Converter board or resistor

I'm planning on swaping out my Jeep's dome light with a selectable red/green/white Lux 3 set up. I know we use converter boards in flashlights to maximize battery life, but is there any reason to use anything other than simple resistors in an automotive setting, where battery life is not really a concern?
Josh

trivergata said:

I'm planning on swaping out my Jeep's dome light with a selectable red/green/white Lux 3 set up. I know we use converter boards in flashlights to maximize battery life, but is there any reason to use anything other than simple resistors in an automotive setting, where battery life is not really a concern?
Josh

Click to expand...

Let's assume 700mA to the Lux3's. Lux3 Vf will be 2.5 - 4V depending on colour etc. So, best case you need to drop about 13 - 4 = 9V at 700mA = 6.3W!!

Worst case 14.4 - 2.5 ~ 12V x 700mA = 8.4W

That's a lot of heat in either a resistor or linear regulator.

I'd highly recommend a buck converter.

AND, what happens if you leave a door open and the dome stays on for a day or night and you're pulling 0.7A -> flat battery. This is definitely a real scenario when camping etc. That's the original reason I development my buck driver for my own 4wd dome modules.

george.

The problem is I want a central switch that controls the color selection of the dome light, as well as both kick lights. With converter boards this means at least 3 boards. When you take into account the fact that I want to use 1 3 watt and 2 1 watts, I may need more than 3 boards - and may spend more than 100 bucks for this...........I was hoping to pull it off for a bit less than that.

trivergata said:

The problem is I want a central switch that controls the color selection of the dome light, as well as both kick lights. With converter boards this means at least 3 boards. When you take into account the fact that I want to use 1 3 watt and 2 1 watts, I may need more than 3 boards - and may spend more than 100 bucks for this...........I was hoping to pull it off for a bit less than that.

Click to expand...

Could be done with one driver board. The switch would be a bit tricky, but they exist. The 3 ways pick one of the three colours - at the output of the driver. i.e. the output constant current is directed to one of three coloured Luxeon strings. A second pole on the switch would change the output current from 700mA (for the 3W) to 350mA (for the 1W). It would take some wiring etc, but appears feasible.

george.

Variable voltage from the charging system. The car does not supply a constant 12V with a smooth output. There are voltage spikes and varying outputs from 11V to 14V. A simple resistor setup can work but it is better to err on the safe side than put in a resistor that is too small and keep blowing not so cheap LUX's. If you have some time and patience you can try a a rheostat or variable potentiometer set at a high setting and keep changing it till you get a brightness you like then measure and replace with a fixed value.