# Calculating the required elements of a PMA?

Discussion in 'Alternative Energy' started by pjl83, Feb 28, 2011.

1. ### pjl83New Member

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Hi.

I made a simple PMA a while back from MDF and to be honest it was pretty rubbish. I think that the magnets were too small and I didn't use enough turns in the coils.

It has got me thinking though. Is there a way of working out all of the variables to estimate the possible output? I am thinking on a larger scale. I want to produce 230v (as close as possible). I understand that it would be complicated and not extremely accurate but there must be an equation out there. I am not too worried about the current at this stage.

Number of turns, resistance per metre or wire, number of coils, size/number of magnets (flux?), revs per minute. etc

Which parts affect current and which affect voltage?

Any ideas. It's all theory for now, I'm just interested in what is possible.

Thanks
Paul

2. ### tcmtechWell-Known MemberMost Helpful Member

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If you are looking for efficient and reliable you will be much further ahead to just buy a common factory made PM motor that has your speed, voltage, and current requirements and use that as a generator.

Through out my years of playing with AE I have came to the simple conclusion that a factory built and re purposed motor beats home brew hands down in cost efficiency and reliability. Its why I use mostly Getty's PM DC servo motors and Fanuc three phase AC servos for my generators now. They take far more abuse than anything I could hand craft while maintaining excellent efficiency and overload capacity.

Being that second hand or surplus commercial PM servo motors come in every shape, size, speed, duty cycle, voltage, and in either 3 phase AC or basic DC its just a matter of looking in the right places to find your match.

3. ### pjl83New Member

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Thats a fair comment, thanks

I have a tumble drier in the shed that only has a broken door. Motor is fine. How would I know or work out what it can produce?

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5. ### tcmtechWell-Known MemberMost Helpful Member

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Unfortunately its most likely a induction motor which by itself wont produce any power unless it was converted over to a PM rotor system. There are a few threads relating to how to do that here too.

After that your output voltage would be determined by the number and strength of the magnets and how fast it was being spun while loaded. The practical output limit would be the original amp rating of the motor and how fast you can spin it before your magnets brake loose.