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  1. #26
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by ratdog View Post
    Faster downhill rides with the extra weight?
    The acceleration of gravity is independent of mass...

  2. #27
    Senior Member Looigi's Avatar
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    Quote Originally Posted by JohnDThompson View Post
    The acceleration of gravity is independent of mass...
    Yes, but terminal speed in air depends on density, other things being equal.
    Ride more. Fret less.

  3. #28
    Member Joe_Hoffmann's Avatar
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    Everyone in this thread misses the cool factor of having a car alternator on a bicycle. My main point in starting this thread was for more of an "art" bicycle setup, not AN ACTUAL REPLACEMENT FOR A DYNOHUB!
    But I should have clarified that. The purpose would be to build a "mad max" style bicycle.


    Obviously a car alternator is not mean for a bicycle, due to the weight and friction. I think if you only desire 6 watts, then the wattage required to spin the alternator would be less than 30 watts, which I think would be do-able for the length of a parade or art bike festival. You could vary the current and voltage into the field coils to produce any power that you wanted. I don't think it would draw 200 watts no-load, but then again I could be wrong. I'm not an electrical engineer.
    oh you'll like this, two wheels and some gears!

  4. #29
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    Quote Originally Posted by Joe_Hoffmann View Post
    Everyone in this thread misses the cool factor of having a car alternator on a bicycle. My main point in starting this thread was for more of an "art" bicycle setup, not AN ACTUAL REPLACEMENT FOR A DYNOHUB!
    But I should have clarified that. The purpose would be to build a "mad max" style bicycle.
    "Cool" is arguable. There's an "alt bike" forum that might be a better audience for this.

    Yes, if you have a point, don't keep it a secret.

  5. #30
    DBA
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    If you can find one, the old VW bugs used to use a 6v system. I'm not sure how heavy the alternators were, but I'd bet they are easier to spin than a modern 12v alternator designed to produce enough juice to run all the electronics in a modern car.

    Personally, I'd just use a bike specific dynamo for lighting purposes, but if you wanted to make a trainer/generator to charge batteries or run a tv during a power outage.

  6. #31
    Member Joe_Hoffmann's Avatar
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    apparently I started this thread in the wrong category.
    oh you'll like this, two wheels and some gears!

  7. #32
    Senior Member RPK79's Avatar
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    Quote Originally Posted by njkayaker View Post
    "Nowadays"??

    That's why it was called "soylent green" in the first place. The whole "it's people" (rather than made from soy/plants) thing being a "surprise" was the point.
    Hello! Spoiler Alert!!

  8. #33
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    Sturmey-Archer's hub puts out about 3 watts if I remember correctly. That's enough to run a 2-300 lumen led light. Even that level of output puts considerable drag on your pedaling. If you want to run a 1000 lumen light it will be like going up a 15% grade all the time.

  9. #34
    Senior Member dougmc's Avatar
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    Quote Originally Posted by darkrider2 View Post
    If you want to run a 1000 lumen light it will be like going up a 15% grade all the time.
    Your idea is right, but you've exaggerated the effect considerably.

    1000 lumens is probably around 10 watts for a good LED. Assume that your generator is typical and 50% efficient, and that's 20 watts of drag. (That said, I doubt a retrofitted alternator would be even that efficient.)

    Let's say a typical recreational cyclist can sustain 100 watts, so that's 20% of their power gone. And yes, that's huge. So on level ground, looking only at air resistance, that would slow them down by about 7% (1-cube root(0.8)). Going up a steep hill, the light would slow them down by 20%. (Though the percentage would reduce if they produced more power (i.e. worked harder) going up the hill, like most cyclists do.)

    But where a 100 watt cyclist could do perhaps 15 mph on level ground, or 14 mph with this generator going ... a 15% grade (and without this light) would slow them down to around 2 mph. (And no, that's not a typo -- I calculated it with 180 lbs of rider+bicycle.)

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