Need Help with calculating load resistors

[indecided]

So here's the situation. I've got LED brake lights installed and the car's computer is giving me brake light out warnings. So to get rid of the alerts, the only real solution is to install load resistors to simulate the load of a incandescent.

The brake light is basically a 1157 5W/21W dual filament bulb. I've figured out that I need two sets of load resistors per bulb, one for each filament because the computer looks at the current draw from both filaments.

I've got some generic 6ohm/50W wire wound resistors, which seem to take care of the 21W filament, but i'm trying to figure out what values I should pick to simulate the 5W filament. Could somebody help me figure out the resistor values which would be equivalent to both filaments? It should be calculated at 14 volts.

I don't know the exact current draw by the LED array, but it's safe to assume they're about 75mA/300mA respectively for each filaments.

Thanks!

PS : i've figured out I would need a 40ohm resistor for the 5W filament, correct me if i'm wrong... I'm still unsure of what wattage to get for it though.

 

[rjvh]

Why do you install LED lights

If it is for being more energy efficient than you will waste that with the instalation of these resistors

as that they only produce heat that will have to be compensated by your aircon in the car and than we don't even talk about the fire hazard it could create

I would look more in the direction of get rid or the alarm signal on your computer

Robert-Jan

 

[indecided]

rjvh,

The LED array is integrated into the newer taillamp assembly which I upgraded to - which is why i'm trying to accommodate them.

Short of breaking the display screen and removing the piezo buzzer, there is no known way to trick the computer besides load resistors currently.

 

[rjvh]

is it not the case that the computer only detect a open circuit at this time due to the fact that the led light only pass curent in one direction

because if the original lamps are not switched on the computer doesn't give a signal either

what if you try to put an resistor (1.5 k ohm) and diode in reverse direction in line parralel to the new light bulp ?

Robert-Jan

 

[rjvh]

by the way what kind of car????

Robert-Jan

 

[indecided]

it's not a open circuit detector, it's a load detector, so I need to load it anyways.

Anyhow, I've figured out the optimum values at 1/2 the expected wattage and will try them out.

 

[Boncuk]

Hi indecided,

using LEDs instead of incandescent lamps makes sense to me. Not only the bulbs turn black caused by condensation of evaporized filament material - hence decreasing light output, but they also have a very limited life time, whereas LEDs have an average life time of 300,000 hours (34.25 years) of uninterrupted operation.

This life time of lamps is pretty much unpredictable, e.g. having to drive a lot on bumpy roads it shortens further.

Using an actually higher resistance than the lamps for the current detector cuircuit proves that the computer just wants to "see" any current flow.

I suggest to try different values to keep losses (and heating) down to a minimum.

As it turned out that a resistor of 25 times the resistance of the 21W bulb makes the circuit detect current flow I'd try a 1K resistor for the back light (5W).

Regards

Boncuk