## Question

Solar, wind, hydro and other non-fossil sources of electricity.
AussieJester   100 GW

Posts: 8736
Joined: Mar 11 2008 3:33am
Location: Perth Western Australia

### Question

Gday people i'm hoping someone Miles? Fetcher? Anyone can help work a question i have been asked so...I was up my local Mens Shed and one of the old boys is building a permant magnet altinator from scratch to use on a 'micro hydro' setup and had a question he was unable to find an answer for :-

"What is relationship between coil resistance and induced voltage for permant magnet alternator"

If you could shed some light on it for me i'd be appreciative and can pass it along to the gent.

Regards

KiM

amberwolf   100 GW

Posts: 25082
Joined: Aug 17 2009 6:43am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

### Re: Question

Well, the more turns of the winding (all other conditions the same) the higher the voltage, so a generalization (that may not always be true between different designs, vs the same one wound differently) would be that the higher the resistance the higher the voltage.

However, without a very low-ohms-reading meter (not your typical multimeter), winding resistance is so low you can't reliably tell the difference between two different motors wound differently by the resistance reading.

So if you're comparing different existing PM motors (or generators), you can spin them from a motor at a known RPM, and compare their output voltage to figure out their windings (RPM/volt, kV), which will tell you what voltage they will generate at any other RPM. (without a load--under load it'll depend on the load amount).

Does that help?

AussieJester   100 GW

Posts: 8736
Joined: Mar 11 2008 3:33am
Location: Perth Western Australia

### Re: Question

Gday AW

Thankyou for taking the time to type out all that information i shall catch up with three ole boy Thursday and let him know..

Will let you know if it helped him out matey

Regards

KiM

craneplaneguy   10 kW

Posts: 758
Joined: Nov 27 2015 9:15am
Location: S.E. Idaho USA

### Re: Question

That may be a long project, like carving an airplane propeller from scratch, with no prior knowledge. Getting the optimum match between the alternator and the pelton wheel (I assume) AND the water flow and head pressure, will take a LOT of trial and error. That's why I bought my Harris Hydro alternator and pelton wheel combo some years ago, and it worked right out of the box. It has an adjustable field strength (I believe that is what it is called) because if you get too ambitious and load the rotor down too much by making too amps, you lose rpms, there is a sweet spot where everything clicks, and a lot of not so sweet spots where they don't. That, and switching out the jets is how you fine tune things. More power (ha ha) to your friend in his project, don't want to be a wet blanket....but there is a lot more going on there then initially meets the eye is my point.