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Contactless Dynamo / Generator Answered

Hi all,

I am wishing to add some sort of dynamo to my bike to power lights. The main reasons are if the batteries get low I will forget to change them, and I will probably forget to turn the lights on. So off I went to eBay and bought a £4 generator and light set. It arrived and today I have been attempting to fit it - to no avail. I have a mountain bike with full suspension so there is no where suitable to fit it to.

So back to the drawing board. I came across FreeLights. The idea itself looks promising (unlike their spelling), however their implementation probably wouldn't be any good for me as it appears to be aimed at thin framed bikes - hacking probably could be done, however I would like to roll my own solution, and create an Instructable in the process!

So anyway, if you are too lazy to read the webpage above, here is how it works:

- A magnet is attached to the spokes
- There is another magnet in a container
- The container has wires around it
- The container connected to the forks so the magnets brush past it

Basically it is like a cycle computer sensor, but it produces lots more electricity! I like their idea, but it seems rather inefficient as the magnet is just randomly spun hoping for the best. They offer a kit version which appears to use a spherical magnet, but even so it still seems rather inefficient to me.

So on to two other possible options. The first is basically the same idea, but the magnet is fixed so it can only spin in one plane. Something like this [Ultra-simple Electric Generator]. The other option is to get rid of the spinning magnet, and instead just have coils like the various wind turbines on this site.

So basically I want to know which method is the best, and given that how I can maximize the power produced. I am thinking just increasing the number of turns, stronger magnets, greater number of magnets on wheels, greater number of 'generators' etc. And then realistically, what sort of power I would be able to get?



killerjackalope: I was thinking about something like that, but there isn't really anywhere I can easily mount the dynamo. Plus I like the idea of a contact less system. Kiteman: I had a look at the BEAM stuff and it looked cool. I was also thinking just coils is a better idea, so I have ordered some enameled wire off eBay and shall do some research when it arrives (once my dissertation is done!).

Maybe make a good coil mounted on the back fork and put a magnet on every spoke, it'd be more effective at producing power, I think, you'd be producing a smoother output aswell...

take a magnet. put it under a paper. put some dust from iron wool on it. shake and watch. the lines that appeared are the magnet's power lines. they are in the entire 3D space around the magnet and similar in shape to those on the page when you put a coil near the magnet some of the power lines go thru the air thats 'in' the loop. electricity is generated when the amount of lines that go thru the loop changes. more of it is generated if more lines change at the same time and if they change fast. use this rules to imagine the efficiency of various designs. for example the animation on top won't generate almost anything. to change this you shall place the coil so it sticks into the screen and is not flat on it (90 deg to how it is now) i'd mount stick magnets in horizontal (right to left) position to the spokes in alterating directions and put 2 parallel coils on the sides (using an assembly like of brakes but with coils instead of the brakes) multiple phase circuit (2 or more coils placed like a wireframe ball and cross on the ends of it) may be more efficient than one big coil

i think a conventional generator connected to the end of the wheel is best most dc motors can be used as generators

Indeed it probably would provide the most power, but it defies the point of having a contactless system. :) I am still awaiting for the enameled wire to arrive, the seller I bought it from was unable to access their premises last week due to storm damage, so has been catching up on back orders.

It might be easier to rip apart a destroyed derailleur and run the dynamo off the chain using some cogs from it, it would also act as a handy tensioner for off roading... That way it'll not be governed by speed as much, in comparison to a single turn of the wheel...

I would go with coils, charging a circuit that will automatically light the LEDs in the dark - google for BEAM pummer circuits.