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converting exercise bike to power generator. what do I need?

Discussion in 'Home Power and Microgeneration' started by [email protected], Oct 27, 2012.

  1. Guest

    I am planning to convert an exercise bike to a power generator in the following way: the belt of the exercise bike drives a hub which has the front sprocket of a mountain bike attached to it. A bicycle chain drives a standardsix speed sprocket (gear) set and derailleur of a mountain bike attached to a hub which also drives a power generator. My ideas that I could switch gears if I wanted a higher workout. I hire work out at a lower gear would mean that the power generator turns faster. So here are my questions: since I'm charging a 12 V battery the power generator cannot output of a higher voltage but must output more amperage when it turns faster. can anybody recommend which cheap power generator I should buy which changes amperage not voltage with higher rotation speeds? What else do I need? Thank you very muchfor your input.
     
  2. Guest

    I've got a better idea. Come and get the one I have sitting out the
    back. It is a commercially built execize bike that used an alternator
    as the load cell. Chain drive to hub on 12 or 14 inch pulley that belt
    drives the alternator. Needs new belt, seat, and other bits - but the
    basics are all there, in Waterloo Ontario. Cheap.
     
  3. Vaughn

    Vaughn Guest

    Serious question: Why?

    You can find many threads here explaining why this is usually a bad
    idea. They are easily searched, so I see no need to restart them.
     
  4. Guest

    Please don't try to talk me out of it. I want to do it. So I would appreciate constructive advice. I am leaning towards a car alternator because they are easily available, cheap and have the regulator built in. Thank you.
     
  5. Guest

    Want a picture of a commercially produced unit (what's left of it)?
     
  6. Vaughn

    Vaughn Guest

    OK. Have it your way.

    Vaughn
     
  7. mike

    mike Guest

    OK, here's how you do it.
    First, do the math.

    Start your car and decide how many engine RPM you need to get the charge
    current you want.
    Then measure the diameters of the crankshaft pulley and the alternator
    pulley. Multiply that ratio by the engine RPM to get the alternator RPM.

    Decide how many RPM you're willing to pedal and divide that into the
    alternator RPM to get the pulley ratio for your exercise bike.
    If you can find a pulley that big, you're good to go. If not,
    you'll need to split that ratio in two pieces and insert another
    idler pulley ratio in between.

    Don't know the exact details, but for motorcycle drive,
    belt is claimed to be more efficient than chain drive.
    You want ALL the efficiency you can get.

    Hook the alternator to the a car battery and pedal away.
    Stock up on energy bars, liniment and pain relievers.

    I don't want to spoil your fun by doing the math, but
    calculate the efficiency of the system = energy obtained by discharging
    the battery divided by the mechanical energy in. Pulling a number outa
    my forecasting orifice, I'd guess it's like 20%.

    Starting with the energy output, you can calculate the pedal force
    at the target RPM required to input that much energy. Multiply that
    by 5. Then double it again, because the force vector varies as the
    sine of the angle. That'll give you an estimate of how hard it will be
    to pedal.

    Do some research on permanent magnet wind generators. They'll likely do
    better
    at low RPM and you won't have to waste a bunch of energy in the field
    excitation, but the conclusion will be the same.

    Report your results.
     
  8. Bob F

    Bob F Guest

    Car alternators take a lot of rpm's. Explore modified ones sold for windmills
    and hydro power.
     
  9. wrote in message
    Too late. As has been said before we humans are only good for a couple
    hundred watts max, and a car alternator is only 50% efficient, hence it is
    still a bad idea.
     
  10. Jim Wilkins

    Jim Wilkins Guest

    I am planning to convert an exercise bike to a power generator ...

    Hwere are some suggestions for permanent-magnet DC motors that -might-
    work for you:
    http://greenterrafirma.com/DIY_Wind_Turbine.html

    To experiment with drive ratios you could make wooden pulleys on the
    generator and use several turns of cotton string for the belt. Tie a
    bowline on one end of the string and adjust the length and tension
    with a tautline loop on the other end. Then the generator mount
    doesn't need to be adjustable. As a kid I used string and wood pulleys
    on rock-tumbler (bird-scaring) windmills in the garden that ran a
    month without maintenance.

    Volt and Amp meters:
    http://www.futurlec.com/Panel_Meters.shtml
    My order of analog current meters took a month to arrive from
    Thailand.

    jsw
     
  11. Dave

    Dave Guest

    My hand rechargeable LED flashlight has a series of gears such that each
    turn of the handle results in the final gear which drives the generator
    spinning 36 times. Could a system such as this be scaled up for use with
    the exercise bike?

    Dave
     
  12. mike

    mike Guest

    It's not rocket science. Simply scale everything up.
    EVERYTHING, including the force it takes to turn the crank.
    You're getting maybe a watt now...if you crank it really fast...
    If you want 100 watts, plan on using 100x the force to turn
    the crank.
    Simple...
     
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