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## How to Make a Simple 200 VA, Homemade Power Inverter Circuit - Square Wave Concept

An efficiency of around 85 % and a power output of more than 200 watts is what you will get from the present design of a power inverter (home built). Complete circuit schematic and building procedure explained herein.
You might have come across many articles regarding power inverters, however you might be still confused about making a power inverter? The present content provides a complete building tutorial of a home built power inverter.

If you are planning to make your own low cost and simple home built power inverter then probably you won’t find a better circuit than the present one. This heavy duty, easy to build design includes very few numbers of components which can be found readily available in any electronic retailer shop. The output of the inverter will be obviously a square wave and also load dependent. But these drawbacks won’t matter much as long as sophisticated electronic equipment are not operated with it and the output is not over loaded. The big benefit of the present design is its simplicity, very low cost, high power output, 12 volt operation and low maintenance. Besides, once it is built, an instant start is pretty assured. If at all any problem is encountered, troubleshooting won’t be a headache and may be traced within minutes. The efficiency of the system is also pretty high, in the vicinity of around 85% and the output power is above 200 watts.

A simple two transistor astable multivibrator forms the main square wave generator. The signal is suitably amplified by two current amplifier medium power Darlington transistors. This amplified square wave signal is further fed to the output stage comprising of parallel connected high power transistors. These transistors convert this signal into high current alternating pulses which is dumped into the secondary windings of the power transformer. The induced voltage from the secondary to the primary winding, results a massive 230 or 120 volts conversion, as per transformer specifications.

Let’s study in details how the circuit functions.

Circuit Description

The circuit diagram description of this home built power inverter may be simply understood through the following points:

Transistor T1 and T2 along with C1 and C2 and the other associated parts forms the required astable multivibrator and heart of the circuit.

The relatively weak square wave signals generated at the collector of T1 and T2 is applied to the base of the driver transistors T2 and T3 respectively. These are specified as Darlington pairs and thus very effectively amplify the signals to suitable levels so that they may be fed to the high power output transistor configuration.

On receiving the signal from T2 and T3, all parallel output transistors saturate well enough according to the varying signal and create a huge push pull effect in the secondary windings on the power transformer. This alternate switching of the entire battery voltage through the windings induce massive step up power into the primary windings of the transformer producing the desired AC output.

The resistors placed at the emitter of the 2N3055 transistors are all 1 Ohm, 5 Watts and has been introduced to avoid thermal runaway situations with any of the transistors.

PARTS LIST

RESISTORS ¼ WATT, CFR

R2, R3 = 39 K,

RESISTORS, 10 WATT, WIRE WOUND

C1, C2 = 0.33 ÂµF, 50 VOLTS, TANTALLUM,
D1, D2 = 1N5408,
T1, T2 = BC547B,
T3, T4 = TIP 127,
T5-----T12 = 2N 3055 POWER TRANSISTORS,
TRANSFORMER = 10 AMPS, 9 – 0 – 9 VOLTS,
HEATSINKS = LARGE FINNED TYPE,
BATTERY = 12 VOLT, 100 AH

Building Tutorial

The below given discussion should provide you with a detailed step wise explanation regarding how to build your own power inverter:

WARNING: The present circuit involves dangerous Alternating Currents, extreme Caution is advised.

The only part of the circuit which is probably difficult to procure is the transformer, because a 10 Amp rated transformer is not easily available in the market. In that case you can get two 5 Amp rated transformers (easily available) and connect their secondary taps in parallel.

Do not connect their primary in parallel; rather divide them as two separate outputs (See Image and Click to Enlarge).

Next difficult stage in the building procedure is the making of the heat sinks. I won’t recommend you to fabricate them by yourself as the task can be quite a tedious one and time consuming too. It would be rather a better idea to get them ready made. You will find variety of them, in different sizes in the market.

Select the suitable ones; make sure that the holes are appropriately drilled for the TO-3 package as shown in the figure. TO-3 is the code to recognize typically the dimensions of power transistors which are categorized in the type used in the present circuit i.e. for 2N3055.

Fix T5----T8 firmly over the heat sinks using 1/8 *1/2 screws, nuts and spring washers. You may use two separate heat sinks for the two sets of transistors or one single large heat sink. Do not forget to isolate the transistors from the heat sink with the help of mica isolation kit.

Constructing the PCB is just a matter of putting all the components in place and interconnecting their leads as per the given circuit schematic. It can be done simply over a piece of general PCB.

Transistors T3 and T4 also need heat sinks; a “C” channel type aluminum heat sink will do the job perfectly. This is can also be procured ready made as per the given size.

Now we can connect the relevant points from the assembled board to the power transistors fitted over the heat sinks. Take care of its base, emitter and the collector, a wrong connection would mean an instant damage of the particular device.

Once all the wires are connected appropriately to the required points, lift the whole assembly gently and place it on the base of a strong and sturdy metallic box. The size of the box should such that the assembly does not get crammed.

It goes without saying that the outputs and the inputs of circuit should be terminated into proper socket type of outlets, to make the external connections easy. The external fittings should also include a fuse holder, LEDs and a toggle switch.

Testing

Testing this home built inverter is very simple. It may be done in the following ways:

Insert the specified fuse into the fuse holder.

Connect a 120/230 volt 100 Watt incandescent lamp in the output socket,

Now take a fully charged 12V/100Ah lead acid battery and connect its poles to the inverter supply terminals.

If everything is connected as per the given schematic, the inverter should instantly start functioning illuminating the bulb very brightly.

For your satisfaction you may check the current consumption of the unit through following the simple steps:

Take a digital multimeter (DMM), select 20A current range in it.

Remove the inverter fuse from its fuse holder,

Clip the DMM’s prods into the fuse terminals such that the DMM’s positive prod links with the battery positive.

Switch on the inverter, the consumed current will be instantly displayed over the DMM. If you multiply this current with the battery voltage i.e. by 12, the result will give you the consumed input power.

Similarly, you may find the output consumed power through the above procedure (DMM set in the AC range). Here you will have to multiply the output current with the output voltage (120 or 230)

By dividing output power by the input power and multiplying the result by 100, will immediately give you the efficiency of the inverter.

If you have any questions regarding how to build your own power inverter, feel free to comment (comments need moderation, may take time to appear).

•  Stumble

1. i know nothin abt phy nd chem....can i make an inverter?? pls help

1. I am sorry, No you cannot, you need to be well versed with the basics of electronics first before attempting any electronic project discussed in this blog.
Regards.

2. Hi swag,can the ordinary stepdown transformer be used as a step up for inverters by connecting the signal back from the secondary?

1. Hi Nemwel,

Yes it can be done, an inverter transformer is actually an ordinary transformer, connected the opposite way round.

Regards.

3. Hi swagat
can i connect a load of 300W to this inverter??

1. Hi Trisom,

No, you cannot connect more than 150 watts of load to this inverter design.

2. swagat,

plz tell me wat should be the design if i want a 300W output and which last for a minimum of 5-6 hours??

3. Hi Trisom,

I think you should first build a smaller inverter like the one shown above, if it works as intended then you can modify it further for getting more power.

Regards.

4. can i make 200va inverter by using this circuit?

SHAHJEE

1. Yes you can make...

5. T1,T2 npn and T3,T4 are pnp. am i right?
and battery's +ve wire is going to power T and -ve is going to pnp T emitter?

1. Yes, T1,T2 are NPN and T3,T4 are PNP, the blue wire from the battery is the positive and the white wire is the negative.

6. Do not forget to isolate the transistors from the heat sink with the help of mica isolation kit.
This sentence, i did not get, please could you help me in this, how to connect? because i have only a heat sink and has 8 holes for 8 transistors, so should i cut it into two parts for fixing 4 transistors or remain as same and what about mica isolation kit?

1. The body of all power transistors are internally connected to their collector, if you connect them directly over the heatsink, all the collectors will get shorted and the transistors will get damaged instantly, that's why a mica isolation is put in between the transistor body and the heatsink while fixing them.

It is better to use separate heatsinks for each of the transistors if you want to avoid mica paper isolation.

7. and for testing purpose, can i test on project board and is there necessary to fix power transistors on heat sink?

1. The transistors can become hot within seconds and may get damaged, so heatsink is required.

2. somewhere i saw, washer use for transistor to fix in heat sink and is there not use of IC CD4047, if we are getting voltage from battery and can i test it by power supply?

3. This comment has been removed by the author.

4. This circuit is based on AMV principle, so no need of IC4047, no you cannot test it with a power supply, you need a battery of at least 30 AH rating to test this circuit.

8. Can i test it by generator dc source?

1. Yes, if it's capable of providing 12V at 8 amp..

9. how can we set the frequency? or would be a fix frequency of it?

1. it is already fixed for the present design, 50Hz @ 220v

10. This comment has been removed by the author.

11. Can i use D313 or D331 instead of bc547? and both can be different, can i use in the circuit?

1. No, D313 or D331 cannot be used in place of BC547....

12. I have made but it's not working, i have put all things but result is zero. what to do?

1. Check stage wise, begin by checking the multivibrator stage first then the driver stage and the output stage...

1. All are 1 Ohms 10 watts, you may reduce the value for getting more power at the output, but do not decrease below 0.5 Ohms.

14. I have made but the output volts vary from 0 to 40V for only 1 second and become 0V, i am not getting a fix 220 voltage. what could be the problem?

1. Initially use only single 2n3055 transistors at the output stages and check the performance, if it takes 50 watts of load would mean it's OK, then go on increasing the number of 2n3055 transistors gradually.
The circuit should starting working immediately if everything is done correctly as explained.

15. Sir i wanna build this inverter can u plz upload the making of this inverter....This will help me a lot...

1. Hi Humayun,

Everything has been explained in the article, if you have specific questions, feel free to ask them.

16. Actually i know a little basics of electronics,that's why i was asking for it.. Can u plz elaborate how to fit the transistor in heat sink and plz tell me how to ground a electronc circuit component for example battery, trnsistor etc...

1. It will require a practical demo, so probably you can see it in youtube, there should many videos posted, try searching it there.

Grounding of parts is not required, just connect everything as shown in the diagram,

The blue wire is the positive and the white wire is the negative of the battery.

You can use any small lead acid battery for experimenting with the circuit, if 100Ah is unavailable.

17. 100 AH battery is expensive plz tell me any other battery useful for this circuit

18. is c2 is connected to both R4 and R6......

19. IS there no need to fit into heat sink( T9-T12) power transistor...plz reply fast

1. From T3 to T12 all strictly require heatsinks...

20. Brother Can i use the Ac-Dc Adapter spec..12 V 500mA max.. instead of 12 v battery just 4 testing...reply fast

1. Brother i wanna make it on vero board plz tell me about the connecting wires for the inverter circuit(Size)etc...

21. Can i use the small connecting wires used for bread board in inverter circuit....

1. Hi Humanyun,

It will be difficult for me to explain every details here, you may take the help of some engineer in your area, because this project is not easy.

22. Hello Swagatam i have got a battery of 12v 7.2AH can i use for above circuit testing...

1. Hi Humayun,

Yes you can use it, but the output will produce only 40 watts of power.

Use only single 2N3055 transistors at the output stages.

23. Swagatam my teacher asked me to make an inverter around 100VA. I need a simple circuit including battery 12v 7.2AH and 2N3055 transistor and 12-0-12 10 Ampere transformer because i have purchased these things. Can u please design a circuit including above things.I have to submit it in next week so do in hurry.

1. Humayun, you can build the circuit which is given in this article.

Use single 2n3055 transistors at the outputs.

24. How much it costs?

25. hi
this is kiran
in the above circuit what happen if i remove t5 to t8 and t9 to t12

1. Hi,
If they are removed the transformer will not get power and there will be no output...

26. sir,
can u say how can this circuit works
and can i try it on bred board

1. No, I am sorry you cannot do this on breadboard.

28. Sir, is it possible to do this project around \$25, because the 100Ah battery would be a costlier one?

1. At the present time it will be difficult because the prices have risen a lot....

29. i have a v guard 600va ups can i replace its battery with a 65AH battery and use it as an inverter

1. If the external battery voltage is same as the UPS battery then you can use it.

2. Hi Jithin,
I think your idea may be a little bit dangerous. Because the charger in 600 VA ups is limited to charge the inbuilt battery. So you cannot charge a huge current battery with that charger circuit.

30. will there be any problem during charging is their a need for external charging circuit

1. Charging will need to done after removing the batt from the circuit and through an external suitable charger...

31. sir this is junver can i use 250v/a transformer in this circuit?thanks.

1. Hi Junver,

yes you can use it.

32. Sir its me junver i already made one of your inverter the simplest it works great it drives 2 cfl 18 watts thats why i decided to make the above circuit because i trust your circuit design..my question are about the above circuit,can it drive 5, 25watt cfl light connected in parallel?can it also drive a celfone charger 50-60hz? This circuit will not work in t.v am i right? But i will make it because in our area black out is always our problem.plese reply asap.thanks for sharing your knowledge...sorry for my english,im not good in it. Peace.may the creator bless you.

1. Hi Junver,

Though I cannot guarantee, I strongly believe the above design will work perfectly according to your above needs.

It will also drive a cell phone charger.

Regards.

33. Hi Swagatam, I have this old Microtek Inverter (600W) that keeps switching between charged and charging and is not stable. Could be issue with relay? Any ideas where I could find its schematic for repairing purposes? Thanks. Would the above schematic also be similar to what it is inside? Waiting for reply thanks.

1. Hi GMagoon,

Inverter circuits can be hugely different from each other with their configurations, so it is almost impossible to diagnose the fault without checking it practically.

I think the issue can be with the preset controls whose contacts might have got corroded, still it cannot confirmed without actually seeing it.

Regards.

2. Hi. Thanks for the reply. Do you however, have any idea where I may find a schematic for a inverter anywhere? Thanks :) Just need a schematic for reference atleast. Thanks.

3. Hi,
There are hundreds of different inverter schematics online based on a huge number of different specs....so it's very difficult to pick the right and the most appropriate one from them:)

4. Hi, thats understood but could you kindly atleast provide me with a starting point / website? Thanks bro :)

5. Thanks. Maybe I should consult a text book instead.

6. This is the kind of inverter I have: http://img841.imageshack.us/img841/9602/microtekinverter.jpg

7. All brands have their own specific circuit diagrams and specs...

34. Hello sir swagatam im mark.can i ask you a question about the diode substitution..what is the substitution of a diode 1N414B and a diode DX2A? Thanks for speedy reply..

1. Hello Mike,

1N914 is one good equivalent of 1N4148,

35. Is there eney indication for the Base& Emeter by the manufacturers for the 2n3055 transistor?

1. You may check the 2N3055 datasheet to confirm it.

36. sir its me junver can the above circuit power up tv 60hz 85 watts? and a 20 watts cfl light? sir are you sure this circuit will work or function? have you already test it by your self coz im planning to make the above circuit thats why im asking you coz it will cost a lot here in our area philippines....

1. Yes this circuit is tested and it is capable of handling up to 200 watts.

For 85 watts you may try the below given circuit, it's also tested:

37. sir this is mark sir my question is regarding this circuit sir http://www.eleccircuit.com/12-volt-to-220-volt-inverter-500w/ what is DX2A? what does it mean? what will be the exact diode of the diode DX2A? and what will be the replacement of diode 1N414B coz 1N414B is not available in our area.... thanls for speed reply.... thanks a lot.....may GOD bless you happy new year sir swagatam....

1. Hi Mark,

Use 1N5402 for DX2A and 1N4007 for 1N1448...these will easily work.

Happy New Year to you too!

38. Sir its me junver again,can the above circuit modified to 500 watts? It it could be modified,how? Thanks

1. Yes it can done, replace the transistors with mosfets.

39. Hello sir its me mark, sir regarding the 500 watt inverter sir is diode 1N414B and diode 1N4148 are they both thesame?im just curious.. And my second question sir is the resistor with no exact wattage,what will be possible exact wattage i will use in order to make it work perfectly? About the DX2A diode it is possible that there are diode namely DX2A? I hope you answer my question im just curious and still not enough knowledge in electronics..thanks..always keep safe wherever you are.you are a good person bec. You share your knowledge unlike others..peace..

40. Sir my name is umeh Cyril, an electronics ENGR. Student from Nigeria; I want to ask if it is ok to use a 14-0-14volt transformer inplace of the 12-0-12 volt.

1. Hello Umeh,

That would give a reduced output voltage....around 160V

41. the circuit you have given, could you please confirm, it could work with solar panel based chargers for charging battery of 200va, and what other care should be taken

1. The circuit is a confirmed one, it will work with all DC power sources as long as the voltage is maintained around 12V.

42. please explain me about switching SPDT relay through opto coupler output. ASAP

1. I'll try to produce it in a new post soon.

43. sir...i am an engg student of elctrical and elex branch.....i want to build a 300 va or around so that a fan and a tubelight can be swicted ON......what are the components required & neccesary guidlines for its construction is required.....plz help sir.....thanks....plz email me at : kushalsomvanshi@gmail.com......thank u sir....

1. you can try the following circuit:

44. hello swagatam,,,i want more escrption about the working of inverter cause i'm gg to prepare a project report s can u help me in finding?

1. Hello Sneha, as you can see i have explained everything in the article....however you can specify your questions, i'll try to explain.

45. Hello Sir,
I have problem regarding Transformer used in the above circuit..I just wanted to simulate it on Proteus ISIS but i don't know how to connect transformer.can u send me a simulation of this circuit.I just need it for verification and to do some changes.I know it would take your precious time but really! really! need it.Please send me its simulation done via any software preferably by Proteus ISIS(any version)
Regards,

My email:bilaljamil1992@gmail.com

1. Hello Bilal,

I'll try to do it if it's possible...

46. appreciated your efforts Mr. Swagatham

47. Hello Sir,

Regards,

My email:bilaljamil1992@gmail.com

1. I am sorry, I am not getting time to do it....

48. Hi swagatam you are really a great one....

49. I’m very happy to see you projects thank for this wonderful site
I’ve got a doubt I’ve seen some 8 pin transformers in inverter circuits whatis that how do i test it and know its ratings.

1. Thank you!

The pins could be the terminals corresponding to particular winding of the transformer. These winding could be connected with a particular inverter circuit for the intended specific safety functions and other similar things.

50. can 0.47mf work 50 volt

1. yes will do, but make R2/R3 = 33K

51. can this transformer work http://www.mpja.com/images/7846-large.jpg

1. yes will do, but preferably it should be 9-0-9V, not 12-0-12V

52. a few questions, how are you connecting the power transistors to each other? then to each end of the transformer (1 wire to one set of 4 other wire to other set of 4) couldn't you just use the heat-sink aren't these npn power transistors? according to your symbol they are so all of their bodies are connected together. what do i search to get the correct transformer? i cant seem to find 12-0-12 10 amp to 220v ac unless this is a step down transformer in reverse? my only electrical shops are ebay or jaycar.com.au It's my first time using transformers. Lastly you said about the 1 ohm 5 watt at the emitters of the power transistors, are they 10 watts or 5 you said 5 at the intro but commented to someone 10 watts or does it no matter for this circuit?

1. The transistors are connected as they are shown in the diagram, click the diagram to enlarge for getting a better view. one common heatsink is used for all the transistors on each channel, meaning two separate for the two channels, if a single common is used it would create a short circuit.

The emitter resistors make sure that the transistors conduct uniformly so that all dissipate evenly.

The wattage of the resistors will depend on the battery AH and transformer amp rating, if its above 40AH and 5amps respectively, the 2N3055 base/emitter resistors will need to be upgraded to 10 watts, for lower wattage a 5 watt would suffice.

Ideally a 9-0-9V/10amp transformer is required, and it'll be a step down type used in reverse for the inverter application

2. Great! thanks for the extra info. So the heatsink can actually connect the 4 power transistors collector (body) to each other for the 2 sets and would this shock you if you touched the heat sink? that's probably why I can't find the right transformer. and to use a transformer in reverse; E.G. 240ac input 12V DC output would be connect battery to the 240ac input side and the 12V dc output side now becomes 220v ac? please let me know how to use it in reverse.

otherwise Great circuits, keep up the good work.

3. That's correct, all transistor collectors of the respective channels join together through the heatsink and connect with the relevant transformer outer taps.

As for the transformer, the winding rated 12V connects with the battery side that is with the 2N3055 collectors....while the 220V side becomes the output for operating the appliances.

4. Thanks heaps! I've bought all the stuff now including heat sinks and case, all I need now is the transformer, it's proven difficult that they don't sell many 10 amp transformers in Australia and when I do find them they are \$30+ :/

5. great, wish you the best!

53. the parts list dose not mach circuit

54. Hey,
i have an 150ah lead aside battery and,one ups 600va e184736 transformer,can you please tell me what type of inverter circuit should i do?

1. you can probably try the following circuit:

2. Hello sir..
This is dipak i am confused here in charging system is they ckt charge battery automatically

3. hello dipak, no the above circuit will not charge the battery...the battery will need to be charged separately using a separate charger circuit

55. can I use 12v 7ah battery for this inverter?

56. Thanx for reply sir, can I use TIP3055 instead of 2N3055.& can I use two 7ah battery in parallel connection..

1. Hi Shrikant, yes you can use TIP3055 instead of 2N3055

57. For power transformer what is turns ratio?

1. you will have to get a made-to-order transformer, or use any standard 9-0-9V/220V/15amp step down transformer...making it at home can be difficult

58. Thanx sir ,
I made it & works fine. :)

1. you are welcome Shrikant

59. Sir ,
I read all blogs ,I have 12-0-12 transformer ,shall i used in your circuit ,it is 4 ams .how much load can be handel?

60. Hi,sir
what is the substitute for diode 1N5408

1. Hi Divya, you can try for any other similar 3 amp/1000V or 3 amp 300V diode....but according to me 1N5408 is the most standard and widely used part.

61. Dear Swagatam Majumdar, I am Krishnaa - From Chennai.
If I use Two 10000MFD capacitors across 12-0-12 side of transformer What will happen?
Can we get smooth 230VAC waveform at output?
Please clarify, My Email ID is "krishnaa_m@hotmail.com"

1. Dear Krishnan, that won't help, instead you can connect both the the capacitors together right across the battery terminals, this will help to reduce harmonics and ripples within the circuit and ensure a much cleaner 220V output...however all these remedies will not keep the 230V constant because the 230V is directly dependent on the battery voltage which will keep dropping with time.

62. Sir how do i change this inverter to solar inverter

1. replace the battery with a solar panel having voltage at least 6V higher than the inverter battery spec, and a couple of watts higher than the inverter transformer wattage.

63. Do you mean that if my inverter battery is 12v i should replace it with 18v solar panel,?? and also if my inverter is 200 watt, the solar panel also must be 200 watt??

1. yes that's right!

64. What the Substitute for Capacitor Tantalum also Battery 12v 100AH ?