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Flashing LED Lights for Bicycle

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The severe cold this last winter froze the engine in my van and I have converted completely over to bicycles to get around town for awhile. Am using a 50 year old Schwinn 10-speed as my main bike and just rebuilt an 18-speed Roadmaster as a backup bike for the occasional flat tire. Pedaling about 2.5 miles downtown to work which only takes me almost 15 minutes. While I am riding I have plenty of time to dream up improvements to make the ride safer and more comfortable. I would really like flashing LED lights all over the bike powered by the spinning wheels.

So the current idea is to attach a magnet to the spokes of the rear tire, then mount a coil on the frame where the magnet passes. This would flash the lights once everytime the tire rotates. Tried to make a test setup last night and it did not work as well as I thought it would.

The coil was a factory air-core choke with about 150 turns of very fine wire, maybe 26 gauge, and measures 1.6mh, it is about the diameter of a dime and 1/4 inch thick. The LED was a 2 volt red soldered directly to the choke without any resistor.
I started out with a magnet the size of a Quarter,  passing it by the coil  by-hand as fast as I could without any light produced. Then tried a 1 inch stack of magnets about the diameter of a nickle and still could not produce light. So I tried to use an 8 inch stack of 2x2x1/2 magnets leftover from building my small Wind Generator and produced some barely noticeable strobing  made from the fastest movement.

I really thought this would be enough to flash some LED lights.
What would be the best way to make this work ?
Was also thinking about using a Bridge Rectifier with it's voltage drop to extend the length of the flash and would probably need some kind of current limiting because of traveling at different speeds.

I get the DIY aspect, but with the cost of these super bright high visibility safety lights anymore, it's just easier and cheaper to grab a rechargeable super bright one online or from Walmart. ..

But, if you are still going to DIY.. I would rectify the output, add a cap to hold the charge for a tad longer on time of the LEDs.
Then add a proper resister and zener diode to limit the maximum voltage so it is predictable, use identical LED(s) in parallel if more than one and add the proper resistance to limit the current.

This is all with the assumptions you can get enough power from that setup, and that you want the LED to flash on for a short time only at the occasions it can source the power each time the magnet(s) come around from the wheel.

Maybe try a non-polarized capacitor parallel with led.. but im with wolvenar , i doubt you will get enough juice...

The coil is the main killer.

Air core has the least concentrated flux... You could stack those magnets until you're blue in the face, it's gonna be a diminishing ROI if the magnetic circuit isn't tight enough.

Achieving that isn't quite what it appears by simply "flipping an axial PMA inside out" with 1 magnet and 1 air coil (or even one on each side).

In an axial PMA, the flux is tightly controlled by the discs and magnets themselves, causing it to "beam across" the gap, which significantly offsets the inefficiency of the air core. In a situation like the bike, the flux is dilute and "flairs" out as it leaves the poles... maybe "aimlessly" is a decent word. Closing it up (look at the brakes for an immediate visual on my kneejerk thoughts) will help tremendously.

That's also an awful physically small coil. You're cutting the turns with a much larger diameter "slice of flux" than the coil, which just further dilutes it's potency and with that kind of difference in diameter, probably is even causing self-canceling effects. An air core coil doesn't have any means of directing the flux thru the center so it cuts more efficiently, so this won't work.

One more thought comes to mind for when it's on the bike... the rim, being steel, is going to also steal some of the flux and short it out... difficult to work around since you can't put a pair on either side even to gain a useful pole out of them, because of the brakes.

This is one of those "what works in the classroom needs performance tweaks before it's useful in the real world" deals. If you were looking to read RPM, I'd say you're on a reasonable path, sorta... Any kind of real power, no.  :-\


Hi Woof, a lot of small engines have a charging coil on them to charge their starting battery if they are electric start. You could get one of those coils and use it to run the LED,s. It does seem that a small rechargeable commercial light would be easier, but then easier is not so much fun is it.
You could also just try getting a piece of steel and winding your own  core on it. You are only looking for low current and low voltage after all.



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