LED Rear light not working when engine running.

J

jirble2

Member
I recently bought a rear LED light for my bike in the hope of attaching it to my white wire battery system, which is all 6 volt. I set up a zener regulator (schematic attached) so that I could have a 3 volt output for the light, which was originally designed to run on 2 AAA batteries. The regulator regulates, and the light lights, but when the engine running the light doesn't light, unless I hold down the push button (momentary) switch on the light, which means I can't go cycling through the different light settings and just leave it alone. When I do hold down that push button switch, the light flickers alot, and the flicker speed doesn't seem to correspond to the engine speed. I am hoping that if I put in a capacitor I can reduce engine interference, which is what I think is causing the problem. Trouble is, I don't know what size capacitor to use, where to put it, or which way to orient it.

Any ideas on a capacitor to use or an alternative solution?

Also, I can't post links (I'm a newbie) but if you go to ebay and search "Tail Rear Bike Bicycle Light Lamp 5 LED 6 Mode" then the first result is the light I bought.
 

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Just try any small cap and see what happens. Or get a different LED light and see if it works with your set-up. You can never be too well lit....I normally run 2 separate LED flashers....one up high and one down low.zpt
 
jirble2 said:
I recently bought a rear LED light for my bike in the hope of attaching it to my white wire battery system, which is all 6 volt. I set up a zener regulator (schematic attached) so that I could have a 3 volt output for the light, which was originally designed to run on 2 AAA batteries. The regulator regulates, and the light lights, but when the engine running the light doesn't light, unless I hold down the push button (momentary) switch on the light, which means I can't go cycling through the different light settings and just leave it alone. When I do hold down that push button switch, the light flickers alot, and the flicker speed doesn't seem to correspond to the engine speed. I am hoping that if I put in a capacitor I can reduce engine interference, which is what I think is causing the problem. Trouble is, I don't know what size capacitor to use, where to put it, or which way to orient it.

Any ideas on a capacitor to use or an alternative solution?

Also, I can't post links (I'm a newbie) but if you go to ebay and search "Tail Rear Bike Bicycle Light Lamp 5 LED 6 Mode" then the first result is the light I bought.
Click to expand...

Forget the capacitor. You have other problems. It looks like your zener is wired to drain the battery down to 3v through the 4.6 ohm resistor. You should be using about a 6.8v zener when trying to protect a 6v battery. That said, I have found that a zener regulator is not needed on a white wire 6v charging system. You cannot regulate a 6v battery output down to 3v by using a zener diode. It will just kill the battery.

Get rid of the zener and 4.6 ohm resistor. If you want to reduce the voltage in order to use 3v bulbs, use a voltage dropping resistor equal to the bulb resistance and in series with the bulb.
 
Scotchmo said:
Forget the capacitor. You have other problems. It looks like your zener is wired to drain the battery down to 3v through the 4.6 ohm resistor. You should be using about a 6.8v zener when trying to protect a 6v battery. That said, I have found that a zener regulator is not needed on a white wire 6v charging system. You cannot regulate a 6v battery output down to 3v by using a zener diode. It will just kill the battery.

Get rid of the zener and 4.6 ohm resistor. If you want to reduce the voltage in order to use 3v bulbs, use a voltage dropping resistor equal to the bulb resistance and in series with the bulb.
Click to expand...

Sounds like a good idea. Trouble is, I'm not sure what the Amps of the light is, and so I can't work out the resistance. If I were to simply try different resistors and measure the voltage as I try them, would that work? Or would I still be trying to find the right size resistor in a fortnight?
 
jirble2 said:
Sounds like a good idea. Trouble is, I'm not sure what the Amps of the light is, and so I can't work out the resistance. If I were to simply try different resistors and measure the voltage as I try them, would that work? Or would I still be trying to find the right size resistor in a fortnight?
Click to expand...

Use a meter to measure the current draw. You can then calculate the resistor needed. If you don't have a meter, just start with a high value resistor and keep cutting the value in half until it is bright enough.
 
Scotchmo said:
Forget the capacitor. You have other problems. It looks like your zener is wired to drain the battery down to 3v through the 4.6 ohm resistor. You should be using about a 6.8v zener when trying to protect a 6v battery. That said, I have found that a zener regulator is not needed on a white wire 6v charging system. You cannot regulate a 6v battery output down to 3v by using a zener diode. It will just kill the battery.

Get rid of the zener and 4.6 ohm resistor. If you want to reduce the voltage in order to use 3v bulbs, use a voltage dropping resistor equal to the bulb resistance and in series with the bulb.
Click to expand...
Hang on... if I put a resistor in series with the light, won't that reduce the amps, not volts?
 
jirble2 said:
Hang on... if I put a resistor in series with the light, won't that reduce the amps, not volts?
Click to expand...

When you use a series resistor to reduce the current, you are reducing the voltage across the light. You can have a 6v supply where 3v drops across the resistor and the other 3v is dropping across the LED.
 
Sorry about the delay, but I managed to get it to work. I got rid of the zener regulator and simply put a 27ohm resistor in series.
 
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