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Old 11-30-2009, 11:31 PM   #72 (permalink)
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Location: Troy, Pa.
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Pasta - '96 Volkswagen Passat TDi
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You could use a single 12V charger, or you could use a 24V charger and wire the batteries in series every time you want to charge them (not a good idea, I think) or you could use 2 12V chargers... Or you could use one 12V charger and wire the batteries in parallel, which will work fine.

Choices....

Of course, this assumes they're 12V batteries, not 6V.

Regardless, if you're charging them overnight, just get a 2-5A 12V charger (if they're 12V) and plug it into the leads that go from the batteries to the relay.

That wiring diagram assumes that the batteries are pre-wired, and the relay/motor are up to the voltage of the pack.

What actually happens in the schema is that you push the button, which draws a few hundred mA to actuate the contacts in the relay. When the relay is connected, the motor gets full voltage, and amp draw is dependent on load. For this reason, there is no soft start, no load start, etc... pedal a little bit, get up to speed, then push the button and keep pedaling, with less effort for the same speed.

So I"m going to assume you have 2x12V batteries, a 12V motor.

Wire the + to the + and the - to the - on the battery posts, giving you 12V total (with higher Ah capacity)

You'll want something along the lines of a starter solenoid from an old Ford or some motorcycles (~$10).

Wire your contacts to the solenoid, and put your + so that the large leads on the solenoid are switching the motor's power supply on and off.

Wire the momentary (thumbswitch) to the solenoid's stator lead (small pin with an S over it), and ground it to the bike's chassis.

Ground the battery pack to the bike's chassis.

Run a + from the solenoid to the motor's + lead.

Run the motor's - lead directly to the battery -.

When you push the momentary, the solenoid should click, and the motor will begin spinning.

Remember, 100W is about 1/8 of a HP. I'm sure it will draw more under higher load, but you don't want to let it load down too much, else it will start to overheat.

This is the simplest way I know of. There is no protection at all in this circuit for the motor or the batteries. Don't drain them too much. Later, if you're froggy, you can get a Voltmeter that reads 14VDC, so you can make sure you never take the pack too low. That motor probably will never draw more than about 8-10A for any length of time without overheating... that's about 100W @ 12VDC.

You can get away with 14G wire, honestly. 10G would be considered overkill for 10A.
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