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-   -   LED tail light problem ( https://www.xt660.com/showthread.php?t=24278)

victohr 10-07-15 13:14
LED tail light problem
 
Hello, sometimes upon startup my tail light go out.
Ive replaced the stock one with a LED Tail light.
The tail light is a CPI(aprilia,derbi) original tail light.
Ive tried to run cables directly from the battery via a relay to the light, still same issue.

The tail light mostly dies on cold start up, its usally possible to restart the bike to get the tail light working again.

I recently installed Xenon headlight, could this be the issue?

Here is a video of it turning off on startup.
https://www.youtube.com/watch?v=d97nL-hdwDE

Pleiades 10-07-15 13:38
It could be the HID. If they (the ballast) don't have a clean earth straight back to the battery negative they can cause all sorts strange electrical issues. Disconnect the ballast and see if the problem with the tail light is cured.

However, as you say its OK on a cold start up, it is much more likely the LED unit itself is at fault. When cool it works, and as it heats up it breaks down.

Most people assume LEDs don't produce heat like normal filament bulbs, but they do, it's just that it is not radiant heat so it's not noticeable. LEDs heat up to fairly high temperatures internally - it's called junction temperature, where the positive and negative parts of the semiconductor meet (the junction).

http://www.digikey.com/Web%20Export/...00607-Fig5.jpg

Juntion temperature is the same reason computer processors, chips etc. need a heat sink and cooling fan and often fail through heat shock. Just take a look at the size of the heatsink/fans on the back of a BMW GS with an LED headlight to get an idea of the heat produced by bigger LEDs!

Try connecting up a standard bulb/tail light and see if the problem goes away, or try another LED unit. LEDs that have failed at the junction cannot be repaired.

victohr 10-07-15 18:35
Quote:
Originally Posted by Pleiades (Post 212317)
It could be the HID. If they (the ballast) don't have a clean earth straight back to the battery negative they can cause all sorts strange electrical issues. Disconnect the ballast and see if the problem with the tail light is cured.

However, as you say its OK on a cold start up, it is much more likely the LED unit itself is at fault. When cool it works, and as it heats up it breaks down.

Most people assume LEDs don't produce heat like normal filament bulbs, but they do, it's just that it is not radiant heat so it's not noticeable. LEDs heat up to fairly high temperatures internally - it's called junction temperature, where the positive and negative parts of the semiconductor meet (the junction).

http://www.digikey.com/Web%20Export/...00607-Fig5.jpg


Juntion temperature is the same reason computer processors, chips etc. need a heat sink and cooling fan and often fail through heat shock. Just take a look at the size of the heatsink/fans on the back of a BMW GS with an LED headlight to get an idea of the heat produced by bigger LEDs!

Try connecting up a standard bulb/tail light and see if the problem goes away, or try another LED unit. LEDs that have failed at the junction cannot be repaired.

Thanks for the reply :)
i have had 3 different led tail lights so hopfully its not the tail light.
I Will try to disconnect the HID as soon as i can.
I mean that the problem Only accours upon cold starts( engine/leds cold)

victohr 12-07-15 22:19
Solution
 
I solved the problem by using a switching relay connected to the startermotor, so when the starter motor is running the power to the tail light is off.

Best regards, Victor


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