Question RE: building led light.

[Lgboro]

Have been researching building my own led lights as commercial ones are just too expensive. Looks doable for a fraction of the cost of ready made lcd lights. I will be charging my battery from tow vehicle, converter and solar and I continue to read that sometimes a battery will put out up to 14.1 or 14.2 volts which would/could burn out lcd lights. Should I base my calculation for current limiting resistors on 12 volt or the possible higher value of 14.2 volts that may occur when the charger is running?

[wannabefree]

Welcome to the world of derating. Derating means just running things at less than the maximum. For example, suppose you have a 1W LED. Run it at .75W. It will be a bit dimmer, but it will last longer and you will still have some margin when your battery is charging. Your battery will be close enough to 12V when not charging it won't be an issue. Electronics can be really imprecise, so a good design always has some margin built into it to account for imperfection.

If you insist on brewing your own, here are a couple useful formulas:
P=I*V and V=I*R where P is power in Watts, I is current in Amps, V is voltage in Volts, and R is resistance in Ohms. With a little algebra you can calculate the resistor you need to limit the current in your LEDs.

BTW - I bought LED lights because I couldn't make them as cheap as I could buy. Try:
http://www.bestconverter.com/12-Volt-LE ... c_126.html and
http://www.etrailer.com/pc-lpl~LPL31CB.htm

[starleen2]

This thread may help

Wiring my LED puck lights

http://www.tnttt.com/viewtopic.php?t=26715&highlight=led

[reiltear]

Hi!

I would use the highest expected voltage in the system which, in case of my truck, is 14.5 volts. According to a different page on the same website Don used to design his lights, the apparent brightness doesn't change very much with a two-to-one change in current, however that will depend on the part number("model") of the actual LED used. Most, but not all, LEDs are designed to work on 20ma or less. Another factor to consider is that the light output(millicandelas) of the LEDs regardless of their color is highly variable and the less expensive ones are not always the bargain. If the vendor doesn't specify what the LED puts out at a certain current, I would steer clear of them. When designing these lights, one also needs to pay attention to "forward voltage drop".

The electronic suppliers I used very often are Digikey and Mouser Electronics. They both have a wide variety of components. This LED from another supplier seems to be a bargain, except the beam of light it emits is probably more suited to a spotlight/reading light application.

PS I do not own any stocks, even in these companies.

[Rigsby]

The ones i am using on my build were designed for a truck which here in the uk run 24v, but on the lamp are rated from 10 to 36v, so i might run two batteries in series for the lights
steve