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.

Update: A detailed explanation can be also studied in this article: How to Make Transformers

Designing an Inverter Transformer

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?

In the following explanation the Primary Side is referred to as the Transformer side which may be connected at the DC Battery side, while the Secondary side signifies the Output AC 220V side.

The data in hand are:

Secondary Voltage = 230 Volts,

Primary Current (Output Current) = 10 Amps.

Primary 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 where 1.152 is a constant.

We select CRGO as the core material.

Calculating Turns per Volt TPV = 1 / (4.44 × 10–4 ×18 × 1.3 × 50) = 1.96, except 18 and 50 all are constants.

Calculating Secondary Current = 24 × 10 / 230 × 0.9 (assumed efficiency) = 1.15 Amps,

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

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

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

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

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

Calculating Primary 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

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gober said…
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
Swagatam said…
Hello Gober,

The above explanation is solely for iron core transformers not for high frequency ferrite the calculations won't work for you.
My answer is
Thise is right answer?
Please replay question?
Swagatam said…
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.
Swagatam said…
Ashok, please divide 400 by the voltage of the transformer to get the approximate current on the relevant side.
imam farid said…
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.

Swagatam said…
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
gowhar khan said…

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"
Swagatam said…
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.

Swagatam said…
....maintain extreme caution while doing the above as the procedure involves lethal mains current.
gowhar khan said…
thank you very much for the reply
gowhar khan said…
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
Swagatam said…
Dear Gowhar,

Yes they should have identical backup time
gowhar khan said…
thankyou for the prompt reply.
God bless you.
Swagatam said…
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.
Swagatam said…
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?
Swagatam said…
104 means 0.1uF, if your circuit requires 0.1uF, then all these capacitors would be OK.
Swagatam said…
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.
Swagatam said…
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.
Swagatam said…
you are welcome Ahmad
Swagatam said…
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.
Swagatam said…
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.
Swagatam said…
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.
Swagatam said…
what is copper plane? do you mean PCB copper ground track?

yes, that's correct
shadab karnachi said…
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.
shadab karnachi said…
is the self looped motor generator is real?
if so why yet, it hasnt come to real world?
Swagatam said…
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:
Swagatam said…
it's fake...
you can study Adams motor for getting cold electricity, which is a true concept.
shadab karnachi said…
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.

Swagatam said…
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.
shadab karnachi said…
I know but where do i connect the power supply for the fan?
Swagatam said…
obviously it will from the inverter battery
bg said…
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.

Swagatam said…
thanks! I'll surely try to present one in this blog sooner or later.
vijeesh kumar said…
Hai Sir,
For secondary winding should we double the turns that is 49 centre tap 49 total 98 turns or after 24 turns should we take the centre tap and again wind another 24 turns.
Swagatam said…
Hi Vijeesh,

please explain your question detail, I could not understand what specification you are trying to make.
vijeesh kumar said…
In the above calculation you got 49 turns for secondary winding.(means in the secondary winding first we will wind 49 turns with 12 swg wire then we take the centre tap then again wind 49 turns,total 98 turns) or we have to take the centre tap from the middle of 49 turns that's after 24.5 turns we take the centre tap and again wind 24.5 turns.
Swagatam said…
It will be from the center of the 49 turns, that is after 24,5 turns or after 24 turns.
Purna said…
i have an 200watt inverter with two irfz44n mosfets. how can i increase its power to 400watt.? can i add more mosfets in parallel? plz reply soon.
Swagatam said…
yes it can be tried in that way.
khennie said…
I really appreciate your tremendous effort in help others out. Please sir, I want you to help me calculate the core size for the primary and the secondary, number of turns, the lamination size for 1kva transformer for inverter. I tried using the method you used above but I halted when it comes to choosing thickness of wire for the secondary in the table because I couldn't find there. Please sir. I want you to give me the wire table that starts from 1 and not 10 and also that of lamination table. I had be very grateful if you do that for me sir. Hope to read from you soon sir.
khennie said…
Pls sir. I want you to help me with the calculation for 1kva transformer inverter. I used the above method but the challenges was that I couldn't find the wire thickness from the table you gave above. Please I will be very grateful if u can upload a table that will start from 1 and not 10 for both thickness and lamination. Or if there is another way of doing the calculation let me know sir. Hope to read from you soon.
Swagatam said…
Thank you khennie, but I am sorry I won't be able to help you with the calculations because I too have no idea regarding the wire SWG calculation which would handle 1000 watts. I got the above data from one of the electronic magazines and I personally do not have any info regarding the specific data that you are asking.

I would advise you to seek the help of a professional transformer maker, he would charge a bit but finally you would be able to achieve the perfect design as per your requirement.
khennie said…
Thanks for your reply,I don't know any professional online but pls if you know one, kindly link me to him
Swagatam said…
getting it online will be difficult, you will have to find it locally in your area, or in your nearest electronic market
Syam M.E said…
Hi Swagatam,
Can you please help me build a 200amp inverter.
Swagatam said…
Hi Shyam,
please provide all the required specifications, i'll try to help
Syam M.E said…
Thank you sir for replying,, actually I am stuck with giving the time delay for the igbt switches in a dual half bridge inverter config. Its for simulation purpose..... because of the dual config. m always getting wrong o/p. please suggest anything.
Swagatam said…
you mean dead time? It's internally fixed in the IC, You can refer to the following diagram for some clue:
John Bello said…
Pls I will like to know the type of transformer that can be used for 1kva inverter and also the rating of the transformer. Thanks
Swagatam said…
divide 1kva with the battery voltage to get the transformer secondary current. the primary voltage will be as per the specs of your country.
John Bello said…
Thanks for ur reply that surelly works
Dozo Phub said…
the article is really interesting. In order to design a distribution transformer, will the core designing be same as sir has done? Or is there any difference? if so, i would like to request your kindness to elaborate on it.
Swagatam said…
Hi Dozo, yes since all transformers are basically intended for controlling voltage and current parameters, their design calculations will use the same standard formulas and systems.
However the range provided in the above article is quite limited and it won't probably have the essential data for a distribution transformer.
Jerico Vicente said…
Hi sir,
In calculating turns per volt, Is the 1.3 a constant no? Does this refers to the magnetic flux density or the saturation of the core?
Swagatam said…
Hi Jerico, it's the flux density and is constant, you may refer to the following post for a detailed info:
vijeesh kumar said…
Hai Sir good morning,
Last week I went to a local transformer/inverter maker for a 800 watt 12-0-12 transformer for an inverter project,he said the primary will be 21 gauge and secondary will be 12 gauge,because of his reputation for supplying good inverters I gave the order for the per above calculation 800 watt/12 volt is 66 amp but the chart is saying 12 gauge can carry only 10amp.He is giving a surety that it will carry 800 watt load.What is the trick they are using.
Swagatam said…
Hi Vijeesh,

you may be right, as per the chart 12SWG should be used for currents not above 10amp but this may be under ideal conditions which will ensure no heating up of the trafo even under full load, however 66 amps is way too high and using 12SWG could be dangerous for this much current.

although I am not an expert in this field, it looks quite obvious that 66 amps will simply smoke the transformer if a 12SWG is used, or perhaps the person may use many 12 SWG in parallel, that could be a valid possibility, and that would be quite OK....suppose he uses 5 nos of 12SWG strands in parallel then it would just do the job.
Can I use Ferrite core for 50 Hz inverter transformer?
If yes give winding details for a 9-0-9 / 230 volt 500 VA transformer
Swagatam said…
ferrite cores don't work with low frequencies, it will require a minimum 10kHz for proper functioning, so it's not possible
Can I connect solar panel to an inverter without a battery?
I have 6x12 volt 100 watt solar panel and a 12 /230 volt 500 VA inverter.
Any simple circuit ?
Swagatam said…
yes you can do that, but make sure that during peak sunshine the panel voltage does not become too high than the inverter specifications.
My inverter circuit board has LM3525, LM 339, 12F508 ic's and IRFZ 44 Mosfets . It is square wave output. Can I change this circuit with adequate components to get pure sine wave out put. If so please give the circuit. Expecting your valuable reply soon.
Thank you
rajapolimera said…
right answer is
1/(4.44*10^-4*18*1.3*50=1.925 not 1.96
Swagatam said…
it could be a modified sine wave or pure sine wave equivalent, can't say with confirmation, although the presence of a microcontroler IC 12F508 and also opamps LM339 indicates a highly sophisticated circuitry which could be a sinewave inverter
I am sure, it is not a sine wave because when I connect an inductive load like fan, a humming noise is produced. Your sine wave inverter circuit using TL 494 is very simple. If any kit or assembled board available online using this circuit please inform details or link
Swagatam said…
OK may be it's not a sine wave inverter then.

Sorry I do not have a kit or assembled board for solving this problem, you may have to inquire it online or in the local market
Dear Sir ,what do we mean by the primary and secondary winding area and what is its significance while winding?
Swagatam said…
dear prathamesh,
the winding area determines the specified number of turns that it can accommodate optimally...that's the only significance it has.
Puneet Sharma said…
how to make 1000 w transformer from above method
Where did you get the (0.9) when calculating the primary current?
Swagatam said…
it's the approximate efficiency count of a transformer, and is a standard fixed value
Saurabh Singh said…
Dear Sir,

Thanks for such a good document, sir I required 50W transformer for 12V system. So, please help me out.
Swagatam said…
Thanks Saurabh,

I have provided all the details in the above article, please calculate the parameters accordingly....
Hello boss! Hope everything is going smoothly. Am sorry I promised to notify you(7,dec.2013). The circuit(oscillator,power stage) worked,and I have been using it, thanks once again,it was because of your assistance,I sincerely appreciate. Can I connect two identical transformers in parallel (center taped) to my inverter? My aim is to multiply the wattage. Extend my regards to your family.***Ahmed***4rm*****NIGERIA*****
Swagatam said…
You are welcome Boss!
yes you can connect two transformers in parallel but only for the primary side....the secondary must be used and terminated separately to separate loads.
Hello Swagatam, My name is Tobi. Thanks for the tutorials. I'm an Electrical/Electronic Engineering student and I love electronics so much. I've been trying to design an inverter of 100watts or more, just for my personal use. I've seen a lot of inverter circuits on google and youtube but each time I simulate them on my circuit wizard software, they don't work properly. So please can you help me out with a cool circuit that works fine or give me a link or something. I'm very good with theories but I want to be good with practicals as well. Please I really need your help. Thank you.
Swagatam said…
Hello Omoregbee,

All the circuits that you have tested on the simulator were probably good...because it's your "wizard" that's not efficient enough to check their results, so leave it aside and try one of the selected inverter designs practically, that's the only way you'll learn things correctly.
Ok. I will try them out practically, and
I will get back to you. Thanks.
Hello sir,this is Abdus, plz show me in figure where is core area part?
Swagatam said…
hello abdus, the central pillar cross sectional area of the "E" stack is the core area
Hello sir,plz tell me which type of area in sence that primary and secondry winding area are to be maitained,i.e circular,cylindrical or other types?please tell me
Swagatam said…
Hello Abdus,

it will be as per the structure of the E core. that is rectangular
Hello sir,please tell me how to calculate the bobbin size?Also tell me,which windinds should be inner side or outer side?
I am not getting understand that how to understand about winding area,ssuppose I completed total no. of turns, but how to know that this winding area will match to calculated winding area?
Also tell me sir,why did you multiply total winding area to 1.3 ,and what is insulation part,and why you multiplied, why not you added it?
Sir, A mechanic told me that a transformer has a number of different-different size,please tell me about this
Plz reply to all queries immediate, Thank you
Swagatam said…
you can refer to this article for more details:
Helo sir,
I want make 230v to 120v 1500watts step down transformer,how will calculate,SWG of primary and secondary,and number of turns,primary's and secondary's.please send details to my mail
Swagatam said…
Hello Manikandan, I have explained the formulas in the above articles please do it according the given info.
PilotChris06FW said…
Hi i am wondering wether it is possible to build an inverter with a toroidal transformer. I have seen a dual input dual output 115/230v to 12v at 300va that is 2 times 12v at 150va each. Would this work via the push pull circuit.? Any advice is much appreciated. I'm assuming if it is possible I would only be able to use it at half its rates output of 150va at 230v
PilotChris06FW said…
Hi, tried to comment before but don't think it worked. My question is- can I use a toroidal transformer in a push pull configuration? I have seen a 300va 115v/230v to 12v toroidal. It's a dual primary dual secondary wound transformer. If this is possible am I right in assuming I will only be able to use it at 230v at 150va?
Swagatam said…
Hi, yes you can use it by connecting it with a matching inverter circuit.

all types of transformers can be used for making an inverter, there are no restrictions in this regard.
PilotChris06FW said…
Thank you for replying so quickly. Was I correct in assuming only half the rated output of 150va at 230v. My reasoning is the dual secondary 12v windings in series to give 230v on the primary. However each 12v singly can only deliver 150va
Swagatam said…
12V in parallel might give you better response at the 220V you can make the two 12V winding in parallel and use a H-bridge inverter circuit to get the best possible results, using single 12V winding will give you 150 watts only
vasu said…
Calculating Gross Area we get = 18 / 0.9 = 20
my doubt is 0.9 is constant value or how did you got this value. thanks in advance
Swagatam said…
it's the approximate assumed efficiency level of the transformer.
Is your SWG table is accurate.Because to many on online. can I design transformer with Constant 42 for example 42/18 =2.33 turn per volt
Swagatam said…
yes all the info provided in the above article are accurate as per my knowledge
Thanks Sir
How to check Transformer secondary maximum voltage & current through dummy load
for example if I have step down transformer with 22-0-22 Vac/3A=132VA how to check this with loaded out please give details.
Swagatam said…
Hi Sandeep you can simply do it by using your digital multimeter at the AC volt and AC current ranges respectively.
Thanks sir
And please tell me how to make 100W dummy load for testing transformer secondary voltage and current.
and tell me if my transformer is 22-0-22/3A=132VA if i used single 0-22 out its current is 6A or 3A and with 0-44 current should be 3A or what i am bit confused.
Swagatam said…
you can use a high wire wound resistor as the dummy load

It should be 6 Amp, because 3amp is for the whole 0-44V winding
Thanks sir
But secondary winded copper wire maximum current capacity is 3.5A how can it gives 6A
Swagatam said…
if the wire is not rated for 6 amp then the wire will get hot, if it's rated at 6amp then the half winding will provide you with full 6 amps
Swagatam said…
....only if the connected load is rated to consume 6 amps
Thanks sir
Can i use this design calculation for tutorial core transformer if yes how to do it properly please help.
Swagatam said…
you can refer to this article:
Sorry for spelling mistake I mean Can i use this design calculation for toroidal (O) core transformer if yes how to do it properly please help.
Swagatam said…
No, it is only for iron core transformers
Toroidal core is also iron laminated shit roiling in circular you have to wound copper wire direct over to the core not any plastic bobbin is used like EI core. can this calculation work. how to calculate core area of Toroidal core have outer dimater,Inner dimater & height. please help
Swagatam said…
Sandeep, the above data is for EE or EI type cores, so I afraid a torroidal core transformer cannot be calculated using this data.
mushtaq ali said…
Sir I have 12kva automatic voltage stabilizer 50 to 220v make sir please their turns and bubain size tell me
Muhammadu Aminu said…
Hello Sir. I am amateur in this field. I want to design a Transformer or a circuit that produce 12v 30am that control my DC motor. Or
Swagatam said…
Hello Aminu, 30 amp is too high, I have no idea regarding it??
mushtaq ali said…
Sir ihave 500 watt inverter please sir transformer primary and secondary turns and bubbin size send my email
Swagatam said…
you can use any desired rated trafo, it does not matter... the output wattage will be reduced or increased depending on the current of the trafo
Raja Farooq said…
Hey! I've a ques about 12v battery inverter that can we use 15-0-15 transformer instead of 12-0-12 ?? will it work ??
Hello Sir

Sorry of asking you again.But I want to know how to make mains transformer with using Toroidal core.I attach Core image and core manufacturer Test certificate. Can you please help me with that information i providw core size is OD-100mm, ID- 60mm and Height-50mm core wet about 1.842 KG (M4 CRGO material)
Swagatam said…
it must be lower than the battery specs, not higher.
Swagatam said…
Sorry Sandeep, I have no idea about transformer winding, you should consult a transformer winder or manufacturer for all the details
dear brother
I want to make a 800-1000w transformer for ips. I have bought all component to make it.
here is the list.
SWG 21 for primary winding,
SWG 12 for secondary winding,
4.5 inch
The transformer is make by 12-0-12V secondry and 0/N-140-220-260V
Plz help me to find out how many turn will be in primary winding and secondary winding
Swagatam said…
Dear brother, sorry I am good at designing transformers, so can't help with it.
Swagatam said…
I meant to say I am NOT good at designing transformers...
can you help me to find out who can tell it?
Swagatam said…
nobody within my reach
sir what is 42 as constant in transformer design means ? How does that constant forms ? I am giving one example of a transformer design in the link given below in which the transformer design uses that constant..

i had a 300 W step down transformer with 5 primary terminals and 4 secondary terminals.... i have deassembled the transformer and done the primary winding part... i have the following doubts .. please clarify those...
(1). According to the video

the area of the core portion is

so no. of turns per volt =
42 constant/21.42 = approx. 1.96...

hence no. of primary windings needed = 230 × 1.96 = 450.8 = 451 turns

and no. of secondary needed = 16 V × 1.96 =31.36

Are these calculations are correct ? Should i have to select 240 instead of 230 in calculation which will result in increase in no. of primary turns...

(2). Which configuration of secondary will be better a centre tapped one or with one normal possitive and grnd configuration ?

(3). how to take 32 V output from the centre tapped config. ?
Swagatam said…
RT, I can't confirm it because I don't often deal with transformers, so although I might have studied the calculations long ago, by now I have forgotten them...

however the formulas given in the above article are absolutely correct and you can follow those accurately.
baber khan said…
our sg3525 inveter when i move the pwm verible so the pin1 vollatge is also chnage so plz tell what is problem in our inveter pin1 i connect with pin9
baber khan charsadwal
Swagatam said…
I don't remember the internal configuration of the IC so can't suggest exactly about the issue, however you must check the voltage at the output pins of the IC...the voltage at the o/p pins must vary in response to PWM variations and that will confirm the proper working of the IC.....but pls remember that this reading will be the average voltage not the peak, the peak will be away equal to the battery voltage
Amos Zaks said…
Hi sir, I tried calculating the specs for a 5kva inverter transformer using 48v dc supply,freq.50hz, output voltage 220 but what I get as the amperes is out of the table so I could not determine the wire gauge.the highest ampere on the table is 16.6. Can you help me out sir please if possible with the specs. My email. Thanks
Swagatam said…
Hi Amos, you can refer to the table which is given in the following link for getting the desired wire gauge as per the current
Kumah Andrews said…
Am Andrews Kumah

Pls sir help me out,what I don't understand in your calculations is this "CA = 1.152 ×√ 24 × 10 = 18
We select CRGO as the core materia". That is, I don't understand where you got the values and also the meaning of CRGO.
Kumah Andrews said…
Pls sir help me out. I can't understand where you got these values "CA = 1.152 ×√ 24 × 10 = 18
We select CRGO as the core material" and the meaning of CRGO. Pls if you can upload the picture of the core of the transformer you measured maybe that will help me understand it better. Thanks
Swagatam said…
Andrews, you can refer to the following article to solve your doubts

CRGO stands for

Cold Rolled Grain Oriented steel
Swagatam said…
Andrews, you can refer to the following article to solve your doubts

CRGO stands for

Cold Rolled Grain Oriented steel
demiliza said…
hello dear swagatanm
i would like to ask you if an inverter output is 24v and i need 220 v for my home supply the creation of my toroidal transformer i have to create first the 24v winding as primary and then the winding of the 220v because in the toroidal transformer the one is on top of the other
also i have a swg table that says the curent the diameter the gauge of the wire if you wish me to send it to you thank again for your help
Swagatam said…
hello demiliza, I cannot suggest about transformers since I do not have much practicals experience with them, however as far as I know the winding pattern is not too critical, although preferably you should wind the 220V winding first and then on top of it wrap the 24V winding.
Abdulaziz Edibo said…
Sir, pls can u help me with a simple circuit diagram of Inverter? Am working on my project pls. My email
alpinejwh said…
Hello Swagatam, Long time ago I'm now back since I was making LED with you. Now asking for your help about the transformers build home made spot weld. I have many Microwave transformers but this time I have large rectangular laminated iron core made by Honeywell was using for old military scanner. This old transformer is larger than other MOT I have. So removed old copper wires and saved for later used. It was tested connect input 120 VAC and output multi-Low voltage from 5 to 24 volt AC. So now left it down to bare iron cord clean up small amount of rust area and ready to add hi temp paint. Now, however, I'm not good on math formula to put wire wrap number of turn of 5" long X 2.625" W X 1" plus thick for primary for 120 VAC. The core measure outside dimensions is 7.1875" long X 2.4375 deep X 3.4375" height. Output Secondary using 0/4 wire welding cable possibly 2 or 3 turns would be less that 2 VAC which may be high amp.

I know I see you don't deal with Transformer Calculation I read on your post.
If all else to give me number of turns for 120 VAC for primary and size of wire gauge recommendations.
So the electronic math formulation is complication as I read about which I'm confused!
So I explained above about the iron cord is laminated rectangular with round edges outside corner with opening
square rectangular inside dimension is 5.25" X 1.5". I was not able to add picture in this post to let you see.

Please let me know if you know someone read my post.

Thanks again,
John Hungerford
Swagatam said…
Hi John, I really wish I could help you with the calculations, but just like you I am too not good with transformer calculations, and moreover the data presented in the above article is restricted to max 8 amps only, while your trafo seems to be above this range.
Saqib Lodhi said…
Hi Swagatam,

I going to a professional transformer winding person after two days to get my 1kva inverter transformer (center tapped). I need your help. What specs should I ask him?

should it stepdown or up?
what should be primary voltage and current?
what should be secondary voltage and current?

Swagatam said…
Hi Saqib,

All transformers can be used as step down or step up depending on which side is used as the primary, for inverter we call it step up since its used for stepping up a low voltage to high voltage.

dividing 1000 watt with battery voltage will give you the primary current

for secondary also the calculation will be the same, divide 1000 with secondary voltage
Sunshine said…
nice God bless you.
Sunshine said…
engineer Swagatam good morning sir thanks very much for ur effort to help us...I made ur circuit.. and it worked normal but when I power my TV the inverter will in drop and come up gradually... pls help....
Swag said…
Hi Sunshine,
it could be due to initial high current draw by your TV.

Is it an LED TV? because normally LED/LCD TVs will not draw initial high current....
Sunshine said…
thanks sir...please help with circuit diagram of power supply using chopper coil such as 6v DC output from 230v ac input
Swag said…
sorry, I do not have the circuit with me at the moment, it is better to use a capacitive transformerless circuit instead.
ram said…
Why we need to consider efficiency while calculating primary current and we didn't consider efficiency while calculating secondary current
Swag said…
when current is high and voltage is low, efficiency can get affected, and needs to be optimized, when the conditions are opposite, efficiency becomes less affected, ...this is my assumption
Rafiq Ahmed Shaikh said…
Which calculation to look for bobbin size?
Swag said…
using tongue width:
Mutolib said…
Tnx u used the word primary and secondary side interchangeably,
Is it not correct to call d 12v battery side as primary side as against ur usage sir..
Am confused with that,
Secondly, if I fabricate my lamination (E/I) core.
Will i need to apply any luvrixant/paint..
Swag said…
yes for inverter the 220 side is the secondary, and for normal step down use it the primary, initially the above article was written for a step down transformer, therefore the 220V is mentioned as the primary...

sorry I am not sure about the minute construction details because I myself referred the article from an old magazine.
Solomon said…
Hello sir, i have few questions to ask pls help me:
1. I dont understand, u said divide 120va by 12v we get 10a, how does 120va come about, am confused.
2. Which of the transformer is the battery side, primary or secondary?
3. Which side of of the transformer contains thick wire, primary or secondary?. Pls help, thanks.
Swag said…
Hello Solomon, what is the required output voltage you need from the inverter?? You have to consider this voltage, and divide it with the battery voltage.

For inverter operation the battery side which is the low voltage side of the trafo becomes the Primary.

I have updated the changes in the above article accordingly.

The battery side consists the thicker wire.
Solomon said…
So now which side should have more number of turns?
Swag said…
the side which is rated with more voltage, the secondary side
Solomon said…
Sir pls one more question, cos i need ur help. In winding the the transformer, should i wind it according to an ordinary AC-DC transformer structure (primary separate and secondary separate then laminating them)? Or i should it according to a voltage stabilizer transformer whereby after winding the primary, the end terminal of the primary is joined with the starting terminal of the secondary winding, after winding the secondary with its center tap, the end terminal of the secondary with the starting terminal of the primary forms the two output as L and N mains. Sir i hope my question and explain are clear, help me because winding transformer is my field of day to day practical, i just want know in which manner inverter transformer constructed as i differenciated above. Pls help,Thanks
Swag said…
Hi Solomon,

you must wind it as per the standard step-down AC to DC type of transformer, and not like stabilizer transformer

inverter transformers are exactly like our ordinary step down transformers which we normally use in power supplies...
Solomon said…
Thank u sir
Emmanuel said…
Hi swagatam, my name t Emmanuel.please sir,i am trying to construct an inverter, I then enter net I found your explanation about how to get turns per volt, so my question is,the Tpv,i.e.1.96v that I sow,is he constant or I have to calculate my own.please sir, may God bless you as you replied back, thanks.
Swag said…
Hi Emmanuel, the 1.96 is the result as per the shown example specifications, it will be different for different transformers depending on the frequency and the core area.
Emmanuel said…
Please sir,do not be offended, I just want to be sure of what am doing.sir,for example ,I like to use a 1000va or 2000va or any watt of stabilizer transformer, can it work and am I going to divide the watt by the primary voltage,to get my primary current as per the shound example specifications.(2)i build one circuit,is using a 12v battery and I get 220v out,when I put 100w bop and my handset charger,then the current from the bop started going down slowly until there will be no current should from the pop, what is the problem sir. (3)what type of battery should I going to use.although,i use a generator battery of 7.6amps.(4)wich side of the transformer will take the ticker gauge wire, primary or secondary.
Emmanuel said…
please sir, about the nick zuein inverter circuit of 2500 to 5000w,pmw,he use a jumper.can I be able to replace the jumper with ticker gauge wire or what should I use to replace it.
Swag said…
Emmanuel, sorry I did not understand what you meant by "bop"....please use correct English with correct spelling, otherwise I won't be able to address or publish your comments.
Swag said…
sorry Emmanuel, I cannot comment or suggest on projects published on external sites. I can only discuss about circuits presented in this website
Emmanuel said…
please sir,what I mean is that.for example, I like to use a 1000va or 2000va or any watt of stabilizer transformer, can it work and can I going to divide the watt by the primary voltage to get my primary current as per the shown example specification.(2)i build one circuit is using a 12v battery and I get 220v,if I put 100w bulb and my phone charger.then,the current from the bulb will start going down completely slowly until there will be no current show n from the bulb. what is the problem sir? (3)what type of battery should I use. although,i use a 12v generator battery of 7.6amps.(4)which side of the transformer will take the thicker gauge of wire, primary or secondary.
Swag said…
Emmanuel, your calculation method is correct, you can go ahead with it.

the voltage may be dropping due to low battery current or inadequate battery charging. Either use a larger battery upto 25Ah or try to charge the 7Ah battery optimally (@ 1 amp rate for 10 hours), and check the response again.
Emmanuel said…
I thank you sir,may God continue to bless you abundantly.
Swag said…
you are most welcome!
Emmanuel said…
Turns Per Volt for 1000 watt Tranformer
Hello sir, I'm sorry to disturb,good morning .i calculate my own turn per volt using 1000w I got,during dividing the 1000w by the primary voltage 12v,i then got my primary current as,my question is that, I match it from the table A, to get the equivalent thickneas of wire but there is nothing like 83.3amp,from the table A, what am seeing is only 10.961 no 83.3.i.e,the rest is 1 figure before the decimal point not 2 figure before the decimal point, so, I'm confused to know my equivalent thickness of copper wire.
Swag said…
Emmanuel, that is right, the table has max data upto 10 amps, so i am afraid higher trafos cannot be built using these tables.
Emmanuel said…
thank you sir,which table can be used to build higher transformer, or is there any possible way for me to get the table from you,if possible, here is my
Swag said…
I am sorry I do not have any calculations for transformers above the specified value in the can perhaps try to increase the dimensions proportionately by comparing it to the available 10 amp dimension of the trafo.
youngking said…
sir thanks for or response, I search for fly back converter but I didn't find any but can boost converter work. I also came across or formular use in designing inverter transformer. now my question is as follows. (1) finding the core area you got but accroding to my calculation I got 55.2 or am I missing something. Iike u said the core area is that centre E should the centre be reduce by width or height. (2) can u explain the word stack .(3) I didn't understand No 16 & 17 calculation that is gross area & the tongue width .(4) what do u mean by total winding area . pls explain the word bobbin .pls don't be angry with my question thanks.
Swag said…
Youngking, I don't remember the calculations now, because I had written this article long back, you can refer to the following post for getting a detailed explanation regarding all the parameters:
Paaker said…
Dear Swag,
i read this complete article. and i have something to clarify. nowadays i am always reading your website to learn and understand about inverters. and get ready all components except transformer. to try one by one just for experience.

from all this articles and almost all the diagrams available on internet about inverters i have understood something about inverter transformers but in real inverters has very different transformers and connections.

on your diagrams and articles
the inverter transformer is very heavy.
and it must have dual input for primary.
and the center tap of the transformer has to connect the Battery Positive line.
secondary line will be 220V direct output.
almost every inverter diagrams show like this.

now i have a fully working Chinese 300W inverter. i just open and see inside. it has very small transformer but its not giving direct 220V output. transformer has 3 pin out put and it connect to 4 IRF830 Mosfets. mosfets are giving output 220V

i just found 2 units of Damaged UPS form scrap shop. both are same brand and it has a very heavy transformer. but primary has only 2 pin instead of 3 pin. and The Battery Positive not connect to the transformer at all. Transformers primary 2 line connect to the heat sink of Mosfet( IRF3203)
(i cannot attach images here either i can show the pictures)

i am confuse with Inverter transformers. can you please explain me why the 300W inverter has small transformer and giving 300watts output.
and why second UPS has different kind of transformer.

Swag said…
Dear Paaker,

The heavy iron core transformers are designed to work with low frequency in the range of 50 to 60Hz, which makes it possible to use it directly with a 50Hz oscillator and get the required 220V AC from a battery for operating any appliance.

The small ferrite core based transformers are specified to work with high frequencies over 30kHz, therefore to drive these transformers we need oscillators at 30kHz, but 220V at 3kHz cannot be used for operating our home appliances, therefore this high frequency 220V is converted back to DC 330V and then back again to 220V AC. All These operations makes the compact inverter circuit very complex, and therefore the heavy iron core based design is preferred for experiments by the new hobbyists.

similarly inverters can become more compact if H-bridge topology is used in which 2 wire transformer can be used, whereas in push pull topology the transformer requires 3 wires and involves an extra winding causing it to become slightly more heavier.

for compact ferrite based inverter you can refer to these designs:
Paaker said…
Thanks again Swag for detailed Answer.

Paaker said…
Hi Swag,
I was trying every of your inverter circuits for experiment. but always most difficult part for me is find a current Transformer. and today I found two units of old Microwave oven transformers. and I have carefully remove the high voltage part. now I want to rewind both transformers one for 1000W inverter, other one for 500W inverter.
both transformers has to use in 12v to 220V 50hz inverters.
Kindly help me to rewind these transformers . what size coil and how many turns I have to wind.

please give some option to attache image while comment here.

Thanks and Regards.
Swag said…
Hi Paaker, I am sorry, I don't have any practical experience with transformer winding or repairing and I do not have any expertise in this field therefore won't be able to help you with the required details.

for image you can use any free image hosting site and upload it there and provide me the link, or you can share the same via Google drive.
Anonymous said…
Isto me leva a acreditar que tenho bastante a aprender
nesta vida. rsss
Swagatam said…
Obrigado pelo seu interesse no meu lado, eu certamente vou ajudá-lo

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