Custom LED Light project ($2 total cost in parts)

[WaterSports]

For those that want a reliable and fairly bright LED light for your bike I built a dirt cheap (only $2 dollars for the whole project) custom lighting solution that might be of use to others.

While this cheap LED flashlight is still really bright and works well without any flicker or issues even when the engine is idling, I would still highly recommend using a battery powered high power 1 Watt or 3 watt LED light in addition to this flashlight since this flashlight does not produce enough light to be of worth other than a visual for others to see you from a distance.

Parts list:

1. LED flash light at the dollar store (usually these flashlights have 3 or 9 LEDs. The flashlight takes 3 AAA batteries so the voltage is 4.5 volts and current usage is around 500 milliamps from my testing with a multimeter)

2. 47 OHM 1/2 WATT resistor, easily found at Fry's or even Radio Shack

Instructions:
Saw off 2/3rds of the flashlight and solder a 47 OHM 1/2 Watt resistor to the positive terminal and then solder the white wire to the resistor (connect it in a series). The negative lead from ground goes to the negative terminal of the flash light. Just zip tie or mount the flashlight however you would like and presto, you're done!

Important Note:
The LED flashlight is capable of taking more milliamps than the output of 500 milliamps from the engine which will kill the engine so the resistor IS NEEDED. I have tested it without the resistor and my engine did die after 2-3 seconds after starting so let this be a warning up front should you omit using the resistor, besides if you skip the resistor and still manage to keep your engine running you'll fry your LED light since the output voltage from the white wire is 7.5V and the light can only handle 4.5V.

 

[RLK]

This is a neat little hack. Thanks! I imagine it would work with a battery bicycle led headlight. What is it about 47 ohms that makes it work?

 

[WaterSports]

It should work with any light as long as you take voltage into consideration. Most LED lights are 4.5 volts (3 AAA or AA 1.5V batteries usually which = 4.5 V)

You must use the correct resistance on the resistor to come up to the correct voltage and amperage reduction. I would highly recommend using a 1/2 Watt resistor otherwise a resistor with less amperage handling capability would likely melt. The resistor does not have to be exactly 47 OHMs. You can get a resistor close to that range and still pull off the lighting.

It's been a few days of riding so far and the light keeps working so the setup seems to be holding up nicely to the specs I've built this to.

Here's a good calculator that will help you with getting the correct resistance should you be working with a LED light that has a different voltage.
LED calculator for single LEDs

For mine, I put in:
6.5 for the source voltage
4.5 for the diode voltage
50 for the diode forward current
which gave me a 47 OHM 1/4 watt resistor. I chose a 1/2 watt since I didn't want to risk burning out the resistor by cutting it close in the event of voltage fluctuations.

Let me know if this helps.

 

[RLK]

Thanks for sharing your smarts. That calculator is awesome. Especially the /draw wiring diagram/ button with different options if you want to run lights in parrallel or in series or a combination.

I dropped some spinach at harbor freight today and found some awesome mini lights that don't mess around. 9! count 'em, NINE 5mm diodes driven by 3 AAAs. 2 flashlights for $4. I bought 4. It'd be very easy to do this and put the resistor inside the inner AAA cage and run leads through a tiny hole in the alum. housing, keeping the weather-resistant* cap and rubber button. Without the lanyard and batt. cage it weights exactly 1 oz. I should buy more of these lights at this price!

 

[WaterSports]

Very cool, please post some pics of your light(s) I'd like to see how they look.

 

[silverbear]

I've been using these light components for a couple years in my copper jewel lights. Nice and bright for the money. I've also used them in my harness leather tin can lights. With the China girl engines I haven't had them burn out yet after many miles and hours of riding using them as fender lights, headlights, tail lights, brake lights with no resistor. They do flicker like mini strobes, but I don't care about that since the idea is to be seen. I tried hooking one up to a HF Greyhound engine and it burned out the LEDs instantly. Don't know what the voltage is on the HF, but it is too much. As a super easy low budget light you can just use one of these lights as is clamped to the handlebar with two hose clamps, one going around the light and the other going around the handlebar tube with the two clamps linked together. You can also clamp a light as is to a rear rack using a little pipe hanger for copper water pipes... kind of a U shape. I haven't tried it yet, but intend to buy some red fingernail polish to give the lens a coating to make it into a tail or brake light. Should work. By the way, fingernail polish makes good touch up paint and comes in many colors including black... you can also use it as cheap lock tite for bolts. Even comes with it's own little brush.
SB