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  1. #1
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    bike trainer/12v generator

    For a winter project with my girl I'm thinking about building a bike trainer/power generator (got welder, metal is cheap, can pick up a small car electric generator for maybe $20, a used battery for another $20). I'm thinking something like the one outlined in http://www.pedalpowergenerator.com/, but without the moronic price tag (it tallies up to almost $1,000).

    Has anybody here built one using a car generator? As a trainer, how well does that work for resistance?

  2. #2
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    Cars haven't used generators since I was a kid. They use alternators now, so that throws an extra complication in. You need more electronics to get back to DC.

    I did the math long time ago, and if I remember right, you would have to pedal most of the day to get 5 cents worth of electricity.

    But it sounds like an enjoyable project, and you never know where it could go.
    mainlytext.com/bike.html Bicycling in winter, the entertainment version

  3. #3
    Faster than yesterday
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    Quote Originally Posted by Closed Office View Post
    I did the math long time ago, and if I remember right, you would have to pedal most of the day to get 5 cents worth of electricity.
    A 1hr TT (assuming an FTP of 250W) would yield 0.25kWh of electricity. Assuming electricity is about $0.10/kWh, that's 2.5 cents (also assuming perfect capture and transfer of the electricity).

    To make ten cents, you'd basically have to ride a century on the trainer.

    I still think it's kind of cool. You could power small appliances up to a personal desktop computer. Though those obviously vary, a round figure is 250W. A laptop would be less. A line conditioner would also help a lot to keep it steady.

    So probably better to think in terms of what you could power with the output vs the amount of money it's worth. With a good setup, you could make it happen.
    Last edited by tadawdy; 11-20-11 at 08:10 PM.

  4. #4
    coprolite fietsbob's Avatar
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    German made tire driven bottle dynamo, AC in 12v is about $400..

    I tried a alternator driven off a stationary bike at a Science museum..
    you cannot work hard enough to make the kind of light as seen in the film
    Soylent Green, in reality..
    its hard to even make a 60w bulb glow more than orange , below incandescent,
    for long.

    you can increase the resistance with a greater electric load..
    measured , yes, in watts.
    Last edited by fietsbob; 11-20-11 at 02:21 PM.

  5. #5
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    This project is more so I can get a neat bike trainer for the winter, and my girl a working understanding of electricity. I have a super compact motherboard that runs off a 19v power brick. If i pair that off a LED monitor I may be able to generate enough watts to play a game

    Modern car alternators indeed generate AC but they have a built-in rectifier to turn it into DC, that should not be a problem. Oldish ones even have a built in voltage regulator but those are not common. The norm nowadays is to shove that into the car ECU.

    I'm just realizing how much I have forgotten. Is there a good website to relearn the basics of electricity?

  6. #6
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    Could you charge a trolling motor battery and run some LED lights for an extended peroid of time. I could use something oike that in the basement.

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