Please don't try to talk me out of it. I want to do it. So I would appreciate constructive advice. I am leaning towards a car alternator because they are easily available, cheap and have the regulator built in. Thank you.
OK, here's how you do it.
First, do the math.
Start your car and decide how many engine RPM you need to get the charge
current you want.
Then measure the diameters of the crankshaft pulley and the alternator
pulley. Multiply that ratio by the engine RPM to get the alternator RPM.
Decide how many RPM you're willing to pedal and divide that into the
alternator RPM to get the pulley ratio for your exercise bike.
If you can find a pulley that big, you're good to go. If not,
you'll need to split that ratio in two pieces and insert another
idler pulley ratio in between.
Don't know the exact details, but for motorcycle drive,
belt is claimed to be more efficient than chain drive.
You want ALL the efficiency you can get.
Hook the alternator to the a car battery and pedal away.
Stock up on energy bars, liniment and pain relievers.
I don't want to spoil your fun by doing the math, but
calculate the efficiency of the system = energy obtained by discharging
the battery divided by the mechanical energy in. Pulling a number outa
my forecasting orifice, I'd guess it's like 20%.
Starting with the energy output, you can calculate the pedal force
at the target RPM required to input that much energy. Multiply that
by 5. Then double it again, because the force vector varies as the
sine of the angle. That'll give you an estimate of how hard it will be
to pedal.
Do some research on permanent magnet wind generators. They'll likely do
better
at low RPM and you won't have to waste a bunch of energy in the field
excitation, but the conclusion will be the same.
Report your results.
