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Sunday, February 12, 2012

How to Design Your Own Inverter Transformer

Designing an inverter transformer can be a complex affair. However, using the various formulas and by taking the help of one practical example shown here, the operations involved finally become very easy.
The present article explains through a practical example the process of applying the various formulas for making an inverter transformer. The various formulas required for designing a transformer has been already discussed in one my previous articles.

Designing an Inverter Transformer with the Help of a Practical Example
An inverter is your personal power house, able to transform any high current DC source into readily usable AC power, quite similar to the power received from your house outlets. Although inverters are extensively available in the market today, but designing your own customized inverter unit can make you overwhelmingly satisfied and moreover it's great fun.

At Bright Hub I have already published many inverter circuit diagram, ranging from simple to sophisticated sine wave and modified sine wave designs. However folks keep on asking me regarding formulas that can be easily used for designing a inverter transformer. The popular demand inspired me to publish one such article dealing comprehensively with transformer design calculations.

Although the explanation and the content was up to the mark, quite disappointingly many of you just failed to grasp the procedure. This prompted me to write this article which includes one example thoroughly illustrating how to use and apply the various steps and formulas while designing your own transformer. Let’s quickly study the following attached example:

Suppose you want to design an inverter transformer for a 120 VA inverter using a 12 Volt automobile battery as the input and need 230 Volts as the output. Now, simply dividing 120 by 12 gives 10 Amps, this becomes the required secondary current.

Want to learn how to design basic inverter circuits?

The data in hand are:

Primary Voltage = 230 Volts,

Secondary Current (Output Current) = 10 Amps.

Secondary Voltage (Output Voltage) = 12-0-12 volts, that is equal to 24 volts.

Output Frequency = 50 Hz

First we need to find the core area CA = 1.152 ×√ 24 × 10 = 18

We select CRGO as the core material.

Calculating Turns per Volt TPV = 1 / (4.44 × 10^-4 ×18 × 1.3 × 50) = 1.96

Calculating Primary Current = (24 × 10) / (230 × 0.9) = 1.15 Amps,

By matching the above current in Table A we get the approximate Primary copper wire thickness = 21 SWG.

Therefore the Number of Turns for the primary winding is calculated as = 1.96 × 230 = 450

Next, Primary Winding Area becomes = 450 / 137 (from Table A) = 3.27

Now, the required secondary current is 10 Amps, therefore from Table A we match an equivalent thickness of copper wire = 12 SWG.

Calculating Secondary Number of Turns = 1.04 (1.96 × 24) = 49.

Calculating Secondary Winding Area = 49 / 12.8 (From Table A) = 3.8

Therefore, the Total Winding Area Comes to = (3.27 + 3.8) × 1.3 (insulation area added 30%) = 9

Calculating Gross Area we get = 18 / 0.9 = 20

Next, the Tongue Width becomes = √20 = 4.47 cm.

Consulting Table B yet again through the above value we finalize the core type to be 6 (E/I) approximately.

Finally the Stack is calculated as = 20 / 4.47 = 4.47 cm

Table A

SWG------- (AMP)------- Turns per
10----------- 16.6---------- 8.7
11----------- 13.638------- 10.4
12----------- 10.961------- 12.8
13----------- 8.579--------- 16.1
14----------- 6.487--------- 21.5
15----------- 5.254--------- 26.8
16----------- 4.151--------- 35.2
17----------- 3.178--------- 45.4
18----------- 2.335--------- 60.8
19----------- 1.622--------- 87.4
20----------- 1.313--------- 106
21----------- 1.0377-------- 137
22----------- 0.7945-------- 176
23----------- 0.5838--------- 42
24----------- 0.4906--------- 286
25----------- 0.4054--------- 341
26----------- 0.3284--------- 415
27----------- 0.2726--------- 504
28----------- 0.2219--------- 609
29----------- 0.1874--------- 711
30----------- 0.1558--------- 881
31----------- 0.1364--------- 997
32----------- 0.1182--------- 1137
33----------- 0.1013--------- 1308
34----------- 0.0858--------- 1608
35----------- 0.0715--------- 1902
36----------- 0.0586---------- 2286
37----------- 0.0469---------- 2800
38----------- 0.0365---------- 3507
39----------- 0.0274---------- 4838
40----------- 0.0233---------- 5595
41----------- 0.0197---------- 6543
42----------- 0.0162---------- 7755
43----------- 0.0131---------- 9337
44----------- 0.0104--------- 11457
45----------- 0.0079--------- 14392
46----------- 0.0059--------- 20223
47----------- 0.0041--------- 27546
48----------- 0.0026--------- 39706
49----------- 0.0015--------- 62134
50----------- 0.0010--------- 81242

Table B

4AX(U/T) ----------------2.383-----------13.039


  1. Hi Swagatam

    Thank you very much for all your effort and help, a very nice article. Is there any way to evaluate an already available inverter transformer (desi inverter 12v i think) for an estimated or exact wattage or amperage, voltage etc.?

    Thanks and regards


    1. You are welcome Sam!

      The current of any transformer may be found simply by through a multimeter.
      The output voltage may be found by selecting the voltage range, and the current may be found by selecting the relevant range in the meter.
      However current measurement should be done quickly to avoid heating up of the meter wire.

      Best Regards.

  2. Hi swagatam,great job with this piece;its very concise and exlanatory.I have very keen interest in electronics and will like you to mentor me on electronics and electronic design.I am a fast learner and will greatly appreciate any material you may recommend and may give to this personal email is can keep personal correspondence with each other on this matter Through this email.thanks for the support.once again,great work.

    1. sir, i parthiban, i very much interested coil winding of transformer. please help my question is howmany turns in KVA? if any DATA SHEET? please send my mail, (example: KVA------SWG-------(AMP)------- Turns per

      [(i.e.,1KVA (1000w)transformer Ex SWG:10 Ex No of turns: 200

      KVA--------SWG------- (AMP)------- Turns per
      1-----------10----------16.6---------- 8.7
      2-----------11----------13.638------- 10.4
      3-----------12----------10.961------- 12.8
      4-----------13-----------8.579---------16.1 EXAMPLEs ]

    2. Possibly I'll try to find the data and inform you regarding it, soon

    3. Sir, any data's

    4. So far no luck, I tried a lot to find it online but couldn't find any relevant data...

  3. TVP=1/(4.44*10^-4*18*1.3*50=1.96?

    1. That's right, it's 10^ -4.....

    2. hello sir, please i want you to help with the equation that i can use to get the thickness of wire that i will use to wind a transformer for both the primary and the secondary and also equation to get the area of the iron core. the parameters that i have are; 220v supply to the primary, 2v,4v,6v,8v,10v,and 12v to be lead out at the secondary, 50hz, and power rating of 3000VA. my email is thank you sir

  4. Thank you - this is a very useful article.

    However, although some of the numbers in the example are clearly variables (input and output voltage and current) and certain of the other numbers derive from them, it's not completely clear to me which parts of the formulas are constants or how they are arrived at.

    For example, 1.152 is apparently multiplied by the square root of the voltage times the amperage to arrive at the core area. Is the 1.152 a constant, and what is that based on? does it change depending on the core material? In Calculating Primary Current, is the 230 multiplied by 0.9 simply to take into account that the transformer is not 100% efficient, or is it more complicated than that?

    Perhaps I am simply missing these things because I did not find any link to the previous article you said you wrote specifically on Transformer Design, and they are all explained there.

    Thanks again.


    1. Thank you for showing interest in my article.

      Here's the link of my previous article where I have explained the making of a transformer more elaborately:


  5. Thank you! I will read this this evening!

  6. Hi,
    I am not able to find any of your Inverter designs at Bright hub. Can you send me the link to all those?
    Nowadays I am studying all sort of inverters. I hope your designs might help me alot.

    1. Hi,
      I have shifted all my inverter articles from BH to here, kindly find them through the search box....I am sure you would find them interesting.

      Thanks and Regards

  7. how is primary voltage 230 when it should be 12-0-12

  8. Dear Swagath, thank you for this input, can you give me a design details on a general purpose inverter transformer for a 600 VA Sqwave.

    1. Thanks!

      For 600VA, the specs would be:

      Primary current = 600/total winding voltage at DC side.

      Secondary current = 600/total winding voltage at AC side.

  9. Hi swagatam
    I need to make a transformer for my school project
    Can I get some help

    1. Hi Ekaansh,

      It is difficult, you cannot wind a mains AC transformer with ordinary tools....not feasible for school project, as far as i think.

  10. Dear Swagath, Can you help me in designing a 600VA transformer for pure sign wave , not able to get one. I was able to source the board, with transformer design.
    Technical details of transformer given
    up to 800VA800VA 4 No* 3Inch ( is this core detail?-what does it mean)
    Input 230V Primary ( SWG 19-360 turns)
    Out put (1) SWG 13- (3*11 turns)- out put volt 7.5V
    (2) SWG 25-22 turns- out put Volt 14.2V

    I am not able to understand the Core details,
    i have a core of size 6.4cm * 4cm
    can i use this if so then the SWG and turns would vary

    1. I do not have any experience with transformer designing so I am sorry I won't be able to help you with it.

      You can ask a professional winder, he would certainly know more about it.

    2. Thank you, it is hard to find people who can help like you, i shall try

  11. thanks alot for those useful information but could you please help me with simple specific instructions step by step to make a 500 watt (or even more )inverter

    1. Thanks! I have tried to explain as much as possible in the article, it would be difficult for me to provide a step by step narration....

    2. ok thanks again my friend but could u please tell me how can i make it a 600 watt

    3. Are you referring to a transformer or an inverter....if it's an transformer, then I'm sorry I am not good at it...

    4. i'm asking for 600 or 800 watt inverter
      i have a 12V 60A car battary
      many thnx in advance

      :: i'm sorry for disturbing but i really dont know much in electric stuff and i need ur help

    5. you can try making this circuit

  12. i want to design and build 2000 watts inverter help with simple diagram and name the material for me am a mechanical engineer, i want to use for my house

    1. you can try the following simple configuration:

      Just attach more mosfets and an appropriately rated transformer for getting 2000 watts

  13. hi could pls help me with any simple method in determine the actual wire guage without a micrometer screw guage cos i have some difficulties with that

  14. why 160v winding for charging

  15. hi Swagatam, i am starting a solar powered generator project in which i am building a 1000W inverter. does the solar charging source have any influence on the inverter design compared to an AC charging source? do you have any example 1000W inverter designs?
    Thanks, Derek

    1. Hi Derek,

      A solar panel source would be controlled by a charger controller, so the inverter or the battery wouldn't have any concerns with the panel directly, so there's nothing to worry.

      I have one simple 1000 watt inverter design in this blog, you can see it here:


    2. Great thanks,

      I am building a solar generator with 1500 W hours of charge. charge controller, batteries, inverter (1000W) @60Hz. i want to build the inverter and possibly the charge controller. Is this inverter circuit applicable? any other advice would be greatly appreciated. I have been searching and find your info to be the most helpful thanks,


    3. Thanks!

      According to me this inverter circuit is correct, and would work as specified.

      As can be seen, the circuit is quite straightforward, and wouldn't be so difficult to build.

  16. hi swagath ,

    how to calculate the design of 12v 1amp transformer

  17. hi swagatam sir, this mohan i want to learn transformer winding. please help me.give some ideas

    1. hi mohan,

      I am sorry i don't have much idea regarding transformer winding.

  18. Hello Everybody.

    Can someone tell why the factor 1.152 is used in calculating the core area? where did it come from. and if possible, is there a formula to be used that states the core area depending on the frequency. I'm asking because i want to use high frequency transformers and i need to know what size for wha tpower

    1. Hello Gober,

      The above explanation is solely for iron core transformers not for high frequency ferrite the calculations won't work for you.

  19. My answer is
    Thise is right answer?

  20. Hello sir. I appreciate ur link but im confuse. How do I do a calculation for 1kva inverter transformer. My values are not just falling in place with that of the table given. Help me pls

    1. yes, I think the above data is limited for upto 20 amp transformer not above that, so im sorry a 1kva could be too large and not within the range of the above data.

  21. Sir, pls tell me that meaning of 120VA

  22. Sir, i am ashok.V from hyderabad. i want design a 400watt inverter batteries. .So what is primary current of transformer and battery current.

    1. Ashok, please divide 400 by the voltage of the transformer to get the approximate current on the relevant side.

  23. hi friend,how are you and your friend,I want to make a transformer for ups to charge 200 amps battery in 30 minute approximately and give good back up and drive about deep freezer (triplet) an water-pump and five fans,five energy savers at once.please
    help me my friend.

    1. hi imam,

      you are probably looking at a 10kva inverter design, i have no idea how to design such a huge transformer, please consult a professional trafo designer

  24. Sir,

    i have just salvaged 2 Nos of ups transformers from an old working UPS "Luminous 750va" double battery, i just want to know that can i use them to build an inverter with a range between 200 to 500 watt power inverter for home. second is that i am confused about the connections of these transformers there are 7 wires coming out from one side and three on the other side. how to identify the wires and check their voltages. i have been posting this every where but i idint receive any response. i shall be grateful if you could help me resolve this thing. the transformer has this marking on it " TX-201-1000-02"

    1. Gowhar, While removing you could have at least noted down which taps are terminated as mains outputs for the appliances.
      Anyway, you can connect your home AC mains across the different taps of the trafo randomly with a 100 watt bulb in series....the taps which produce minimum glow over the lamp could be assumed as the 220V winding of the trafo....

      Once you locate this you can keep the mains input with the 100 watt series bulb connected, and take a DMM for checking the AC voltages across the remaining this way you can go ahead with the required identifications.

    2. ....maintain extreme caution while doing the above as the procedure involves lethal mains current.

  25. Dear Sir,

    i have a question, suppose i will get an inverter and ups with same rating including batteries, will they give same back up time.
    waiting curiously for your reply

    1. Dear Gowhar,

      Yes they should have identical backup time

  26. thankyou for the prompt reply.
    God bless you.

  27. Good day sir! Nice work keep it up

  28. Hi swagatam, iam ahmad thank you very much for this article.Pls sir can i rewind a transformer rated 1000watts for an inverter that is to produce 850 or 750watts? Or let me say any transformer that its wattage is above my requirement(watts). Can i match the current i got using the above formula with AWG bcos there is not SWG wire in my place and even if there is the current i got is not within the above table. Pls assist.

    1. You don't need to rewind the 1000watt trafo, you can use the same trafo for obtaining lower wattages...the optimization will simply depend on the battery current which can be reduced as per the requirements.

  29. Hello sir! Iam ahmad. Thank you very much for the reply, god bless, may you continue to reign.Pls sir am i on the right path by building a 750watts inverter using SG3524, L7809 voltage regulator, and four IRF3205 mosfets, 1000watts trafo?.what will be the voltage of 104 caps? Iam using 2k2, 10k, 1k, 200k resistors,will they be a quarter watt?. I want to replace 260k with 200k resistor and 100k variable.I appreciate alot

    1. Thanks Ahmad!

      By default the 104 caps can be 50V rated, the resistors 1/4 watt rated. I am not sure about the resistor replacement of 200K...can you show me the exact link?

  30. Ahmad-i bought three 104 polyester caps, two of the caps have; 1A 104J,while the third one have 104k 100v writting on it.pls sir will they serve?

    1. 104 means 0.1uF, if your circuit requires 0.1uF, then all these capacitors would be OK.

  31. Ahmad* Ok sir, but what about the replcement(260k with 200k resistor and 100k variable),and the mosfets? I want to use four IRF3205 (two connected in parallel on each side),and i need 750watts as the final output. Is it okay? Thanks

    1. Your link did not open the circuit page, it opened the homepage of the site....provide the exact link of the diagram, only then i would be able to say anything.

    2. Ahmad, I have checked the link, yes you can use 200K + 100k variable preset a pin#6.

      first try with single mosfets only...if it works perfectly then you can add one more mosfet in parallel on each channel.

  32. Ahmad****Thank you!!! Very much sir, you are one in a million. Once am through with the inverter and it start working i will let you know.thanks again, my boss

  33. Ahmad*** good day sir! I encountered problem while selecting a trafo, my aim was to purchase a 12v-0v-12v ups trafo that would match with my requirement;750watts,12v car battery(though,later i would replace it with a truck battery),but when i went for it i only saw trafos with these specs:6.8v-0v-6.8v(650va), 150v-0v-150v(1200va), 800va(no voltage written). Am confuse right now. Pls sir i would like to know weather ups trafos can perform the task(based on inverter circuit on the website:simplecircuitsandprojects), if they can, what specs should i look for? And if they cant, what type should i go for? Pls explain comprehensively. Pls sir can i use 220k resistor in place of the 200k? 200k is currently unavailable in my place. Thanks

    1. you can use the 6.8v-0-6.8v trafo for the referred circuit application, it will surely work.
      220k will be ok in place of 200k.

  34. Ahmad*** thank you boss! I feel relieved now

  35. Ahmad***Hello sir! Iam doubting weather 6.8v-0v-6.8v trafo can give me 220volt output with 12v input, can it? The trafo was salvaged from 650va ups,what amount of load can it carry? ---can i use any salvaged ups trafo with primary volt above 12v-0v-12v to give out 220v using 12v bat input? Let say 15v-0v-15v or 16v-0v-16v. Thanks

    1. 6.8v trafo will give 400v at the output, you will need to adjust the PWM pot or the load correction pot for adjusting it to 220V.

      You can try 12v or other trafos also, if you wish.

  36. Ahmad*** thank you very muc sir! Pls dont mind my too much question, this is my first time in building a circuit. Sir, based on my understanding mosfet(particularly irf3205) has three pins, and pin 11 and 14 of an ic are connected to the gate(mosfet first pin),and trafo wires to the second pins(drain),while the third pins(source) grounded.But yesterday i saw a ups circuit and its trafo wires connected to transistors metal(metallic surface through which screws are bolted) and i was a kind of confuse. Pls explain to me in detail how mosfets are connected. Thank you sir

    1. Ahmad, don't bother about such details, concentrate on the basic technique and use only the three leads of the mosfet,

      use the metal tab for attaching heatsinks only and nothing more.

  37. Ahmad*** hi boss! Does all the different components share the same copper plane when grounding?

    1. what is copper plane? do you mean PCB copper ground track?

      yes, that's correct

  38. Ahmad***thank you a million times boss! I have started coupling and nearly done.

  39. hi,
    can we make an inverter for very small voltages like .5 volts using amplifying transistors like 2n2222 or 2n3904, and the output should be around 3-4 volts ac, that can power 2 leds. if yes can you tell me such a circuit. also about transformer, how does it is built for such a low voltage ?
    i need it because i am participating in inspire award.

    1. I think we have discussed this earlier, anyway just to remind you we can use a joule thief circuit for this, you may refer to this article for more details:

  40. is the self looped motor generator is real?
    if so why yet, it hasnt come to real world?

    1. it's fake...
      you can study Adams motor for getting cold electricity, which is a true concept.

  41. well I am making an inverter which should be of 100 watt using 12v 7Ah battery. Can you tell me a circuit, also I am a beginner in making inverter.
    Also my teacher insisted me to put an cooler( i dont no why) off coarse a fan, but i told them that it is not necessary but he made it strict to add an fan. so can you tell me how to add a pc fan to an inverter circuit.
    it would be a great help.


    1. You can try the following circut, it will easily handle 100 wats provided the trafo is correctly rated.

      Fix the fan over a suitable slot on the cabinet facing the mosfet heatsink such that it throws the breeze on the mosfet heasink.

  42. I know but where do i connect the power supply for the fan?

    1. obviously it will from the inverter battery

  43. Please do design a 5Kwatt inverter transformer.

    this will be much more needed since we are all globally going for green energy. And 5kwatt inverter is much sought after, than low power inverter.

    1. thanks! I'll surely try to present one in this blog sooner or later.


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