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how would I go about charging a car battery with a bike without making the bike unusable for transport? Answered

I am trying to build a non-Gas powered motorized bicycle, and I realized that it may be possible to have multiple power inputs like wind and solar feeding the charge. however, as a jobless 16 year old, I can't test my ideas. I am attempting to create a bicycle that charges while you pedal, storing energy in the car battery. then, the car battery can be used to power a motor powerful enough to keep the bike in motion. Also, yes I know that this would likely be VERY bulky, but I can come up with a solution for that.
please help me if you can.

2 Replies

frollard (author)2011-01-13

If you want any reasonable amount of energy, it's verging on violating the laws of physics.

How hard is it to speed up from zero on a bicycle? =
Work = Force * Distance
Force = Mass * Acceleration
thus, Work = Mass * Acceleration * Distance (you could add friction loses here but we'll ignore that for good spherical cow).

While you are speeding up it takes more work than when you are maintaining speed because a change in speed is acceleration. The reason bikes are so great is once you get up to speed they have very little drag, and can use that energy to coast for a long time.
IF you add a dynamo to power ANYTHING, it will extract energy from your forward motion, and you'll slow down. If you want to maintain speed, you'll have to keep pedalling, an equal amount harder to how much energy is drawn from your momentum by the dynamo.

Just remember Energy out = Energy in minus losses (friction, conversion, etc).

Adding more 'stuff' to the bike will also increase its mass, making it require more work to accelerate the same amount.

The only feasable way to put power in a battery for usage later is something called regenerative braking. It involves using your momentum to charge the battery - and since you can extract a lot of power with a dynamo you can brake quite quickly. When it comes time to accelerate, not much beats using an extra electric motor. Expecting to chartge the battery all the time while riding is like expecting to ALWAYS ride uphill. A great workout nontheless.

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caarntedd (author)frollard2011-01-13

I instantly thought regenerative braking and was going to answer until I read your last paragraph.

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