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Electricity Generator Answered

Hi all,

Quick question. If I attach Neodymium magnets to bicycle rim (separating it by waste rubber tube) and copper winding to bicycle mud guard how much electricity can be generated? What needs to be done to increase the same?



4 Replies

Toga_Dan (author)2018-03-21

I think ive seen a similar project somewhere. maybe on this site. maybe not.

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Jack A Lopez (author)Toga_Dan2018-03-24

I can share some pictures of some homemade alternator toys. I never got around to writing instructables detailing the construction of these, so all you get are some pictures, and the explanation in this post.

One has the magnets attached to a spinning wheel. The other has magnets attached to an oscillating, flip-flopping piece of metal, formerly a hacksaw blade.

The essential trick for both of these was to choose a pre-wound coil, with a huge number of turns.

I mean, if you've seen the formula for Faraday's law of induction, for a pickup coil, specifically:

V(t) = -N*(dPhi/dt)

Obviously, one way to make V(t) larger, is to make N larger, and that is sort of what is guiding my choice for a coil with a really large number of turns.

(The other way is to make (dPhi/dt) larger; i.e. more magnetic flux through the coil, or faster changing flux, or both.)

Unfortunately, winding coils, with thousands of turns, with wire so thin, it is like hair... this is somewhat challenging. So it would be nice if there were a cheap source of pre-wound coils out there.

Getting to the pictures:

The coil I am used to make the spinning wheel type alternator, this pancake-shaped coil was removed from one of those solar-dancing flower toys, which can be found at the DollarTree(r), which has a store in my town.

The coil used in the twangy, oscillating alternator, that one used to be the tick-tock, two-step stepper motor, from an analog clock.

Anyway, regarding the pickup coil found inside the solar-dancing toys,


I thought that might be of interest to you, Dan, since I know you like to take apart stuff from the dollar store. Previous posts you have made to this forum, suggest this is true.

By the way, getting back to the topic of generator design, the trade-off of using a coil with large N, large number of turns, to get higher induced voltage, is more turns of thin wire tends to make the total resistance (in ohms) of the coil large as well. This large series resistance limits the amount of current, and thus power (current*voltage) that can be drawn from the alternator.

As a consequence of this, the pickup coil from the dancing flower toy, which has a DC resistance of, like, several hundred ohms, seems to be best matched to wimpy little loads, like LEDs, and pocket calculators, and junk like this.

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virajmoghe (author)Jack A Lopez2018-03-25

Thanks Jack! This definitely helps

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