How to Build a 400 Watt High Power Inverter 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 few 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

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Swagatam said…
It is a square wave design
Sadiq Abubakar said…
Dear Sir
i am a student a i want to connect my on 400w inverter circuit in my project pls i nit assistance from you sir.
Swagatam said…
Dear Sadiq,

what help do you need?
P Ramamurthi said…
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
Swagatam said…
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.
gowhar khan said…
this is the excellent work you are doing, sir, i just want to know i have some old ups , like 600va etc. can i use its transformer in the above circuit
Swagatam said…
thanks Gowhar!

Yes you can use it.
Swagatam said…
Thanks very much, if you could not build a simple Low Battery Cut-off and Overload Protection, it means you are very new in the field and therefore could drastically fail with the above circuit also, because the above circuit is much much difficult.

try something simple, may be you can begin with the following design for learning:
daniel said…
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.
Swagatam said…
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.
Swagatam said…
Daniel give me the link of the circuit I'll check it..
Swagatam said…
you can use TIP35 or 2N3055 in place of BDY29, mosfets are critical devices and could be very sensitive so I would suggest you to stick with transistors only.
Swagatam said…
it can be built by employing more number of transistors and higher wattage transformer
Swagatam said…
yes that can be done...make the stages separately and test them separately before integrating them together.
nirmal smarty said…
hi sir we are going to do ur 400 watts inverter....we want to know how it is working and which technique is used in it
nirmal smarty said…
sir i want to know how will be the output waveform and the function of each component
Swagatam said…
Hi Nirmal, it's a ordinary square wave inverter, I strongly believe that the above design will work, however I have not tested it practically.
nirmal smarty said…
can we use the squarewave directly to domestic loads like fan and light......
Swagatam said…
yes you can operate lights and fans, just make sure you connect a 0.22uF/600V capacitor across the output of the inveter transformer
nirmal smarty said…
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
nirmal smarty said…
sir what should be the transformer rating in kva for this inverter
OneWorld said…
Hello Sir, this is Larry:
Please sir could you kindly post a circuit on 1000watt (1KVA) inverter.
Thank you in anticipation
Swagatam said…
Nirmal, the connections that you have done looks to be completely incorrect, inspect the diagram carefully and do it exactly as given.
Swagatam said…
multiply the input voltage and current of the transformer to get will depend on individual needs.
Swagatam said…
hello larry,

i have already have this circuit in my blog, please use the search box to find it.
nirmal smarty said…
sir the output of the 4093 will be square or sine wave
rahul kumar said…
can i build that circuit on pcb.please post a video regarding construction of given circuit on pcb
RK RAO Valluru said…
Hi sir...... I want to make home inverter of 2000 VA capacity with in built charger.please suggest me the circuit and give some details.My email id is plz help me..
Swagatam said…
Hi RK do you want a square wave inverter or a sine wave inverter??
RK RAO Valluru said…
i want to make square wave inverter
Swagatam said…
OK, please make the following basic circuit set up first and make it work to produce 100 watts, later I'll explain how to upgrade it to the required 2000 wats.
Siva Pratap said…
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.

Swagatam said…
Dear siva, all inverters require battery or a DC input for producing the AC output, without connecting battery the inverter will not operate.
Rustico Luga said…
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
Rustico Luga said…
Sir can u post a pictur of this circuit with actual parts that already finished instal,,:-) sorry for my another request,,thank u again n more power to u sir,:-)
Swagatam said…
Rustico, the part beside R9 is the relay coil which activates the NO, NC contacts when energized or de-energized.
Swagatam said…
it's not been tested practically yet, but according to me it's reliable design and will surely work
Rustico Luga said…
Sir moore power to u,i have a question,the built in charger get the power soures to inerter power out put or to the main power electric company
Swagatam said…
.....from mains electric grid.
shah hussain said…
sir can I use this circuit to get an output of 100w using 6v battery
Swagatam said…
Shah, yes it will be possible only if your battery is rated at around 25AH or more
shah hussain said…
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
Swagatam said…
6V 4.5ah will produce a 15 watt inverter
How would I go about doubling the wattage rating to 800w?
Swagatam said…
more transistors in parallel with the NPN transistors
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.
Swagatam said…
Aminu, you can try the last circuit from the following link:
Unknown said…
Hi Mr swagatam please how do one determine the capacity of inverter after production
Pls can i charge d battery as d inverter circuit z running as itbworks in cars
sanjib laskar said…
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.
Swagatam said…
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
sanjib laskar said…
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.
sanjib laskar said…
Forget to say what is the value of R1 to R6?
Swagatam said…
Sanjib, you can use 12/30amp trafo with a 12V battery, and instead of BDY transistor you can use TIP35
Swagatam said…
you can use 10K 1/4 watt
Swagatam said…
sorry it is for the gate outputs only, for the power transistor base you will have to calculate as per the given formula
sanjib laskar said…
ONLY TIP35 IS used instead of BDY29. One more question is that any other changes is required or not?
Swagatam said…
yes, that's right, rest can be as it is.
rinus said…
Hello Sir,can you give me the values of the resistors 1 thru 6 then i can check my calculations
i blow up already some tansistors
i use de dec3716 (5of them in 1 section) and the bdx53 in a little different confuguration
Swag said…
Rinus, R5, R6 can be 10K, the other will need to be calculated as per the transformer rating
rinus said…
My transformer is primair 110 and 2*12V 40A
i'm stack with the calculations
pls help me
you can give me the values you use as an example
Swag said…
R = (Ub - 0.6) x Hfe / ILOAD

= (12 - 0.6)10 / 40 = 2.85 ohms

you can try 10 watt resistor.
rinus said…
thank you very much
Raj said…
Sir, Please provide me the same function (i.e Built in charger for battery) inverter circuit for 12V battery
Swag said…
Raj, you can use the same circuit for a 12V battery also, just make sure to use a 12V battery for the charger section, and also the 7812 IC will not be required in that case, and 12V will need to be used in the formula for calculating the transistor resistors. Relay will also change into a 12V relay

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