# PMG power calculations

Discussion in 'The Projects Forum' started by ablank, Oct 4, 2010.

1. ### ablank Thread Starter New Member

Nov 3, 2009
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I looked but couldn't find a good guide for calculating power from a PMA/PMG,
so I wrote my own ... but I'm no EE!

I'm most interested in making sure the Calculator math is correct, but if you notice ANY inaccuracies on the site I'd love to correct them!

2. ### ablank Thread Starter New Member

Nov 3, 2009
4
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Anyone??? Advice for calculating air gaps & resistance? Any way to calculate current? Please?

3. ### retched AAC Fanatic!

Dec 5, 2009
5,201
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Hold on... This will take until over the weekend to get serious views, I suspect.

I know, I dont have the time to go through the site yet.

4. ### wayneh Expert

Sep 9, 2010
12,405
3,256
What you've asked for is extraordinarily difficult, and I think empirical experience will get you farther faster than a theoretical approach. I've spent a great deal of time collecting data and trying to model such things, and it's not easy. The laws of physics are a helpful start; it is true that the EMF will increase linearly with both the number of windings and with the speed of rotation of the magnets. And you can make estimates of the permeability of the air gap and of the volume between the coils.

But, if you're interested in POWER instead of EMF, that's where things get dicey. The system has inductance, which means that it has an impedance that increases with frequency. So power will peak at a higher load resistance as your frequency increases. Depending on the frequency and the wire gauge, wire resistance may also be a contributing factor to power loss.

An alternator under load develops a magnetic field that offsets the applied field. I'm not sure there are good predictive models of how power varies under load under these circumstances.

One thing you CAN model is how rectification to DC affects the power transfer from an AC source, and how filter cap sizing can affect this.

5. ### ablank Thread Starter New Member

Nov 3, 2009
4
0
Thanks- as long as someone who knows better than myself can look it over sometime!

True, but I don't have the option of experimentation (though I'd love to) since \$\$\$ is short.