Fitting LED's ?

[Cozzie Bhoy]

Tried to fit some led's to the park lights on theoctavia and they won't work. A mate said its something to do with the new type loom. Is there anyway to get them to work?

[mannyo]

The octavia has a bulb failure system, the LED bulbs have the wrong resistance so the car thinks something is wrong and cuts the power. Getting them to work is very tricky, because you need to add resistors to the lights which makes the LEDs dimmer losing any advantage.

[chavdarlk]

The octavia has a bulb failure system, the LED bulbs have the wrong resistance so the car thinks something is wrong and cuts the power. Getting them to work is very tricky, because you need to add resistors to the lights which makes the LEDs dimmer losing any advantage.

In fact, the additional resistors have to be placed in parallel with the LED pack, thus not affecting it's brightness.

The only disadvantage is that consumed power equals thats of the conventional bulbs.

[Genoa1893]

...Just because I'm curious as a monkey,

does the bulb failure system work sensing the current drawn by load or the voltage drop?

[chavdarlk]

...Just because I'm curious as a monkey,

does the bulb failure system work sensing the current drawn by load or the voltage drop?

Only the current.

[dan_the_v8man]

if you want to go down the resistor root, get a multimeter and measure the resistance of the existing lamp, you want a resistor of similar resistance. because the LED's have such a high resistance, when put in parallel with your load resistance, the difference will be close to nothing

other way around it is measure the current taken by the existing lamp and use a bit of ohms law to work the required resistance

[Basil]

The only disadvantage is that consumed power equals thats of the conventional bulbs.

so no change to your electricity bill then.....:P

[Simon TDI Sport]

You could have fitted them the wrong way?? They only work one way. Found this out when fitting them to my vec b.

[dstev2000]

Nope, either way the car will shut them down after a few seconds, bong at you and show a little orange bulb icon on the dash.

This aside the polarity does need to be correct once the bulb failure system has been spoofed :P

Ebay has no end of resistors for this very application.

[chavdarlk]

if you want to go down the resistor root, get a multimeter and measure the resistance of the existing lamp, you want a resistor of similar resistance.

This would not work, because the resistance of the cold lamp is about 5-15 times lower than the lighting one.

other way around it is measure the current taken by the existing lamp and use a bit of ohms law to work the required resistance

OK, this is correct (only for small lamps), but the best way is to calculate the resistance from the power:

P = U^2 / R

R = U^2 / P

R = 160 / P

[sebulbus]

The typical bulb is 5W. At 12v that's 0.42 Amps.

A typical LED has a power consumption roughly in the area of 50-150 mAmps, or only 0.6 to 1.8 W. To sync ~4W through a resistor things are going to get reasonably hot. Probably hot enough to melt plastic.

Best bet would be to disable bulb checking for the front lights, think it is possible with VCDS.

[Cozzie Bhoy]

Cheers guys, Sounds like a bit of messing around just to get the leds working. The standard 5w bulbs don't look too bad after all !!