clanger
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| posted on 22/8/08 at 06:31 PM |
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LED Brake light mods for an elec novice - help needed please
Hello Electrical/Electronic guru's.
Please tailor your answers into simple non electrical terminology please. Most things mechanical engineering is my strong point, electronic/electric
black magic is not !!!
Anyway, my problem. I have a little project which involves changing my current normal rear brake light setup of my enduro bike to a hopefully led
setup. Normal bulbs do not last long off road !!
I have acquired, shall I say, a suitable 12V rear led light unit, but............its either on or off, if you see what I mean.
How can I get the unit to put out a dual light intensity such as a normal steup for example 5w/21W ?
Can I jam a resitor in sowmehere or somtheing to alter the intensity when the brakes are applied. How do I do this ? At the moment there are two
cables coming from the led unit earth or 0V & 12V i'm assuming. The wiring on the bike has 3 cables, earth, 12V to the 5w filament in the
bulb and 12v to the 21w filament.
I know its possible to buy off the shelf units for my needs for about £30 but as I've got something, I thought there might be a locost
challenge somewhere along the line before I shell out.
Any suggestions or guidance greatly appricated. ?
Cheers
[Edited on 22/8/08 by clanger]
[Edited on 22/8/08 by clanger]
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BenB
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| posted on 22/8/08 at 06:42 PM |
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Use a put a resistor in series with the LEDs. Put a switch (either micro-switch of the brake leverl or a hydraulic pressure switch) in parallel with
the resistor.
Finding the right resistor will be a bit of trial and error. You'll need quite a chunky resistor too.
I'd use pissy little resistors to find the right resistance then buy a big chunky fella for the actual bike. The wattage of the resistor will
depend on how much juice you're removing from the 12v....
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tegwin
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| posted on 22/8/08 at 10:10 PM |
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Dont forget you will need a pair of diodes!!!
Otherwise when you put the brakes on, the front light will come on as well
Consider the diode as a one way valve...
Simply connect the feed ot the 21W side of the bulb straight through the diode into the lights, and feed the 5W feed from the sidelights through a
resistor into a diode into the lights....
Without knowing exactly what LEDs you are using I cant suggest a resistor...
But when I build conversion kits I usually use 1/4W resistors of around 200R (ohms)....but it might be a bit of trial and error on your part!
[Edited on 22/8/08 by tegwin]
 
Rescued attachment bike light.JPG
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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02GF74
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| posted on 23/8/08 at 07:50 AM |
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^^^ yep; that circuit wold work - good point about the side lamps.
youo don't need the diode in wire from the brake.
I wold suggest starting with a 10 ohm 2 W resistor and then increasing value if bulb is too bright; decrease if too dim.
alternativey fit diodes in series instead of the resistor - these drop about 0.7 V - about 4 to 6 of these in total would be about right.; some linke
1N4006
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tegwin
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| posted on 23/8/08 at 09:02 AM |
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You are right, you dont NEED a diode on the brake feed...
But for piece of mind, I think I would anyway!
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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clanger
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| posted on 23/8/08 at 10:00 AM |
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Brilliant, thanks boys. Even an elec knob like myself can do that......................I hope 
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MikeRJ
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| posted on 23/8/08 at 11:51 AM |
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Or you could just buy a standard LED replacement for the dual filament 21/5 Watt lamp. They are very cheap now, e.g.
ebay clicky
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