Magnetic powered bike light

Erasmus · Apr 5, 2006

This afternoon I was thinking the dynamo and the light on my bike are old technology:
- today we have very strong small magnets, so-called rare earth or neodymium magnets
- today we have LEDs which have a much higher efficacy than incandescent bulbs

The readings of my bike computer are registered by a small magnet that is mounted in the spokes of my bike. Apparently the movement of the small magnet generates an electric impulse.

Then I was wondering whether it is possible to power LED lighting on my bike by mounting those small rare earth magnets on my spokes which can result in an electric power.

Now my questions are :
- what exactly should I have to make on my frame in order to generate as much electricity from the magnets as possible?
- do the magnets on the spokes have to be mounted in a special way (since they have 2 poles)?
- if I mount a bunch of those rare-earth magnets, can it be possible to run Luxeon LEDs?

A Google search learns me some smart people have thought of this before :
- http://www.treehugger.com/files/2005/11/goodbye_batteri.php

It would be great if some guys here on CPF can help me out, because I don't know that much about magnetism and power generation.

Cheers,
Erasmus.

Handlobraesing · Apr 6, 2006

Erasmus said:
This afternoon I was thinking the dynamo and the light on my bike are old technology:
- today we have very strong small magnets, so-called rare earth or neodymium magnets
- today we have LEDs which have a much higher efficacy than incandescent bulbs

The readings of my bike computer are registered by a small magnet that is mounted in the spokes of my bike. Apparently the movement of the small magnet generates an electric impulse.

Then I was wondering whether it is possible to power LED lighting on my bike by mounting those small rare earth magnets on my spokes which can result in an electric power.

Now my questions are :
- what exactly should I have to make on my frame in order to generate as much electricity from the magnets as possible?
- do the magnets on the spokes have to be mounted in a special way (since they have 2 poles)?
- if I mount a bunch of those rare-earth magnets, can it be possible to run Luxeon LEDs?

A Google search learns me some smart people have thought of this before :
- http://www.treehugger.com/files/2005/11/goodbye_batteri.php

It would be great if some guys here on CPF can help me out, because I don't know that much about magnetism and power generation.

Cheers,
Erasmus.

There's such thing as hub-dynamo that is located around the wheel axle and has less noticeable drag than a rim dynamo.

Erasmus · Apr 6, 2006

Handlobraesing said:
There's such thing as hub-dynamo that is located around the wheel axle and has less noticeable drag than a rim dynamo.

Indeed a hub dynamo exists too, but that's not really what I'm looking for

jmw19 · Apr 6, 2006

Erasmus,
I believe most bike computers use a reed switch to sense wheel speed - it doesn't generate any power, just closes when a magnet passes close by. It would be neat if one was charged by riding, but I don't know if any exist.

Regarding the wheel-mounted magnets, I do know there's a real flasher that uses this setup - it's just standard 5mm leds, though. See http://www.freelights.co.uk/ . There was another, rear-only setup a few years ago, but I can't find it now.

Rare-earth magnets are stronger than standard, but my understanding is the field drops off faster as well. So the magnets would need to be very close to the coils to work well. Seems to me a hub dynamo could be better engineered, and I know they're capable of powering Luxeons - see http://www.peterwhitecycles.com/inoled.asp for one example. Plenty of cyclists are using Luxeon replacement bulbs, too.

Sounds like it's time to try an experiment or two, and see how much current your idea could generate. With a simple circuit and a storage capacitor, you might be on to something.

Jon.

monkeyboy · Apr 7, 2006

For bicycles, the hub dynamo is just about as efficient as you can get. You don't get energy for nothing, turning your wheel into a giant dynamo as you describe, will probably create just as much drag as the hub dynamo and will have more air resistance. The only disadvantage to a hub dynamo over a regular dynamo is that it cannot be completely disengaged so creates a small amount of drag when it is not being used.

PeLu · Apr 7, 2006

If German is not a problem,then read the 'prayer wheel', everthing you ever wanted to know about bicycle lights and probably much more:

Your attempt has been made many times and abandoned for a good reason. I agree that a hub dynamo is close to the perfect solution.

I laso tried these 'free light' and it is not much more as an additional attention catcher.

altis · Apr 7, 2006

Have a read of these:

http://www.nabendynamo.de/
http://www.baldurdash.org/OtherStuff/www.nabendynamo.de/detail.htm

mdocod · Apr 8, 2006

head over to http://www.otherpower.com/ and have a good study on the projects they have been doing with wind generators and rare earth magnets... I've actually built a custom generator from Neodynium magnets from hard drives and hand wound coils, all epoxied and pressed to old car rotors... They've done some other fun projects too, including a small generator to run an LED night-light, powered by a pet rodent on a running wheel...

then go over to their other site and have a look at some of the magnets they sell... http://www.wondermagnet.com/

just don't order any magnets too big, you're bike will stick to a man-hole-cover and throw you overboard.

Magnetic powered bike light

Erasmus

Flashlight Enthusiast

Handlobraesing

Banned

Erasmus

Flashlight Enthusiast

jmw19

Newly Enlightened

monkeyboy

Flashlight Enthusiast

PeLu

Flashlight Enthusiast

altis

Newly Enlightened

mdocod

Flashaholic

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