshooting becomes relatively easy. The following tips will illustrate how to repair DC to AC inverter:

Inverter is “Dead”:

Check battery voltage and connection, check for a blown fuse. If that’s OK, open the inverter outer cover and do the following steps:

1) Locate the oscillator section; disconnect its output from its preceding stage and using a frequency meter confirm its proper working. No frequency or a stable DC indicates a possible fault with the stage. Check its IC and the associated components for the remedy.

2) In case you find the oscillator stage working fine, go for the next stage i.e. the current amplifier stage (power mosfet). Check each device using a digital multimeter. Remember that you may have to completely remove the mosfet or the BJT from the board while testing them with your DMM. If you find a particular device to be faulty, replace it with a new one, and check the response by switching ON the inverter.

3) Sometimes transformers also become the major cause for a malfunction. You can check for an open winding or a loose internal connection in the associated transformer. If you find it to be suspicious, immediately change it with a new one.

Although it won't be that easy to learn everything about how to repair DC to AC inverter from this chapter itself, but definitely things will start "cooking" as you delve into the procedure through relentless practice, and some trial and error.

Still have doubts...feel free to post your specific questions here.

359 thoughts on “How an Inverter Functions, How to Repair Inverters – General Tips

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. i get 240volts at d transformer output at 13 volts but when i plug my t.v (79watts) d volt drops to 201volt with a bulb of 60watts it drops again to using 4 mosfet(irfp250) 2 in parallel with 1000watts tranformer

    • 88 AH is OK, I will need to see the circuit diagram, without seeing I cannot diagnose the problem.

      Probably you will need to connect more mosfets in parallel for pulling the power to higher levels.

    • Increase the mosfet gate resistor values, connect a couple of more mosfets in parallel, I hope you know how to connect them in parallel.
      Each mosfet should have its own individual gate resistor.
      Mount all of them on large heatsinks.
      For safety use separate heatsinks for each mosfet.


  3. Good day,

    I would like to make an efficient automatic relay switch between 220V AC main and 220V AC inverter out, can you help me out? I have experimentally made relay connections already but I think its not efficient coz my relay is always on at standby. The relay is directly supplied by 220v ac main or 12v dc from 220v ac main which uses NC pin for 220v inverter output, NO for 220v main and COMM pin for UPS final output. But I was thinking that I misused the relay by letting it ON 24/7. I was thinking that it would be better that the car battery will power the relay when the 220v ac main is lost. A simple transistor circuit might be able to do this job but I dont know how to make it coz I haven't studied electronics.

    I hope you can help me out.


    I have made an automatic car batter charger using your simple two transistor circuit with relay. It works well.

    • I guess you used the battery charger DC output for powering the relay, that is why the relay never switches off because it is always getting the power from the battery and also from the mains DC when 220 v is present.
      In that case just use two diodes, and connect them in the following manner.

      join the anode of the two diodes together and connect the cathode of one diode to the relay and the other diodes cathode to the battery positive, in this way only the mains 12v DC will reach the relay and the battery DC will remain blocked.
      The relay will be on only when mains 220V is present and will switch off when 220V power fails.
      I hope you got the point.


    • Thanks for the reply, I would like to have the relay that is switched off when the 220V AC mains is present and will turn off if the 220V AC mains is lost taking its power from the battery.

      Kindly confirm this diagram:

      I found just now please advice me if I'm correct with me understanding, that when the input voltage of 4Vdc or greater is lost it will trigger to turn on the relay taking its power from power supply, in my case battery. I'll just put a small transformer to supply the circuit input of 4VDC and up.


    • The diagram is OK but unnecessarily complicated, why would you need an extra transistor stage when the relay can be directly driven from the power supply itself.

      Using battery for driving the relay will unnecessarily waste some battery power.

      It's your wish you can use the shown circuit, technically it's OK.


    • Good day,

      I'm a little confused about the two diode connection, please enlighten me.

      I also tried that circuit in the link but it doesn't work as described in its description.

      as described:
      "The following circuit will allow you to drive a 12V relay using logic voltage (an input of 4V or greater will trip the relay)"

      in my understanding, the relay will turn off if there is a supply of 4V in the input, but as I have made, the relay is ON when 4V is present and OFF when lost.

      What I'm looking is the circuit that will turn off the relay when there is an input of 4V and UP (from 220V AC main), taking its power from the battery. In this case the relay will remain cool during a long period of normal power condition.

      But in the case that what I'm looking for is not possible, I just want to ask if it is ok for the relay to be remained ON 24/7? Because I observe its hot.

      Thank you very much.

    • You would either require one more transistor to revert the actions or simply replace the NPN transistor in the circuit with a PNP one.
      Use a BC557 in place of the exixting 2N3904 transistor and do the connections exactly as suggested below:
      Keep the 2.2K resistor as it is.
      Remove the 4.7K resistor, it's not required.
      Connect the emitter of the transistor to the POSITIVE of the battery.
      Connect the relay coil across the collector of the transistor and NEGATIVE of the battery.
      CONNECT A DIODE ACROSS THE RELAY COIL, WITH ITS CATHODE CONNECTED TO THE COLLECTOR AND ANODE TO THE GROUND. The diode protects the transistor from the generated back emfs from the relay coil.
      The other diode is not required.
      Connect the battery negative with the ground of the circuit.
      Now as long as a POSITIVE (from the power supply) is applied directly across the base of the transistor and ground, the transistor remains shut off, the moment the POSITIVE supply is removed the transistor gets biased through the 2.2K resistor and activates the relay.


    • Great! you interpreted my explanation correctly. I'll publish this video in the article "how to make a relay driver stage"

      If you could tell your good name to me, I would like to include it there.


  4. My inverter keeps burning down two transistors H1061, it's an inverter of 500W, with 12 transistors 2N3055, and 4 9013 or so, my question would be: what with I should replace these H1061? Thanx in advance

  5. How did you connect the FETs (tell me the connections)? Do you have the flyback diodes in place? Were these mosfets already present with the inverter or are you trying to modify the inverter using them??

  6. H1061 are not FETs, they are "TRIPLE DIFFUSED SILICON NPN TRANSISTOR", the flyback diodes are in place, the H1061 are already present with the inverter, not trying to modify the inverter. anyway thanks for reply and for your time.

  7. hello sir /bro this mohammed azmir im doing bussiness in inverters and batteries i have small query please solve !! now trend is going to solar inverters and solar battery is it charge in climate 25degres if climate is cool pannels are charge too batery

    • Hello Muhammed,

      It's true, at lower temperatures solar panels work more efficiently and generate more current, however if a good charger/controller is utilized the excess current won't affect the battery.

  8. Hello Swagatam,
    Thank you for endeavoring to answers everyone's questions here. I am using an inverter off-grid which is the only source of electricity where I am in West Africa. I have a Chicago Electric 1500 Watt 115 V, 60 Hz inverter. It worked great for a couple years and whenever I measured its output voltage with my multimeter, it was around 105 volts. (I assume this was due to the slightly lower peak voltage of the modified square wave it puts out.)
    Recently, and suddenly, it started putting out about 180 volts. Fortunately, my CFL bulbs did not explode the first time I realized this (I noticed something was wrong when I put on a fan and it started spinning much faster than usual), but I am afraid to damage 120 volt equipment with the high output voltage, and so I have attached a step-down transformer for now (this gives me 90 volts which lights up the CFL bulbs, but the fans run slow, and TV and stereo don't come on at all). Obviously, what I would really like to do is fix the inverter so that it puts out 115 volts again! Any ideas what the problem could be?

    Thanks in advance

    • Hello Vedicaudio,

      Your inverter requires immediate attention because the fault is serious. I think the PWM section of your inverter might have stopped working.

      It would be better to get it repaired instead of using it in this abnormal conditions.

      Only an experienced technician would be able to diagnose the fault because all inverters employ slightly different topology and configurations.


  9. Am through with the inverter, so how can i know the size of transformer and battery to use. and how to calculate this with the applied load to enable it last for a long time. thanks

  10. HI I have a 2.5kw inverter supplied by 24 2 volts batteries and charged by solar panel. my system is 24 volts and I am in Spain. I use the system to run my pool motor. My problem is that the inverter is giving me 270 volts and that has burned my pool motor? DO you think that a the inverter can be adjusted down or could it be because I dont have the batteries and the inverter grounded…? any help would be appreciated. thanks

    • Hi, the problem has nothing to do with grounding, may be it doesn't have an output regulation facility or may be it's not working.

      There's nothing manually you can do about it.

      one method would be to decrease the battery voltage to 20V to 22V, that would proportionately produce a lower voltage at the output

  11. hi,i have a 1000watt inverter,it powers up,the fan comes on,usb output ok but no 240v,the fuse had blown at the back but no improvement once replaced.any ideas,thanks paul.

  12. Hi,

    I have a question, I have a 600w inverter that seems to have developed a fault. The inverter is only used to power a handful of powersaver bulbs in my house when the power goes out using a 12v car battery. On my last use when normal power returned to the house I switched off the inverter from the built in switch on the inverter and then went and switched on the mains for the house. The input power was still connected to the inverter. I use a 3pin plug on each end and connect 1 end to my interter and the 2nd to a wall socket in my house. When I swithed on the main switch it tripped the trip switch in the house and I think the inverter got damaged as well. Now when I connect my inverter to my 12v battery I get a continuous buzzing sound coming from the inverter like the input power is low, even with nothing connected to the output of the inverter. I just wanted to know what could have possibly blown. The fuses are ok and when opened nothing seems to have been burnt or blown visually.


    • Hi,

      without a proper schematic it would be difficult to correctly understand the mentioned connections, if you can provide a complete drawing then probably I can trace out if anything's blown inside.

  13. i have an Inverx 650 VA inverter overload at no load mistake the phase output line connected to input phase supply after that the mosfet IRF 740 fleshed away after changing them only two were short circuited the inverter goes to permanently overloading at no load with red light i have no diagram for refernce.replacing the whole line Mosfet's in parallel or something else.

  14. Greetings Swagatam,
    My inverter has burned up a capacitor and the board specifies a different cap than the original, should I change the cap to the requirement printed on the board or just us the same original was 250V 470uf board has 450V 330 uf printed on it in this location

  15. Hello,
    I have a Go Power 1500 inverter and was using 4 – 6v AGM batteries to power the RV. The inverter when turned on goes into it's start up procedure and when finished it goes immediately into overload. I installed 4 new (same) batteries and it continues to do the same thing.

    I disconnected the inverter when the issue first happened and the batteries swelled and started smelling so I removed those too.

    Is there a component inside the inverter that would make the inverter revert to overload even with brand new batteries and everything else is fine?
    No tripped GFCI, or inline fuses blown etc.

    I didn't open the cover and inspect for any burnt components yet and the inverter itself doesn't smell like a capacitor etc. has burned.
    Is there anywhere that repairs these as Go Power doesn't repair their units so, I was forced to buy another inverter!

    Thanks in advance.

    • An overload situation might occur only under two conditions, if the connected battery voltage is much higher than the specified limits, or if the output load exceeds its predetermined level.

      As long as the battery voltage is correct and output is not over loaded, even 100s of batteries connected in parallel wouldn't cause any issues or tripping.

      So, there's certainly some other serious issue with your inverter, not something which you can diagnose at home.

    • Ok, understood on the non home diagnosis of the unit. Where can I send it for repairs and what is the labor charge usually to repair it? I realize parts would be a cost too.

      Go Power doesn't repair their own units as mentioned prior.

      Thanks in advance.

  16. Hello Swagatam, I damaged. I mistakenly connected mains to the output terminal of my inverter.It stopped working with fault alarm indication on its LCD. What are the likely components that could be damaged?. It is transformer type inverter.

  17. Hi Swagatam. My 5000W 12V to 230V PSW inverter's fan speeds up as the temperature of the unit rises (or as the amp draw increases, not sure which is the case). At lower speeds it will slow down as load or temp decreases, but if it reaches top speed, it gets "stuck" there and never returns, running at high speed, unless the unit is shut down and powered up again. How can I fix this to have it always return to lower speeds when it cools down?

    • Hi Andries, it will be difficult to diagnose because different models have different circuit topologies, and configurations, which are unique to those models, so it's not possible to troubleshoot without practically seeing it.

  18. Hi, i have a 2500 watt 12volt/240volt inverter, on the same system i also have a generator which takes over when the batteries are low. I have 2 rotatry switches operating the electric, however as expected i turn the generator power while the inverter power was also live thus putting 240 volt power to the 240 volt supply from the inverter.
    This tripped the breaker on the generator and although i have reset that the inverter now does not work.
    It has illuminations lights on it, it makes a pulsing noise and there is a slight smell of burning although the fan still works.
    What do you think? (not of me lol but of the inverter please)!!

    • Hi, although im not very sure, if the smell is from the inverter while it's in switched ON positioned would certainly indicate a damaged tramsformer winding, but if it's happening in OFF position then it would need some investigation to see exactly what's burning (lol)….most probably it's the inverter winding that might have gotten slightly damaged due to the generator voltage in-surge.

  19. I have in the motorhome a 1000 W 12v to 220V (240) inverter which produces no more than AC 200 V from the 85 Ah leisure battery. On the engine switched on it goes down to even 183 V. Please advice what could be an issue

    • your batteries could be producing lower than optimal voltage or may be are not fully charged.

      you could try verifying the same by replacing them with new batteries.

  20. My issue with a ready-made inverter is not considered here. From the beginning, this inverter worked fine for charging, but always made capacitive-input devices behave erratically when plugged in. The trackpad on the laptop doesn't move the pointer on the screen properly, and has a lot of jitter. Problem disappears when the device is unplugged from inverter. And perhaps more dangerously, a particular USB charger plugged in the 120V outlet (I know it's an inefficient use of the inverter 😉 gave me a discharge from touching the metal case of the tablet. This charger doesn't have any issue when plugged in at home, even though the mains is ungrounded. Maybe it was the charger or simply static electricity build-up on me from repeatedly moving to and from the driver's seat.

    Still, how would I know what could be at fault in this case? I have no oscilloscope to verify the waveform or possible spikes, though I'll see if I can build a USB one.

    • Selim, are you sure the inverter is generating the correct RMS voltage? you can confirm it by checking the output voltage with a multimeter set at AC 250V range.

      If it shows over 150V, the high voltage could be causing the issues.

      Or it may be due to the high amount of harmonics from the inverter.

      Try adding a 0.22uF/400V capacitor right across the inverter output terminals and check the results.

      Inverters normally do not have a neutral, they have an alternating phases coming out of both their outputs pins, that's very unlike our mains AC, this could be the cause of the slight shock that you are getting from the charger body.

  21. Hello sir, i have a microtek inverter which was working nicely from couple of year but suddenly i got one problem……sometime its stop working and indication show for overload and fuse blow while its output load and fuse are ok……and when i restart the inverter then its working again……what is the reason behind this

    • hello my life,
      it seems to be an internal circuit problem, which needs to be diagnosed by removing the circuit board and checking with a multimeter,,,,it would be difficult to troubleshoot by assuming.

  22. Off grid small house system. The inverter is feeding 40v AC back over the 12v batteries. In this state, current positive terminal to ground is 8 u Amps, as measured with a multimeter. This is making 12v backup generator live to 40v ac and zaps someone when they go to start the generator. Also the 40v ac appears to be interfering (but I'm not certain) with various charging cycles from solar and wind controllers. Can you give some clues as to further fault-finding techniques or suggestions please?

    • I guess the 40AC is connected with the battery through a bridge and a voltage regulator, in that case the battery could be safe, but a human could feel the zap due to his body earth passage.

      You can try isolating the 40AC to the battery section via a transformer, the primary could be rated at 40V and the secondary slightly above the battery voltage rating.

  23. Hello sir, i have a microtek inverter which was working nicely from couple of year but suddenly i got one problem….wen i start it or increase load on it…… it starts generating abnormally high sound and output voltage i very low but at that tym it blows CFLs and mobile chargers……. after few minutes it will behave normal

    • Hello Sharad,
      The automatic voltage correction feature of the inverter seems to be malfunctioning, it will need to be diagnosed practically, can't suggest much without inspecting.

  24. Hii I have a 800VA Inverter & 150Amp Battery attached to it. My inverter is not showing the charging signal and indirectly charging it by overcharging the battery. Few days ago I topped up my battery by distilled water and after that I found out that the battery is not charging and over that when check with tester current is being shown on both the terminal of the battery.
    Plz let me know about the problem and give me some solution for it.

    • try charging the battery with an external battery charger unit and then connect it with the inverter, the fault could be with your inverter's charging system.

      If the battery doesn't charge optimally through an external charger it would indicate a damaged or a sulfated battery and will need to be changed

  25. Hi,
    I used my 300W inverter (12Vdc to 230Vac) to power a double tube flourescent light fitting. The total wattage of the light fitting is 130W. The tubes lit up, but then after switching off the light fitting and then switching it back on, the inverter failed. There is a red LED indication on the inverter which means that there is a fault. What could I have blown? Could the high inrush current have blown some component, or could a switching surge have blown some component? What is the most likely component in the inverter that could fail due to the inductive load which I subjected it to?
    Please reply soon, Riyaz

    • Hi, Normally a good inverter will not fail even if its outputs are short circuited, so a tube light should have noway affected its operations.

      Can't say what might have happened to it without a practical examination, looks like a part failure inside..

  26. Hello sir howcr u….
    My problem is that i m having a luminous 800va inverter 150amp battery attached to it…it's charging led were not working…so when i was repairing that touched in heat sink of mosfet…after that none of the led's are working…it's not a big issue but….main problem is that inverter giving low output voltage 150 volts…on load and on no load…i measured it's battery charging amperes…which is 12amps…i tried different battery but problem is same….are mosfet's blown up??? If yes how can i check them with multimeter….???

    • Hello nitin, if the output is low then it could mean a few of the fets are fried or working asymmetrically…check the amp without load by connecting an ammeter in series with battery positive…if it's high without load would confirm a serious fet malfunction

    • Hello sir…there are two series of 5-5 mosfets each in my inverter…so one mosfet was looking cracked…so i changed whole series of 5 which was chn 608 with chn 347…when i connected battery it was working…but whenever i put load on it…,it started switching power on off immediately…and its relay started making noise…i remove load…after few minutes…a mosfet fried again with a pop sound…and a little transistor 639 started smoking….can u determine what's the exactly problem ???
      Wish u a happy diwali…

    • Hello Nitin, I think the oscillator stage is frozen in your inverter which is causing the mosfets to short circuit through the trafo winding….disconnect the mosfet and the power buffer stage from the board and check whether the oscillator is working or not.

  27. Hi, Swagatam i have a problem with a 750w modified black&decker inverter if i connect more than 30w it protects itself but the votage doesnt even drop, i already checked the frequencies and they are ok so what are your thoughts for this problem. thanks in advance.

    • Hi Roger, I think the overload protection circuit could be malfunctioning, try to locate the overload cut off relay or the particular circuit section, remove it and then may be you can try troubleshooting the possible fault in it.

  28. hell sir,
    my home inverter doesn't give output. when mains power cutoff, inverter indicates on position but, could't give output. battery rating 12V, 135AH. how can i identify the fault, how to solve the problem or how can i repair…..???


    • Hello Sushant,

      there are two things which might be causing this problem:

      battery power not reaching the inverter, battery not charged or the relay changeovers are faulty and not transferring the relevant power lines across the output

  29. Hi! Hope you are doing fine. Can you help me with my power inverter? I have this TBE 1000W power inverter that was working fine until it made this long beeping sound. I removed it from the solar panel system and connected it directly to the battery and it still is making the beeping sound. The battery is fine because it is being used in another solar panel system. What could be the problem? Thanks in advance!

    • Hi, I am sorry it would be very difficult to diagnose or judge an internal fault of a system, because there could be several reasons for a particular faults, not possible without practically checking it.

  30. Hi,

    I have a Silverline 1000W inverter that made a smell and stopped working!

    A visual inspection showed a pin burned and the IC plastic cracked on the SDC 7500 chip.

    I was going to solder a DIL socket in and try a new IC but I can't seem to find one online.

    Also would you know what sort of fault further downline might have taken this chip out. Its the Vcc pin 12.

    It seems to be a difficult IC to source?

    Would you have a circuit diagram of this inverter?

    Your comments greatly appreciated,


    • Hi, I compared the pinouts of your inverter IC with a more commonly available IC TL494 and they looked exactly similar.

      So I think you can try replacing the burned SDC7500 with a TL494 and check the response.

      However I can be difficult to understand or judge the actual reason behind this damage, because normally the supply to the electronic stage is always regulated and through a step down transformer.

      I have a simple inverter version which is comparable to the one that you are using, if you have previously built electronic circuits then probably building this one from the start won't be a problem for you, here's the design:

  31. Hello, could you tell me in 3 lines what is the main difference between repairing inverter and non inverter air condition ? I do not find an easy explanation to tell to someone else. Thank you.

    • An inverter in an air conditioner is used to control the speed of the compressor motor to drive variable refrigerant flow in an air conditioning system to regulate the conditioned-space temperature.

      By contrast, traditional air conditioners regulate temperature by using a compressor that is periodically either working at maximum capacity or switched off entirely

  32. Good day,
    I've got a IR series pure sine wave inverter with 48volt system. I only notice this last week where my inverter shows a 9% constant load from 6pm to 6am (night time) even if I turn off all switches in DV box. Thus no electricity flowing yet shows a constant 9% load. Yet before it jump to 9% constant load for night time – the normal load is 1%-3% at 5pm. Any idea what might be causing this. Thank you in advance

    • Although it would be difficult to judge without testing it practically, any circuit that might be associated with the output winding of the inverter transformer could be malfunctioning and leaking power….you can try temporarily removing the connections of the circuit associated wit the output of the trafo and see if the issue rectifies, otherwise it could be something more serious.

  33. I am an electrical engineer but not so much into inverter. Your problem made an interesting reading so thought of of understanding it more.
    We need to confirm that
    1.0 There is no load being fed by circuit not routed through distribution box.
    2.0 Confirm the working of indicating meter by using clip on ammeter, before and after 5 PM. Measurement should be done at output wires from inverter to box.
    3.0 In case clip reading donot change in correspondence with panel meter, we may doubt problem inside inverter.
    4.0 during daytime, switch off all load and confirm meter reading.
    These observations may lead us in understanding the problem

  34. What would happen if the AC and DC "collide" within the power inverter? The inverter is connected to solar batteries, and it is used as an alternative to power the lighting in our house. But someone turned both the main circuit breaker for the lighting, and the alternative circuit breaker "on". The circuit breaker connected to the power inverter and the solar batteries got "tripped". When i turn off the main circuit breaker and turn on the alternative solar circuit breaker, it is not working. It seems that the power inverter got broken when the two circuit breakers were turned on at the same time. Is there any way to fix the inverter?

    • If DC is connected with a same potential AC, then the during the negative cycle of the AC, their would be an explosion or a short circuit, burning both the DC fuse (if any) and the AC fuse (if any)…..if the DC potential is much lower still their would be an explosion and short circuit for both the cycles…if DC potential is much higher still their would be an explosion for both the cycles….but nothing can be confirmed without a practical investigation

    • if there are any fuses in the middle you can check those whether or not those are burnt and replace them….or check the relevant voltages before the circuit breakers to see if the circuit breaker was the only device which might be damaged and possibly change those with new ones.

  35. Sir this anbarasan iam interesting to service inverter i already sent my request but no response once again i request in 850va inverter mosfet explide after change mosfet abnormal heat produce in the mosfet heatsink is there driver problem please reply me

  36. Hi Swagatam, I have an inverter ( 300W Meind ) which short circuits when I give power to it to power on. When there is no fuse, it doesn't do that. When the switch is ON, it trys to BEEP for low power.

    It had a blown capacitor which I replaced it with a higher vlotage. ( 16 to 25 )

    There are no blown or burnt components.

    Please help me, I don't want to spend more money on buying another inverter.


  37. I have a 2200W inverter to provide back up power for a sump pump. The inverter goes into overload (and blows an inline 15A 125V fuse) every time anything is plugged into the output plug.

    This particular inverter is designed to plug into wall AC to keep the batteries charged and pass through 'wall' power when it is available. When power goes out it switches to battery power and inverter mode to power my sump pump.

    Whether the unit is passing through 'wall power' or in 'inverter' mode as soon as anything is plugged into the ouput outlets there is a 'buzzing' / 'vibraton' and an overload condition. It seems like there is a short occurring when anything is plugged into the outlet.

    What could be the problem? I am not sure where to look for the shorted condition … transformer? Why would it only short when something is plugged in… and why would it short when passing through current from the wall as well as when producing inverted power from the batteries?

    Note – this unit used to function normally…. so it must be a worn or failed part / condition.

    • I think some internal circuit stage might be malfunctioning and shorting the output possibly through a relay, on detection of a load.

      You can troubleshoot it by tracking and locating the "load" wires which may be terminating from the trafo output, and temporarily disconnect everything that might be associated with these wires….after doing this you could check whether the problems persists or not…if still it continues to behave in the same manner then the problem could be assumed to be on the primary side….

  38. Hello good sir,

    I have a 300W 12 V DC to 230 V AC Mascot Inverter in my boat, which supplies a tv-screen and an underwater camera. The problem is that most times the screen will not turn on, it just makes a ticking sound. But when I pull the plug and wait a couple of minutes with the engine running, it will usually start when I plug it in again..

    I measured the inverter inlet and it says 16 V, and the outlet is only around 190 Volts. Should it not be around 230 Volts? I have a 12 V 125 AH battery. I'm a rookie when it comes to electronics, so I hope you'll have an idea whats going on.. :]


    • Hello Nozthis,

      It could be due to insufficient initial current for the inverter to start the load…you can put a switch in series with the load, and initially keep it switched OFF….you can switch it ON once the inverter and the engine has gathered enough strength…..or alternatively you can upgrade the battery with a higher AH rated battery.

  39. Hello Sir Swagatam,
    My inverter was affected by a thunder strike. It can still be powered on when the power cable is plugged. The heat sink is observed to heat up when power is being supplied but the inverter does not function anymore as before. The capacitor at the end near the power supply line is tested with a multi-meter and seen to be ok. There are no visibly burnt components on the panel (motherboard) when closely inspected. How do I fix this problem?

    • Hello Chinda,

      It would be extremely difficult to judge the fault from here, because s thunder lightning can be so powerful that even if it brushes-of an electronic circuit, the small sensitive devices could get damaged permanently without getting burnt.

      It wouldn't be a wise idea to speculate without practically checking it.

  40. Hello Mr.Swagatam
    I have 500w inverter which I use with car battery and by mistake I placed the positive (catch) with the negitive bettery output and placed the negative (catch) with the positive bettery output
    Since then the inverter is not working.
    I wonder whats the problem and how do I fix it?

  41. Swagatam Sir, Good Evening 🙂

    I have luminous inverter UPS LB 800 VA and been using it for last 7 years. Now it doest not charge battery althogh smart charging LED blinks. smart charging LED remains blinking despite main power cut. Battery is functional as other inverter charges it well.
    Sir your immediate reply is solicited and thanking you in advance.

    • Hi Amar,

      you can check the voltage across the charging output points, and also the current available from it.

      voltage can be checked using a multimeter on DC V range, while the current can be checked by selecting the DC 10 Amp slot or the highest amp range in the meter,

      If the output is absent or is too low you can assume something's not correct in the circuit or may be the output power device is blown.

  42. Hi Swagatam, My inverter shows battery low in 10 mins time, I have checked the distilled water in the battery and filled it. I worked fine for 2 days and back to the same. What should I do ?

    • Hi Dan,

      is your battery too old? anyway you can confirm the condition of the battery by removing it from the inverter and by checking it with an appropriate load, if it shows quick discharging symptom or if it shows sluggish response while getting charged you can assume it to be dead or in a bad condition….

  43. Im just a kid don't know much about electronics. The thing is my inverter fuse keeps blowing up in seconds after changing it to more powerful ones. What can i do? The input voltage isnt high. Its usually around 220v

    • sorry, it would be difficult to judge the fault without a practical look….may be you'll be able to trace it someday once you have grown up and learned adequately about electronics….

    • Hi Satyendra, the fault could be hidden in the circuit board section and difficult to judge without a practical assessment, so I am sorry it won't be feasible to detect without checking.

      One common reason could be a blown fuse, or a burnt wire…you can check for these.

  44. The 800 VA inverter has 40A orange coloured fuses on the board. Please check these four fuses for integrity. These are located on board.
    Also check that toggle switch for vacations is not in off position. If it is in off then LCD display shows trikle charging by flickering filling nozzle.
    Please check that battery is healthy
    Also ensure that inverter has s switched on as indicated by small green LED.

  45. Good day, sir.
    I have a Coleman Inverter PMP3000. I made a mistake when I connected on a reversed polarity. All fuses are busted. I changed all the fuses with new ones but when I connected it again with the right polarity, all the fuses got busted again. What is likely the cause of the busting of fuses? Please advise. Thank you very much. God bless.

    • Good day benz, it's surprising that your inverter did not have a reverse polarity protection, anyway now it seems it's been damaged quite a lot, and the internal power devices could be burnt…. you'll need to open it completely and check the power devices using a multimeter.

    • Thank you very much for your reply,sir. Yes, it has no reversed polarity protection;
      I opened it and so far my ocular inspection shows NO sign of burnt out power devices, resistors, capacitors,etc. Looks clean and net in all its parts. I haven't used the multimeter as I give this feedback, I'll complete first ,then I'll inform you. Thanks again,sir.

    • thanks Benz, electronics can never be confirmed with mere eye inspection :), you'll need a multimeter for this…fuse blowing off even when connected correctly indicates that the output devices are most probably burnt or shorted.

  46. Good evening sir,
    I have a Schumacher 1500 watt inverter that was mistakenly connected to the 12 volt battery backwards ( + to -) and (- to +). There was an audible pop sound and then nothing. After connecting properly still no response. From your experience is this likely to be repairable? I have very limited experience or knowledge on the subject but I'd like to know if there is a chance of repair.

    • Hi Randy, your inverter problem appears to be similar to Benz's inverter problem….it's really surprising how the manufacturers missed the reverse polarity protection, which is extremely important in such equipment which require external battery connection.

      anyway, the problem is definitely repairable.

      you could probably follow the positive line and check the stages which are being connected with this line.

      Most probably you would find this line going to the PCB of the inverter which might be having many associated ICs and other devices…so you could check whether these ICs are directly involved with the positive line or not, if yes, then it would imply that these devices could have been damaged due to the wrong battery connection.

  47. Dear sir,
    I am using micortek EB 850 inverter gor last 4-5 years. Today I found Mains to UPS mode is not working. In mains power supply mode displaying full charge (New battery just 2 months old) battery in display, Once main power supply is off, all display light off in inverter, and no power output also.
    I have checked the fuse, it is OK.
    I have checked there is no loose connection also.
    Please help.

    Thanks & regards,
    Suman Rana

    • Dear Suman,

      The problem could be in the change-over driver section which could be operating through relays or mosfets or IGBTs…this section might not be transferring or switching in response to the detected power failure.

      so this section will need to be traced and troubleshooted, perhaps one of the driver transistor could have gone faulty.

  48. Dear Sir,

    I have a 5000w power inverter. When you switch to inverter use, it begins to beep although battery is not weak. When you turn on the charging unit to charge battery, it beeps as well. What could be the cause and how can this be fixed.

    Thank you.

    • Dear Nikki,

      It would be difficult to locate the exact fault without a practical check up, but broadly it could be due to a faulty part in the low battery sensor circuit stage or a bad solder point in this stage

  49. Dear Sawagatam,my UPS Infosec x3 2000 one side 4 FET burnt. I replaced all four. Opposite side all four ok. But still UPS not works and display shows 0 with continous beep.

  50. Thanks for the quick reply Brother ! i would like ask for learning and understanding in this UPS. four FET one side and four FET opposite side, In each side 2 FET are insulated with layer with heat sink and other two each side without insulated layer piece.what is the logic? And battery charging how happens? with which rectified dc voltage and from where?

    • Dear ali, again it would be difficult to judge unless and until it's actually and traced from top to bottom because inverter circuits come in many different varieties with specific configurations, so all have their own exclusive design and operational methods

      ……for the battery charging your UPS must be deriving the input from your mains AC, even if a transformer is not included it could through an SMPS circuit stage.

  51. Hello Swagatam. I have a 2.4kva (24v) inverter system with 2 batteries of 12 v (100A) each. I have noticed recently that after a full charge, the low battery alarm comes on in like 5mins but power may stay up to 7hours with the alarm. Please kindly advise.

    • Hello bassey,

      I think the low voltage detector stage has gone faulty or the preset adjustment could have been affected or the preset itself has become faulty…you may check for one of these issues.

  52. Hello Swagatam,

    I have a Hyundai 3.4kw inverter generator (HY3600SEI). The generator engine starts first time and runs up to speed. The green AC ready light comes on for about 3 seconds and then go's off (power is removed from output socket) and the Red overload light comes on and stays on.

    If I apply a load (any size load up to 3400 watts) within the 3 second time frame that the generator starts and energizes with green light (Power available), the load will power up and run for hours producing power. If no load is applied, red light comes on and power is no longer available without turning off engine and restarting.

    Any idea's?


    • Hello Warren, it appears like the inverter is equipped with a "no load cut-off" feature and that's a good feature to be included in the system.

      I think you should keep the load connected initially and switch ON the inverter in this position to bypass the concerned feature?

      and possibly connecting 3400 watts may not be crucial, you can try with a 100 or 20 watt load and check the response., it should do the trick.

  53. Hello Swagatam,
    i have been following the conversations you have had with different people with different questions, i am really impressed with your intelligence and willingness to help other people, thanks.
    However i have my own problem which believe you will help.
    My inveter is 500 watts and i use it for only the TV which is 100 warts and 3 energy saver bulb 12 watts each. Now my inverter is working but the green light is off and the voltage gauge is down, what could be the problem and what are the dangers if possible any suggestions for fixing the issue?

    • Thank you Joseph, the pleasure is all mine:)

      If your inverter's power output related operations are normal, then the failure of the indicators cannot be considered as a critical issue….it could be simply due to a damaged part or so in the indicator circuit stage which might be affecting its working….you can check the specific stage and change the faulty part after locating it correctly that will hopefully solve the problem for you….

  54. my inverter is showing a short circuit warning. i have checked all mosfets. they are in good condition. what might be the reason. can u help me about the common circuits for shortcircuit detection or help me to find the damaged component

    • try disconnecting the wires that are terminating to the transformer from the mosfets and check the response….you can also try connecting an ammeter in series with the battery positive and check the current….if it's high at switch ON would indicate a short, or else the warning could be assumed to be a false or malfunctioning.

  55. hi Swagatam I have an inverter that just installed in my car and with direct connect to the battery with aligator clips. when I plug in a small 230V radio in the inverter. the radio comes on and then goes off again constantly. I know it is not a faulty radio. it works in a normal house plug. Do you have any suggestions on this?


    • Hi Nik, the problem could be due to the very small load presented by the radio, which is prompting the inverter's "no load shut off" feature to activate….try using a 100 watt bulb and see whether the issue still persists.

    • Hi, check the voltage across the fan wires, if it's OK then the fan could be faulty, otherwise the circuit which is responsible for producing the voltage could be faulty.

  56. Hello sir.i have a ups Lebanon make.3700va,.it's now beeping n indicating inverter off/charger on from time to time.what might be the problem n what's the remedy for that.?
    Thanks in advance.

    • Hello Jack, the "mains to INV" changeover relay stage could be malfunctioning, open the inverter and check the relay stage which is responsible for implementing this changeover, and check the transistors or the IC associated with the relay switching action.

  57. Hi Sir, if I charge my phone and iPad this does not happen but the moment I put on my 120w TV my 900va Indian inverter based on MOSFET technology trips into Low battery with alarm and goes back instantly to invert and power the TV.

    Sometimes I will have to off and on the inverter a few times before it works. What could please be the issue, is it the inverter or battery as battery reads between 11v – 13.5v

    Thanks in anticipation.


  58. Hi Sir, My inverter goes into Low Battery modend instantly goes back to normal inverting when I put on my 120watt TV. Sometimes it will go into Low Battery and will not recover until I off the inverter and on again. Meanwhile my battery still reads 11v – 13.5v and when it works, it gives me backup up to 14 hours.

    Can it be the inverter or the battery that has problem? Kindly assist.

    • Hi Billy, It will be difficult to pin-point the fault but surely it's around the "battery level detector" stage….could be a bad solder point on the IC leads, you can check it and re-solder the points and check the response.

  59. hello sir,
    i've 850 su kam inverter. its problem is that it does not charge batter when mains is on and when it is in inverter on mode it doesn't shows mains. also when mains is 220 volts the inverter outputs is just 96v. again on inverter mode the output is 220volts
    i changed the relay…but problem is same
    plz reply me

    • Hello Amit, it looks like there's some kind of loose connection in the wiring, check all the connectors especially the wires which are coming from the transformer to the output socket, and also the connections between the relay and the transformer.

      Clean the PCB with a brush and check if all the solder points near the changeover relay are fine.

  60. swagatam sir….. microtek sine wave inverter shows over load on load n keeps on buzzing … i changeD the relay the connecteions were damaged … still ot shows over load on no load n keeps on buzzing…. is that the function ic problem or else??

    • Aqib, try checking the stage which is responsible for activating the relay, it could be an opamp which is configured to sense overload and could have gone faulty and might be causing the relay to trip…therefore locate this opamp or whatsoever stage it may be and check the reason behind its malfunctioning, and possibly replace the faulty part with a new one….

  61. Good Morning Sir,

    I have recieved a lebanon made inverter to repair that has one transfo (used for both charging and DC-AC ivertion), Six mosfet (IRFP250n) each three are in parallel, Inverter board, A big relay close to the transfo and Battery charging ciecuit.
    The inverter is not working. I check it following the guidlines you provided above and I found out that, the inverter can work when 220 AC power applied to it but it cannot work on battery.

    The foulties area are summarised bellow..

    1. It cannot charge the battery while the transformer has provided the DC voltage through the help of the Big relay.

    2. If battery is connected, a relay on battery charging board is moving.

    3. Also, there are two big resistor of about 10 or 15watts connected in parallel that spilt into pieces (unfortunatelly it has no details on it, I would have change it and try the inverter) but, when I arranged it and apply AC power I can see the charging LED lighting. But to me, I think this resistors are what prevent inverter to accept the battery, because they are working as a trigger.

    1) Sir could you please suggest what is wrong?
    2) And, what type of the resistors should I try?

    Thank you Sir.

    • Aminu, it will be extremely difficult to judge the faults without a practical check up…so I won't be able suggest much.

      for the resistors, you can replace them with 12V flashlight bulbs and check the response for the time being, if it works then you can experiment with may be a 100 ohm resistor initially, and see its effect on the performance…. and modify the value accordingly.

  62. Sir,
    I did not find the 100 ohms, but I found a pair of 300 ohms 20watts and 330 ohms 10watts.I connected each pairs in parallel and I tried each but the pair of reaistors are getting too much hot and smoky. If I leave it for some time, It charge the battery.

    Sir is there some solutions?

    thank you very much.

    • Aminu, disconnect the battery and then check whether the resistor becomes hot or not, if yes then it's not correct and might need further investigation, if the heating stops then you are probably in the right direction, and can try checking the path of these resistors up to the battery and assess the cause of the heating up of the resistors.

  63. My inverter trips with overload indicator coming on when power fails, it continues in this condition even when all load is disConnected and the inverter is reset. But strangely, functions well if I disconnect it from the mains and reset it even with full load connected.

    • there could be a related capacitor which could be linked with the mains supply and stays charged keeping the over load cut-off latched, as soon as the mans is removed this capacitor could be discharging and releasing the latch.

      • then it could be difficult to assess the fault because it appears that the neutral line of the mains is involved with the inverter operation, and connecting the plug could be connecting the neutral with the inverter and causing the issue…you may have to call a technician for a practical check up

    • Sir, but the overload tripping returns if the input is connected to main while no power supply is coming from the supply company. Also, the overload happens only if the supply company stops the supply, turning the mains off does not cause tripping.

  64. Sir,i have a 1.5kva inverter.My inverter shows short circuit on the dashboard but I have changed all the mosfets and even capactiors.i noticed that only 4 mosfts get hot on powers the inverter out of the 8 mosfets used.what could be thhe problem? thanks

    • Kenn, connect 12V car bulbs in series between transformer taps and the mosfet drains…and check whether the brightness is equal on the bulbs or not….if not then probably trafo could be damaged or malfunctioning…or may be the oscillator is not providing identical frequency across the mosfets…or there could some other hidden aspect which you can diagnose sing a DMM.

  65. Thanks for ur prompt response.The brightness varies on the mosfets,also on isolation of the transformer,i still get the shortcircuit error on the dashboard.i cant see any physically damaged device,how do I find d oscialltor circuit & anyother means of troubleshooting it?

    • If the short is showing even after disconnecting the transformer then I think the problem could be somewhere in the mosfet stage….you could try removing the whole mosfet stage and check the situation again by switching ON power….

      the frequency could be checked at the source which connects with the gates of the mosfets…you can use your DMM's frequency range for measuring the same.

  66. i have removed the whole mosfet stagge including the drivers (Ir2110) but when I switch on I still get Short circuit on the dashboard.It really looks like a complex situation…Any Ideas?

    • since you have disconnected the whole circuit now it should be much easier to find the shorting locating, you can do it by using a multimeter or by connecting a series bulb with the input and then by disconnecting the remaining stages one by one until the bulb switches OFF.

  67. i am having o-general inverter split air-conditioner two year the outdoor timer board was
    faulty, i am changed. it is working for past two i am got fault the timer board.
    the indoor unit blink two times means , the o-general enginneers says, the outdoor timer to be changed.they says. how the timer board will get frequentlyfaulty?

    • 2 years is quite a long period of time and things can get faulty within this period, change it once more and this time tell the engineers to show you what exactly they are changing and also confirm the operating parameters of the unit….and do not give them the old module….keep it with you and check it afterwards whether it was really faulty.

  68. Hi swagatam
    I have a sukam 750va inverter. for the last few days its giving unique problem whenever i connect only a ups through it, ups starts giving fast tic tic sound of relay and when i connect it to a power point which isn't through inverter, it works fine. and when i switch on a tubelight or a fan ups' relay tic tic sound instantly stops. what could be the possible reason . i have measured voltages through and without inverter it's almost same. however when i measured dc voltage which charges the battery it was 13.9v instead of 12. please help me in this … thanks

    • Hi Suresh, it will be difficult to understand the issue without checking it practically….but the 13.9V is not bad, it's correct for charging the battery.

  69. Hi, I've a sine wave 2000W inverter. It has started showing bt in its display. What could be the possibility? I'm unable to get any help right now.

  70. The problem could be with your fan and or with your inverter, most probably it could be with your inverter….I think the output harmonic filter circuit might be malfunctioning, an involved capacitor might have gone short or faulty.

  71. I just have 12VDC 1000W inverter. I connected to a battery 100AH. It gives me 230V to power my lights and fans.When the battery runs down. I powered down and stop the inverter. Second day I charged the battery to full capacity and I connected to supply power . It does not supply power again . What could go wrong? Kindly help.

    • check the current consumption by connecting an ammeter in series with the battery positive, if it shows zero then there could be a loose connection somewhere, or a fuse blown or other similar issue, it will need to be diagnosed with a meter.

  72. hi dear my name is Daniel.
    i just started to repairing electronics today i received one inverter 12 volt DC 1000va hibride this inverter is showing fault 3 when i connect battery with it could you please help me in this what should i do for it repair ????
    your kind response is awaited


    • Prince, which inverter circuit did you build? please provide the link

      the transformer wattage and the battery AH must be rated correctly as per the load wattage for it to function correctly

  74. Hi Swagatam. I am sorry if I am posting this question as a repetition and maybe it was already answered. I connected my new 2000 KVA inverter today and fear due to a short circuit in wiring have busted it. (It showed a fault related to short circuit us well). Now ups is working only on main power supply only. As soon as I switch off the main, Inverter also dies instantaneously. l intend to repair it or alteast check for the fault myself. Can you please guide from your experience what can the fhoblem be. Many thanks

    • Hi, if you think you have shorted something while the inverter was in the battery mode, you can track the connections which connect the battery with the inverter devices and check for a possible shorting. initially remove the battery and check the resistance across these connections and check if it indicates a short, and keep following the lines until you discover the faulty part or the fuse or whatever may be responsible for the issue.

  75. Hi Swagatham
    I have a 4 year old 850VA Sukham inverter backed up by a 150AH Exide Tall Tubular battery of the same age. Sometimes when the power goes off, the inverter immediately goes off to low battery. But when I checked the battery via a multimeter, it showed 12V. If I keep inverter off for some time( say 30 mins) and switch on the inverter it starts working properly(ie there is no low battery siren). In order to test if the battery was weak, I tested the battery by switching off the main power so that the inverter starts working. At that time the inverter worked properly for about 3 hours with lights, fans , TV switched on. I am not able to replicate this problem at will. So this is a random problem which happens. What could be the issue?

    • Hi Mells,

      Is this happening every time or occasionally? If it's happening randomly then the problem could be difficult to judge without a practical test.

      Most probably the problem could be in the battery charging controller section where the battery voltage monitoring circuit could be malfunctioning.

      your battery is OK for sure…the problem is in the charging controller changeover section

    • check battery current by connecting an ammeter in series with the battery positive, if it's normal or zero without load, then the fault could be in the indicator circuit

  76. Hi Swagatham,

    I recently bought an Exide ECO 900 Inverter (Square wave inverter) and I am facing the below issues.

    1. The output voltage of Inverter shows 290V when I use it with 2 fans and one nightlamp, And the voltage getting drop to 250 to 260V only if I use more appliance at a time (3 Fans, 3 Tube light, 1 LED TV). And it is hard for me to use all these appliance at night while sleeping. I am scared since the 2 Fans are running too fast at night while using Inverter specifically having a Infant baby in my Home.
    Need your advice asap to get this issue resolved please.


    • Hi Santosh,

      The only quick remedy for this is to add a good quality electronic fan dimmer with the fans and reduce the speed appropriately.

      The other method is to use a lower voltage battery in your inverter, for example if the existing battery is rated at 12V/50AH, then you can replace with a 9V or 10V/50AH or 60AH battery.

  77. Hi Swagatam,

    Thanks for your advice 🙂
    Now I have add the Fan regulator to reduce the speed.

    I am already using a battery of 12V with 200AH to have more back up.
    May we have any other suggestion instead of replacing the battery, since I already spent a more on buying the above battery ? Also If I replace the low voltage battery, I doubt if I could use all other appliance at a time when needed.
    And adding a stabilizer from Inverter output will work out for this issue ?

    Also need to know is there any fault in my Inverter or this is the general character of Square wave inverter. If yes, i shall replace my inverter with the better quality one, since I bought the Inverter via Online only 5 days back, so I return it back as damaged product.


    • Hi Santosh, you can use a selector switch between the two batteries, when additional loads are connected you can switch to the 12V/200AH battery, and for smaller loads you can switch to the 10V/200AH battery.

      Your inverter could be without an automatic output voltage correction circuit which might be causing this issue, if you wish to have this feature then you can replace your inverter with a new one which has all these correction features built in.

  78. Hi,swagatam.I have a ups using with my p.c.When there is main it gives 250 volt output;but during the mains off,it gives only 150 volt.I checked the battery is o.k.then what may be the problem?

    • Hi Alok, how did you check the battery.

      It needs to be checkered while its operating the inverter…connect an ammeter in series with its positive, and a voltmeter across its +/- terminals…the readings should match the load requirement specs, if not then your battery could be faulty and needs to be replaced

  79. i have a modified sine wave inverter that can has a maximum rated power of 1000w, now i was messing around with it and trying to connect it to my room (from an electrical port with an on-off switch) but i forgot to turn the switch off and as a result it connected to the main house electricity and thankfully i only blow one my electric switches but i managed to get it back running using a spare plug-in cable, and now my inverter will turn on with fault, switch to power for a second then back to fault instantly and permanently, what possible cause that made the inverter goes like that? what is the possible issue/broken part inside it?

    • where did you accidentally connect AC mains in your inverter? normally the AC would be required for charging the inverter battery…so I can't visualize where exactly where you might have applied mains by mistake.

    • the house electricity was accidentally mixed with my modified sine wave inverter electricity and as a cause the switch broke and the inverter stopped working, it was from the 220v output from the inverter, and i direct plug it to the house electric outlet by accident

    • in that case the secondary winding of the trafo could have got damaged if it's a ferrite trafo, and due to the sudden AC influx there could have been a back EMF on the primary side damaging the fets….so the fault could be significant and needs to be diagnosed deeply.

  80. Hie swagatham,
    When i try to charge my battery with the inverter still connected (with inverter not in use and switched off), the battery doesnt charge..but when i disconnect the inverter from the battery terminals leaving only the panel it charges just fine…what could be the reason causing my battery to not charge when connected to an inverter thats not in use?

    • Hi, what kind of charger are you using? does it contain some kind of critical sensing circuitry? because if the charger is a simple power supply then this should not happen, may be your charger's sensing circuit is detecting something in the inverter and not allowing the battery to charge while it's connected.

      also make sure the inverter is not consuming anything from the battery while it's idle..check this by connecting an ammeter in series with the positive wire which connects the inverter with the battery (+)…if it's not consuming anything then it's fine and you may try a different charger unit and see the response

  81. Hello Mr. Swagatham
    I have truepower 850va square wave inverter,I want to replace its pcb
    with sukam torque pcb 900va so I want some help to buy the correct
    components which will protect my appliances from burning out. So can you help me to get the specs of the components which are circled in the red color from attached photo.
    I hope to check this link to know what I mean:

  82. Motherboard is changed to a new one for Sukam Smiley 1400 VA inverter. Later just on connecting to batteries & without even connecting to load it showed: overload. The repaired person told it has to be adjusted & taken back. Is it the same or due to board incompatibiliy

    • the technician is probably right, there could be some internal settings in the board which are not correctly adjusted and needs readjusting, and therefore it needs to be taken to the workshop and corrected

  83. HI i just bought a 150 A battery . I have 800 VA inverter which when plugged in with the mains even though the battery is fully charged , my meter runs faster than when plugged in on mains solely.
    What might be the problem?

    • Hi, check the current consumption by connecting an ammeter in series with the battery positive…this will show whether or not the meter is showing the correct response or some other hidden issue.




  85. Hi Swagatham,
    I have 850VA inverter. The AC input fuse keeps blowing whenever I switch on my iron box Even when its not on inverter i.e. when the power is there. I have tried with higher rating fuse however it didn't worked.

    Now I have placed a changed over switch to bypass inverter. Can you help?

    • Hi, I think the problem is with your ironbox not the inverter…do this:

      open the inverter and connect a second temporary fuse at the socket where you are plugging in the iron, and check whether or not this fuse blows….if it does then your ironbox may be faulty….for a changeover switch, the connections from this socket can be used with a 30 amp DPDT switch for the required modification

  86. hello sir
    i have a APC bi800i 800va inverter. when i connect it with 185ah battery it shows fault led light signal and does not produce any output. plz help me with this..

    • sorry, that would be difficult to judge without practically checking it…

      check the output of the transformer which goes to the load.. may be there's some kind of shorting.

    • Hello Ahmed, please check the entire line which connects the supply source to the battery via the PCB, check which part is not allowing the current to pass to the battery, simply replace it with a new one.

  87. My dad has gudlite inverter 1400va when the battery gets full charging indicator stops blinking and fan will stop working but after 2 years when the battery gets full, charging indicator stops blinking but fan will work for 2 hours, is there any problem with the inverter?

  88. Hi, I have a 100watts inverter which I use to power bulbs round my house when power goes. When power returned I forgot to switch off the inventor first before turning on the mains so mains electricity flowed through it and its now just making a beeping noise when I hook it up to the battery and turn it on. What could have been damaged?

    • most probably the mosfets or the power devices are burnt…because the AC might have powered the transformer in the reverse way causing heavy current to flow into the mosfets blowing them off…this is my assumption.

  89. Hi I have microtek600 inverter which is not charging 150 ah battery even after proper connection and terminal of battery shows live current when tested with tester plz give solution

  90. Hello, I had very high voltage in my house this morning and upon changing the phase to the lower one I discovered that all the lightning points in my house connected to my inverter are not working including the fans, bulbs, sockets etc but the ones not connected are working. And the inverter is also not charging pls what do I do. Hope its not a major damage. I need your reply to allay my fears.

  91. Hello, please I have a 5kv inverter showing an error on the display saying "Fault" !MCB TRIP! and it's nt giving output. Could d MCB be faulty or its something else? What would you recommend @Swagatam. Thank you

    • hello, there could some short circuit somewhere, you can confirm it by adding a 12V car lamp in series with the battery positive, if this lamp lights up brightly without any load at the inverter output then there could be some short circuit somewhere which you will need to locate step wise.

  92. I have a 1000W 22VDC-45VDC grid-tie inverter that I used with solar panels.
    Yesterday it failed on me and causes troubles.
    I took an ohm meter and the input DC terminals are shorted out.
    What causes that and can it be fixed?

  93. i have 5kva direct online ups .problem is It is not working properly shows internal fault. I open control board seen for any components or elements fails, I found all dc batteries good all fuses good 1 12VDC fan stucked and remaining 2 fans good 1box capacitor 30uf-250VAC complete swells and damaged along with 4 DC capacitors 560uf-450VDC damaged and found 2 IGBT’s fails K25N120 . I know up to this. I needs suggestion for what also to check in board and on what reason this failure happened in board? please give me replyme quickly, i needs to replace elements and get in condition online

    • It would be impossible to judge the faults unless I know the working stages of the inverter and study the entire schematic of the inverter.

      you can try replacing the faulty parts with new parts and switch ON the inverter with a series fuse,and without any load..and check the response step wise

  94. I have an inverter rated 3000w;24v. Initially in good condition, it takes 4Amps from battery on no-load. After a lightning strike, it trips off when switched on. I dismantled the system and observed on one flank, some burnt resistors and mosfets. I replaced burnt resistor and all mosfets on the flank. The system powers now but vibrates. Also it now takes 10Amps from battery on no-load. What can I do to resolve?

    • that clearly indicates that your mosets are short circuiting the battery, or the mosfets are not oscillating.

      disconnect the transformer wires from the mosfet, and check the frequency at the gates of the mosfets, if there's no frequency would indicate a blown circuit board. then you might have to investigate deeper in the board

  95. Hello Sir,
    I have a Microtek Inverter 800 VA and 160 AH Battery. I was not using the unit for 1 year. When I switch it on now, the power LED gives a feeble light and a small beep sound (momentarily) comes and the unit goes to dead. After that there is no indication of power. The front panel board is off. No indicator of mains , battery charging etc. When power is ON, I am getting around 240 volt in the output.
    What could be the problem?

    • Hello Bala, did you check the battery? I think the battery may be dead…you can also try opening the cover and cleaning the boards with a brush and check if all the connectors are connected properly….please make sure you do it after disconnecting the unit from the mains and from the battery.

    • I disconnected the battery terminals and tried to switch ON the inverter. My guess is , the front panel should show some indication , right? But it is not showing anything. Will not the transformer power the board? . The unit looks clean inside (no dust on fan) , all the fuses (on the board & cabinet) looks fine.
      The battery is showing around 7 V DC. One basic doubt, does the battery needs to be in charge for the inverter board & panel to work?

    • yes transformer must certainly illuminate something on the panel….I think you should check all the connections from the transformer….this can be done using a voltmeter.

      even without the battery the inverter must respond.

      By the way if the battery is a 12V battery then 7V indicates deep discharge, almost dead, and it should be immediately charged upto 14V, if fortunately it's still alive

  96. Hi Swagatam, I have a sinergy sure sine wave 1000va inverter with *protection* short circuit warning. I noticed it yesterday while trying to switch on the inverter, however the night before I used the generator to charge it. When I try switching on with the MAINS on it beeps with the warning still on the dashboard but when the MAINS is off the *protection* short circuit goes off the dashboard with normal display but when you try switching it on, it beeps with the *protection* short circuit on dashboard. Please what do you think might be the issue? Please help… Thank you

    • Hi Anthony

      If the inverter and the battery charger sections are functioning normally, then it's probably only the protection display circuitry which may be malfunctioning.

      I think the generator might have produced a much higher voltage than the mains and this might have caused some problem in the "protection" short circuit display board section.

      But it's important to know whether the overall features of the inverter are working normally or not? If it is then there;s nothing to worry, you just have to remove the display section and check for the possible fault.

  97. Hello sir. I have one doubt about using 800va it is good condition but sometime come to ups mode when main supply on mode condition.suddenly interchange the main supply to ups mode but have EB supply is there.

    • Hello Syed, check for any loose connections, either in the mains plug or at some other relevant location….or may be the relay changeover section of the UPS is malfunctioning due to some serious issue or due to some smaller issue which could be solved by some cleaning and dusting.

  98. Hi Swagatam
    I have a Sterling Power Products 300W pure sine wave inverter with a board made by Wenchi & Brothers in Taiwan, the model number being WHT-150/300A. Unfortunately even though the device has been working in the past it stopped working today – with a big spark coming from inside it.

    I have opened the device and found that C75 (which is located at the base of the MOSFET IRF740 labelled as Q35 on the board) has burned out completely. It may have also damaged the resistor next to it (I think it is R124 but I cant see it clearly enough).

    I realise you dont have access to the circuit diagram (I have asked both Sterling and Wenchi & Brothers for this info) but hopefully the following pictures will help.

    I have a couple of questions please:
    1. What could have caused this destruction of the capacitor? I see no other shorts etc on the board and the inside is very clean with no dust etc.
    2. If I replace the capacitor and possibly the resistor, will the problem likely just return? Is is likely to have been caused by a malfunction elsewhere in the circuit? Perhaps on the MOSFET?

    It seems such a shame to just have to throw this device away if it cannot be repaired so any help you can provide will be gratefully accepted.


    • Hi Mas,

      It could be difficult to judge the fault from the picture since the tracks are not visible distinctly….however a capacitor can never blow even with a short circuit. a capacitor will blow only when its voltage rating is somehow exceeded, so suppose the capacitor voltage rating is 100V, and if it's subjected to 105V then it might explode.

      resistors will definitely burn due to a short circuit, however a resistor is always connected with the gate of a mosfet, and a gate of a mosfet always has a very high resistance which implies that the resistor cannot have a chance of any short circuit….but if due to some reason the mosfet internal structure collapses that could possibly connect the resistor with the drain voltage and could lead to a catastrophic conditions, and that could even mean the IC linked with the resistor also getting damaged in the process.

      However I am not sure how much is the extent of this possibility, because normally the gate of a mosfet is well isolated from the drain / source of a mosfet.

      So thees are my assumptions according to which you could possibly trace the fault or may be wait until the schematic arrives to you.

    • Hi Swagatam
      Thanks very much for the reply. Interesting points you make – I will try to test the MOSFET and see whether it is functioning normally – hopefully it wont be and that will give me the root cause. Unfortunately the company has refused to send the circuit diagram (I suppose that is not all that surprising). But I have asked what the value of the capacitor is. If they refuse to tell me I will try and identify it based on pictures etc from the internet – the other ones on the board which look similar to the burnt out shell of the capacitor that blew have all had their writing erased so not possible to tell.

      Thanks again for the help

  99. Hello Swagatham,
    Today I bought an IPS Exide 1050va, when I connect battery with inverter and turned switch on, it gives no backup. But when I put the power plug into the socket, it works normal though mains have no electricity!! So, what's the heck on it?

    • Hello Ashik, after plunging in and starting the inverter, if you remove the plug, dies the inverter continue to run? If not then the inverter circuit functionality could be associated with the mains neutral wire and that's the only way it may have be designed to operate.

  100. Hello Swagatham

    i have a invertor of Luminus Tez and we see that before some time battery is not charging and Charging Zip is blinking continuously , we clean the battery terminal and even not charge battery…plz help

    • Hello Satish, please check the current by inserting an ammeter in series with the positive line connected with the battery….you can also confirm the voltage across the charging outputs using a voltmeter without battery connected.

      if both these or one of these reading produces a zero result or lower than expected, in that case your charger circuit could be internally malfunctioning…

  101. Happy new year, pls i saw my sukam 1400 on smoke, so i put it off, then on cooling down, i try to putit on, but its not working, no ligths at the dash board. Pls what can i do to fix it. and possibly what is the cause of the smoke and how to avoide future accurance

    • Happy new year,

      sorry that could be difficult to judge without a practical testing because a smoke could be caused due to many different reasons. The result of this could be serious damage or minor, can't pinpoint without checking

      you can check the fuse or the parts around the fuse…also the mosfets could have gone faulty probably

  102. Dear Swagatam,

    I have a SU-Kam Falcon 800 sine wave inverter. It is around 6 years old. I bought it with a SU-Kam Big 180ah tubular battery. The battery went out a few days ago, at least it tested no voltage, and I bought an Exide 150ah Inva Tubular. The inverter was checked and found to be fine! So we hooked up the new battery!
    Where I live we have both 2 phase and 3 phase current going on at different times of the day, as this is village and small farm agri area also, so we have power cuts when the phasing goes on.
    At the start, the battery was fine, but after the first power cut, the inverter stayed on instead of switching back to "mains and charging' cycle,which means the battery was still supplying the current while the current was now back. I had this problem with the SU-Kam for the last 2 years, so the SU-Kam serviceman told me to purchase a 1kv stabilizer so stabilize the incoming current so the inverter would be able to switch into the mains and charging phase, so I did. However, I found there were times when the inverter still stayed on after the current returned!
    Yesterday, all day the inverter stayed on, even though there was current!! I shut off the inverter and switched the wall switch to main current!
    I already called the battery company, who came out on the first day this happened, and they said it was low current from the EB itself!!! They suggested I use the stabilizer! But, I am wondering if the inverter has a problem, because it did not switch to mains and charging after futs, but stayed on inverter the full day! I kept shutting it off, because I didn't want to overuse the battery or kill it's load!

    I am confused at what is the problem! I am thinking of seeing if I can find a good condition used inverter to check if it is the fault of the inverter or WHAT is the problem? Now, I have shut the whole thing off!!! Can you help?
    Thank you, Chandi Devi

    • Dear Chandi Devi,
      A stabilizer is irrelevant for the issue because a changeover circuit is the simple circuit which can be operated with a couple of good quality relays…and these relays can be controlled with a 12V SMPS or a simple 12V regulated transformer power supply.

      the problem ie definitely with the inverter and the technician seems to be clueless regarding this simple issue.

      you can probably solve the issue using an external relay changeover system with a battery charger which cab be independent of the inverter and yet provide you with the required automatic mains to battery changeovers and also charge your battery while mains is present

  103. Thank you Swagatham,

    I can't find my post, so I hope this reply gets attached to it.

    So, you are saying to add an external relay changeover system with a battery charger?
    Is this in lieu of the inverter? Or just for the time of the changeover?
    Are you saying that my Su-Kam Inverter cannot be fixed?
    Are you also saying that I should NOT purchase a new inverter?

    As you can tell, I am an electronics moron.
    Do you think the servicemen from Exide will be able to get this together for me?
    Will this all cost more than a new Inverter?
    Are you saying that a new inverter will encounter the same problem?

    The exide servicemen came again tonight, because whole day the Inverter was on and I just shut the whole thing off. I called them and they WANT to get it right. But, even with the Electric switch on EB (not battery) and the button of the inverter OFF, I found the inverter charging with mains ON when they came at 6pm. This was ONLY in the evening; the whole day was only inverter and I shut it all off. How can it charge when it is all off?

    The whole thing is weird.
    Please, a little more info would be helpful for me.

    Thank you again.

    • You are welcome Chandi Devi, you may have to click the "load more" button to see the hidden comments, it's hidden under this button.

      I suggested the idea of an external changeover just to make the operations independent of the inverter unit since the chaneover/charging operations are crucial to the inverter and the battery.

      You can definitely get the inverter repaired if you wish so, that's never an issue.

      If the whole thing is concealed and wired then it could be difficult to use external circuits with it, rather it would be better to get it completely examined and corrected by the repair personnel.

      Alternatively you can buy a battery charger and an inverter separately and then wire them externally as per my circuit suggestions so that in future such complications never arise or is easily tackled.

  104. I bought 2 APC smart UPS 3kv and they developed a fault suddenly not too long from when i bought them. The first one will work for 2hrs and after then it will start blinking all the led display light that it has and the output voltage will cease from supplying. The second UPS of the same model just stopped charging suddenly and whenever its is plugged to AC, it will also be blinking all its led light and start making a disturbing sounds. Pls what do u think i can do to that?

    • It does not seem to be a general kind of fault rather a model specific fault, will be difficult to diagnose without a practical test….for the first unit you can try testing it with small loads and see whether the problems repeats or not, if not then the problem could be due to overheating of the devices inside.

  105. Hi

    I have a 5kv MPP Solar Invertor.My problem is its failing to charge the batteries when the panels are connected to the invertor but when I connect the panels directly to the batteries they are being charged.I would then reconnect the wires to the invertor and I can have the power for the house.No fault is showing on the LCD beside the non flashing of the charging light.

    Thank you

  106. Hi Swagatham,
    I have a 5000VA SINERGY DSP sine wave inverter. I have owned this for over a year. Recently, I have been getting the *protection* short circuit indication with a loud continuous tone. This happens about 15 minutes after the mains loses power. I have to manually turn the inverter switch off and on before it operates again but only lasts for about 10 to 15 minutes before the short circuit display comes on again. When the mains is powered it works normal. Any idea what to check please?

    • Hi Oloruntoba, It can be difficult to identify the fault without checking it practically, it seems to be some internal malfunctioning of the relay changeover circuit stage. you will have to consult the company's service engineer for troubleshooting

  107. Hi, I have a power Tech-on 1000w pure sine inverter. I use it as a back up power source normally connected to batteries under charge with regulated solar panels. After 13 months, 1 month past warranty period, it no longer produced AC output but green indicator light comes on as usual with no fault led coming on. My past experience with inverters was usually replacing the power mosfets. However I did that and also main transistors on both sides of power transformers (2) after trying to diagnose, I lost the steady green led. Have you heard of this issue? I cant find a schematic and the manufacturer does not offer any repair service. I would really like to know if this is a fixable issue. Any help appreciated

    • Hi, the LED indication cannot be considered as the final judge of the situation…the LED could be ON due to some other issue. the main diagnosing must be conducted across the transformer leads and the battery leads, and the oscillator section….if the oscillator sends the signal to the mosfets, and if the mosfet drives the battery voltage to the transformer then an output will be available.

  108. I have measured the battery an transformer just to find that the output is not there. Mainly because the input is all positively charged with no negative present. It has two Daughter cards one has a pwm generator with oscillator out. Is that what is driving the mosfets? I assume the fets are Beiing pushed high and low when it's working correctly it is a pure sine so I have 8 fets at the two transformers and 4 at the output stage which appears dead. It also uses 3 opto couplers to switch the high side to some extent. Any ideas? I need a schematic for this. It is a power tech-on ps1002 1000w pure sine inverter

    Sent from my iPhone

    On Mar 27, 2017, at 4:03 AM, Swagatam Majumdar wrote:

    Swagatam Majumdar has left a new comment on the post "How an Inverter Functions, How to Repair Inverters…":

    Hi, the LED indication cannot be considered as the final judge of the situation…the LED could be ON due to some other issue. the main diagnosing must be conducted across the transformer leads and the battery leads, and the oscillator section….if the oscillator sends the signal to the mosfets, and if the mosfet drives the battery voltage to the transformer then an output will be available.

    Post a comment.

    Unsubscribe to comments on this post.

    Posted by Swagatam Majumdar to Electronic Circuit Projects at March 27, 2017 at 3:33 PM

    • The measuring will need to be done by connecting an ammeter in series with the battery positive must indicate the correct specified amount current, otherwise it would indicate a faulty mosfet or a faulty oscillator stage or both together.

      Sorry I do not have a schematic for this…basically all inverters work with an identical principle so fault finding shouldn't be too difficult, if it's done by isolating the stages and checking them step wise

  109. Hi Swagatam,
    I have one Microtek SEBZ & other Bajaj make UPS both for 12V single battery DC to 230V AC.
    I have added them with battery bank of 24V, such a manner that each battery is fed to each inverter but there is changeover switch which can alternate their AC output manually. They can never put online simultaneously.Trouble starts with Bajaj inverter when on load it reverses the output live terminal.
    That means when I load it checking the load socket of 15A plug it shows power to the neutral& vice varsa. The other Microtek is working fine. Worthy to mention I have single live wire connection for inverter to load & Neutral & earth being used from electricity mains. Inverters so connected with single battery because I have my 300Wp solar panel of 36Vmp so I have connected them in 24V from 12V & getting better result.

    • Hi Asimkumar, I could not understand one aspect, if you are using the mains Neutral for the load, does that mean that you have connected only one wire from the respective inverter and the UPS and left their other wires unconnected?

      Please clarify this point, once I understand this I will try to sort out the problem for you.

  110. Hello Mr. Swagatam
    My friend gave a manual AC-DC inverter battery charger, it was not working because of a damaged 5 pins mini relay, the specs of the relay is as follows:
    10A 120VAC
    10A 24VDC
    I change it with the following one:
    10A 125VAC
    10A 28VDC
    COIL 6 VDC
    the problem is that inverter mode not working, but when grid is on and put the switch on charging mode I get output

  111. N/C of a damaged relay has a different position than chinese relay, when I soldered the relay I changed the wires too, but I have a problem, the transformer produced noises and I used multiple fuses but the result was the same, when I connected the pulb, it didn't light properly (produces very weak light then it was damaged). there is a ceramic resistor of 30w 0.1 ohm conneted to the middle pin of SPDT switch and fuse, do you think the problem is with the resistor because when I changed that resistor with wire I got same result too

    • You will have to identify the N/C, N/O and the pole of the relay for making connections correctly.

      the resistor may not be affecting the response because 0.1 is too low, but it's better to remove it anyway.

      If the transformer is producing noise, that indicates a short circuit being produced by the relay operation, so i would suggest you to first confirm the contact details using a multimeter before implementing it practically

  112. hello SIR

    without changing the relay when I put the switch on charging mode output

    wasn't there, but when I soldered the new relay in the place of the original

    one inverter didn't work at all, I searched the net to know how to identify

    relay pins and I figured out that the ON and NC are in opposite direction so

    I soldered the relay as shown in the following pic:!wEAFSLAJ!hy0iDcSWAuZXdqOYmEj4v90XiVMn_o3Amxkm3lh6QBg

    and when I put the switch on charging mode output was there but in inverter

    mode I got low voltage around 48V instead of 220V.

    please download the following pics may be you'll find the problem because

    there is another relay and physically is good but I haven't test it!QcZWhAbZ!A0gvwNFx3e_gDiUKOo4qz-eqANfgbaqnKdP8MkrghYw!5VIlnaSR!MDXLriAU6kUqGdxbCO7o_obfenSFPjCOADVdcYePgaI!9U4SRSyK!YZIgaSCleGPbxcS1GeiN6bhdYZxiyvfCOfNtdwIdN-c!QV4S2aab!8z7R_LL1jHEWfLp4doXpjvzb8Gl0R2xTc5BifJIj-kE!RJACUIpK!ikEvHfv9qV1KSbQ5oLugydJrML6bhwbvxb1KNobPNw8

    • Thanks Ahmed, I have checked the images and it seems you have already figured out the pinouts of the relay correctly and have wired it correctly….but it's strange how you are getting 48V instead of 220V.

      However I am having difficulty in understanding how the relay is switching the battery charging voltage which is supposed to be DC and how come it is also switching the 220V AC??…if possible please draw a rough schematic and show it to me so that I can understand what voltages the relay is connecting to and where exactly these voltages are going…??

  113. You were correct, the problem was with the relay pins, When I told you that the inverter wasn't working I was wrong for running the inverter battery should be attached and I think it's normal for the transformer to produce humming sound because it is a square wave inverter.
    I want your suggestions for the followings:
    1) Is it safe to run 32 INCH LED TV?
    2) I installed 8A fuse, Which fuse will be suitable because it's not written on the case of inverter?
    3) Is it normal for ceramic resistor getting hot?
    Thank you so much sir

    • OK, no problem!

      1) All LED/LCD TVs have an in built SMPS circuit which will confortably convert any form of AC to DC for the operation, it a square wave can eb used without issues.

      2) for the TV you can use a 2 amp fuse, will be enough.

      3) if it's a high watt resistor then little warming can be OK, otherwise it can be a problem…then it must be checked.

    • I read your topic about Solar Panel/Battery/Mains Changeover Relay Circuit and I built one to suit my requirements my goal is thet, when grid is there charging is done thru inverter and the solar charge controller charging the second battery but in the absence of grid the solar charge controller charging the battery which connected to the inverter.
      could you see the following diagram please I want to be sure if it's safe to use this circuit.

    • actually without proper symbols, I am having difficulty in simulating the design the design in my mind,

      Ok I'll check this new diagram and let you know you soon…

    • I have checked the diagram, it looks OK to me….the second battery will start charging when the first battery is full.

      and the 3 pin socked will get the inverter mains whenever Grid mains fails….but the battery will be always connected with the inverter which can cause slight consumption all the time….

  114. Shivam Singh I have an arise inverter . It usually sparks at input plug when I consulted electrician about it he said sine box is fused . I want to know what is the reason of its fuse and how it can get repaired.

  115. Dear sir, when I switch the main supply off. And I checked the switches which are on inverter then it shows 330 volts. Isn't it too much for my appliances.. Also when I put tester in these switches the light glows in one of the hole.but when I turn switch on. Light glows in both live and neutral. Is there any problem with my inverter

    • Varun, it seems like your inverter does not have a voltage regulator, and therefore 330V could be dangerous for smaller appliances. to correct this you can use a lower voltage battery.

      mostly inverter transformer secondary work in a push pull manner which causes their output wires to switch between LIVE and neutral alternately and therefore will show live at both ends…it is normal and nothing to worry about

  116. In my home inverter when power goes it is not start automatically from battery .But if I change the switch position regulated mode /Deregulated mode (any change ) then all appaliencence run from battery .I need to change every time if power go.

    • it seems your changeover relay section has some fault…you must open the inverter and check the section which is responsible for executing the automatic changeover and check why it may not be responding to the power failure

  117. My invert er was working perfectly all of a sudden it stop bring output and leakage was observed on the neutral point but when inverter is disconnected the leakage will disappear. what us the cause?

  118. Hello Swagatam Majumdar
    I think You know the features of Sukam eco 1100 solar inverter, I want to mod falcon 1050Va inverter to make it work as sukam eco 1100, there is many options to do that like sukam solarcon,rehub and others but I'm planning to buy solar charge controller like victron bluesolar 75|15A
    and integrate it with the inverter to make it as solar inverter, solar charge controller can provide 15A if loads consumes more than that it takes the remaining from grid. Is it that possible?

    • Sorry, I do not have much information about the features of these equipment because I do not deal with them very often…so I won't be able to help with this…

  119. I have a 1 kva inverter. wherevere AC main power supply turned off i need to manually change the white wire( of inverter) at the output socket of inverter. i am confused why it is not auto adjustable.

  120. Hie bros

    Am new here and also newbie to electronics and I want to explore, learn as and become an expect. I have been following your posts for a while.

    Am desperately in need of your help.

    I have a 3kva 2,4kw mks apex DC to Ac pure Sinewave inverter off grid. It was working fine all along with load of about 170watts during day and about 300watts at night. Sometime last year during the day, I heard popping sound in the inverter and suddenly a buzzer and an error code 05 ( output short circuited). I opened it and found from the output array, one side one mosfet had blown casing and the other had one leg blown,the other two were fine. I checked for any other components failure but could not find any and I replaced with new ones and worked again finely for about 4 months and repeated the same. This time it blew two resistors near the mosfets ie 100ohm and 4.7ohm, I replaced all but when I turn it on the error code 05 is shown and no AC output.

    I tried checking every component I could except for the ICs becoz I don't know how to diagnose them. Where could be the problem? NB the big caps on the high voltage area are charging when I turn it on.

    Please help.

    • Hi Francis bro, you will have to identify the exact position of these resistors….If it's one of the gate resistors then the problem could be more serious, since that would mean the driver IC has been fried this time….because normally the gate resistor is isolated with a high impedance, but if it is blown then the associated IC might be also blown.

      But the main thing to consider is why these short circuit issues are happening repeatedly? and isn't there any fuses connected with the battery or the trafo output…?

  121. HI All,

    i have an inverex inverter which is now not giving battery output to load after phase and neutral swapped of AC supply by mistakenly.
    what should be the probable cause.


  122. Hi Sir, i have inverex inverter and not taking load on battery while AC power is off.
    problem started after phase and neutral swapped at AC input to inverter mistakenly.
    swap resolved but still the problem is there
    only one circuit breaker present (outside boday) for input circuit and that is fine as its function well on AC input means battery charged properly and load also taken well but when AC supply get off, all load gets zero while battery showing 4 (max) cells charged.

    • Hi Support ALU, the input phase/neutral can be connected anyway round, that cannot cause any problems to an inverter or AC operated unit. You seem to be misjudging the fault…the fault could be due to some other reason not because of phase/neutral swapping….you will have to diagnose the fault by inspecting the various stages using a DMM.

  123. I have 5kva/96DC Inverter , recently replace new batteries 8 pcs x 200Ah, after connecting all batteries I started the inverter and its tripping with alarm on and panel reads 2 messages ''MAIN FAIL INVERTER ON'' and ''PROTECTION'' SHORT CKT/OVERLOAD after replacing batteries it does not charge and Batteries are not fully charged , Does it require fully charged batteries before installation of new batteries?
    What could be the issue of getting this messages and inverter triping

    • It looks like some kind of internal technical fault…it's not due to low battery…otherwise you would have got a LOW BATT indication.

      still, you can try charging the batts externally and try again to see the effect.

      It will need to be examined by opening the inverter, It cannot be judged by assumptions

  124. Greetings to you sir, my index inverter, 48v 5kva was affected by lightning and now it is displaying overload fault even when no load is attached. What should I do sir. Thanks.

    • Hello justin, that can be difficult to troubleshoot without an actual check up, because the lightening might up burnt some sections of the inverter which will need to diagnosed thoroughly for identifying the fault.

      you can do one thing, open the inverer and check the voltage directly across the transformers output wires, if it shows proper voltage and is able to power a specified load, then we can assume the fault to be in the overload indicator section, which could be then separately investigated

      • Thanks for your response. Done the check as directed, it can power a load. Tested the sensing transformer 400/0-23V, its output voltage is 11.6V. All other components like the diodes and resistors in the sensing area are ok. Thanks

  125. Hello,
    I have a chicago electric 750W power inverter and tge fuses are good, however, there is a diode ( I think) yhat has burnt up right by the dual red wires running to the hookup location. Can’t make out the the color rings in it at all. Can you help me?

  126. I am using EXIDE 1050VA ,12V inverter ,when there is any short circuit I have to on/off inverter even if the short circuit is removed,can this problem be eliminated as if there is any fault in inverter supply ,inverter should turn off,but if the fault is removed it should turn on automatically, please help…

    • It seems the inverter is designed by default to latch up during a short circuit, and I think it is a recommended feature, and should not be changed. however it can be modified by opening the relevant stage and by checking and removing the part responsible for this action.

  127. I have Sukam 650 inverter from 2 year working ok but now I change my home and I connected inverter but there is a problem that when main supply on fan speed is ok but when supply off or gone inverter output is low and also fan speed very slow while my battery is new purchase on august 20 ,2017 what is the solution of my problem

    • This can happen only because of one reason, battery not charged optimally, check the inverter output with a meter and with a load connected, if it shows a drop in voltage would mean the battery is not charged properly, and will need to be charged for some specified period of time.

  128. Hello sir,
    i am ausing a su-Kam 600VA sine wave inverter. at the of house shifting accidently connected my battery in reverse polarity ,therafetr i have changed the polarity but it is not working and seems it has got damaged.visual inspection shows no sign of damage. can it it be repaired ? if yes then can you plz tell me the important steps to be taken……i read similar amswers but worried whether su kam might be having diffrent circuitry……plz help

    • Hello Subhash, that is very strange, how can a reputed inverter brand not include a reverse battery protection??….if that’s true in that case you might have burned a few crucial stages of the inverter circuit such as ICs and fets, which cannot be predicted without actually checking it….even a fuse couldn’t have prevented this from happening…I would recommend calling somebody from the company and explain him about this issue and the possible remedies.

  129. @Swagatam, my inverter was unknowingly reversed the input terminals, +ve from the battery connected to -ve of the inverter and vice versa. Leading to death of the inverter. Is this repairable?
    help to to my gmail:

    • Hi Julius, it is definitely repairable, however it could be a lot of hard work to test and replace the burnt parts, which could include ICs, mosfets and other semiconductors.

  130. Dear Swagatham,

    I have Sukam sturdy sinewave inverter 650VA. I recently started facing an issue with it. When i give the battery connection the Mosfet starts burning? I have replaced the Mosfets with removing the connectivity of the Inverter transformer. But still the same problem persists. I am not sure what to do with this issue.

    Need your kind help.


    • Dear Shyam, if the mosfets are burning even after replacing them then possibly the driver circuit is burnt and is not oscillating.

      Before connecting the mosfets check whether the gates of the mosfest are being supplied with the required oscillations or from the concerned IC circuit

  131. I have 2000watt inverter. After Thunder strikes it can no longer supply light again, but the green and red light keep blinking. After like some seconds the inverter will be hitting very serious!!
    Pls,, sir can you help me?

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