I recently installed an H7 Led Headlight kit 12V/25W in place of a standard halogen 55w bulb. Lights are great, but they flash periodically during can-bus Cold/Warm checks to see if a bulb is out.
I was advised to install a 55Watt 6Ω Resistor that will prevent the LEDs from flickering during checks, but work normally when switched on.
Now from my basic electronic knowledge I calculated using Ohm's-law the resistor needed as:
for the halo I1 = 55W / 12V = 4.58A and
and the LEDs I2 = 25W / 12V = 2.08A
so the difference of 30W is 2.5Amps that translates into:
R = V/I = 12 / 2.5 = 4.8 Ω
My question is (provided my calculations are correct :P) will the 6 Ω resistance cut off light output from the LEDs or was it indeed correctly recommended or I should look for a ~5 Ohm ?
Best Answer
The LED light has some electronics in it and that confuses the headlight-OK-current detector. The resistor sets a certain minimum current to fool that detector.
That 6 ohm resistor will actually conduct 12 V/6 ohm = 2 A and dissipate 12 V * 2 A = 24 W, so not 55 W !
It depends on your car's headlight-OK-detection-current if that 6 ohm will do the job. It could be that 1 A through a resistor is already enough, then you could use a 12 ohm resistor. But it can also be that it needs that suggested 6 ohm.
I doubt if going as low as 4.8 ohm is really needed, that also wastes a lot of power.
The thing to do is to try it out and see what works.