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, which is able to transform any high current DC source into readily usable AC power, quite similar to the power received from your house AC 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
Calculating Inverter Transformer Voltage, Current, Number of Turns
Step#1: First we need to find the core area CA = 1.152 ×√(24 × 10) = 18 sq.cm where 1.152 is a constant.
We select CRGO as the core material.
Step#2: Calculating Turns per Volt TPV = 1 / (4.44 × 10–4 ×18 × 1.3 × 50) = 1.96, except 18 and 50 all are constants.
Step#3: 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
Step#4: Next, Secondary Winding Area becomes = 450 / 137 (from Table A) = 3.27 sq.cm.
Now, the required Primary current is 10 Amps, therefore from Table A we match an equivalent thickness of copper wire = 12 SWG.
Step#5: Calculating Primary Number of Turns = 1.04 (1.96 × 24) = 49. The value 1.04 is included to ensure that a few extra turns are added to the total, to compensate for the winding losses.
Step#6: Calculating Primary Winding Area = 49 / 12.8 (From Table A) = 3.8 Sq.cm.
Therefore, the Total Winding Area Comes to = (3.27 + 3.8) × 1.3 (insulation area added 30%) = 9 sq.cm.
Step#7: Calculating Gross Area we get = 18 / 0.9 = 20 sq.cm.
Step#8: 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.
Step#9: Finally the Stack is calculated as = 20 / 4.47 = 4.47 cm
Table A
SWG------- (AMP)------- Turns per Sq.cm.
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
Type-------------------Tongue----------Winding
No.---------------------Width-------------Area
17(E/I)--------------------1.270------------1.213
12A(E/12I)---------------1.588-----------1.897
74(E/I)--------------------1.748-----------2.284
23(E/I)--------------------1.905-----------2.723
30(E/I)--------------------2.000-----------3.000
21(E/I)--------------------1.588-----------3.329
31(E/I)--------------------2.223-----------3.703
10(E/I)--------------------1.588-----------4.439
15(E/I)---------------------2.540-----------4.839
33(E/I)---------------------2.800----------5.880
1(E/I)-----------------------2.461----------6.555
14(E/I)---------------------2.540----------6.555
11(E/I)---------------------1.905---------7.259
34(U/T)--------------------1/588---------7.259
3(E/I)-----------------------3.175---------7.562
9(U/T)----------------------2.223----------7.865
9A(U/T)--------------------2.223----------7.865
11A(E/I)-------------------1.905-----------9.072
4A(E/I)---------------------3.335-----------10.284
2(E/I)-----------------------1.905-----------10.891
16(E/I)---------------------3.810-----------10.891
5(E/I)----------------------3.810-----------12.704
4AX(U/T) ----------------2.383-----------13.039
13(E/I)--------------------3.175-----------14.117
75(U/T)-------------------2.540-----------15.324
4(E/I)----------------------2.540----------15.865
7(E/I)----------------------5.080-----------18.969
6(E/I)----------------------3.810----------19.356
35A(U/T)-----------------3.810----------39.316
8(E/I)---------------------5.080----------49.803
It is very helpful
Hello Swagtam. Please can I get the full table A and B chart. I need a current rating for 30Amps wire.
Hello Simon,
Unfortunately the tables are limited to 10 amp current only, and I do not have the data for currents above 10 amp.
OK sir. Thanks for your prompt reply. Can I still use the values in my calculation without the Primary Winding Area?
No problem Simon, but I don’t think the transformer can be completed without the primary winding area, so that may not be possible.
Please what guage for small step down transformer should I use for AC supply of 110v 50mA,
You can calculate it as per the formulas provided in the following article:
https://www.homemade-circuits.com/how-to-make-transformers/
Greetings Swagatam, thanks for your informative site. Where the transformer is the load in a H bridge inverter circuit and the DC is a 12volt battery, what should the primary winding voltage be? The inverter is a 1000w 220v output and all the mosfets are blown.
Thanks Ben, the transformer primary winding can be 0-12V, but preferably it should be slightly less, around 0-9V.
Please sir, for knowledge reason, why is 0-9v is preferable. Thanks.
Hi Seun, The transformer voltage must be slightly lower than the battery voltage to compensate the battery low voltage conditions. Suppose a 12V transformer produces 220V when the battery is 13V, then if the battery voltage drops to 11V, the inverter voltage would proportionately drop to 186V which is not good…this issue is avoided by using a relatively lower voltage transformer.
Thanks Swagatam, I am grateful. Please explain when it is 9v transformer, how it plays out.
Hi Seun,
As a rule of thumb you can use a 9V transformer when the inverter is a 50% square wave inverter with a 12V battery. For a PWM inverter you may have to check the average DC the PWM generates, which can be used to determine the primary voltage spec of the inverter
Pls can u recommend any textbook about dese transformer equations u used.
Yo can search it online you may many find good options.
Okay tnks a lot
Hi, I can’t calculate this: “First we need to find the core area CA = 1.152 ×√ 24 × 10 = 18 sq.cm”
For me the result is = 56,463
Hi, thanks for pointing out the mistake in the formula, please check it now. The square root is for 24 x 10 combined.
It seems to be correct
sir please how can i use 5kva stabilizer transformer as a center tap transformer for my inverter
You can use it, it will work only as long as the center tap winding specifications matches the battery and the circuit output specifications.
please sir how can i identify the primary side of 5kva stabilizer transformer
use a series 40 watt bulb and feed a 220V AC randomly across the unknown wires. For the 220V wires the 40 watt bulb illumination should be minimum or almost zero.
sir can irf3205 two on each channel with 12v 100ah battery drive 5kva stabilizer transformer
It will drive the transformer, but the output will be 200 watts max.
Input&Output, Primary&Secondary depend on the ‘function’ the transformer (tr) is performing:
Inverter/Step-up (I) mode Or Battery Charging/Step-down mode (C).
Normally, Primary refers to Input side, while secondary refers to Output 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
In the above, the Inverter mode is assumed, so Secondary/Output = 230 Volts.
Then primary I, and V should be Input and not Output, IMO.
Though understood, better to include a #Definition/assumption statement – Inverter Mode.
Hello,
Googled and located your site. Gr8 design info on how to build an inverter from scratch. I did BE EEE 40 years back, don’t remember any theory now, nor practically worked on inverter or any other circuit design.
Here is my silly basic query:
My old squarewave 750VA, 24V (2*12v battery in series) inverter’s MOSFETs burnt.
I think the copper transformer is intact.
I want to use the transformer and convert it to a 12V sinewave inverter, by replacing both the existing boards.
Is it possible?
If yes, where can I buy the rquired switching circuit board.
Thanks
Thank you for visiting my site, glad you liked the design and the content of this site!
Yes that’s possible…I think if you search online the phrase “sinewave inverter module” you should be able to get the right circuit board for your application.
The board should be available in amazon and other similar online shopping sites.
thanks for your quick response, i found couple of boards for 12v system.
however these boards do not specify the transformer specs
so what I am still not sure is, will it work with the existing transformer, which is wound for 24v?
will the primary ( dc volt side) windings be not different?
just want to make sure before I buy it.
Are you referring to EGS002 module? The transformer primary is supposed to be connected between the external mosfet bridge circuit. The transformer primary voltage will depend on the battery used. Yes a 24V transformer can e used, and will require a 24V battery to operate the external mosfet stgae with the tramsformer.
Following few search results.
Indiamart.com
1. Su kam sine wave inverter board 12 volt 900va from 1500/-
Amazon.in
1. RASHRI ; One For All Su-kam Pure Sinewave 900KV Inverter kit, 900VA Inverter Board, PCB, Inverter Motherboard 1948/- (same as indiamart?)
2. Rashri Su-kam 1000 watt Pure sinewave Inverter Board, Motherboard, PCB 2279/-
3. Alam 12V Sinewave Inverter Board Upto 1000VA (Suitable for All Sinewave Inverter) 2600/-
and many more 12V boards, including boards for Luminous and Microtek inverters.
Put it other way, a 12V system board will NOT work if connected to a 24V transformer, right?
beacuse, a 12V system requires 12-0-12 transformer, 24V needs 24-0-24 and my existing 24V transformer is likely to be 24-0-24.
And how much VA depends on transformer windings, thats secondary. I can choose a board with highest VA that the transformer can support.
When I search, I specifically get the EGS002 board based results, and is the recommended one according to me.
The 12V board will work for 24 V or any other voltage also since the 24v will be used across the MOSFET bridge, while the 12V will be used to power the circuit board.
The transformer VA will depend on the MOSFET rating and the battery capacity.
I searched for 12 v pure sinewave inverter board, EGS002 does not showup always.
But if I search for 12V pure sinewave inverter board and click View all, EGS002 shows up.
Forget about Google’s targetted/preferential … search results.
The description says … Inverter Module, EGS002 is a driver board …
SKU: 896558
1. 5V single power supply – for what?
..
It does not talk about what Ah, V, battery is supported to provide 230V ac, nor the transformer specs.
Most important, figure does not show Mosfets mounted on big heat sinks, or transformer.
I feel it is just a ‘driver/pre-processor’ board. IMO, the ones I have listed is what is needed.
Yes it is a driver board.
The 5 V is probably the operating voltage for the driver microcontroller circuit.
The power mosfets, and transformer needs to be configured externally and integrated with this driver board, which gives you the freedom to upgrade the inverter power to any desired levels. You can refer to this article to learn more regarding how to upgrade the battery, trafo and mosfets appropriately.
https://www.homemade-circuits.com/how-to-calculate-and-match-inverter/
I scratched my head yesterday, and few more strands of hair fell down on my already bald head :).
But I recollected RMS, Peak V, Half, Full, Bridge rectifiers …
My requirement: Use my existing 24V system transformer, with a new 12V pure sinewave inverter board with 12V battery.
I dont agree – “The 12V board will work for 24 V or any other voltage also since the 24v will be used across the MOSFET bridge, while the 12V will be used to power the circuit board.”
There is only one 12V battery, where is 24V?
The eg you have given assumes a 24V battery system, with 10A ( I or O?) current; which results in certain no of windings, gauge etc.
For a 12V system, all these will be different, especially primay windings.
I have a transformer that is for a 24V system, and the circuit is accordingly designed.
For a 12V system, no of primary windings should be double?
In the Inverter Mode, Primary PCM 24V DC input is stepped up to 230V AC secondary output.
If I connect a 12V inverter board to my transformer, it may give perhaps 110V AC?
Not sure what rectifier (full or bridge) is used in all these inverter boards.
In the Charging Mode, my transf with Full wave rectifier will give 24V DC, damaging the 12V battery.
Assuming my transf is center-tapped 12-0-12, I can use 12-0 leads with a custom-made inverter board with a bridge rectifier for charging.
Or modify the charging circuit in the off-the-shelf 12V inverter board by converting Full to Bridge wave rectifier.
But if its not center-tapped, it cannot be used.
Please correct my understanding.
You can check the following circuit diagram. Here you can the mosfet bridge is supplied from an external voltage source which can 12V, 24V, 48 V etc
https://www.homemade-circuits.com/wp-content/uploads/2022/12/EGS002-CIRCUIT-DIAGRAM.jpg
But I am not sure whether the EGS002 has a charging system or not?
Thanks.
I got this:
1000W DC 12V 24V To AC 110V 220V 380V High Frequency Power Inverter Board Car Converter
AIO board – switching, control & transformer.
Supposed to have a provision to connect a 12/24/48v battery – good.
Though 1000W, says Car Converter- cannot be used as home inverter.
And in $ from China, and squarewave. But gives a good design idea.
My faulty inverter has separate control and switching boards.
– gives the flexibility to choose a switching board of the required VA.
– maybe less costly to service, as only one of the 2 boards needs repair/replacement.
In my case, I need to replace the burnt switching board only.
OK, if it suits your needs you can use it, no problems!
How to make 1250VA 1000 watt 260v _12v ups transformer ?
Good day Sir, please what wire gauges for 2.5kva primary and secondary?
I used gauge 13 whose amp capacity is 8.6 but while charging the 16amps Circuitbreaker trip off until I used 25amps breaker, why?
Hi Seun, sorry I am not sure about that, because there’s no way I can calculate the wire gauge of a 2.5kva transformer.
Good day Sir, please I want to learn how I can wind a transformer coil with secondary coil connected to another joule thief transformer
Or any link or guide
Hi Seun, sorry, presently I do not have the details regarding the question that you have asked.
Can the above core area, turns per volt formula work extremely well with ordinary iron core transformer?
Yes, the formulas are for the ordinary iron core transformer.
Hello sir , thanks so much for the detailed information and teaching. I haven’t make any transformer before, but want to have it a try , hoping that the information gotten will be of help. in the transformer you divided 120/12 = 10amp, my question is if is 500w, should I divide it by 12 , using what I got as my amp ? Sir
You are welcome Amos, you have to divide the wattage by the battery voltage to get the current. 10 amp transformer is the max capacity that can be calculated using the tables given in the above article. Alternatively you can use 24V or 36V battery to reduce the current and apply the tables explained in the above article.
Thanks sir, I appreciate.
Good day Mr Swag, thanks so much for your surport. Pls I have an issue below.
Having rewind my 200watt stepdown trafo to 200watt trafo center tapped with the above info trafo winding, which I got TPV @ 1.7v/v.
1.7 *230= 391 turns
1.7* 240=408 turns
1.7*8=13.6 for 8-0-8
Sir the isue now is once I plug it for testing it will draw or dim the light, which may show it is drawing current. I don’t know what to do.
Please sir any advice?
Hello Godspower, if plugin the primary side with the mains is causing the other mains lamps to dim, that’s a serious issue and it means winding number of turns are less or not tightly wound. You may have to add more number of turns and make sure the turns are tightly and efficiently compressed.
Thank so much sir, I will re- work on it.
Good day sir, please how true is this notion? that any transformer can be designed using this formula
42/CA which will give TPV multiply by the voltagate of both primary and secondary to know the number of turns? That 42 is constant and does not change.
Please sir I also have this stepdown converter transformer 300watt and I want to rewind the transformer to centre taped. Pls will the capacity be upto 300watt after rewinding?
Will it work as a transformer for small inverter.
Hello Godspower, I have so far not come across this logic or formula, so have idea about it! If you rewind your transformer correctly then the wattage will not change. Yes it will work for center tapped inverters
Thank you sir.
So when calculating for secondary current which of the output voltage do I use,is it the 120v, 230v or 300v ?
You will have to take the 300 V into account.
How about designing the transformer to get multiple outputs like:909 to 120v ,230v ,300v
You can put tappings on the 220V winding to get the various voltage outputs
Plz sir, one more question, if i’m to convert the transformer to 500w should i calculate the TPV for the new transformer wattage using the core area of the transormer
Wattage is determined by voltage and current of the winding….so find the appropriate voltage and current for 500 watts and calculate the parameters accordingly.
Thanks
I mean rewinding it to get 9-0-9v to 230v,500w transformer
yes you can rewind it.
Hi Mr swag thanks for your nice s,but I have a pretty little problem,how can I convert my old 1000w voltage stabilizer transformer to get a 9-0-9v to230v,500w inverter transformer without changing the core,I will be fine with a quick response.
Hi Nimel, you will have to feed the AC mains from the AC side of the transformer, and check the secondary wires for the 9-0-9 V output. Once you identify the 9V wires you can then use those wires for the inverter application
Very nice explanation Sir. Thanks.
Thank you Onyi!
I have a transformer out of a old cnc control very heavy puts out 38vdc and 18vdc could that be used im not sure what there called its round rather than square
all types of step down transformer can be used for inverter application by configuring them with an appropriately dimensioned circuit, the same is true for your transformer also….
I am building an inverter of 12v and I just remembered I have an old UPS sitting around. The UPS is 24v, has 2 batteries. The transformer has 29.5v, 15v 0 15v in the secondary and 255v, 220v, 185v and 0v in the primary. I was wondering if i could use it for a 12v inverter since i was able to get 12v 0 12v in the secondary when i used 255v wires on 230v. Can I use it to invert the 12 from the inverter back to 230v?
How can I use this transformer for a 12v inverter?
thank you again
joe
Ideally, the transformer voltage should be a little lower than the battery voltage, for producing the correct output AC voltage. With 15 V, or even 12 V, the output may not reach 220V correctly. Even if reaches 220V initially, it will keep dropping to lower levels as the battery discharges to 11V. But just for testing sake you can go ahead and give it a try.
Thanks for sharing your wisdom and experience with us!
I’m considering purchase of one of the chinese such as
Two questions. I’d like to use a toroidal core to wind a 240vac on a center tap secondary. The idea will be to do a 240-120-120-240vac split for use in North America (Canada specifically). Have you done a tutorial on specifications for a toroidal step up transformer (I plan on active cooling of the transformer to increase power capacity so windings would need to be for higher current ratings than typical for the core)
Second question: Thoughts on how to increase the rating of this board? IE mosfet banks to increase capacity. Would IGBT’s be a better choice?
Thanks again,
Doug
The board looks cool for an inverter application, Sorry I haven’t yet published a torroidal core type transformer details. I will surely try to hunt for the info and post it soon in this blog.
Yes, you can add more number of MOSFETs in parallel, or replace them with high power IGBTs for increasing the power handling capacity of the module.
Dear sir,
Please sir, what determines the power rating of an inverter?
2. Please sir, for the Elite600VA pro UPS, does it mean that the UPS transformer is 600VA which can deliver a Max output of 360W?
Godfrey, the VA is the Apparent power rating of the transformer, which is the product of the output RMS voltage x the output max current. Now, it will depend on the load connected to the transformer which will determine the true power in watts. If the load is resistive then the the output will be almost 600 watts, if the load is inductive then it will depend on the power factor of the load which will need to eb taken into account.
Okay sir, thank you very much.
Dear sir, please sir I have got a UPS transformer with center tap 7-0-7V/165-275V and also 16V winding for battery charging from Mercury Elite600VA Pro UPS
Please sir I want to check the current rating on the 7-0-7V winding using the shunt resistor method you told me.
1. Please sir should I connect the resistor across 7V or 14V?
2. Please sir the resistor I want to use as shunt is 0.1ohms 5W. Please sir is it Ok?
Hello Godfrey, It is OK, you can go ahead, but measure the voltage across the shunt quickly, to prevent transformer heating
…you can connect it across the 0-7V tap
Thank you very much sir, am sorry sir for repeating the question, I didn’t notice you had replied. Am sorry about that.
Thank you.
No problem Godfrey!
Thank you sir. Please sir should I connect the shunt resistor across 7V or 14V
Dear sir, please sir I want to know how to measure the following from the core without using formulas, because I have a UPS transformer I want to disassemble and rewind based on calculations for use in the pure sine wave inverter circuit you designed.
Thank you.
1. Core area(CA)
2. Tongue width
3. Stack height
4. Window area
Please sir, include a diagram showing the four dimensions.
Thank you
Hello Godfrey, for modifying a readymade transformer, you can simply apply the following formula:
Es/Ep = Ns/Np
where,
Es = Secondary Voltage,
Ep = Primary Voltage,
Ns = Number of secondary turns,
Np = Number of Primary turns.
Okay sir, thank you
Dear sir, please am confused here:
You said “simply dividing 120 by 12 gives 10 Amps, this becomes the required SECONDARY CURRENT”
But you calculated secondary current again from this:
Step#3: Calculating SECONDARY CURRENT = 24 × 10 / 230 × 0.9 (assumed efficiency) = 1.15 Amps.
Please sir my question is:
1. I don’t understand what the required 10A and the calculated 1.15A for secondary current mean.
2. You said again: “Now, the required Primary current is 10 Amps”
Does this mean that for a 9-0-9v, 10A transformer, the primary and secondary currents are 10A at full load?
Please sir put me through, I just want to get the difference , and be clarified.
Thank you
Hello Godfrey, the 1.15 Amps is for the 230V side winding, as I explained earlier you must divide the wattage with the voltage.
so 24 x 10 gives 240 watts for the entire transformer, and dividing this 240 watts with 230 V gives the indicated value, (deducting the 0.9% efficiency)
The primary, and the secondary side current rating cannot be the same since the winding voltages are different.
Okay sir, I really appreciate. Thank you.
Please sir, I would like you to confirm if am correct of the following:
Let me still use the 230v/12-0-12v , 10A transformer to ask my questions:
1. Please sir I learnt that transformers are rated in volt-ampere:
My question is, is the VA of the transformer in question 12 x 10 = 120VA or 24 x 10 = 240VA?
2. Please sir, is the (power)wattage 12 x 10 = 120W or 24 x 10 = 240W?
Does this formula: Power = VA x 0.8 (power factor) not applied here?
3. Please sir, is the 10A of the transformer in question the current of the low voltage winding (which is 12-0-12V) or high voltage winding (which is 230v)?
Thank you sir
Godfrey, the power factor has not been considered in the above article, it may be calculated while making the inverter.
the 10A is for the 12-0-12V side
Thank you sir
Please sir I want to know how to construct an inverter circuit and transformer that can carry big load AC.
I don’t know whether converting dc-dc and DC to AC is making inverter to have power to carry load.
Please I need help from you, answer base on your level of understanding to my level also.
Thank you sir
Hello Wise, you can read the following article to know how to make an inverter
How to Design an Inverter – Theory and Tutorial
Calculate Battery, Transformer, MOSFET in Inverter
Good day Sir Swagatam, please how can I prevent my inverter transformer from getting hot and loud sound while on freezer. Thanks.
Seun, the only way is to use a bigger and higher wattage transformer and MOSFETs, or use a ferrite based inverter for having a more efficient and compact design
Thanks for your reply, please could that be reason for my Tv to show flickering lines while the freezer is on, despite adding more filter capacitor.
No, the lines on the TV screen could be due to the crude inverter output waveform. The lines may not appear if a pure sine wave inverter is used
Hi,
Thanks for this article. I have a question regarding the frequency used in the calculation.
Imagine if we try to make a pure sine wave inverter using SPWM where PWM frequency is about 60khz. But the sine wave frequency is 50Hz. The 60khz SPWM will be fed directly to transformers primary through mosfets and the secondary of the transformer will be connected to a capacitor to filter out 60khz high frequency.
In this setup, should the frequency used for transformer calculation be 50hz (output frequency) or 60khz (input pwm frequency)?
Hi, the number of turns should be calculated for the 50 Hz frequency, but the core must be selected as per the 60 kHz frequency, and this should be a ferrite core.
Hi Swag, I enjoy your articles. Where is a good online source for cores and bobbins suitable for these projects, preferably in the US?
Thanks
Thank you Graeme, you can get them through online stores like digikey, mouser etc. which are all US based
Hey Swagatam,
I have an old 100 amps, 220/45 volts welding transformer. I wanted to know if I could use this transformer to make an inverter of 5000 w with 48 v input and 220 v output. I also have 4, 12 v batteries, 100 amps each for this purpose.
Thanks.
Hi Danyal, do you have a center tap at the 45V side of the transformer or is it a two wire transformer?
Hey Swagatam,
I have checked the secondary wiring of the transformer and there is no center tap or loop in it.
Hey Danyal, in that case you will have to go for a full bridge inverter circuit
Thank you, much obliged.
Glad to help!
Can I use irf3205 to make 5000w inverter
Hi Swagatam, for this 120va inverter trafo design, primary current is 10A for 12v, but for sec current you did 24*10/230*0.9=1.15A, why not use 12 instead of 24. With 120A capacity the corresponding will be 0.58A for 230v( current capacity for sec side). Please help me to clarify my confusion. Thanks
Hi Adeyemi, 24v is used because transformer is 12-0-12v. For 120 watts, the high side voltage will be rated at 0.58 A
Thanks sir for the reply. With 12-0-12v transformer and 10A current, will the inverter capacity be 120watts or 240watts.
120 watts, because you are using a center tap topology, for H-bridge it will be 240 watts.
Thanks Chief Swag, I am getting it, so from your calculation of the gauges and voltage, the secondary side of the above the wattage of 1.15A for 230v, that is 240watts, 120w primary, and 240w secondary, is that OK.
Thanks Adeyemi, if the primary is 120 watt, the secondary will be less than 120 watts, it cannot be 240 watts. In a center tap topology since only 50% of the primary is used at any instant the overall wattage of the transformer becomes 120 watts (minus the losses).
In a full bridge topology and 24V battery, the primary/secondary will be 240 watts (minus losses)
Thanks Swag for being elaborate, is it appropriate to use copper guage rated around 0.6Amp for the secondary side to equal the 120watts of the primary.
Thanks Adeyemi, you will have to calculate it using a readymade data or software.
Please sir, is the stack calculation of 4.47cm not too small
Adeyemi, 4.7 cm tongue width looks quite big and should be correct for a 10 amp transformer
OK sir, Thanks. Please how is trafo rated. A friend bought one ready made around my own size and was rated 1kva centre tap
Hi Aadyemi, just like any other device, transformers are also rated by their voltage and current rating.
OK sir, can I rate this your design more than 1kva because it weighs more than the ready built trafo rated 1kva on weighing scale
Hi swagatam, please i want you to post me H-Bridge circuit diagram using irf740 for inverter and i need correct circuit. Thank u
Hi Saeed, I have already posted many H Bridge (full bridge) designs in the website, please find them through the search box. You can replace the MOSFETs with IRF740
Informative article, just what I was looking for.
Good day mr Swag, pls ist possible to use the above formula to build 2.5kva inverter even if we can not find the swg in the table.
Godspower, only up to 10 amp range is possible from this tutorial. Higher values than this is not possible unfortunately…
Thank you very much sir, am very great full for quick response. thank for the Good job.
You are welcome Godpower!
Good day sir Mr Swag.
pls sir for example I calculated my TPV to be 0.8, now should I aproximate it to 1.7?
Please Sir, what is the difference between Turns Per Volt (TPV) and Volt Per Turn (VPT)?
Ebere P, you can read it in this image:
https://www.homemade-circuits.com/wp-content/uploads/2019/08/VPT.jpg
Please for inverter design which Primary voltage is the best for 12v battery for modified sine inverter some say 10.5, 11v and 12v to calculate for number of turns
Please use 11 V.
Please what is the rationale for 11v, for knowledge sake
There’s no hard and fast rule. 11V is a reasonable value which will ensure an output voltage that’s always near +/- 10% of the normal output voltage level.
Sir,I have confirmed the output from the points that go to the battery, without a battery connected it’s reading 27.1v.
Evans, it is impossible to get 27V from 13 V without a boost converter, not sure how you are able to get it?
Sir,then i think maybe there is a boost converter coz am telling you what I can measure with my multimeter and read. Help if any with a circuit diagram of a boost converter for 24v inverter.
Evans, you can try implementing the following circuit:
https://www.homemade-circuits.com/high-power-dc-to-dc-converter-circuit-12-v-to-30-v-variable/
fine,thank you very much
Sir swagatam, please enlighten me on this; how do pure sine wave Inverter transformer with an output of 13v ac manage to charge a 24v battery from low to fully charged and they do charge very first. What’s the logic behind this?? Please sir am really ineed of the knowledge,thanks.
Evans, that is not correct. transformers are not specified as sine wave or square wave types, and battery charging efficiency is determined by the charger specification not the transformer.
Noted sir. My Inverter has a single two wire transformer,with an output of 13v ac. It’s automatic inveter such that in the presence of mains power,the inverter automatically supplies the mains power to the appliances and after some delay,the inverter starts to charge the batteries and vice versa. Now during charging,I measured the voltages on the battery banks and on my multimeter, voltage indicated a steady first rise. Am left confused since 13×1.41=18.33v, which is not enough to charge 24v battery. In the beginning I expected a reading of 20v ac from the transformer so that 20×1.41=28.2v which is able to charge 24v battery fully. So sir if at all you have some ideas,share with me on how it’s able to charge a 24v battery fast with a 13v ac transformer as I can witness here. Thanks in advance.
Evans, please confirm the output from the transformer without connecting the battery, because 18 V can never charge a 24 V battery.
Sir,I have confirmed that sir and indeed it’s 13.1v. I disconnected the transformer and tested it separately.
Evans, Please check the points which go to the battery terminals (without any battery connected)
Sir swagatam what can cause a film capacitor rated 225uf/330va to bulge? How can I correct this? Can I add more of this in parallel? My inverter has a film capacitor that has bulge and whenever I connect anything,it destroys it immediately. Even dimmer switches have been destroyed too.
A Capacitor will bulge if the voltage across it exceeds its rated value.
Okay sir swagatam let me check and I’ll let you know.
Hello sir, please what value of Es will I use to calculate the number of turns for the secondary of a trafo based 12v battery. Is it 12 or 14.4 to get the desired charging voltage after rectification. Thanks Swag
Hello favour, use 11V for a 12V battery since it is the minimum voltage for the battery
But I need 14.4v to charge
we are discussing an inverter circuit here, not a charger circuit.
Hello sir swagatam,how many amperes can awg6 handle? If I use awg6 to rewind a transformer and use 2awg10 to another transformer,which transformer will have more current? Lastly sir,if am to design a 6000W inverter,which awg size should my transformer be winded with? Thanks.
Hello Evans, I am not a transformer expert, so suggesting the wire gauges will be difficult for me. I am sure there are online calculators which can be used for knowing the relationship between wire gauge and current handling capacity
Thanks sir,the article you suggested was of help.
Glad to help Evans!
Also sir ,if I have a 24v inverter rated 1500va,and I want to make it to 6000va,what can I do? Av got an example of the said inverter with me,the mosfets uses are 80nf55 and from the specs,the mosfets can switch up to 80A and 55V. The inverter has 6 mosfets each side. The transformer is also huge but when I try to load a 2200w microwave,it cuts the supply off and indicate o/l. How can I ged rid of this and enable the inverter to load as many appliances as possible??
Your battery must be also rated equally to handle the load current. Your 24v battery must be rated at 300 to 500 Ah
Thank you sir swagatam,av got 2
12v batteries rated 200Ah each connected in series.
400 Ah should be just OK.Check the voltage while it is being used with the inverter load.
Hello Swagatam,
A great and wonderful work you’ve been doing. God bless you real good.
Can this transformer design be used for the sine wave inverter you updated here: https://www.homemade-circuits.com/sinewave-ups-circuit-using-pic16f72?
Thank you John, If the recommended transformer is an iron core transformer then yes it can be implemented for the mentioned circuit…
Hi swagatam,my name is ibrahim from Nigeria i would like to thank you for the detailed explanation of transformer design,may God reward you.sir ive gone through the calculations which are very clear to me my only problem is i want to design a 1kv inverter transformer i dont have problem with the calculations but the table. Can you please help me with a table chart that can handle upto 100amp? thanks and God bless
Thank you Ibrahim, I do not have a precise table for inverter application, but I have a general wire and current chart which you can refer below:
https://www.homemade-circuits.com/56492-2/
I hope this might help to get a rough idea regarding the wire thickness.
ok sir,thanks alot i really appreciate.
Hello swag! Am SAM thanks so much for the detailed information and help… please to design 24v
center tap inverter transformer, when the primary is 12- 0_ 12, does it have negative effects? Thanks
Hello Sam, there’s no negative effect for a center tap transformer.
Please Sir, what about when it’s 24_0_24 for 24v inverter?.
Hi Sam, can you please specify what kind of negative effect are you referring to?
Ok sir, I mean when your battery is 24v and the transformer is 24_0_24… Will there be more battery drain or Will that cause harm to the transformer?
The current drain will be more when the battery voltage is higher than 24V, and will gradually come down as the battery voltage lowers to the transformer specifications. It is a normal thing and will not have negative effects on the transformer.
hello sir, I hope you are doing well and how is your work? sir, I thank you for the automatic cut off voltage regulator circuit which you send it to me in a couple of some days back. sir, this time I I need your advice. I am a Nigerian, from TARABA state.sir,between electronics and power or electrical, which one is more better to study so that one can be easily self reliance and he shall be accepted quickly when looking for a government work. the reason behind my question is that, I’m a student from mautech Yola university, and we just resume to run the first semester 300level.so,we are ask by the University to choose one in between the two to follow. although, I read electronics during my technical secondary school.
Hello Emmanuel, Electronics is better because it has a wider scope and the future world will be heavily dependent on this subject. However electronics can be a lot more difficult than electrical, so choose wisely.
hi sir, I can stop thanking you. please sir, can I get one of inverter circuit and a cut off voltage circuit I.e,when the battery full, will stop it from charging and when it’s run down a little, like 10 percent out it will get it back to charging. please sir, that is my email. (emmygangba@gmail.com).
Thank you Emmanuel, you can try the following circuit:
https://www.homemade-circuits.com/self-regulating-lead-acid-battery/
This will self regulate ON/OFF at about 10% below full charge level
hello sir, I’m still thinking you. sir you said my battery voltage is lower than the transformer ratting, please sir can I have explanation of how your know the transformer rating.
You said your transformer is 15V and battery is 12V.
hello sir, thank you for the reply! the load I used was one bulb and my phone charger,thou it is charging the phone well, but when I connect the supply wire to the battery, the supply wire started getting hot as well with the two mosfet. so, the battery ratting is 62Ah.i have tested the transformer according to step down, just as you said, the voltage spec I got was 15v
Hello Emmanuel, in your case the battery voltage is lower than the trafo rating so there shouldn’t be any heating due to transformer primary. You can check by disconnecting the drain of the mosfet from the transformer taps, if the mosfet don’t heat then the problem could be somewhere in the transformer.