Alternator/dynamo idea help.

[r_chez_08]

Hey
I have got 3 12v (I think) electric motors for free they are only the little ones, but I thought I would connect them to my jackshaft, and see if I could charge a 12v battery for lights on my kart. So far I know I need a diode in my circuit to stop the battery powering the motor, but I wondered if it mattered if the battery was charged off less than 12v or more, when I rev up and down? If so is there any way of keeping the voltage at 12v? Thanks

 

[KieranM]

Not too sure if it will work. its the same idea but not 100% the dynamo and motor are the same, i know you wont get the same power from the motor. I tried it with a 9v on my bike ages ago and took a lot of speed for even a dim light

 

[devino246]

I have a scooter motor that i attatched to my drill press to test. Its a 24V 8A (192W) @2600rpm motor.

At 2340rpm, it produced 20.4V. At 3100 it produced 27V. That should mean that at 2600rpm, the voltage output would be 22.6V. Thats a voltage drop of only 1.4V or 5.8%.

Im a little tired so i may not have done the math quite right, but if the amperage drop is similar, according my my calculations, there should be an amperage drop of only .464, resulting in an amperage of 7.54. In the end, that results in a wattage of approximately 170W.

Now, if we have no gear reduction from the engine, at idle you would produce 15.6V and 5.2A (81W). At full throttle, you'd produce 31.1V and 10.4A (323W). So there you have it


Please note, this is a brush motor

 

[r97]

if i remember correctly an electric motor has to rotate in the opposite direction to generate power. maybe i'm wrong though, i may need a bit of sleep, lol. do some good research before you waste materials.

 

[devino246]

if i remember correctly an electric motor has to rotate in the opposite direction to generate power. maybe i'm wrong though, i may need a bit of sleep, lol. do some good research before you waste materials.

Nope. Reversing the motor would simply switch positive to negative and negative to positive.

 

[Cyfun]

Why not just rig up a $30 Chevy alternator like here? http://www.diygokarts.com/vb/showthread.php?t=451

 

[r_chez_08]

Because I'm cheap

 

[r_chez_08]

@ devino thanks for the idea of the drill press, I may try it with my motor and see what it produces.
I know the little motors won't produce much power, but it still will build up over time, and then hopefully I don't need to charge my battery so often.
If a motor puts out over 12v into the battery, will it kill it? And what about under 12v?

 

[fowler]

it shouldnt hurt it to go under but over might
i think it is more the amps u need to consentrate on

 

[r_chez_08]

How can you test amps? I tried with my multimeter, but it gave no reading? I tried a 6v battery which gave no reading also.

 

[devino246]

How can you test amps? I tried with my multimeter, but it gave no reading? I tried a 6v battery which gave no reading also.

Im pretty sure you need some sort of load tester to test amps. Something like this should work for a small motor. A regulator off an old car that uses a generator(instead of an alternator) would work best for a larger motor.

 

[r_chez_08]

Ok thanks. I will get one of them then.