Motorcycle Undimming Light


Introduction: Motorcycle Undimming Light

I had a small motorbike whose light got dim when rpm were lower.

in start I tried some big led but as voltage got lower they got exceptionally dim.

so I used lm338(similar to lm317) to regulate voltage(v input was 8-13 volts) lm338 is used to upgrade it to even higher outputs and hence more light.

Things needed

1.100 ohm resistor 1w=3


3.diodes=4(bridge rectifier)


5.leds to your need

the zener diode,diode and resistor in last are needed if you are using some cheapo ic

Step 1: Diodes

I used bridge rectifier to ensure that no reverse polarity will occur as mechanics some times roll over the wires moreover easy installation con be done as these ic's don't like reverse polarity.i used doubled up diodes as these were of smaller size

Step 2: Ic Adjustment


so let r1 be 10 ohm and r2 be 20 ohm by combining two resistors


Step 3: Led

add led panel.mine taken out from old portable light

I later on used two one watt leds

Step 4: Cover Up

cover up a little to make safer.



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    11 Discussions

    Hmm, nice idea, but I still want to use standard bulbs or standard replacement LED bulbs. Do you have some idea how to achieve same result?

    4 replies

    You can read my other instructable about motorcycle headlight.
    From standard you mean 12volt ones? Then you need some boost circuit to raise voltage and then apply same circuit. Lm317 can be adjusted. Just google for its calculator.
    Another dangerous option will be to take current directly from alternator and manage it.
    But you need to tell me input voltages prior to making any decision.
    Remember if there is less power production then dont imagine for a big light ;)

    It is 12V supply. I have to confess, I doesnt measure real voltage. It is friend bike, we just tried best bulb options for best light output, since most affected was head light, and he goes for trip. But since then I still thinking, what do do with it, even when he told me it is OK like it is now..

    hmmm.....simple solution would be to get a chinese made led light. they have a buck regulator and according to box specs it works anywhere between 6-25 volts dc. So if you suspect some noise you may add a bridge rectifier prior to it. Otherwise install it simply.

    Following is a 9-30volts led light

    Thank You, this is realy good idea. Now just find right shape and dimensions, and I can go for it. Thanks again!

    use 1w heatsink assisted led if ic is giving 4volts i.e above 3.6 volts. these leds usually dissipate more heat and survive while epoxy ones die

    guys I am out on countryside enjoying biking so I had no board etc

    I will upload good pictures when back I think some people might be annoyed

    This is the most shittiest wiringjob I have seen in my life.

    2 replies