Need some way of dimming LED taillights.

[Soliddrummer]

Okay, here's the scenario. I got some LED tail lights on my bike. The idea is that they are always on as running lights, and also hooked into my brake light switches to get brighter when the brakes are applied. Pretty standard stuff here. My issue is that the running lights are about 85% of the total brightness, i.e. when I apply the brakes, the lights only get about 15% brighter. So the question is, is there something I can wire into my power feed to the taillights, to dim them. That way, when I apply the brakes, the light gets significantly brighter. Is this a resistor thing, a capacitor thing? I don't know if simply reducing the voltage, will result in just a dimmer light. Help!

 

[MrBillohnooo]

I would use a mopar ignition resistor. Some of them are set in epoxy. These were used on 60s_70s Dodges, Chryslers etc. Get the one set in epoxy. It will reduce the voltage to about 8 to 9 volts. Leds will still be bright enough.

 

[Dieselchanic]

Resistor is what you need.

You can buy a pack of assorted resistors from Radio Shack and experiment with them to get it how you want.. Would need a soldering setup and some heat shrink tubing also.

I've used 1/4 watt resistors. I'm not a guru so I dunno if that's on spec or not..

 

[Soliddrummer]

Cool, thanks guys, I'll get some assorted resisters and see what effect I will get. Soldering and shrinking in line is no problem at all, as I've built the entire harness from scratch anyways. This is the last piece of the puzzle!

 

[TwoManyXS1Bs]

I recently needed to dim down a chipLED (panel indicator), had to use a 3k 1/4 watt. 1/4 watt is okay if your selected resistor is greater than 610 ohm...

 

[xjwmx]

Is this like a regular led tail light? If so, one possibility is that you have it wired reversed, i.e. taillight wire to the brake "filament" and brake wire to the regular tail light.

If that was the case it would be real bright all the time and would get only a little bit brighter when you hit the brake.

Reverse what you have now and I suspect the situation will improve.

 

[Soliddrummer]

Huh, xjwmx. That is a hell of an idea right there, that could possibly be the case, I can't wait to get in there and switch my wires around and see what I get. I would NEVER have thought about that!!! Thanks everyone!

 

[xjwmx]

I would NEVER have thought about that!!!

I'd never have thought about it if I hadn't done it to myself before Mistakes are positive things...

 

[Conrad Russell]

I have an LED tail light molded into the back rest on my bike and yes your light can be and probably is wired in reverse.Should be a simple fix

 

[MrBillohnooo]

Nothing like a "duhh" moment! I have done it, and didn't think of it!
Back to k.I.s.s. (keep it simple stupid) lol

 

[TwoJugs]

I understand that LEDs only light up when wired with the correct polarity (one way). Wire it he other way and you get nothing. Most tailights I see have multiple LED bulbs. They light more of them for brake brighness, less for running lights. An inline resistor will do what you want. As mentioned Radio Shack sell them cheap. I am no electronics expert but I know many here are. They can probably give you an idea on what values you need. You can always wire in a selctor switch to allow a bypass of the resistors too that will adjust the brightness when needed.

 

[xjwmx]

I understand that LEDs only light up when wired with the correct polarity (one way). Wire it he other way and you get nothing.

He won't be changing polarity; but just connecting brake where tailight is now, and tail light where brake is now. Three wires going to the bulb, brake, tail, and ground.

 

[Soliddrummer]

Xjwmx is right, changing the two connections won't change polarity, it only reverses the running and brake lights. I won't have a chance to test this theory until Tuesday morning when I'm back in the shop, but I suspect simply switching the two powered feeds to the lights, will solve the problem.

 

[peanut]

don't forget if you put equal 2x resistors in parallel the total resistance is halved and if you connect 2 equal resistors in series the resistance is doubled.

If you can't achieve the result you want with the resistors you have , try doubling or even trebling some of the resistors until you achieve what you want then you can measure the total resistance with a multimeter and order the correct resistor value .

Alternatively what I would do is fit a variable resistor (volume control )so you can adjust the brightness according to conditions and preference .Once you know the resistance you require you can get really tiny variable resistors like this

 

[Dieselchanic]

^^^ Potentiometer is what those are called and yes that would work altho it would be a little harder to install cleanly inline... Led stands for light emitting diode. A diode is a one way valve for us rednecks.. So of course they only light up wired one way.

Not too long ago I went thru all the research to learn how to build my own led lights. (Not the diodes themselves) The taillight on my xs actually has an led panel inside I built myself.

Most of your dual function lights use the same diodes for both functions... They simply have one power wire wired direct and one thru a resistor with a diode in each to keep the power from back feeding thru the other wire...

 

[Conrad Russell]

I think you have the idea,keep it simple.I have used LED lights on many custom builds so as to mold into fenders and things like that.If you bought an LED light that was meant to be a tail/brake light,switch the wires!I have a couple examples in my album you can check.

 

[Soliddrummer]

Yeah these came from eBay, they are actually very well made and pre wired to run as tail lights with one wire for running lights and a separate wire for brake lights. I'm pretty sure we got the problem licked just by switching my two powered wires. But I'm looking into resistors as well, just in case.