How to Make a Simple 200 VA, Homemade Power Inverter Circuit – Square Wave Concept

An efficiency of around 85 % and a power output of more than 200 watts is what you will get from the present design of a power inverter (home built). Complete circuit schematic and building procedure explained herein.

Introduction

You might have come across many articles regarding power inverters, however you might be still confused about making a power inverter? The present content provides a complete building tutorial of a home built power inverter.

If you are planning to make your own low cost and simple home built power inverter then probably you won’t find a better circuit than the present one.

This heavy duty, easy to build design includes very few numbers of components which can be found readily available in any electronic retailer shop.

The output of the inverter will be obviously a square wave and also load dependent. But these drawbacks won’t matter much as long as sophisticated electronic equipment are not operated with it and the output is not over loaded.

The big benefit of the present design is its simplicity, very low cost, high power output, 12 volt operation and low maintenance. Besides, once it is built, an instant start is pretty assured.

If at all any problem is encountered, troubleshooting won’t be a headache and may be traced within minutes. The efficiency of the system is also pretty high, in the vicinity of around 85% and the output power is above 200 watts.

A simple two transistor astable multivibrator forms the main square wave generator. The signal is suitably amplified by two current amplifier medium power Darlington transistors.

This amplified square wave signal is further fed to the output stage comprising of parallel connected high power transistors. These transistors convert this signal into high current alternating pulses which is dumped into the secondary windings of the power transformer.

The induced voltage from the secondary to the primary winding, results a massive 230 or 120 volts conversion, as per transformer specifications.

Let’s study in details how the circuit functions.

Circuit Operation

The circuit diagram description of this home built power inverter may be simply understood through the following points:

Transistor T1 and T2 along with C1 and C2 and the other associated parts forms the required astable multivibrator and heart of the circuit.

The relatively weak square wave signals generated at the collector of T1 and T2 is applied to the base of the driver transistors T2 and T3 respectively. These are specified as Darlington pairs and thus very effectively amplify the signals to suitable levels so that they may be fed to the high power output transistor configuration.

On receiving the signal from T2 and T3, all parallel output transistors saturate well enough according to the varying signal and create a huge push pull effect in the secondary windings on the power transformer. This alternate switching of the entire battery voltage through the windings induce massive step up power into the primary windings of the transformer producing the desired AC output.

The resistors placed at the emitter of the 2N3055 transistors are all 1 Ohm, 5 Watts and has been introduced to avoid thermal runaway situations with any of the transistors.

PARTS LIST

RESISTORS ¼ WATT, CFR

R1, R4 = 470 Ω,

R2, R3 = 39 K,

RESISTORS, 10 WATT, WIRE WOUND

R5, R6 = 100 Ω,

R7-----R14 = 15 Ω,

R15 ----R22 = 0.22 Ohms, 5 watt (can be connected directly if all the parallel transistors are mounted on a common heatsink, separate for each channel)

Capacitors

C1, C2 = 0.33 µF, 50 VOLTS, TANTALLUM,

Semiconductors

D1, D2 = 1N5408,

T1, T2 = BC547B,

T3, T4 = TIP 127,

T5-----T12 = 2N 3055 POWER TRANSISTORS,

Misc.

TRANSFORMER = 10 to 20 AMPS, 9 – 0 – 9 VOLTS,

HEATSINKS = LARGE FINNED TYPE,

BATTERY = 12 VOLT, 100 AH

Inverter Building Tutorial

The below given discussion should provide you with a detailed step wise explanation regarding how to build your own power inverter:

WARNING: The present circuit involves dangerous Alternating Currents, extreme Caution is advised.

The only part of the circuit which is probably difficult to procure is the transformer, because a 10 Amp rated transformer is not easily available in the market. In that case you can get two 5 Amp rated transformers (easily available) and connect their secondary taps in parallel.

Do not connect their primary in parallel; rather divide them as two separate outputs (See Image and Click to Enlarge).

Next difficult stage in the building procedure is the making of the heat sinks. I won’t recommend you to fabricate them by yourself as the task can be quite a tedious one and time consuming too. It would be rather a better idea to get them ready made. You will find variety of them, in different sizes in the market.

2N3055 Pinout Diagram

Select the suitable ones; make sure that the holes are appropriately drilled for the TO-3 package as shown in the figure. TO-3 is the code to recognize typically the dimensions of power transistors which are categorized in the type used in the present circuit i.e. for 2N3055.

Fix T5----T8 firmly over the heat sinks using 1/8 *1/2 screws, nuts and spring washers. You may use two separate heat sinks for the two sets of transistors or one single large heat sink. Do not forget to isolate the transistors from the heat sink with the help of mica isolation kit.

TIP127 Pinout Diagram

Constructing the PCB is just a matter of putting all the components in place and interconnecting their leads as per the given circuit schematic. It can be done simply over a piece of general PCB.

Transistors T3 and T4 also need heat sinks; a “C” channel type aluminum heat sink will do the job perfectly. This is can also be procured ready made as per the given size.

Now we can connect the relevant points from the assembled board to the power transistors fitted over the heat sinks. Take care of its base, emitter and the collector, a wrong connection would mean an instant damage of the particular device.

Once all the wires are connected appropriately to the required points, lift the whole assembly gently and place it on the base of a strong and sturdy metallic box. The size of the box should such that the assembly does not get crammed.

It goes without saying that the outputs and the inputs of circuit should be terminated into proper socket type of outlets, to make the external connections easy. The external fittings should also include a fuse holder, LEDs and a toggle switch.

How to Test

• Testing this home built inverter is very simple. It may be done in the following ways:
• Insert the specified fuse into the fuse holder.
• Connect a 120/230 volt 100 Watt incandescent lamp in the output socket,
• Now take a fully charged 12V/100Ah lead acid battery and connect its poles to the inverter supply terminals.
• If everything is connected as per the given schematic, the inverter should instantly start functioning illuminating the bulb very brightly.
• For your satisfaction you may check the current consumption of the unit through following the simple steps:
• Take a digital multimeter (DMM), select 20A current range in it.
• Remove the inverter fuse from its fuse holder,
• Clip the DMM’s prods into the fuse terminals such that the DMM’s positive prod links with the battery positive.
• Switch on the inverter, the consumed current will be instantly displayed over the DMM. If you multiply this current with the battery voltage i.e. by 12, the result will give you the consumed input power.
• Similarly, you may find the output consumed power through the above procedure (DMM set in the AC range). Here you will have to multiply the output current with the output voltage (120 or 230)
• By dividing output power by the input power and multiplying the result by 100, will immediately give you the efficiency of the inverter.
• If you have any questions regarding how to build your own power inverter, feel free to comment (comments need moderation, may take time to appear).