Electronics > Beginners

Car alternator LED flicker

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andrewlapham:
Hi, I have put a string of 4x LED's in series around my key barrel in my car for some much-needed illumination.  basically, the LED's are connected in series with a 120ohm resistor to keep the current limited to around 20mA. this works fine but I've already had to replace one of the LEDs as it died. Every now and then a get some crazy flicker out of the LEDs and was wondering if you could suggest any simple circuits build-out of passive components I could use to stabilize the LED's a bit.
I realize the simple solution would be to only have them on while I'm starting the car at night but I really like the pink glow (They are pink LEDs) and would like them to stay on while I'm driving.
Cheers.

Jwillis:
If they are like most other LEDs then 20mA is probably at their peak tolerance ,Try 15mA instead.They'll only be slightly dimmer with a lower current. Where are you sourcing the power from.That could be whats causing them to flicker.

mcovington:
Remember also that the voltage in a car varies a lot -- it is not 12 volts -- it is as low as 11 with a weak battery, or as high as 15 charging.

andrewlapham:
I've based the source voltage for around 14v as this is the voltage being pushed out by the alternator when the car is running. I have thought about reducing the current down to 10-15mA but still, I just think it needs a bit of smoothing aswell.

JustMeHere:
Cars are very dirty electrical environments.   For example, you have "load dumps" from your alternator.  The starter will back EMF when it shuts down.

You need to have TVS.  Also,  it is a good idea to use a current regulator over just a simple resistor to run the LEDs.

I haven't done much research on car electrical systems, but I have read a post or two around here.  Think of your car's electrical system as a warzone.

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