I would like to replace the bulb based tail/brake light and rear indicators/flashers on my bike with one integrated LED unit (flashers in brake light).
These are pretty expensive, and since I'm on a budget I'm looking at building one myself.
I've found some seemingly suitable 12v LEDs. I was hoping to use these to save me bothering with limiting resistors. However, one thing that bothers me is the max voltage rating of the LEDs and the rather unpredictable supply voltage. I've not yet measured it on my bike, but usually you would expect about 13v with the engine running. The absolute max voltage rating of the LEDs I'm looking at is 14v – do you think this is too close? Would the LEDs stand a higher voltage for short periods? (e.g. poss slightly higher V when at high engine revs when overtaking)
How would you protect against this? Would one resistor for the whole set of LEDs suffice? (one resistor supplying multiple parallel LEDs). Any suggestions on what kind of resistor to use? Perhaps it would just be better to use standard votage LEDs if I am forced to use resistors?
Anyway – any advice appreciated!
Best Answer
If the voltage from the battery is fluctuating - you could look at using a voltage regulator to keep it stable. You can get fixed value regulators (no resistors or other components required!) or variable ones (2 resistors are used to set them, but they're both quite easy to use). The one I've used, LM317T adjustable voltage regulator, requires the input voltage to be around 2v more than the output voltage (in order to stay stable) and they have a maximum input to output differential of 40v. In other words - you want to have LEDs that are rated at a lower voltage than your supply - then use the voltage regulator to reduce the supply and provide the correct voltage for the LEDs.