This is a heavy duty design of a Pulse Width Modulator DC/AC inverter using the chip SG3524 .
I've been using it as a backup to power up all my house when outages occur since aprox. 6 years non stop.

If you like the work and intend to build the circuit don't forget to click on the "I made it" button so I know how many people benefit from the design, Thanks.


1> The schematic circuit design is for a 250 watt output, while the pics are of my 1500 watts inverter that i built, to increase the power of the circuit you have to add more of the Q7 and Q8 transistors in parallel, each pair you add will increase your power by 250 watts, ex: to get 750 watts of power from the inverter you need to add in parallel 2 of Q7 and 2 of Q8 to the original design.

2> If you increase the power transistors you have to enlarge the T2 transformer to match the new needs, the circuit's transformer is rated 25 amps to handle 250 watts of 220v, for every 1 additional amp you need on the 220v side you have to increase 10 amps on the 12v side, of course there are limits to the thickness of the winding so if you need more than 750 watts i recommend that you use a 24VDC supply instead of 12 volts:

DC voltage and Transformer "T2" size recommendation:
Power Supply Transformer Winding
750w 12VDC P:24V "12-0-12" / S:220V
1500w 24VDC P:48V "24-0-24" / S:220V
2250w 36VDC P:72V "36-0-36" / S:220V
3000w 48VDC P:96V "48-0-48" / S:220V
3750w 60VDC P:120V "60-0-60" / S:220V
4500w 72VDC P:144V "72-0-72" / S:220V
5250w 84VDC P:168V "84-0-84" / S:220V
*The transformer should be "center tapped" at the primary side.
**You can make the secondary 110v if needed.
***The transformer in the pic is a custom made (48V center tapped / 220v ) 2000 watts, weights like 10 kilos.

****Do not supply the driver circuit with more than 24VDC max., look at the pic of how to connect the batteries and where to take a 24dc where from.

3> R1 is to set the PWM duty cycle to 220v. Connect voltmeter to the output of your inverter and vary VR1 till the voltage reads 220V.

4> R2 is to set the frequency to 50 or 60 Hz (R2 range is between 40Hz to 75Hz), so guys that do not have a frequency meter are advised to blindly put this variable resistor mid-way which should drop you in the range of 50~60 Hz.
If you want you can substitute the variable resistor with a fixed resistor using the following formula: F = 1.3 / (RxC)
in our case to get a 50Hz output we remove both the 100K and the variable 100K both from pin 6 and we put instead a 260K fixed resistor and we leave the 0.1uF (the 104 cap) as it is, this change should give out a fixed 50Hz as per the formula :
1.3 / (260,000 ohm x 0.0000001 farad) = 50Hz
But in reality it will not exactly give 50Hz because the 260K resistor has a specific error value margin so does the capacitor, that's why i recommend a variable resistor so that accurate calibration can be achieved.

5> Use either tantalum or polyester film "as in pic" for the 104 caps, ceramic disc caps change value once hot and this in turn changes the frequency of the inverter so they are not recommended.

6> Pin 10 of the SG3524 can be used to auto shut down the inverter, once a positive voltage is given instead of negative to pin10, the SG3524 will stop oscillating. This is useful for persons wanting to add some cosmetic makeup to their inverters like overload cutoff, low battery cutoff or overheating cutoff.

7> Wiring connections on the power stage side should be thick enough to handle the huge amps drain from the batteries. I marked them with dark black on the schema also I included a pic so you see how thick those wires must be.

8> The design does not include a battery charger since each person will be building a custom version of the inverter with specific power needs. If you are ordering a custom made transformer you can ask them to take out for you an additional output wire on the primary side to give 14v (between point 0 and this new wire) and use it to charge a 12v battery, of course this needs a separate circuit to control charging auto cut-off. But anyway this is not advisable because it will shorten the life of the transformer itself since using it as a charger will toast the enamel coating layer of the copper wires over time. Anyway .. YES can be done to reduce cost.

9> A cooling fan will be needed to reduce heat off the heat sinks and transformer, i recommend getting a 220v fan and connecting it to the output T2 transformer, when you power up the circuit the fan will start this will always give you a simple way to know that 220v is present and everything is OK.. You can use a computer's old power supply fan if you like.
Note that the fan must suck air out from the inverter case and NOT blow inside, so install it the correct way or it will be useless.
Also note how I fixed both the heat sinks and where the fan is, in a way that the fan sucks hot air from like a channel between the 2 heat-sinks.

10> 2 circuit breakers are recommended instead of fuses, one on the DC side and one on the AC side, depending on your design
Ex: for a 24vDC ( 1500 watts design ) put a 60Amp breaker on the DC side and a 6Amp on the AC side.
For every 1amp of 220vAC you will be draining like 8 to 10 Amps from the 12v battery, make your calculations !

11> The 2 Heat sinks should be big enough to cool the transistors, they are separate and should NOT touch each other. "see the pics"

12> Important: If you're building a big design that uses more than 24VDC as power source, make sure not to supply the driver circuit with more than 24v maximum. (EX: If you have 4 batteries 4x12 = 48v , connect the v+ supply of the driver circuit to the second battery's (+) terminal with a thin 1 mm wire which is more than enough. this supplies the driver circuit with +24v while supplies the power transformer with +48v) "see the batteries pic example"

13> "Optional" : Deep Cycle batteries are your best choice, consider them for best results .. read more

14> Be cautious when building this circuit it involves high voltage which is lethal, any part you touch when the circuit is ON could give you a nasty painful jolt, specially the heat-sinks, never touch them when the circuit is on to see if the transistors are hot !! I ate it several times :)

15> The optional "Low voltage warning" is already embedded in the PCB layout, you can disregard it and not install it's components if you do not need it. It does not affect the functionality of the main circuit, it just sounds a buzzer.

16> The Motorola 2N6277 is a durable heavy duty power transistor, it is used in many US tanks for it's reliability but unfortunately it is a very hard to find part, instead you can substitute each 2N6277 with 2 x 2N3773 or any equivalent.

17> I've included an optional "Battery level indicator" circuit diagram that has 4 LEDs, you can see it installed on the front panel of my inverter pic, it is functioning great and shows precisely how much juice the batteries still have. I have included a small relay that is powered by the last LED to auto shutoff the inverter once last LED is off.

18> Also included an optional "Overload circuit", it is very easy to build and can be calibrated to the desired overload current threshold cutoff point through the potentiometer VR1.
R1 is rated 5watts for inverters upto 1000 watts. For bigger versions of the inverter like 1000 to 3000 watts inverters, replace R1 (1 ohm, 5watts) with (1 ohm, 17watts) which should handle loads upto 10 VA.
Make sure you install a proper relay to handle big current drains.

19> Please guys take your time to read and understand my notes, browse and read the posts and questions asked by others because there are many useful information listed in replies. The main reason for me not answering your question is because it has already been asked before and answered upon.

20> It would be nice and inspiring for others if you take some photos and show us how you built your version, any additions to the circuit are mostly welcomed to be listed here, we can all benefit from them.

21> Please click on the "I've made it" button/icon if you did build the circuit so I know how many people benefit from this design.

22> Testing your completed circuit with crocodile clips or thin wires WILL NOT WORK ! You'll get wrong voltage readings.

<p>Thank you for your sharing ! but i have some questions related to power stage parallel mosfet IRFP250. In datasheet, IRFP250 have power dissipation 190w. what is power handling of IRFP250? and how can i calculate power handling of IRFP250 in datasheet ?</p>
<p>I have used 2N6033 power transistor in place of 2N6277. My circuit is working till the power transitor 2n6033 but i am not getting the output. my transformer is 12 volt to 220 volt and 25 amp. am i using a wrong transistor? Please help.</p>
<p>This my first at instructables, can this be modified to do 24v to 240V at 2500-5000Watt?<br>Where do I get the stuff?<br>Do I have to make the PCB myself.<br>I&acute;m a retired Software Engineer, who once was an Electronician.</p><p>Thanks for the good effort</p>
Sir nick thanks for this amazing work im going to start building it <br>Please any body answer and excuse for mis understanding <br>In pcb draw i couldnt find the cap and resistance connected to 7812<br>Also its written 7808 sorry but its my start
<p>Use 7812 not 7808. </p>
<p>hi @nick.. how can i set the frequency of the circuit, i dont have CRO but i have multimeter. i am new in this plz help. Thanks</p>
<p>Hi, read note '4&gt;'</p>
I got it only in transistors &quot;Motorola 2N6277&quot;
Nick <br>Help me to purchase<br>I coudnt find out the resistors and other component numbers <br><br>And I would like to build 5000watts inverter and also I need how many transistors should I buy and others tooo please help me Nick <br><br>Other guys please help me <br><br>Because I coudnt find out the circuit diagram that's why I ask you buddy's please help me <br><br>Any one please reply me
Reply me as soon as possible
Nick I got 250-5000watts transformer how many transistors should I use
<p>Dear I can not get 2N6277 or 2N3773. But I got 2N6544. the datasheet of 2N6544 better performance. Can i use this transistor with in same design?and also now I design the driver stage using micro controller and I want to design power stage inverter </p>
How much to build totally <br>The estimated cost in your place
My friend take your design his final year project that's I ask you to full details <br>He want to make documention Note <br>Please help me <br>He student of BE EEE in India
I am not Wilfred s2 <br>This is Sabu b<br>
Nick I have confidence <br>Give the detail like <br>Transformers <br>Circuit board<br>And other component<br><br>I think your design is incomplete check Pcb board layout and made board backside it's different <br><br><br>And I would like to make 250 to 5000watts power inverter <br><br>What is the different from other inverter to this<br><br>After connect this to home . If I give load of 300 watts it will work same way I give load of 4000watts isn't work <br><br>I want to make such type inverter <br>Please help me Nick<br><br>
Dear Nick I would like to build 250 to 5000 watts inverter <br>I am from Kerala, India and I want to know the total power transformer should I build <br>And what are the other spears I should buy <br><br><br>I am not professional <br>I am software test engineer <br>I would like to make <br><br>Please help me people <br>And special Nick please reply me <br><br>mailbox.sabut@gmail.com<br>If you can text me in whatsapp 09585135851
Dear SabuB,<br>Thank You for your interest and message, please note that working with this inverter requires knowledge in reading schematic diagrams and the electronic components, more.. this specific project involves high voltages that are lethal so I advise you not to do so, instead seek a professional help.
Nick I need your contact number for make 250 to 5000 watts inverter please make a misscall or mail me <br>09585135851<br>mailbox.sabut@gmail.com<br>greens.sabut@hotmail.com
I would like to make this but what is the transformer details and also where I can buy please reply me guys
<p>Dear Nick </p><p>I really thank you very much to share this smart solution.</p><p>I want to build this type of inverter from solar power as main input system and i need run 1KVA - 5KVA my home appliances becasue the power is breakout 4 or 5 time a day more than 2 -3 hourses. </p><p>Could you help me to make this inverter by sending all steps and basic documents </p><p>my email kaledawitesmelealembd@gmail.com </p><p>thank you </p>
<p>Hi kale97,</p><p>All details needed to build are already listed here, you need nothing more than read and review the user's comments and understand properly the concept and what you're doing. Good Luck.</p>
You two schematics. 1 type incomplete black nd white whiles the is wat is been used on the cover page of the instructible. They are all in the pictures u hv uploaded.
Hi Nick , in some of the schematics u have provided, the resistor on da irfp250 is 10k whiles the other is 100. Please can u clarify. Tnks
Hi leviitu,<br>Where is this? I can't find it.
<p>Thanks for your reply Nick. My issue is solved. Now my transistors does not heat without any load and i can alos adjust the output voltage through R1 2.2k potentiometer.</p><p>Thanks again. </p>
I wish you can post for everyone else what was the problem.
<p>The Problem was with the diodes connected with the transformer, when i removed them the inverter starts working fine. And one of the power stage was not working due to a loose connection.</p>
<p>Hi Nick i build the inverter of 500W but i have some problems </p><p>1) when i attach the battery with the inverter the power transistors heated up without any load and i received approx. 50 volts at the 220 volt side of the transformer. I checked the diodes attach with transformer and they were shorted(cooked). Now my question is if i replace the they will be shorted(cooked) again. so what I have to do to solve this issue.</p><p>2) The second problem is that by varying R1 potentiometer of 2.2k, the voltage at the 220v side of the transformer does not vary.</p><p>Plz reply as soon as possible. I have only three days left in submitting my project.</p><p>Pictures are also attached. </p>
<p>Remove the diodes, they have no effect on the performance of the inverter.</p><p>You say &quot;the transistors heat up&quot; then you said &quot;i made the inverter with mosfets&quot;.. this is confusing. Anyway non of them should heat up except for 2 reasons:</p><p>1- one side of the power stage is not working, this causes the other side to heat up and the transformer will give a loud buzzing sound.</p><p>2- A problem with the transformer. Disconnect your transformer from the circuit and connect the 220v side to the wall outlet and test the 12-0-12 if it is exactly giving what it is supposed to.</p><p>NB: Check if any of the transistors/mosfets is probably burned.</p>
<p>All the 4 power transistors heated up with in 30 secs without any load and the transformer does not produce any buzzing sound.</p>
Tnks very mch for replying Mr Nick
<p>hello Nick could be clarified for the components in detail please sent to you via e-mail Deddy_ischandar@ymail.com, because I want to test the circuit,</p>
<p>Thanks for your innovations i build the inverter and it work, sir kindly give note on overload protection circuit. mail@ adelusioluwatosin01@gmail.com. </p>
<p>Hello Nick,</p><p>Im interested to build your pwm power inverter, but i don't know the amps of transformer that i will use, because I want to built 1500watts power output, may I ask what is the match rated amp of the transformer. for that?</p>
Power Supply Winding<br>1500w 24VDC P:48V &quot;24-0-24&quot; / S:220V
<p>&quot;1500w 24vdc: p:48v&quot;24-0-24&quot;/s:220v &quot;, ...is 40 amps transformer is enough sir for 1500w?.what is your recommended amps transformer sir?</p><p>Thank you Sir., </p>
<p>Thanks for your reply Nick. Now I want to connect a battery charger circuit. Where should I connect it in the above schematic diagram?</p>
Nice work Mr Zouein. Am makin efforts to build the same thing but pls how do i get access to the notes?
<p>It's all listed and numbered: 1&gt;, 2&gt;, 3&gt; .. etc</p>
<p>Hi Nick Can I place D1047 transistor instead of 2n6277 as they are not availble here.?</p>
<p>Equivalents should work with no problem</p>
I have constucted the circuits and am so happy it worked its the 5kv but the problem am having is having a functiona battery charger with autocut off 4 a 12v 400A battery ...pls help its my final year project in school.
<p>Happy to hear that you built a functional design, there are many many autocut-off circuits for chargers on the internet, this should be easy to find. Please upload some photos if you can. </p>
<p>Hi, i have constructed inverter circuit using SG3524, but its frequency is very high, how can i reduce its frequency and use AC output?? Can u pls reply me fast</p>
<p>Hi Nick, i managed to build this inverter and in the beginning it worked very well until when suddenly it started burning the mosfets. I replaced the 3524 IC together with new mosfets but again they blew off. I am using a transformer which i got from a UPS and i did not custom rewound i just used it the way it is, i later replaced the electrolytic capacitors all of them but no change, in fact the mosfets over heats within 30 seconds even without any load connected please help what do you think could be the problem? am Darlington from Eldoret Kenya East africa</p>
<p>did you solve your problem with the mosfets?</p>
<p>Hi Darlington, the mosfets should not heat without a load unless there is a problem at the transformer side. Check your protection diodes, maybe one of them is cooked. Anyway using 'any' transformer is a diversion from the original design.. many things could go wrong.</p>
Hello .what is the furmula to built the transformer base on this project.ex.the size of the wire and core can u give this?

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