Electric motor questions. (Didn't find search answers) - Page 1
Forum section: electronics / beginners

author: rebelrider.mike
author_rank: Contributor
timestamp: December 27, 2018, 02:22:33 pm
content: 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?

author: Benta
author_rank: Super Contributor
timestamp: December 27, 2018, 04:09:02 pm
content: 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.

author: MarkR42
author_rank: Regular Contributor
timestamp: December 27, 2018, 06:55:52 pm
content: 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.

author: jolshefsky
author_rank: Regular Contributor
timestamp: December 27, 2018, 07:33:09 pm
content: 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.

author: eKretz
author_rank: Frequent Contributor
timestamp: December 28, 2018, 12:05:02 am
content: 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

author: Psi
author_rank: Super Contributor
timestamp: December 28, 2018, 02:07:06 am
content: Something like this for $47.79 would work better than a starter motorhttps://hobbyking.com/en_us/propdrive-v2-5060-380kv-brushless-outrunner-motor.html8S @ 90A = 2.7kW burstI'm not saying get that one. Ideally you want a motor with feedback.Just saying that there are many better options and they don't have to be super expensive.Also, Here's an inexpensive e-bike 12V motor from aliexpress.Even has a chain sprocket on it.https://www.aliexpress.com/item/12V-24V-250W-Brush-DC-Gear-Motor-MY1016Z-Electric-Bicycle-Motor-MTB-Bike-Scooter-Ebike-Brushed/32917121642.html

author: rstofer
author_rank: Super Contributor
timestamp: December 28, 2018, 03:14:52 am
content: Maybe you can find some things here that will help:https://electricscooterparts.com/Google for 'electric skooter project'

author: beanflying
author_rank: Super Contributor
timestamp: December 28, 2018, 03:32:20 am
content: Without machining bearing housings for the starter motor DON'T as others have already mentioned.I have made several R/C glider winches using a range of starter motors from Lucas M45's (we have used M50's at 3-4kW peak back in the arc) to the more modern Bosch types. Current spec(rules based reasons)is about 1kW limited and we run them for 10-20 second maximum bursts. Bearings at both ends and they work a treat.That said there efficiency in in the toilet they will overheat at continuous duty and you need to add bearings so go buy a motor with those things fixed already

author: mikerj
author_rank: Super Contributor
timestamp: December 28, 2018, 02:26:22 pm
content: Quote from: rebelrider.mike on December 27, 2018, 02:22:33 pmNo they don't, a 24v motor of equivalent power rating will have different windings internally. If you apply 24v to a 12v brushed motor, the current and RPM will be approximately doubled (i.e. four times the power) and it will very quickly overheat.

author: woodchips
author_rank: Frequent Contributor
timestamp: December 28, 2018, 04:18:08 pm
content: Why not use a cordless drill?In my experience the drills far outlast the batteries so any number of them around.

author: Zero999
author_rank: Super Contributor
timestamp: December 28, 2018, 05:48:46 pm
content: As mentioned above, forget about using a 12V started motor. Don't even thing about running a 12V motor off 24V, if anything you'll be better off using a 24V starter motor from a bus and run it from 12V for greater reliability.I think your best bet is to work on your fitness and lose some weight if needed, then you'll be able to climb the hill without an electric motor!

author: rebelrider.mike
author_rank: Contributor
timestamp: January 01, 2019, 10:50:48 pm
content: Well, I will do what I can with what I have. If it works, I'll let you all know. Thanks for the responses.

author: fsr
author_rank: Regular Contributor
timestamp: January 08, 2019, 05:25:11 pm
content: There are some motors designed to be installed on wheel hubs in bicycles to assist the user. You should get one of them.