Electronics > Beginners
Electric motor questions. (Didn't find search answers)
rebelrider.mike:
Hi folks. I have a car starter motor I'd like to try using to drive an eBike. But I have questions that maybe you all could help me with.
At the moment, I plan to use a 12V battery that can deliver up to 134A continuously. That would give me something like 1,600W, but would require some beefy cables to carry the current. I wonder if I could use 24V and cut the current in half? Still leaves me with the same Watts. But do motors work like that?
Also, I know that starter motors are meant for high Amps but breef usage. I'll be using it for (relatively) low Amps but longer usage. Several minutes at a time; enough to get me up the hill. I wonder if I'm going to have heat issues? Would higher Voltage and lower Amps generate the same heat?
Benta:
A starter motor is a bad choice for this application.
As you mentioned yourself, it is not designed for continuous duty, even at low currents. At least the brushes or bearings will wear out quickly.
But there are other issues:
regulating a starter motor is a nightmare, it's simply not designed for it. At the very least, you need tacho feedback to control it.
Also, it is designed to give a short, very high torque burst, and will probably kick you off the bike.
MarkR42:
Don't ebikes mostly use brushless multi-phase (3 phase? more?) motors? I think they are lighter and more controllable but require a more complicated controller.
Car starter motors are presumably brushed DC motors which are intended for short duty cycles. Unless modern cars use these multi-phase things too for their starters, as hybrids, plug-in hybrids etc do.
jolshefsky:
If the batteries and starter are what you have on hand, it can work. That was the old (e.g. pre-1990s) way to make a quick-and-dirty electric bike with readily available parts. Smaller than monstrous cables will work but they will act as resistors. This can be a good thing (peak current limiting) and a bad thing (the wires-as-resistors will heat up, and if they're too small, can melt or burn insulation.)
If you're buying new parts, do yourself a favor and get a brushless motor and a controller for it instead. I find the cheaper controllers are pretty "how ya' doin'" (in the parlance of our times) but ones that are made well are substantially more expensive—definitely a case of "you get what you pay for." Designing your mounts with the ability to replace the controller, battery, or motor with better options in the future is the way to go.
eKretz:
I've seen projects where guys used modified alternators to make electric bikes and gokarts. Seemed to work pretty well.
Edit: https://youtu.be/IKqy3rRWJQE
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