and yet another coil question...

[TheCasualTraveler]

Either I am finnally getting this or I'm completely wrong but I'm wondering will a coil with say 100 turns produce the same volts as other coils of differant diameter wire but the same number of turns? Assume that all other things are the same, magnet strength etc. I know that larger wire will cause the coils to be larger than smaller diameter wire, but for the sake of disscussion lets say they fit the same area regardless of wire diameter. Or for that matter we could say the coils have only 1 loop of wire. In that case, all other things being the same would the voltage produced (I'm not talking current here) be the same in a 18 gauge wire as it is in a 22 gauge or a 14 gauge?

[electronbaby]

if the diameter of the magnet rotors are the same, and the magnets are the same and if the airgap and RPM are kept the same in both scenarios, the answer is YES.

the # of turns is in direct correlation with voltage produced.

Usually the only reason to adjust the inside diameter of the coils, is to make sure there is no cancellation due to the shape of the magnet and the associated shape of the flux path permeating it. In most instances, it is acceptable to make the ID of the coil slightly smaller than the magnet is wide due to the fact the flux path is usually so tightly focused in an axial design, it narrows as it leaves the magnet.

To answer your question, the voltage would be the same for those wire guages if the turns would be kept the same. The thinner wire would of course have a higher resistance, and therefore a lower current output.

[TheCasualTraveler]

That was too easy. So simple yet in all the reading I didn't see it till now. In that case I suppose when you design a PMA you can determine the  voltage and cut in you want and then simply use the largest size wire that will fit. Wow, that takes a lot of the mystery out of this coil stuff, thanks.

[TomW]

Andy;

Hehe, I thought I heard a loud "click" awhile ago musta been when you locked on to it.


Bada Bing..

Cheers.

TomW

[Flux]

Not quite as easy as that but at least you have a decent starting point.

Turns determines cut in speed. Wire size is a bit more tricky as you now have to get a reasonable balance between the power of the prop in a given wind and the current output of the alternator at a speed that suits the prop.

If you can't hit this compromise within the winding space available then you need to alter the magnetic circuit and try again.

Imagine the case where you chose far too small a magnet rotor, you could get your cut in speed by choosing the turns, but if you found that you needed much thicker wire than the winding space allowed to get your desired power at prop working speed then you are stuck.

If you went the other way you could reach a stage where the fully wound alternator was far too powerful, you could add external resistance or you could wind it with thinner wire than that dictated by the winding space. It would work fine but be very costly compared with one optimised for the prop size.

A good starting point is to see what size and number of magnets are common for a given size machine. For example 12 pole ( 24 magnet) 2 x 1 x 1/2" magnets seem right for 8/9ft prop.

[blueyonder]

 hi andy that was a great question you asked.

 it sure helps me understand things aswell.GREAT ANSWERS.

[finnsawyer]

Just imagine the thinner wire having a non conducting coating around it that makes its overall diameter the same as the thicker wire.  In that case nothing else need change.  You will have the same number of turns and hence the same voltage, but with the thinner wire you will have a higher resistance, which means the alternator will produce less power at a given RPM.  Generally going to a thinner wire would mean the builder wants more turns and voltage, not the same.

[TheCasualTraveler]

Expanding on this coil business...

     As I see it now, the whole idea of "Test Coils" takes on a new meaning. If I was building alternators and not following a specific plan I might try this to calculate coils. First build a test bed of a steel disc, say 12 inches diameter. Affix it to a motor that can be set to specific rpm's. One way would be to use a DC motor with a Pulse width modulator to control it.

(side note, for those of us that don't have anything to measure rpm's do they still make those discs with lines like bar codes on them that when spun under flourescent lights indicate the rpm's? They were used to calibrate or check phonograph turntables.)

     Anyway now you have a base disc where you can draw circles at 8 inches, 10 inches, etc. Also you could draw out lines indicating the 360 degrees of a cicle at 5 degree intervals. Now you can arrange your magnets on the test bed for 6 pole, 8 inch diameter or 12 pole, 10 inch, 16 pole 12 inch whatever. Then get a $5 package of magnet wire from Radio Shack and you wind test coils for the TYPE and SHAPE magnet you will be using. I think there's enough wire in that 3 pack to make a 50 turn, 60 turn, 70, 80, 90, ect coils, and it doesn't matter what gauge you use. You find which coil gives you the volts you want at a given rpm*  using given magnets at a given speed/ diameter disc and then make your real coils using larger wire at that number of turns. To determine what size wire you can get into the area alloted it you could use the info Flux gave me in this thread,

http://www.fieldlines.com/story/2008/1/19/32356/2251

     I know that there are variables, physical dimensions, losses due to resistance, eddy currents etc. that will skew results somewhat, but on the whole, is this sound thinking?

* for 9 coil, 3 phase I think that would be 1 coils volts times 3 times 1.7

[thirteen]

For those who wind their coils I went to goggle and looked up ham radios and there were several roils of wire different sizes for sale. Thought that might help somone. Just a idea  

[Lumberjack]

You can use a digital bicycle speedometer to measure the rpms....