Join Date: Aug 2011
Location: Montana U.S.A.
Bikes: Too many to list, some I built myself including the frame. I "do" ~ Human-Only-Pedal-Powered-Cycles, Human-Electric-Hybrid-Cycles, Human-IC-Hybrid-Cycles, and one Human-IC-Electric-3way-Hybrid-Cycle
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12v e-bike systems are possible (I have built a few myself and have another low voltage build planned) but to my knowledge there are no commercial kits designed for that low of voltage and I've had to build all mine nearly from scratch. One notable exception is the Cyclone brand name gear head motor that is designed to use an external Kelly brand brushless motor controller. That motor will run on 12v although with reduced power output and Kelly does make a controller that will go as low as 12v to use with it but you do have to adjust the gearing by using a smaller tooth count chain-ring for the motor on your freewheeling crank set-up and or a larger driver freewheel on the motor output so that the motor running slower at the lower voltage still matches normal human pedal cadence.
I have one bike myself that uses that set-up:
----- Kelly #KBS24101X
controller (12v-24v, up to 45A continuous)
----- Cyclone External Controller Gear Head Motor
----- Staton-Inc 1.37x24 Freewheel Adapter to fit motor gearbox output shaft
----- White Industries 20t output freewheel unit
----- 36t Motor Input Chain-Wheel On SickBikeParts ISIS Heavy Duty Freewheeling Bottom Bracket
----- 48t Crank Output Chain-Wheel
----- 13-34t 8-speed free-hub and rear derailer on rear 26" wheel
Works well and gives me 8-gears on the rear. It's a pedal along with the motor kind of e-bike though since the motor isn't very powerful running on that low 12v voltage level and limited amps to keep from burning up the motor (adjust controllers programmable max amps to 35 which as much as that motor can take) so its only a 420-watt system and you usually never get more then half of the maximum electric watt input to an electric drive system back out as usable mechanical power (you generally assume only 50% efficiency on an electric motor when it is running at maximum, efficiency is much better when it isn't running at maximum output.) Long story short I probably never get much more then 200-watts mechanical output from it which isn't a whole lot of power but it does work without having to build completely from scratch. My other scratch build 12v drives are capable of at least 500-watts mechanical output power but they are built from scratch using motors not originally designed for e-bike use with a lot of effort to adapt them to that purpose.