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Help with electric bikes? Answered

I am designing an electric bike (gas prices at $4 means I need one) and had a set of prerequisites to fill, and was wondering if anyone here could give me a quick hand. First thing is, I'd really like for it to have regenerative braking of some kind to extend the range, but am very unsure as to how to do this. I also plan on charging the bike at my school; so a built-in charging unit will be a necessity. I need a range of about 10-12 miles on a single charge, is this too much to ask? The plan is to use a pair of 12v 8 amp-hour Lead-Acid batteries (http://www.sciplus.com/recommend.cfm/recommendid/14608) and a 12vDC cordless drill motor to provide power. Is this too "weak" of a system? I have a 10-speed mountain bike that I'll be using as the base frame. Any help would be much appreciated.


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everything you are asking is compleatly reasonable, accept for your motor choice. If you are trying to do this on the cheap, I would check out my instructable, specifically step 3: obtain materials. If this is a bit to complicated for you, or you really want an assist instead of a full electric, do a little reaserch into friction drive. also, with a 10-12 mile range, you will not need regenerative braking. my first electric bike, a fully electric friction drive, with a 24volt powerchair motor and two 35 AH SLA batteries would give me greater than 20 miles on a single charge, which sounds like it would more than meet your requirements.


10 years ago

Yes, that is too weak. Avoid lead acid unless your budget says you REALLY need to use it, because the power to weight ratio is a HUGE burden with them. Your options really are:
SLA / WetLA -- cheap per watt but may need maintenance and lower power
Nickel Metal Hydride -- moderate price but huge performance gain
Lithium ion/Polymer --lots to choose from, highest price, highest performance
All of the above rate in C, a measure of how much current can be pulled from them proportional to their total volume. Higher C = good. You need a battery pack that is suitable to your choice of motor in both voltage and amperage. Voltage and Amperage go hand in hand to determine the performance (Acceleration). Total storage will determine your run time and subsequently your range. It's a chicken/egg problem of deciding on the motor or battery pack particularly on a budget when deciding what tech to use/what is available.

The motor: A drill isn't cut out for moving a bike - maybe as an assist 'every now and then' but really it would overheat and be sad. You really want a hub motor with integrated bike controller/charger if you want regen braking. They range in wattages from 100-1500. *(750 watts = 1 horsepower)

The controller - again you probably want to go with a tried and tested design that won't a) cook your batteries, b) start on fire and kill you, and c) not get you stranded. A few searches should yield good results. You'll need a battery monitor/charger/maintainer, a throttle control, and a motor controller.

There are lots of resources here on how to build an ebike on ibles, or even a google search shows a lot of forums dedicated to the art.