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Old 12-22-2008, 06:40 PM
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Prasinos Prasinos is offline
Motorized Bicycle Elite Member
Join Date: Dec 2008
Location: CT
Posts: 257
Default Re: 12 volt fog lamp as headlight

After finding out that my engine put out 7.5 volts instead of 6, I went through my dads immense collection of light bulbs trying to find one designed for this voltage, the only 7.5 volt light bulb I found only draws .25 amps and is not even close to the brightness desired for a headlight. After visiting a local hardware store, NAPA, and radio shack I found that the bulb I had at home was the only one to be found rated for 7.5 volts.
With this information i decided that using a bulb from a 6 volt flashlight would be the closest thing to perfect for my bike. I took one apart and found tht the bulb was actually rated for 4.8 volts, if 4.8 can handle 6 I did not see why it couldn't handle 7.5, so I tried it. The engine cut out immediately after connection the first time, so I revved the engine slightly on the second try and found the light worked, though it flickered according to the rpms.
To remedy this I attached 2 capacitors from a tv circuit board in parallel with the light bulb, this got rid of most of the flickering and allowed the engine to idle while the light was turned on, though the idle had to be sped up slightly. After installing a switch and putting all of this into the water resistant housing of a battery powered bike headlight I now have a bright headlight that doesn't need replacement batteries.
Installing a few more capacitors should eliminate the flickering even further and allow the bike to idle at a lower speed. For now though, I am very pleased with the results had. Though I don't expect it to happen Il let you know if the bulb burns out due to the slightly higher voltage.

Id post pictures but my wiring is so catty wampus it wouldn't help explaining much.

Last edited by Prasinos; 12-22-2008 at 06:44 PM.
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