Making a Sine Wave Inverter from an Audio Power Amplifier
The article explains an innovative idea of configuring a few ready made units like a power amplifier, a couple of DC motors and a battery into a sine wave power inverter.
I have already discussed many inverter circuit diagrams here ranging from the most ordinary hobby type idea to the very sophisticated modified sine wave and the true sine wave inverter types. However these designs are all too technical and definitely not meant for the layman. The ideas explained are not simple and require prior expertise with electronics to understand them, and also a thorough knowledge regarding practical electronics to build them.
So does it mean a lay man would be unable to understand these magnificent power houses? And does it mean that a layman is not entitled to enjoy the benefits of a homemade sine wave power inverter, which can be not only lot of fun to build but also very cheap and reliable as compared to the commercial counterparts.
The following section will clearly show how a sophisticated true sine wave inverter can be built by virtually anybody having ordinary technical skills and knowledge.
The idea explained below is not a circuit based unit which needs assembly using PCBs, electronic components etc. rather here we buy ready made units like amplifiers, motors, batteries, transformers etc. and integrate all these for constructing the final piece. Let’s learn how it can be done within an hour.
WARNING: THE CONCEPT IS ONLY ASSUMED BY THE AUTHOR AND HAS NEVER BEEN CHECKED OR VERIFIED PRACTICALLY, BUILD IT AT YOUR OWN RISK AND IF YOU HAVE SUFFICIENT FAITH ON THE FEASIBLITY OF THE EXPLAINED CONTENT.
The Concept: Inverters as we all know are nothing but voltage amplifiers or steppers. The best known method of stepping up voltages is through transformers where isolated windings are used for achieving staggering voltage level multiplications. Basically the process takes place through magnetic inductions for transforming high current fluxes to high voltage outputs.
To comply with the above process, a high AC input is required which can be stuffed into the relevant winding of the transformer for getting the desired 230 or 120 volt AC power. However since the whole purpose is to convert a DC source to mains levels, we first have to convert the low level DC to the low AC input. Ith square wave inverters this is easily achieved by using ordinary astable circuits, but a square wave output is what we are absolutely not looking for, so how do we actually “manufacture” a true sine wave input for our prototype. Off course we can do it using complex opamp circuits like a “bubba” circuit, but since here we don’t want to involve much of electronics, a simpler solution would be to use a small DC motor for the purpose.
A motor as we all know can be rotated by applying power to it, the rotations are caused by constant twisting interaction of the permanent magnet and the induced electromagnetic effect. If we reverse the process, that i.e. if we rotate a motor by applying external mechanical force, we can induce a fair amount of varying potential across its winding terminals and the received voltage will have an sinusoidal wave form. The waveform will be perfectly natural and a true sine wave.
If this sine wave input is amplified to the desired levels, then perhaps our mission can be simply accomplished. Instead of embarking on complex mosfet circuits meant for inverter applications, I thought it was a better idea to feed the above sine input to a high power audio amplifier procured ready made from the market.
One such sample amplifier model is shown here. The outputs which are meant to be joined to speakers must be joined with our power transformers. If the amplifier is a stereo then we can use a pair of transformers and terminate the AC outputs of the transformers to separate AC outlets so that different appliances can be connected to them.
The motor which actually manufactures the sine waves is driven by another motor attached with pulley/belt mechanism. The driving motor is operated with the available battery power.
You will require the following parts and units for the making this true sine wave inverter:
A ready made high power audio amplifier
Transformer – Rating should match with the power of the amplifier. If the amplifier can deliver 500 watts at 50 volts, it means the input winding of the transformer must be rated at 50 volts and 10 Amps.
Alternatively the power amplifier’s power supply transformer can be removed and used for the purpose.
Suitable cabinet for accommodating the whole assembly.
Nut, bolts, washers, wires, battery etc.
It’s quite simple and all about integrating the procured units as per the given diagram. The whole system along with the amplifier, transformer and the motors may be housed inside a bigger metal cabinet and fixed appropriately. The motors especially must be tightly clamped with the base of the inverter cabinet to avoid vibrations and noise. The cabinet must also include all the terminals specified with the unit, fixed externally for the battery connection and the AC outlets.