12v stability?

[Russ]

I'm building an LED brake light to mount on the rollbar. How stable is the 12v on a Seven (two wire alternator on a Zetec)? I realize this is more a generic car question than Caterham-specific. I can add a voltage regulator, but that doubles the cost of parts. I could scope it myself, or add a logger to my Megasquirt ECU, but surely one of you already know the answer.

Since this is a British car and my windshield wipers occasionally make a slow salute on cold startup, I suppose the correct answer is to add the voltage regulator.

-russ

[Doug Liedblad]

Put a volt meter on the battery while running, it should be no more than 15 volts and closer to 14 is what I generally have.

You should be fine but Slomove is the PhD and I think in Electrical Engineering and he has the trick LED stop lights.

[Russ]

If it's battery voltage, then I'd better throw a regulator on my LEDs. I imagined there was something providing stable 12v. Though a quick reality check shows I've been through all the interesting bits of my Seven and would have noticed extra thingies. Especially after tearing out everything when putting in the ECU.

FWIW I just burned in my design for a few hours and it didn't melt, and was cool to the touch. And it is very very small, and very very bright. I hope it will wake up sleepy drivers and help the occasional person who follows too close while staring at the car.

-russ

[slomove]

Yes I am the guru and everybody bows to me, please :)

But seriously, Doug is right. Don't overdesign this thing. LED are not that sensitive to current overload and you will probably have some current limiting resistors in your design, anyway. At the end it may make the difference between 20,000 hours or 30,000 hours of continuous braking. If you are really worried, post how you wired the LED and I can have a look.

Doug, sorry to disappoint you. While I am EE by trade, the PhD is in mechanical engineering. To speak with Johnny Cash some things just happen that way.