Alternator

Is there a specific car alternator that is preferable, power-wise or make and model?

Offered by Doug.

I will give you my opinion for what it is worth. I think any size above 30 amps should work. The reason being, the peddler is going to have trouble sustaining the pedaling on any kind of medium to high amperage. Your biggest concern should be getting the right ratio of pedal rotations to alternator shaft rotation. If this is off then it will be too hard or too easy to pedal. Now that I think about it. It might be smart to feed back some of the output through the field coil in series with a rheostat. This rheostat could be adjusted to determine the amount of charging rate and thus determine the ultimate rotational push on the pedals. One would not use the 12V regulator in this case.

A link that should help in understanding alternators is Alternator Functions

Offered by Mike.

This isn't very hard to do at all. First, almost all the standard car alternators out there are alike. I know for a fact that all GM cars use Delco-Remy alternators. These little guys put out about 60-70 Amps at 12-14 Volts. Now essentially they are AC Generators (hence the name alternator) but on the back there is a little plastic box and cover. Inside that box is a set of Diodes and a voltage regulator. This makes sure that the output is a fairly constant 12-14V DC. Now I know from experience that those diodes do not last long (especially with heat) but outside of the hell-of-an-engine they should last many years.

So all you need to do is find a way to rig up a belt. Anything will do (nylon pantyhose work awesome in an emergency) just tie a small knot and the nylon will make a pretty good belt. Rig up the belt to the pulley of a bike crank and you have a man-powered generator. But remember, the more current you draw (like when charging a totally dead battery) the harder it will be to crank. Watts in = Watts out.

Another consideration is the pulley ratio and speed. This is not as complicated as it seems. A car at idle spins at like 700-1000 RPM. Now I know from looking at my car that the main engine pulley is about 12" diameter and the alternator is about 3". So that's a 4:1 ratio which means the alternator probably likes to spin at about 4 to 5000 RPM. I know that some alternator somewhere has a speed rating on it. But suffice to say that we need it to spin at least 2000 RPM. Easy, since you can probably pedal about 200 RPM, you need at least a 10:1 ratio. Now the alternator pulley is 3" so you need approx. a 30" pulley on the bike. Come to think of it, maybe using the tire itself as the pulley may help.

Offered by Robert.