I would like to build a generator from an old exercise bike?

Question

I have a bike with a cast iron flywheel that i can easily mount a serpentine belt to. I can handle the building, what i need is info on the generator/alt and voltage regulation. I have a alternator for a 1990 cavalier that i could use, or i have heard a treadmill motor works. Do i just hook the alt. to a 12 volt battery and pedal? Do not know what to ask, you tell me what i need to know. How do i keep from overcharging the battery?

Answer 1

I know a little about electricity, so maybe I can help a little. The alternator from the cavalier would work perfectly since it already converts the motion from the engine into a 12 V DC current for the car battery. I would make sure the treadmill motor works though, because that kind of motor would be dealing with alternating current instead of direct current. You need DC current to a battery, or it simply won't charge like it should. Plus, a motor works differently than a generator from what I understand. I think it depends on what kind of motor you are dealing with. Some have brushes, others have just coils, some deal with AC and others with DC.  Although in theory a generator is the same as a motor, but just used in reverse, you have to make sure that treadmill motor will output 12 volts when you turn it.  It may require some extra parts, like a diode, some capacitors , or a transformer. As for the battery, it will simply stop charging or moving current when it is full. Some battery components can continue to heat up though if they have a continued charge applied, so I'm not sure what to do about that part. My best educated guess is that you can just keep applying charge and nothing serious will happen (but not positive on that idea).

Another thought: you need to make sure whatever motion you put into the generator, you get close to 12 V DC output. You could test this with a simple device such as a voltmeter. If you have a gear ratio on the bike that makes the generator turn slow, it will take forever to put any charge into the battery.  The voltage should remain fairly constant on the generator, but you need sufficient amperage. Amperage is what will charge the battery, not the voltage. For example, let's say you can run the bike at about 100 Watts or 200 Watts for a reasonable workout assuming the bike had no other built in resistance. That would mean you would want an amperage of between 8 to 16 amps to charge the battery, since Power=Amps*Voltage.

And another clarification: Yes you should be able to simply hook up the alternator to the battery and pedal, although remember what I said about gear ratio and amperage above. The alternator already has the parts built in to convert current to 12 V DC. Just make sure you connect 12 V, and not -12 V(which would happen if you connected the leads in reverse- although I'm not sure that this is crucial since I'm not positive on what a battery looks like inside besides the lead plates in sulfuric acid- this would just let you know which is positive and negative)

Answer 2

YOU WONT HAVE THE STAMINA TO OVER CHARGE THE BATTERY.

Answer 3

The Cavalier alternator will work.The field [f] plug needs to be connected to the main terminal which is connected to the battery positive post.The negative is connected to the alternator housing.The alternator shaft needs to spin at at least 800 RPM at which time it produces 12 volts.Below that it drops out and doesn't work.You aren't going to overcharge any batteries because it has a built in regulator and no one is that strong.