high speed alternator

[freeenergy6]

i have a weed eater that i would like to have a small charging coil, and since you guys build alot of your own alts figured some one would be able to answer this question

i'm going to use the flywheel magnet and wind the coils on the laminates from an old magneto

i want it to generate 12v at about 5000rpm hopefully 5-6amps just need to run a small headlight

so i was wondering how many turns to get 12v at 5000rpm with the flywheel magnet of a weedeater, and how thick of wire to get 5-6 amps

[KilroyOdin]

Hi, here is link that should put you in the ball park.  18 awg should give about 5 amps.

[freeenergy6]

nice, half the problem solved thanx a lot^^^

so now i just need an idea as to how many turns of wire

[bob g]

how big around is the rotor, that will be a determining factor

that will be needed as well as

single phase? or three phase?

i am assuming single phase?

figure on a coil with maybe 10 turns to start and then a tap every other turn

out to about 20 to start

then try it out

lots of guessing based on very little info

fwiw

bob g

[Flux]

Magneto type alternators for small high speed engines probably defy normal analysis.

These things always end up reactance limited and the number of turns will decide the reactance and hence the short circuit current.

Voltage doesn't really come into the issue as long as you have enough. If you only want it to light at very high speed then perhaps it wouldn't reractance limit and you would then have a light that varied drastically with engine speed. I assume you intend not to charge a battery for such a simple thing.

All I can offer you as guidance is that Villiers lighting coils were typically wound with about 200 turns of something like #16 wire. Much will depend on your magnet system.

You could probably do a test coil and see what short circuit current you get and choose a lamp to suit. These things produce the same current into a 6 or 12v lamp so the power goes up with lamp voltage that you choose. If you get too many amps for the lamp you want you could use a diverter resistor in parallel or wind with more turns to limit the current.

If you want to charge a battery then again I think it will limit to constant current unless you do something very complicated, so the same thing applies. in this case the battery would determine the voltage and you would have more freedom in the choice of turns.

Strange project you may have fun, good luck.

Flux

[KilroyOdin]

http://www.6pie.com/faradayslaw.php

[KilroyOdin]

http://www.6pie.com/faradayslaw.php

I hope it will post this time....

[freeenergy6]

its a single coil not planning on charging a batt just powering a small headlight like 50watt

how do you guys keep the voltage consistant in varied wind speeds

will do a test coil sometime

[Ungrounded Lightning Rod]

The battery clamps the voltage.  This causes the current - and thus the torque resisting the motion of the mill - to rise steeply with increasing RPM.

If the wiring were superconductors and the magnets strong enough the speed of the mill (and output voltage) would rise in proportion to the wind up to cutin - and above that the RPM wouldn't increase at all while the current would rise steeply to provide enough torque to keep the RPM constant.  Because the coils, wiring, and battery have some non-zero resistance the RPM rises in winds above cutin (though much less than in proportion to the rise in wind speed), creating the additional voltage at the mill to drive current through the resistance to charge the (essentially fixed-voltage) batteries.

None of which applies to your genny-drives-lamp case.  You need to wire your magneto to provide the right voltage for the lamp at the operating speed and accept some brightness variation with speed variation or add some sort of voltage regulator after the genny so the lamp will be at constant brightness.  (Or maybe the inductance limiting in the genny will do the job for you - but I wouldn't count on it if you're just hacking around.)

[Flux]

This is a very different requirement from a windmill. The little magneto lighting coils run in current limit with reactance rising with speed to compensate the rising voltage. If the current is constant then the voltage across the light will stay constant with speed.

The only other way to do it is to design for the correct voltage just below your expected speed and use a regulator. This method would let you get very much more power out than the conventional scheme where you limit at constant current from a low speed.

Reacatnce limiting is highly undesirable on a windmill as the power needs to rise rapidly to keep the prop loaded. Once the alternator limits current the prop starts to run away unless you have pitch control.

Flux

[DanG]

One coil maybe - but balance the magnet disc, one magnet and two counter weights 120° apart or three magnets etc..

A good example would be a Roto-Zip saw, I believe they have passive LED illumination built in at the tool chuck area...

[freeenergy6]

I'm using a flywheel on a weed wacker

i'v been looking for a regulator for a decent price but haven't found one