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  1. #1
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    Looking for a 12v Crank motor (mid drive)

    Hi,

    I bought this summer a big 12v AGM battery rated at 100AH.

    Most electric bike build use 24/36V motor. I wonder if I could reuse that 300$ battery with a 12V battery. I currently use the battery with my canoe. The motor can draw 30A for 1h30 (50% depth of discharge) and it moves 300lbs fairly quickly on water. I think 12V should be enough to propel me on a bike...

    Edit: I think the motor I am referring to is a mid drive motor. I use on my canoe a Minn Kota 24Lbs trust motor 12v. My neighbor has one too and he is willing to sell it to me. I might grab it to put it on the bike. I wonder if that`s going to work well.
    Last edited by mooder; 07-11-14 at 08:07 PM.

  2. #2
    Transportation Cyclist turbo1889's Avatar
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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.

  3. #3
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    My goal is to make this:
    Electric Snow Bike Conversion - DIY'er - YouTube

    From what I understand, you say this is not going to be possible due to the small power output?
    I am not aiming to go too fast, just want to move (faster better of course).

    Thank you very much for your detailed post, very helpful

  4. #4
    Transportation Cyclist turbo1889's Avatar
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    It's possible, its just you usually have to build completely from scratch. And yes low voltage means you get less power out of the same size motor so you have to use an awful big and powerful motor (heavy and takes up a lot of space) to get high power output at only 12v.

    Some of the big AstroFlight motors (32xx series) are big enough and available in winding configurations that will produce a lot of power from only 12v and you can get Kelly brand name controllers to run them off at that low voltage level at high amp levels.

    So if you have the skills, time, and money it is certainly possible. You just aren't going to find any easy "kit" solutions for that low voltage level. Its all DIY scratch work when you get down to only 12 volts and even then finding suitable components that will work together is still a chore.

    If you push your voltage up to 36 or 48 volts then a whole lot more options open up to you with a lot of available kit options and a huge component selection.


    Oh, and by the way I can't completely tell from the video but it almost looks like that guy in the video is using a cyclone gear head motor kit on his bike but by his gearing, power level, and sound it looks like he is using at least a 36v system if not a 48v. At 12v the power level from that same motor (which is one of the few kit motors that runs fairly well on only 12v) would be a third or less of what that guy is using.
    Last edited by turbo1889; 07-12-14 at 11:59 PM.

  5. #5
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    I understand this is not going to be easy or even work at all. I just want to try. I am in physic engineering and get bored a lot during winter time, so why not. Plus spending for a motor isn't a waste as I still can resell it or use it for something else. I can lose 1000$ and still survive until summer...

    I gave up on the 12V route... To many disadvantages. Plus, Li-ion batteries are considerably lighter than my lead-acid (70lbs!). With that added weight, I think I would get even less than the third you suggest.
    Do you recommend any 36V/48V battery?
    How many amp a typical 36V/48V crank motor draw? Of course it varies with speed and the effectiveness of the configuration but I just need a rough idea how many AH needed to have plenty enough juice.

    My research leads to some build with DIY battery pack from recycled laptop batteries. I am kind of interested trying that too. I have a lot of support at school from technicians and the security of the build should not be a concern (engineering school). What do you think of such build? I understand this is potentially very dangerous and I don't have any experience with batteries but the technicians at school always make sure our set-ups are secure.

    It seems the price for a 48V - 15/20Ah is around 450-550$US. I haven't looked yet for motors.

  6. #6
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    I actually own a 12V bike motor. Sadly, it's one of these....

  7. #7
    Transportation Cyclist turbo1889's Avatar
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    Ah, the old brushed motor friction roller kits, that takes me back so many years.

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