Inverter idea - would it work?

[RobSmith]

I have just been thinking about an inverter idea.

If I had a small electric motor, with a large flywheel for speed stability, spinning at 3000 rpm with a permanent magnet attached to the shaft. This magnet would pass within coils to give a small sine wave output. This output would then be the input into big transistors or mosfets to provide the current and polartity amplification of the 48v dc supply to give a 48v ac supply into a step up transformer to get 240v ac.

It would not be as efficient as a modern off the shelf box but it might be an amazingly simple thing I might have the components for in the shed.

Any thoughts?

Rob

 

[duke37]

This seems to be a complicated way of going about it, in particular, you will have to make an alternator. The speed may not be constant with varying supply voltage.

A 4047 CMOS chip can produce signals to drive two mosfets in antiphase. This is simple and cheap. Mosfets will be more efficient and easier to drive than transistors, they should be rated for at least 150V.

 

[jackorocko]

Really is that all there is to an inverter? I mean that seems ridiculously simple in concept.

 

[davelectronic]

There might be some limits on current output, at least as much as the generator and step up transformer can safely handle, if thats all fine your components need to reflect the power levels the max and above that the generator and step up transformer can supply, but i expect you know all this already.

 

[BobK]

For any real power, you do not want to feed a sine wave to the transformer. The transistors will be operating in the linear region and thus heat up considerably.

Inverters either use a modified sine wave (google) or use PWM to approximate the sine wave while having the transistors always fully on or off. Your choice of these two methods depends on what you are driving with the output. If it is just lighting for instance, a modified sine wave is fine. For sensitive electronics you want a true sine wave (done by PWM).

Bob

 

[RobSmith]

For any real power, you do not want to feed a sine wave to the transformer. The transistors will be operating in the linear region and thus heat up considerably.

Inverters either use a modified sine wave (google) or use PWM to approximate the sine wave while having the transistors always fully on or off. Your choice of these two methods depends on what you are driving with the output. If it is just lighting for instance, a modified sine wave is fine. For sensitive electronics you want a true sine wave (done by PWM).

Bob

Thanks for the replies,
I have seen the 4047 chip and am using that to make a simple square wave inverter.
I want a bigger inverter for off grid use. That wants to be a sine wave output hence the idea of generating a true sine wave with a motorised signal maker and then amplifying this sine wave signal.
We will be wanting to drive our laptop, digital tv box and stereo kit as the most sensitive items and the washing machine which may have fairly sensitive circuitry too as well as fairly heafty motor load.
Our biggest load would be my welder but that is crude enough inside to not worry what sort of shape feed it gets. I rewound the transformer in the welder and have figured out that there is limited science going on in there.

I am just poking the possibilities but if I end up with a PWM setup as you describe and that is how the 'real' ones work then that is what I shall probably end up with.

Rob