How to Build a 400 Watt High Power Inverter Circuit with Built in Charger

Interested to make your own power inverter with built in charger? A simple 400 watt inverter circuit with charger that can be very easily built and optimized has been provided in this article. Read the complete discussion through neat illustrations.



A massive 400 watts power inverter with built in charger circuit has been thoroughly explained in this article through circuit schematics. A simple calculation to evaluate the transistor base resistors has also been discussed.

I have discussed the construction of a couple of good inverter circuits through some of my previous articles and am truly excited by the overwhelming response that I am receiving from the readers. Inspired by the popular demand I have designed yet another interesting, more powerful circuit of a power inverter with built in charger.

The present circuit though similar in operation, is more interesting and advanced due to the fact that it has got a built-in battery charger and that too fully automatic.

As the name suggests the proposed circuit will produce a massive 400 watts (50 Hz) of power output from a 24 volt truck battery, with an efficiency as high as 78%.

As it’s fully automatic, the unit may be permanently connected to the AC mains. As long as the input AC is available, the inverter battery is continuously charged so that it is always kept in a topped up, standby position.

As soon as the battery becomes fully charged an internal relay toggles automatically and shifts the battery into the inverter mode and the connected output load is instantly powered through the inverter.

The moment the battery voltage falls below the preset level, the relay toggles and shifts the battery into the charging mode, and the cycle repeats.

Without wasting anymore time let’s straightaway move into the construction procedure.

Parts List for the circuit diagram

You will require the following parts for the construction of the inverter circuit:

All resistors are ¼ watt, CFR 5%, unless otherwise stated.

R1----R6 = To be calculated - Read at the end of the article

R7 = 100K (50Hz), 82K (60Hz)

R8 = 4K7,

R9 = 10K,

P1 = 10K,

C1 = 1000µ/50V,

C2 = 10µ/50V,

C3 = 103, CERAMIC,

C4, C5 = 47µ/50V,

T1, 2, 5, 6 = BDY29,

T3, 4 = TIP 127,

T8 = BC547B

D1-----D6 = 1N 5408,

D7, D8 = 1N4007,


IC1 - N1, N2, N3, N4 = 4093,

IC2 = 7812,

INVERTER TRANSFORMER = 20 – 0 – 20 V, 20 AMPS. OUTPUT = 120V (60Hz) OR 230V (50Hz),



Circuit Functioning

We already know that an inverter basically consists of an oscillator which drives the subsequent power transistors which in turn switches the secondary of a power transformer alternately from zero to the maximum supply voltage, thus producing a powerful stepped up AC at the primary output of the transformer.

In this circuit IC 4093 forms the main oscillating component. One of its gates N1 is configured as an oscillator, while the other three gates N2, N3, N4 are all connected as buffers.

The oscillating outputs from the buffers are fed to the base of the current amplifier transistors T3 and T4. These are internally configured as Darlington pairs and increase the current to a suitable level.

This current is used to drive the output stage made up of power transistors T1, 2, 5 and 6.

These transistors in response to its alternating base voltage are able to switch the entire supply power into the secondary winding of the transformer to generate an equivalent level of AC output.

The circuit also incorporates a separate automatic battery charger section.

How to Build?

The construction part of this project is pretty straightforward and may be completed through the following easy steps:

Begin the construction by fabricating the heat sinks. Cut two pieces of 12 by 5 inches of aluminum sheets, having a thickness of ½ cm each.

Bend them to form two compact “C” channels. Drill accurately a pair of TO-3 sized holes on each heat sink; fit the power transistors T3---T6 tightly over the heat sinks using screws, nuts and spring washers.

Now you may proceed for the construction of the circuit board with the help of the given circuit schematic. Insert all the components along with the relays, interconnect their leads and solder them together.

Keep transistors T1 and T2 little aloof from the other components so that you may find sufficient space to mount the TO-220 type of heat sinks over them.

Next go on to interconnect the base and emitter of the T3, 4, 5 and T6 to the appropriate points on the circuit board. Also connect the collector of these transistors to the transformer secondary winding using thick gauge copper wires (15 SWG) as per the shown circuit diagram.

Clamp and fix the whole assembly inside a well ventilated strong metallic cabinet. Make the fittings absolutely firm using nuts and bolts.

Finish the unit by fitting the external switches, mains cord, output sockets, battery terminals, fuse etc. over the cabinet.

This concludes the construction of this power inverter with built in charger unit.


How to Calculate Transistor Base Resistor for Inverters

The value of the base resistor for a particular transistor will largely depend on its collector load and the base voltage. The following expression provides a straightforward solution to calculate accurately the base resistor of a transistor.

R1= (Ub - 0.6)*Hfe / ILOAD

Here Ub = source voltage to R1,

Hfe = Forward current gain (for TIP 127 it’s more or less 1000, for BDY29 its around 12)

ILOAD = Current required to activate fully the collector load.

So, now calculating the base resistor of the various transistors involved in the present circuit becomes pretty easy. It is best done with the following points.

We start first by calculating the base resistors for the BDY29 transistors.

As per the formula, for this we will need to know ILOAD, which here happens to be the transformer secondary one half winding. Using a digital multimeter, measure the resistance of this portion of the transformer.

Next, with the help of Ohms law, find the current (I) that will pass through this winding (Here U = 24 volts).

R = U/I or I = U/R = 24/R

  • Divide the answer with two, because the current of each half winding gets divided through the two BDY29s in parallel.
  • As we know that the supply voltage received from the collector of TIP127 will be 24 volts, we get the base source voltage for BDY29 transistors.
  • Using all the above data we can now very easily calculate the value of the base resistors for the transistors BDY29.
  • Once you find the value of the base resistance of BDY29, it will obviously become the collector load for TIP 127 transistor.
  • Next as above using Ohms law, find the current passing through the above resistor. Once you get it, you may go on to find the value of the base resistor for the TIP 127 transistor simply by using the formula presented at the beginning of the article.
  • The above explained simple transistor calculation formula may be used to find the value of the base resistor of any transistor involved in any circuit

99 thoughts on “How to Build a 400 Watt High Power Inverter Circuit with Built in Charger

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
    • Without mosfets it won't be easy to raise the power upto 600 watts, using transistors will make the circuit too bulky and non practical, so mosfets are a must here….

    • P1 sets the battery overcharge tripping point which must be set accurately and therefore it's a variable resistor.

      If it's not set properly, the battery might overcharged and destroyed.

  2. Hi! Mr. Swagatam, can you please design inverter circuit using CD4047 chip, with a pure sine wave output and a capacity of 2000watt for us? Using two 12volt li-ion battries connected in series(24volt), with automatic voltage and current control build-in charger.
    Please don't use mosfet in the design because they are prone to damage as a result of spike. A number of trasistors connected in parallel prove to be more stable(i.e last longer) and can serve the purpose.
    Prove to be kind by considering my request.

  3. Hi Eng Swagatam, I read one of your previous articles about how to connect two or more transistors in parallel and you pointed out the significance of the emitter resistors as they are required to avoid thermal run away but the emitter resistors were no where to be found in this 400w inverter scheme diagram. Why sir? thanks Abdulganiy

  4. Happy new year sir. Wishing you a prosperous 2013. I think base resistor of all transistor based circuits is normally calculated to know the specific value that will sufficiently saturate the transistor which in turn switches the connected device. The calculated value can be further reduced to allow for more increased power. Is my suggestion right sir? . Thanks

  5. Warm GREETINGS to you Sir! Pls you said we should use a digital multimeter to read the value of the resistance that would be used to calculate the I-load by connecting the multimeter leads to one half of the transformer secondary winding. Pls i dont really understand this fact, can you please explain this to me very well. And again, if am to use MOSFETs, should i eliminate all other transistors (T1…T6) in the power stage? And to overcome the possible spikes produced by MOSFETs with time, i intend using a blocking diode on any of the two leads of the MOSFETs combination. Please if this idea would work, tell me the MOSFET and the best diode to use, and how to connect them because love MOSFETs very well for their high power amplification. Thank you sir! More greeze to your elbow.

    • Hi Genetik,

      Since the transformer winding becomes the collector load of the particular transistor, the current through this winding should be calculated for finding the base resistance value of that transistor, as per the formula. The winding current can be found by first finding the resistance of the winding and then using Ohms law.

      Yes, if you are using mosfets then all transistors may be removed….today all mosfets have their own built-in blocking diode so I don't think an external diode would be required.


  6. Good day sir! Please I'm designing one of your numerous inverter circuits based on CD4047 IC and two MOSFET transistors (IRFZ44) but am using two D313 transistors since thats the one i have here at my disposal. Right now I'm at the power stage. After connecting the transistors (D313), i powered the circtit with a 12V DC supply and used an analog meter to read the value of the transistors output voltage by placing the meter leads on the collector and emitter leads of the transistors. The meter showed a deflection of approximately 150volts with the meter knob set to 250volts AC. I wonder if my reading is currect enough, then if it is, how do i go about winding a suitable 220volts step up transformer for this circuit. What gauges of copper wire should i use for the primary and secondary winding, and what minimum number of turns should the primary and secondary coils have to withstand the current input and output respectively. Thanks man! More greeze to your elbow.

    • Good day!

      I cannot say much until I see the circuit diagram…….. please provide the circuit link so that I analyze the fault.

      It will be very difficult for you to wind a transformer, it's better to procure it ready made from the market. Even I don't have much knowledge regarding transformer designing.

  7. welcome sir
    – if i connect 12v 35ah battery how much time the battery take to recharge ?
    – and what will be the value of resistors r1—r6 in this case ?? because i didnt understand how i can calculate them
    – if i want to connect a small fan for cooling between which terminals i will connect it ??

  8. Thanks Mahmoud,

    any lead acid battery should be charged for at least 10 hours before using it again.
    you can use this formula: R1—R6 = (Ub – 0.6)*Hfe / I

    Ub = battery voltage

    I = transformer watt divided by battery voltage.

  9. please am want to know if this circuit is a pure sine wave and if it is a pure sine wave inverter then what kind of techniques or method used in the circuit to produce it.

  10. Sir
    Though I know a little of electronics my knowledge is very limited.On seeing your " how to make a 400 Watt inverter I am tempted to try to do this. kindly guide about
    inv on,p1,n/i n/o.What components I have to fit in there & their values.My email address is Thanking you

    • INV ON is the LED.

      P1 is a variable resistor or a preset.

      N/O and N/C are the relay contacts.

      Please note that the above circuit is not for newcomers, there's a big chance that you may fail to make it work due to lack of complete knowledge.

  11. Hi sir you done a great job you a very brilliant man thank you for posting and also for sharing what you have in your mind god bless you,sir i saw many of your circuit and i build one of them the Low Battery Cut-off and Overload Protection but unfortunately it didn't go through for me,but sir i wont to build this 400w inverter my question is can i use cd4017 or 4040 cos it very difficult to get 4049 in my country.can i use mosfet IRF44,IRFZ250 OR 260 0R 2N3205,please sir itstis inverter a modify sine wave or pure sine wave? thank you im looking forward to hear from you soon.

  12. Hi sir im Daniel i snt you soo many questioning about the GSM Car Security System but no reply, now i am in the inverter circuit,i want to build the inverter the one that you used (TIP32C) the (1first) question gos to the transformer is the fmer 12-0-12 right? what about the additional wind that show 38v its should be wind 38v or same 12v? (second) can i replace the TIP32 with IRFP250 OR 260 if yes something have be change in the circuit (3rd) its this circuit a pure sine wave or modified sine wave?(4th) can i build this circuit without scope meter,only i have is digital meter.thank you sir im looking forward to hear from you soon.

    • Hi Daniel,

      I have already provided more than enough data in the car GSM article therefore I have stopped answering to comments under that article. The project is strictly for the experts in the field so anyway there's no point in making that project if you are not an expert.

      Which inverter circuit are you referring to?
      pls provide the link.

  13. im Daniel,ok sir thank you im talking about the one that use 11 TIP35 AND THE BASE transistors is 100 ohms the out put show 230cAC and the one behind also show 38v where is that going to connect.again it is a pure sine wave?thank you

  14. sir i want to build this How to Build a 400 Watt High Power Inverter Circuit with Built in Charger but in my country it difficult to get BDY29 so can use any most felt like IRF3205,to replace bdy29 if its possible to what can do should i remove the BDY29 including with the TIP127 also or i should live the tip127 there?thank you im looking forward to hear from you.

  15. ok sir thank you for the reply,can this circuit How to Build a 400 Watt High Power Inverter Circuit with Built in Charger be build up to 5000W? i wish you marry XMAS.

  16. ok sir thank you very much for the help im very appreciate im going to build it and i will let you know yeah can i use 2 12v btt in series cos im thinking about the charger can it charge 2 12v btt in series which is 24v dc? thank you.

  17. sir,
    we connected the schmitt NAND gate circuit using IC4093 (vcc =+12v, vss =gnd) and gave 24v an input to first nand gate N1, through c1 and R8.. we obtained +12v at n4 gate output and 0v for n2 gate. we expect a square wave output. we got a pure dc output… what will be the actual output from the nand gates… please give your valuable suggestions…. as possible we started to do this inverter….. thank you

  18. Dear sir,Thanks for useful information.
    Please tell me what happen if we not connected 12v truck battery in this circuit,is it(12v battery) for giving solar power at night times ?also give information about cost.


  19. Sir i have only a little knowlege in electronic symble,i just want to know the kind of parts bisides ot d9 is that a transformer and what is the value thanks u sir i want ur reply soon,,more power to u sir

  20. if I use 6v, 4.5Ah battery than what will be output power……?
    Actually I wana make a 100 or 50 w inverter with inbuilt charger using 6v, 4.5 Ah battery plz suggest me the circuit

  21. Sir,
    What type of simple Inverter can i desing to operate Fans, bulb, Soldering Iron and Tv/dvd?
    Lets say, the one with 220v 50hz, 150watt.

    I need your help on, partlist needed for the above invater construction.

  22. Please sir tell me if i changes some & there are give below
    1)if i use invertor transforMER 12-0-12/ 20amp or 30 amp & Charging transformer 0-12/3amp or 5 A
    2) Battery voltage is 12v /100AH
    3)What is the value of R1 to R6 ,i cannt calculate because of Iload? what is ILOAD value?
    After using this ,the o/p will be 400w or not.If not what should made changes for this circuit?

    Plsease reply.

    • Sanjib, you can use any transformer as per your own preference, as long as the supply to the circuit section is 12V, and as long as the battery voltage matches the trafo voltage there won’t be any issues.

      ILOAD can be achieved by dividing the trafo wattage with the battery voltage, in your case that will be simply 20 amps I guess

  23. sir if i use invertor transformer 12-0-12/30 amp and battery is 12v,then any problem is happened or not? Actually,Iload is simply 30amp.Thats why i am thinking that transistor & diode is capable to withstand or not this against 30amp.That is the my question.

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