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 normally may be divided into three important stages viz. oscillator, amplifier and the transformer output stage.
Oscillator: 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 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"
DC to AC Inverter, Repairing Tips
In the above explanation a couple of things become very critical for obtaining correct results from an inverter.
Firstly the generation of the oscillations, due to which the process of voltage induction is able to take place across the windings of the transformer.
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.
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.
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 InverterOnce 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:
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.
In case you find the oscillator stage working fine, go for the next stage i.e. the amplifier stage. Check each device using a digital multimeter, you may have to completely remove them from the board for the particular tests. If you find a particular device to be faulty just replace it with a new one.
Sometimes transformers also become the major cause for a malfunction. 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 a lot of practice and some trial and error.
Still have doubts...feel free to post your specific questions here.
Queries and Solutions Regarding Inverter Fault and their Troubleshooting
bina load k load show karta h inverter what is the fault could you tell
Swagatam Majumdar May 14, 2016 07:58 PM
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
Santhosh May 18, 2016 01:02 PM
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.
Swagatam Majumdar May 18, 2016 05:19 PM
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.Delete
Santhosh Kumar May 18, 2016 08:37 PM
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.
Swagatam Majumdar May 19, 2016 09:32 AM
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.
ALOK PUI May 23, 2016 01:26 PM
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?
Swagatam Majumdar May 24, 2016 07:39 AM
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
Truth Jun 1, 2016 04:17 AM
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?
Swagatam Majumdar Jun 1, 2016 07:15 PM
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.
Truth Jun 1, 2016 07:28 PM
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
Swagatam Majumdar Jun 2, 2016 10:18 AM
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.
Anonymous Jun 5, 2016 01:52 PM
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?
Swagatam Majumdar Jun 5, 2016 09:55 PM
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
Ahmed Qaid Jun 7, 2016 03:58 PM
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:
Swagatam Majumdar Jun 7, 2016 08:32 PM
Hello Ahmed, it's not properly visible...please specify what those components are?
Ahmed Qaid Jun 13, 2016 07:07 AM
I bought a normal pure sine wave inverter and a separate solar charge controller. the power in my country 3 hours off then 2 hours on then 3 hours off then 2 hours on, the power keeps running in that pattern. To protect my battery I have to turn off my inverter to prevent charging from inverter but my question is that, is there any relay could do the following job: when power is there inverter charge the battery and solar charge controller stop working but when power cuts off, solar charge controller start charging the battery
Swagatam Majumdar Jun 13, 2016 01:20 PM
you can try the following concept:
Ahmed QaidJun 13, 2016 03:42 PM
vemula Jun 11, 2016 04:52 AM
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
Swagatam Majumdar Jun 11, 2016 05:25 PM
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
Ahmed Qaid Jun 17, 2016 08:41 AM
Is there any way to reduce ceiling fan buzz when using square wave "truepower 850va" invereter?
Swagatam Majumdar Jun 17, 2016 02:16 PM
you can try including an LC filter network at the output of the inverter and check if that helps
Ahmed Qaid Jun 20, 2016 08:32 AM
If mosfets are faulty inverter will still working?
which capacitor film should I need to connect it to the output of TP850VA square wave inverter?
Swagatam Majumdar Jun 20, 2016 09:22 PM
Nope, if power devices are faulty the inverter will smoke or shut down, it simply cannot work
try a 0.47uF/400V capacitor
Unknown Jun 20, 2016 11:00 PM
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?
Swagatam Majumdar Jun 21, 2016 05:06 PM
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.
Ahmed Qaid Jun 21, 2016 03:25 AM
IS BTA16-600B THE EQUIVALENT OF BTB16-800CW?
Swagatam MajumdarJun 21, 2016 05:08 PM
almost similar except some features
Ahmed Qaid Jun 22, 2016 07:36 AM
1) MY TP850VA HAS BTB16-800CW TRIAC BUT IN MY COUNTRY IS NOT AVAILABLE SO THERE IS NO DAMAGING IF I USE BTA16-600B?
2) IS IT SAFE TO RUN MY LCD TV ON MY INVERTER (SQUARE WAVE INVERTER)?
3) CAN YOU PROVIDE ME A LINK FOR 0.47uF/400V capacitor? BECAUSE WHEN I SURFED THE NET I FOUND THAT X CAPACITOR IS THE RIGHT TYPE FOR MY NEED?
Swagatam Majumdar Jun 22, 2016 03:37 PM
1) yes you can replace it with the mentioned triac
2yes it is safe.
3) search for 474/400V capacitor you will find it.
Ahmed Qaid Jun 30, 2016 08:37 PM
I searched electronic shops and I find 474k/630V, is it ok to use instead of 474/400V
Swagatam Majumdar Jul 1, 2016 11:14 AM
630 is better than 400...so no issues you can use it.
Ahmed Qaid Jun 23, 2016 01:23 AM
THANK YOU SO MUCH
Unknown Jun 24, 2016 08:13 PM
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?
Swagatam Majumdar Jun 26, 2016 08:54 AM
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
Anonymous Jun 29, 2016 08:58 PM
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..
Swagatam Majumdar Jul 1, 2016 11:05 AM
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.
Ahmed Qaid Jul 10, 2016 04:25 AM
I have a 16w rechargeable fan but 2 resistors of its pcb were burnt out, I went to a repairer and changed those 2 resistors but the pcb doesn't charge the battery so can you help me to fix that, the following link https://drive.google.com/file/d/0B_2QrDIghjN1Z3RZSHRsVzlrb00/view?usp=sharing has a pic of pcb and the red circle denotes to those resistores. the battery is 6v7ah
Swagatam Majumdar Jul 11, 2016 12:49 PM
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.
Ahmed QaidJul 13, 2016 03:10 AM
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?
Swagatam Majumdar Jul 13, 2016 08:27 AM
the transistor which is utilized for driving the fan could have gone faulty...check it and if possible replace it with a new one
pankaj singh Jul 16, 2016 09:24 PM
I have Su kam inverter for household use. It suddenly got dead in night i also checked the fuse. fuse is perfectly right
Swagatam Majumdar Jul 17, 2016 08:53 PM
check the battery connections, or any other relevant connections within the inverter unit...
Kabwe Chileshe Jul 28, 2016 01:12 AM
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?
Swagatam Majumdar Jul 28, 2016 11:35 AM
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.
abhi Aug 5, 2016 11:01 AM
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
Swagatam Majumdar Aug 6, 2016 08:05 AM
not sure, could be some internal malfunctioning, the authorized service personnel will know it better
Unknown Aug 11, 2016 07:43 AM
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 to allay my fears.
Swagatam Majumdar Aug 11, 2016 03:11 PM
please check the fuses associated with the relevant outputs of the inverter....
Anonymous Aug 31, 2016 11:05 AM
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
Swagatam Majumdar Aug 31, 2016 03:52 PM
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.
Chanakya Dinesh Sep 23, 2016 07:59 AM
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 me quickly, i needs to replace elements and get in condition online
Swagatam Majumdar Sep 23, 2016 05:39 PM
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
Onyekachi Obidum Oct 16, 2016 09:04 AM
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?
Swagatam Majumdar Oct 16, 2016 10:25 AM
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
Balasubramanian (Bala) Oct 17, 2016 05:52 PM
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?
Swagatam Majumdar Oct 18, 2016 07:16 AM
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.
Balasubramanian (Bala) Oct 18, 2016 04:56 PM
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?
Swagatam Majumdar Oct 19, 2016 07:50 AM
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
Anthony A Obott Oct 26, 2016 12:50 PM
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
Swagatam Majumdar Oct 26, 2016 05:05 PM
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.
Syed Karimullah Nov 10, 2016 12:06 AM
Hello sir. I have one doubt about inverter.im 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.
Swagatam Majumdar Nov 10, 2016 11:23 AM
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.
Mas Dokas Nov 15, 2016 04:08 AM
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.
Swagatam Majumdar Nov 15, 2016 05:00 PM
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.
Mas Dokas Nov 15, 2016 06:59 PM
Thanks very much for the . 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
Swagatam Majumdar Nov 16, 2016 08:22 AM
Thank you Mas, I hope you will be able to troubleshoot the fault with some effort, if you get stuck somewhere you can always come back here for a possible solution.