Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to change bulbs to LEDs

  1. Apr 16, 2016 #1
    I have a small motorcycle and have changed the incandescent bulbs to LED. It seems the bulbs were powered by AC off the magneto generator and AC thru the rectifier powered the 6 volt battery.
    Is it ok to run LED this way or should I add diodes like in option a or b of diagram?

    Attached Files:

  2. jcsd
  3. Apr 16, 2016 #2


    Staff: Mentor

    LEDs and their supporting circuitry, come in many forms. You can buy LEDs for AC or DC and for many voltage levels. You need to find one that fits the way you want to power it.
  4. Apr 17, 2016 #3
    Option C.

    Put a current limiting resistor in series with the LED. At least if this is an indicator light.

    If it's a brighter light (headlamp, tail light, etc.) you might want to consider more energy efficient options.

    You might also need a flyback diode (option A) if the line is noisy from the spark plug.
  5. Apr 17, 2016 #4


    User Avatar
    Gold Member

    Option 0.

    If your LED units are rated at 6 vdc, you are set. They'll just blink imperceptibly fast.

    Your options A & B in your first image make little sense to me. Option A looks like a short circuit.

    Is the second image a diagram of your motorcycle's wiring?
  6. Apr 17, 2016 #5
    On second thought, I have to agree with OmCheeto here. :blushing: You do not have the required background to be making this modification. The parts need to be selected with the right values. Additional parts may be needed (such as a blocking capacitor for the flyback if a flyback is needed). And then there's the safety issue of modifying something away from the manufacturer's specifications.

    We really can't reverse engineer equipment we can't see when people may be harmed by our decisions.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Threads - change bulbs LEDs Date
Synchro Signal Frequency changes Sunday at 6:06 AM
Resistance of a tungsten filament bulb at 20 C Feb 24, 2018
Magnetic flux in tap changing transformers Nov 23, 2017