The article deals with the construction details of a mini inverter. Read to know how to build an inverter which can provide reasonably good power output and yet is very affordable and sleek.
There may be a huge number of inverter circuits available over the internet and electronic magazines. But these circuits are often very complicated and hi-end type of inverters.
Thus we are left with no choice but just to wonder how to build an inverter that can be not only easy to build but also low cost and highly efficient in its working.
Well your search for such a circuit ends here. The circuit of an inverter described here is perhaps the smallest as far its component count goes yet is powerful enough to fulfill most of your requirements.
This simple mini inverter circuit can be completed through the following easy steps:
Cut two sheets of aluminum of 6/4 inches each.
Bend one end of the sheet as shown in the diagram. Drill appropriate sized holes on to the bends so that it can be clamped firmly to the metal cabinet.
Also drill holes for fitting of the power transistors. The holes are 3mm in diameter, TO-3 type of package size.
Fix the transistors tightly on to the heatsinks with the help of nuts and bolts.
Connect the resistors in a cross-coupled manner directly to the leads of the transistors as per the circuit diagram.
Now join the heatsink, transistor, resistor assembly to the secondary winding of the transformer.
Fix the whole circuit assembly along with the transformer inside a sturdy, well ventilated metal enclosure.
Fit the output and input sockets, fuse holder etc. externally to the cabinet and connect them appropriately to the circuit assembly.
Parts Required for the simple inverter circuit diagram
You will require just the following few components for the construction:
R1, R2= 100 OHMS./ 10 WATTS WIRE WOUND
R3, R4= 15 OHMS/ 10 WATTS WIRE WOUND
T1, T2 = 2N3055 POWER TRANSISTORS (MOTOROLA).
TRANSFORMER= 9- 0- 9 VOLTS / 8 AMPS.
AUTOMOBILE BATTERY= 12 VOLTS/ 10AH
ALUMINUM HEATSINK= CUT AS PER THE REQUIRED SIZE.
VENTILATED METAL CABINET= AS PER THE SIZE OF THE WHOLE ASSEMBLY
How to Test it?
The testing of this mini inverter is done in the following method:
For testing purpose connect a 60 watt incandescent bulb to the output socket of the inverter.
Next, connect a fully charged 12 V automobile battery to its supply terminals.
The 60 watt bulb should immediately light up brightly, indicating that the inverter is functioning properly.
This concludes the construction and the testing of the inverter circuit.
I hope from the above discussions you must have clearly understood how to build an inverter which is not only simple to construct but also very affordable to each of you.
It can be used to power small electrical appliances like soldering iron, CFL lights, small portable fans etc. The output power will lie in the vicinity of 70 watts and is load dependent.
The efficiency of this inverter is around 75%. The unit may be connected to your vehicles battery itself when outdoors so that the trouble of carrying an extra battery is eliminated.
The functioning of this mini inverter circuit is rather unique and different from the normal inverters which involve discrete oscillator stage for powering the transistors.
However here the two sections or the two arms of the circuit operate in a regenerative manner. Its very simple and may be understood through the following points:
The two halves of the circuit no matter how much they are matched will always consist a slight imbalance in the parameters surrounding them, like the resistors, Hfe, transformer winding turns etc.
Due to this, both the halves are not able to conduct together at one instant.
Assume that the upper half transistors conduct first, obviously they will be getting their biasing voltage through the lower half winding of the transformer via R2.
However the moment they saturate and conduct fully, the entire battery voltage is pulled through their collectors to the ground.
This sucks-out dry any voltage through R2 to their base and they immediately stop conducting.
This gives an opportunity for the lower transistors to conduct and the cycle repeats.
The whole circuit thus starts to oscillate.
The base Emitter resistors are used to fix a particular threshold for their conduction to break, they help to fix a base biasing reference level.
The above circuit was inspired from the following design by Motorola:
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