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 Width (cm) | Winding Area (cm²) |
|---|---|---|
| 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 |
With over 50,000 comments answered so far, this is the only electronics website dedicated to solving all your circuit-related problems. If you’re stuck on a circuit, please leave your question in the comment box, and I will try to solve it ASAP!
Hello sir, please how can I use 1 single transformer with secondary output with 8 ends to charge a 4 battery sets in series, 48v. I want to use the trafo to charge the batteries individually not as a whole.
Hello Daniel, What are the voltage and current specifications of the 4 batteries and what are voltage and current specifications of the transformer output wires? Please let me know this, i will try to figure it out.
Thanks sir, Engineer Swatagam, I appreciate. The batteries are lead acid 26ah/12v each, 15v, 3A trafo rating.
Thanks Daniel, ok, but the voltage and current values of each output from the transformer will be also required…
output rating of the trafo is 15v, 3amps for each of the secondary windings
Ok, thanks, however, unfortunately if the batteries are connected in series then they cannot be charged directly through aa DC supply, rather it will require an automatic changeover circuit which will detect the low charge levels on each of the batteries and connect the supply to those specific batteries in a sequential manner.
Here’s one example circuit for your reference:
https://www.homemade-circuits.com/lipo-battery-balance-charger-circuit/
Hi!
I would like to buy a 72V VDC transformer for 72v Li-ion battery to 220VAC on 15kw. Where Output 220VAC 50Hz on 80 Amperes if it can be done, and input VDC 72V with a few Amperes to connect the battery to it. So I need an inverter transformer, capable of powering 2x 4000 watt server computer power supplies that will have 16 Amperes each. Does this transformer work in your opinion? Or should I buy a 220V VDC transformer?.
Hi, If your load is rated to operate at 220V AC 16 amps then your transformer must be able to satisfy this much power, that is all is required from the transformer.
If the primary side of the transformer is 72V, then its current rating must be 4000 / 72 = 56 amps.
Hi! thanks the response!
The batteries Li-ion is 72v 50Ah 150Ah BMS, it work?.
72 * 50 = 3600 watts, which cannot power 2 * 4000 = 8000 watts.
You will need at least a 120 Ah battery, which may provide a backup of not more than 60 minutes.
Hello sir, for experiment purpose, is it possible to build a 80v input transformer to 12v output, Stepdown
Hello Daniel,
Yes that’s possible, you can create a transformer with any voltage ratios, as you like.
If I use double 15awg wire in primary will it work? Current rating will increase?
Yes it will increase the current capacity of the transformer, make sure to upgrade the secondary side also.
Ok. Thanks
Thanks a lot
Please help me, I want to build a 66-84v(72) 1500w, H-bridge inverter, how can I select the quantity of MOSFET to design the inverter, thank you
Hi,
No need of adding MOSFETs in parallel. You can use the following MOSFET, just 4 will be enough for your H-bridge configuration.
https://www.mouser.in/datasheet/2/196/Infineon_IPP045N10N3_G_DataSheet_v02_09_EN-3362488.pdf
Sorry, this MOSFET model PP045N10N3 is not within my reach. I can use some of these serial MOSFET example: Irfp264
Irfp460
Irls4030-7P
Irfp4468
104r5ns
The IRLS4030-7p appears to be the best candidate, you can use four of these in your H-bridge:
https://www.infineon.com/dgdl/irls4030-7ppbf.pdf?fileId=5546d462533600a401535671d8902713
Can I use microwave transformer as inverter transformer?
You can use any transformer for making an inverter as long as its winding matches the required voltage specifications.
Please kindly assist me in producing my mini inverter that can power my home appliances up to 220v in AC.
Please build the 3rd modified sine wave inverter schematic from the following article, which uses MOSFETs. First build and test this, if you succeed then I will tell you how to upgrade it for more power:
https://www.homemade-circuits.com/modified-sine-wave-inverter-circuit-2/
Please I need help I have a toroidal iron core transformer I want to use and design inverter transformer frequency is 50Hz the core dimensions are: OD=16.8cm, ID= 7.6cm and H=10cm how do I calculate the power of the transformer, core area and turn per volt.
Thanks
Sorry, I don’t have the formulas for calculating toroidal transformers…
I’m confuse on inverter transformer and stabilizer transformer my challenge is that can I use stabilizer transformer core to design inverter transformer I have an 8kva stabilizer transformer core ring type can I use it to design inverter transformer of 7.5kva/72v.
Yes, that’s possible, you can use a stabilizer transformer core to design an inverter transformer.
Hello! How much Ampere should I use when using a power inverter that is 1000 watts? Lets say, is it sufficient or safe to use a 30 or 50 amperes of transformer?
The transformer can have any specifications depending on the requirement, it is not an issue. For 50 amp transformer the battery voltage will need to be 1000/50 = 20 V
What do you mean the battery voltage? For example, I have 12-0-12 volts, 1000 watts. So I need my battery would be 24 volts?
The battery that you use for the inverter. For 12-0-12V transformer the battery voltage will be 12V not 24V.
I think in an inverter design the transformer primary voltage should less than the rated battery voltage or the secondary voltage should be little higher than the rated output voltage.
Another thing I want to ask you my brother is:
At what input voltage rating Will a transformer used in a 12volt pure sine wave inverter will be, is’t 7volt or 13-14volt will the transformer input voltage be?
Thanks in advance.
Emmanuel, yes, the transformer primary voltage should be slightly lower than the battery voltage spec.
For a pure sine inverter you will have to measure the gate/source SPWM average voltage of MOSFETs, this will provide you the average value for the transformer primary voltage.
Thanks for your quick response.
Please can you list out the gate to source spawn average voltages and their corresponding voltages to the input voltage rating of the transformer.
Example: for 7volt transformer what will be the gate to source average voltages and so on.
Thanks in advance.
First you will have to build the inverter circuit with SPWM fed across the gate source of the MOSFETs, then manually measure the DC voltage across the base/source of the MOSFETs. This result will be equivalent to the value of the primary voltage of the required transformer.
Thanks for your quick response ????.
If I should get you right, you mean that if I should have 5volt DC in my SPWM circuit as my gate to source spwm average voltages then the transformer primary voltage will be somewhere 5volt to 7volt?
Thanks in advance
I am assuming that you already have a sine wave inverter/oscillator circuit setup with you. In this situation if you measure the gate/source DC voltage of the MOSFETs, that will give you the primary voltage of the transformer.
My gate to source spwm average voltage of the MOSFETs is somewhere 1.1volt to 1.5volt, it varies depends on the load. So what will be my transformer primary voltage?
Please check it without a transformer. If still it shows 1.5 V then something’s wrong with your SPWM generator, it cannot be so low….it should be around 4 to 6 v for a 12V battery.
Yes is still 1.5volt without transformer connected to it.
I’m designing the configuration of a PWM to SPWM CIRCUIT type of oscillator circuit that you shown in your other post. When the oscillator is on PWM mode (that is without attaching the other high frequency PWM circuit that will break down the low frequency PWM), i do have 4.8volt in my gate to source voltage but when I attach the high frequency PWM circuit, it brings down the gate to source spwm voltage to about 1.5volt.
So could it be that I need to boost the gate to source spwm average voltages with an amplifier stage driver?
Thanks in advance.
I guess you have used the concept explained in the following article.
https://www.homemade-circuits.com/designing-a-sine-wave-inverter-circuit-from-the-scratch-tutorial/
In that case you will have to confirm the SPWM waveform with an oscilloscope, without an oscilloscope it can be impossible to know what is causing the SPWM to drop to 1.5V.
You can also check the SPWM average DC voltage directly across the op amp output, ad see whether it is 1.5V or not. In any case an oscilloscope will be required.
https://www.homemade-circuits.com/dso138-best-small-oscilloscope-for-electronic-hobbyists/
Yes that is the design that I used.
But I don’t have oscilloscope to confirm the waveform of my SPWM generator.
What i really want to understand is that if i should get 6v at my MOSFETs gate/source terminal it means that my transformer will be 6v 0 6v in it primary and the secondary will be 230v?
Yes that is correct….but without an oscilloscope a sine wave inverter cannot be built.
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
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