Instructables

Increase the speed of an electric motor?

My electric bike, seen here, was built for my senior project. I was limited on motor choice, and had to go with the best I had, an old powerchair motor. After 2 successfull attempts at building an electric bike, I have discovered that it is impossible to go faster that 25 mph with with one of these motors. As you can see on my instructable the bike has 6 speeds, with a top speed of 20mph in first gear. however, when I shift gears, the motor rpm's decrease instead of the speed increasing. I have heard before that it is possible to run an electric motor at higher voltages than it is rated, so I was wondering, if i could add a seperate switch and a "booster battery" of sorts, that as long as I monitered the voltage so as to not let exceed 24 volts, if this would be feasible. My only other option would be to add a second motor in parallel with the first, and on the same drive belt. The first option would be the easiest, if it could work without damaging the motor. Any help would be appreciated.
Thanks,
iloveairsoftstuff

iceng3 years ago
Raising voltage on a DC electric motor almost always works, But two things can really damage it.
  • 1) A motor running on more voltage will run hotter, Don't let it   get so hot that your wire windings start to smell (burning varnish) very detrimental.
  • 2) A motor on even more voltage can eat it's brushes on the commutator faster then it can get hot.  Only clue you get is some sounds and the welder like arcing if you can see into the brush cavity.
Also sounds like you are both battery and motor limited. When you change to a higher gear and the motor speed does not climb back up near it's previous speed after a while.

Good work on your ible.

A

the mechanical engineer (author)  iceng3 years ago
so how much can I raise it for how long without serious consequences? I have heard that they can be run safely at 50% greater voltage, so would 36 be ok?
I don't know your specific motor,
Trial and error is a valid discovery technique.
Most DC motors can easily withstand a 50% increase in voltage above their Nameplate Design is correct.
Just watch the temperature of the frame under load.
If the temperature starts to spike ! Kill the power immediately and let it cool down,

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LeviMc2 years ago
If you add rare earth magnets to the outside you can make it run faster without altering the voltege
iceng LeviMc2 years ago
Yes, Unless your control circuit uses back EMF for speed control then if you add magnets to increase flux the motor would slow and if placing magnets to reduce flux it would speed up.

Actually in a simple motor increasing the permanent magnetic field improves torque and that overcomes friction better with the result that the motor runs a little faster.

Hope this helps.

A
karlpinturr3 years ago
From the experiments I used to do on 1.5v model motors, rechargeables used to spin the motor faster than 'normal' batteries. I always assumed it was a function of more amps/watts from the rechargeable.

If your motor DOES work on the same principal, then the rule should hold true. So, 2 batteries in parallel ought to work.

However, I would suggest looking at your ratios first, so you don't have to figure out ways to fit another battery on your bike, keeping it balanced, etc.
caarntedd3 years ago
It sounds like the gearing is too "tall" or the ratios too far apart. If the revs drop when you change up, you don't have sufficient momentum to change into the next gear on the cluster. Look at the gearing. 20 mph in first is pretty good, you should be able to go faster than 25 with closer ratio gearing.