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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.

Notes:

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.

Note15-Feb-16: (48V center tapped means: P:48V "24-0-24" / S:220V)

Note18-Feb-16: Test your transformer before doing this project. Disconnect the transformer from anything it is attached to, connect the 220v Secondary side directly into a 220vAC outlet and test the Primary side with your voltmeter, you should get exactly the voltage necessary for this project as per the table above. If not then don't waste your time building the project, it will not work.

****Do not supply the driver circuit with more than 24VDC max. because the voltage regulator "7812" will burn. Look at the pic of how to connect the batteries and where to take a 24vDC wire from.

3> R1 is to set the PWM duty cycle to 220v. Connect a voltmeter to the AC 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 are heat sensitive, they change value when 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 inverter like "overload cut-off", "low battery cut-off" or "overheating cut-off".

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 thick black lines on the schema also I included a pic so you see how thick those wires must be. (You can make the driving circuit section on a breadboard for testing purposes but NOT the power stage).

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, and yes equivalents work too.

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.

Update 18-Feb-16: There are cheap readily available, professional looking Battery level indicators these days for a couple of $, consider them in your project. LED meterLCD meter

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 the circuit on a
breadboardwith crocodile clips or thin wires WILL NOT WORK ! You'll get wrong voltage readings. Don't come back crying that you're getting a 150v output or so.

Please sir<br>I must confess am inspired By this. I want ask. Can a modified sine wave inverter be able to carry loads like refridgerator, hot plate, industrial fan, and the modem photocopying machine? Please clear me.
<p>Hi Nick, I have started this project with some scrap parts from a broken down old ups. The original design was very inefficient. I'll add more pics as I go along.</p>
Hello Can you give me an outline of your design
<p>square wave? not pure sine wave? </p>
<p>Hellow sir here is the PCB of my power stage. Is it ok ? Does the connection is enough thick to give me best result sir ? </p>
<p>up for this... </p>
no you must not install the power transistors on pcb, mount them directly on aluminium heatsinks and solder the thick wire directly to them.
<p>yes sir i will do that...........those pic are in proteus software where i didn't get Heatsink but when my pcb will be printed i will connect two heatsink for each two set of mosfet ...... and i will connect the transformer 12-0-12 side directly to the heatsink . that just a pcb designing software version Sir. where i make some wire so thick whose are referred by you on schematic and will add huge amount of soldering lead when i will solder it. I am using mosfet here which is not like your n6277 metal....... its like the picture i gave...... so it is not possible to connect them throw heatsink as you have done. Sir is it ok?</p>
<p>nice! </p>
Hi Nick, Thanks soo much for your support. I came to your site about 3yrs ago and you were able to give me all the basics of PWM inverter. Now i have been able to develop your circuit and can now use same transformer for charging and feedback. I want you to check from my site.<br><br>http://helpersalone.blogspot.com/2016/08/inverter-with-charger.html<br><br>Thanks very much. you are a blessing to humanity
<p>Hellow sir .........I need your help. Can i get your PCB pleas</p><p>It will be very helpful to me sir.pleas</p>
<p>Hello Sir wish you good day. actually I am trying to complete this project for few days. and finally 10 days ago I printed it on PCB and add all component those you refereed. But till the project is not complete 100%. I am giving you a large description on what I do and what is the feedback from this circuit.</p><p>First of all the changes I made :</p><p>1. I can't find bc327 so i used bc557/B892/1020 respectively all are pnp transistor and the much similar with bc327.</p><p>2. I have used 2k pot instead of 2.2k.</p><p>3. I have connect two mosfet IRF44 and the gates of each mosfet is directly connected to B1 and B2 terminal on the circuit .</p><p>4.I have used a 0.6amp 220/12 transformer as the feedback transformer and a 4amp 12-0-12 /220 volt transformer as T2 ( I have tried with 300 watt trafo also... but for now just using 4 amp just for trial with it i am glowing a 26 watt bulb)</p><p>5. I have connected 220 volt side of both transformer in parallel .</p><p>Thats all i did.</p><p>Problems:</p><p>1. Voltage regulation not working. Normally I connected a volt meter to the output i got 213 volt using 2.2k pot...... and can't get much from it. But when i connect a 26 watt bulb voltage goes down to 107 volt only. But if i set the output voltage (without load) at 40 volt and connect the load the voltage raise up to 70 volt. And some times the voltage bounced up and down the light also bownced its glowness accordingly.</p><p>Inverting part is working fine and I did not set the frequency cause I have not the equipment(oscilloscope) to do that.</p><p>What is my mistake Sir ? What should I do now .</p><p>I am from a village and here loadshedding is a big problem . Pleas help me to complete this project so that I can Help all of my villagers . Pleas sir.</p><p>With best regards. :) </p>
<p>please send a couple of pics of your complete setup showing the battery size, the power mosfets and the power transformer connected alltogether, i need to see the thickness of the wirings you're using also.</p>
<p>Hellow Sir hope You are well.</p><p>I am facing the same problem now also... My inverter section is ok but the voltage regulation part is not working correctly. I have used all of the componect those you referred only bc327 replaced by 1020 with correct pinout. now I am using 200 watt transformer and 30 watt battery and two IRFP250 mosfet. when i set my output voltage to 130 or around by varying 2.2k pot then if i connect a load of 5-30 watt the output voltage increases to 145-150 volt but if i set without load voltage above 130 then if i connect any load voltage dropped to 100 v or around. Such if i set the output voltage to 220 and then connect a 5 watt bulb as load the voltage droppes to 190 volt. and without feedback transformer I get 227 volt output and with feedback it is 222 volt max. what is my problem sir. please help </p><p>Your obedient :)</p>
<p>The following may cause voltage drop:</p><p>1- The connection wires between Battery-Mosfets-Transformer are not thick enough (read my note #7 and look at the pic).</p><p>2- The power Transistors or Mosfets are not fixed on heat-sinks therefore heating and degrading in performance.</p><p>3- The battery is not big enough, old or maybe not fully charged. (connect your voltmeter to the battery and switch the inverter ON with some load and monitor if the 12v supply drops. Even a 0.5 volt drop could reduce your AC output by 10 volts!) 12v must be stable and constant at all times.</p><p>4- Frequency is not set properly to 50 or 60 hertz.</p><p>5- PWM is not set properly to 220v</p>
<p>Thanks a lot Sir I will fill up all of Your demand soon........... and will notify you about result............. but please make me sure that the 1020 transistor which i used instead of bc327 does it making any problem ? I am giving you details about two... Why you use that transistor sir........ I found some circuit online those don't use any transistor in voltage sensor section they just connect a 10 k resistor between pin 2 and 16 ..and a 100nf to pin 9 and gnd and directly connect output of feedback transformer to pin 1 after bridging the ac to dc. </p>
<p>Sir another question, about the frequency you calculate that the resistor should be 260 k to produce 50-60 Hz but here you used 100 k constant resistor and 100 k variable resistor in series then how it can give me 260 k resistance to produce 50-60 Hz frequency . Is there anything wrong on calculation or my understanding ? </p><p>Best regards Sir. </p>
<p>Ok sir .....camera of my phone is so bad........ i will take some pic tomorrow and post them ............ thanks for being with me sir</p>
<p>Sir now I have replaced 2k pot with 2.2k and noticed that when the output is 130v without load if then i connect a 5 watt load its gose down for a while and instantly be 130v again .....i mean voltage is remaining same here but if i increase the load voltage droped again......... I am using a 3 Amp battery here .........is it the reason ? if i use a large battery will i get 220volt constantly ? I used a 30 amp battery also but that time i did not notice .........just then if the voltage without load was 50 then connecting a 40 watt load increases the output to 90 volt............</p>
<p>Please Sir help me............... last 10 days i am working on it ............lastly the voltage regulation is not working ........... I wrote details in previous comment......... pls help me sir.........</p>
<p>This circuit is designed by Karigor Electronics? :)</p>
<p>No sir PCB printed by them.........</p>
<p>No sir...... I gave the picture of urs and they printed it for me........... Its a printed pcb provider..........and they advertise such the way may be............. I gave them ur PCB and the make it on software and after printing the game me that pcb....... I have been charged for that...... sir</p>
<p>sir my pwm section is not working........pls help........... all others are ok.......... i just used b892 instead of bc327 ......10k variable instead of 2.2k ...all others are same as u .......but without load the output is 220v when i connect the load gradually the voltage decrease gradually...... but when i am changing the variable i have noticed that at a point the voltage without load is 60 then if i connect the load the voltage being increased....... pls help me sir</p>
<p>Sir I made it ... the inverter part is working so good but the voltage regulation part is not working ......... I am having 230v as output but when i connect a 30watt bulb the voltage goes to 60v only........... and that is happaing when the feedback transformer is not connected. when i connect my feedback transformer the i get only 80 volt output but if i use 47k resistor instead of 3.9 k then i get 190v output but also then the voltage goes to down while load is connected.... what is the problem.......... i made the circuit with those component u referred just the bc327 transistor was not available in my nearest store instead of that i used bc557 first after failing i have used b892 instead of bc327 does it making the problem ......... T1 Transformer is a self made one where i get 11.5-0-11.5 if 220v is connected on primery side..... and T2 is a 12-0-12 center tapped 3amp transformer but i have used 12-0 loop only.........and in power stage i just use irf44*2 mosfet .........didn't use any other transformer or diode or resistor................ what is the problem sir..........pls help ..............pls sir </p>
<p>Sir i made it but having a little problem........ due to feedback Transformer... when i connect it the output voltage goes down to 50 volt but without it i am getting 230 volt sir. What is the fault .....should i avoid the feedback transformer ? </p>
Sir what is the rating of T1.. is it 0.5 amp in 220v side or at 12 volt side?
Doesn't matter, whatever is available will work, this is for the sensing circuit.
Thanks a lot Sir ........ I need another help Sir, does a 15 amp rated center tapped transformer means 15 amp for each 12 volt loop ......then for two 12 volt loop is it 30 amps ? I am confused about the wattage rating of a center tapped transformer actually because a 300 VA transformer means on 220 v side it should be 300/220=1.4 amp current then on 12-0-12 side what should be the current .... will it be 300/12=25 amps or 300/24=12.5 amps ? Please help me to remove my confusion Sir . <br><br>Best regards :)
<p>Since the transformer will be working on AC, it means alternating current will enter 1/2 the transformer at a time and the other half will be off. This means 300/12=25 amps.</p>
<p>But Sir I found a previous comment of yours where somebody was asking &quot;for a 300 watt inverter what should be the rate of current in transformer&quot; you replied that it would be 15 amp . but now to me u r saying that it would be 25 amp ? </p><p> Please sir i am so confused ....... ple make me clear....... i am asking you directly that for a 240 va Inverter what should be the transformer ratting ? 12-0-12 v 10 amp or 12-0-12 v 20 amps .......i mean if the transformer is winded with a SWG 12# and its 10 amps wire then can i expect 240va output from this transformer ? </p>
<p>The power drawn by computing equipment is expressed in <b>Watts</b> or <b>Volt-Amps</b>(<b>VA</b>). The power in <b>Watts</b> is the real power drawn by the equipment. <b>Volt-Amps</b> are called the &ldquo;apparent power&rdquo; and are the product of the voltage applied to the equipment times the current drawn by the equipment.</p><p><a href="http://www.power-solutions.com/watts-va" rel="nofollow">http://www.power-solutions.com/watts-va</a></p><p><strong>The power rating of the UPS</strong><strong>:</strong></p><p> ...It is a standard in the industry that the Watt rating is approximately 60% of the VA rating for small UPS systems...</p><p>N.B. You can not make calculations and wind your transformer accordingly and expect to take full power from it, there are a lot of loss factors, always add 25% as a loss factor to get full power.</p><p>There is barely any difference in the cost of winding a 10, 20 or 25 amp transformer, the formula which best worked for me was 250 watt / 12 = 20 amps + 25% = 25 amps (<strong>see note </strong><strong>2&gt;</strong>)</p><p>For a 300 watt system I suggest that you go with 300/12= 25 +25% = 30 amps to get 100% guaranteed results.</p><p>The transformer's power rating is the backbone of this project, the more you give the more you take, be generous.</p>
Hi nick and all<br>Sorry for my english, thank you nick for your schematic. I'm succes building many inverter with your schematic. First inverter 2 year ago (ujang4488), and all my inverter working perfect. This last my inverter, 20 amp transformer + feedback (using same transformer and I added 12 volt output for feedback) + battery charger (adjust voltage with ic lm317). This all fiture only used 1 transformer.
<p>Hello friend I need your help... I want to do all with one transformer also... how can i do. pleas contact me my facebook link is www.facebook.com/The.Sonet </p>
Sorry, problem networking. I cannot send pictures
Thank you for your project
<p>You're welcome.</p>
<p>Sir , Can you give me the PCB layout in pdf format pls... I need this for my house . pls sir pls</p>
<p>i wonder if the transformer used in your system is linear or not</p>
<p>Thanks for your circuit but i am getting a maximum of 6v at pin 11 and 14. pls any help?</p>
<p>Thanks for your circuit but i am getting a maximum of 6v at pin 11 and 14. pls any help?</p>
i want to ask is it the same if for cp transformer 12-0-12 i use two transformers 12v single secundary and connected them in series?
and the 220v coil in parallel ?
I made it. And it work better thanks
<p>You're welcome.</p>
<p>Good morning sir, I made this and it work nicely. </p><p>Many thanks for sharing this. God bless you</p>
<p>Thank You.</p>
I'm yet to make my due to lack of vR1
<p>Try with any nearest value you can find. 5k</p>
<p>Please how can i download the pdf file</p>

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