DIY headlight LED help

[stu_c]

I have some 5mm LEDs in my car headlights which automatically come on when the vehicles ignition is turned, for some reason some of the LEDs have blown and now sure why, they are all 12V rated with resisitors fitted as standard.

When I put the ignition to the first click they come one then when I crank the car over they dim for a split second then brighten up when the cars running I wonder if its this thats causing them to blow if the alternator has a voltage spike?

I have the LEDs fitted like DRLs going from bottom
To top

they have blown about 3 times now and to fit them is a real pain as I have to take the lights apart but I love the look of them.

is there anything you guys would recommend doing or what LED bubs to use, would be greatly apprecitated.

[DIGItonium]

The LEDs are probably seeing transients, so any sort of spike in voltage or reverse voltage can damage it over time. Plus, the LEDs are subjected to over 12V when the car is running (~14.4v).

What you can do is wire up a 12v linear regulator to the LED string. Hopefully it'll help keep a stable 12v and give it some protection.

[SouthArk370Z]

There is a difference between "standard" 12VDC and the 12V of a car. A fully charged battery puts out about 13.2V and the charging system will put out over 14V.

If your LEDs are rated for a 12V automotive system, then DIGItonium is probably right about transients/spikes/droops killing your LEDs. Power filters (same ones you'd use with a stereo) will probably work.

If they are rated for 12VDC, then over-voltage is the problem and DIGItonium's regulator should do the trick. You can also use a dropping resistor in series. You will have to know the current draw of the LEDs and do some calculations.

[paperboy42190]

when doing your calculations ALWAYS use 14.4v as input.

That being said, what value resistor did you use? there's many variables to what value and having the wrong value can be just as bad as not having resistors. white leds typically have a forward voltage of about ~3.2v, and also how many are you putting in a series? Just need to do a couple simple calculations.

there's a lot of ppl who say they use resistors so everything will be fine, but that's not nearly good enough, the value make a big difference.

[stu_c]

Anybody recommend a good place for the LEDs and regulator :-/

[SouthArk370Z]

I've had good luck with DigiKey but it's been several years since I ordered anything from them.

[DIGItonium]

Quality 5mm high brightness LEDs can be sourced from Nichia, Cree, Kingbright, etc.

Check out this BuckToot LED driver. It has a wide operating range, but it has more than enough power for your needs. I use these for m projects. It's non dimmable, so it'll try its best to regulate down to low voltages, which can help with engine starts:
https://www.sparkfun.com/products/9642
7027-D-350 BuckToot LED Driver - LED Supply.com