Anyone ever try 12volt car batteries for an ebike?


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11:56 AM
Aug 17, 2018
This is probably a stupid question, but has anyone ever hooked up a regular car battery and starter to the chain of a bike? I've got a bob yak trailer and I'm amazed how much weight I can comfortably pull. I I've got room for 4 batteries easy. Would the gearing / pulley size be an issue? Is there any stamina in a 12 volt battery for that type of work?
I've seen it done in Presteigne 2006 and it made for an 'entertaining' watch. There was a loud clunk of the pinion gear engaging as the solenoid plunged it into the ring gear (not sure if it went via the chain though) and then a horrendous noise which sounded like a rapidly rising siren as the motor (very) quickly accelerated the bike. Unfortunately it didn't last long due to the rest of the bike not being strong enough to support the power. I believe the problem experienced was broken spoke(s).

Had this not caused its demise then I suspect overheating of the starter motor would have. These things are only designed for short service cycles before needing an extended period to cool down. Even with the ability to disengage entirely via the solenoid actuation, it still wouldn't be feasable. As I say though, it was fun to watch and have speed past (if not momentarily).
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Okay, so it sounds like a starter motor isn't necessarily designed to be cranked over and over and over.... This makes sense. But it still seems that car batteries should be a viable energy storage option. They are certainly easy to charge. Are there any other 12v motors that could be used that are better suited for such an application? How about the electric motors used to jack RVs up and down? Or... Any other ideas? It would be a fun experiment. And it would be a bonus to be able to "jump" your batteries from a friend with a car and alternator before a ride home...
Certainly would be once the motor burns out from exceeding its duty cycle!