Generating electricty

Discussion in 'Electric Bicycles' started by breaksalltherules, Feb 21, 2010.

  1. I have been looking into building a low rpm generator to recharge batteries, run lights, recharge GPS etc. Just wanted to share what I have found out so far.
    This is a great site for electric motors to use as a generator with many low rpm motors. I am thinking about coming up with a speed multiplier (basically a reverse gear reduction box) to take wheel rpm and increasing it to a more efficient range for use with the generator.

    Also found this

    It has a speed controller that I think could potentially be used to decrease motor/generator rpm's so you wouldn't need the multiplier.

    I looked at the hub generators and while I like them I would like to be able to disengage it if I'm not recharging or powering anything.

    Would love some ideas, comments or opinions from all the inventive folks on here.

  2. Also

    Just found this motor with a built in gear reduction (multiplier if you are running in reverse) and rated 6v at 370 RPM. Using that with a roller atached to it and running it directly off the tire, it would seem to be close to ideal range during cruising speed.
  3. motor_head

    motor_head Member

    all you would have to do for the hub genny is disconect the wires with a switch or whatever and there will be no drag
  4. Well that's good to know! I'm actually looking at having multiple ways of generating electricity for long distance travel. I want to be able to charge household batteries for flashlights and GPS so I don't have to keep buying new ones and lighting and turn signals for the bike. I realize that these engines aren't able to produce much power so I know these is demanding a lot from them but I wouldn't have to run the recharge system constantly. Maybe even not every day.
  5. AussieSteve

    AussieSteve Active Member

    You might not get enough power out of that motor for your purpose, depending on intended load.
    As a motor, it's only about 3W and as a generator you'll get less than that out of it.
    Also, running a roller from the tyre, it will probably work without further gearing. The tyre:roller ratio would be huge.

    ... Steve
  6. I'm a little confused about what electrical rating I should be looking for. With the gear box, I know the RPM range would work but any idea on what amp/watt ratting I would need?
  7. AussieSteve

    AussieSteve Active Member

    I'll assume that you know what you're doing with gearing, I didn't do any calculations, but the old type 6V bicycle dynamos that run on the side of the tyre didn't need additional gearing. The dynamo turns many many times per wheel revolution. You could do the calculations using JPilot's 'GearRatio.exe'.

    Regarding power ratings, that's a hard question to answer. There are too many variables.
    ie. What load you will put on the generator, that is, how much current you'll be drawing, then there's the actual efficiency of the motor as a generator to consider.
    Trial and error is my method.
    There are 3 threads going on simultaneously on this general subject.
    Check the others out for a bit more info. They're in 'Lighting and Electrical'. (Where this really should have been, but not to worry.)
    I'm currently building a similar thing to run off a shift-kit jackshaft, using a 12V, 120W DC motor to charge a 12V 7Ah SLA battery.

    ... Steve
  8. I saw your other thread. Sounds like you are making good headway with your project. The reason i wanted to use something other than a normal bicycle dynamo was to see if I could generate more efficiently than the crappy cheapo ones I have found and not pay $70 to $150 for a good one. Which dynamo are you using?
  9. AussieSteve

    AussieSteve Active Member

    I'm not using a (friction-drive) dynamo. (I've hated them since I was a kid.)
    They're very inefficient, at about 50%-60% and also wear the tyre.
    Also, I wanted more power than they produce. The 12VDC, 100-120W motor can produce 4A at 12V, (50W), without much trouble if I spin it fast enough.

    ... Steve