Problem with L.E.D. 'STOP LAMP' indicator
03-12-2015, 08:06 PM
#1
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Problem with L.E.D. 'STOP LAMP' indicator
My car is a US 83S. I have recently done an interior LED conversion. The conversion included replacing the warning lamps in the instrument console. Everything is nice and bright and works well, except that the 'STOP LAMP' indicator does not ever go completely off. After starting the car the 'STOP LAMP' indicator lights until the brake pedal is depressed the first time. But, with an LED in that position it never goes completely dark and remains dimly glowing after pressing the pedal. Has anyone else noticed this problem? Any nice solutions? The only simple solution I can see is to take the instrument cluster back out and put an incandescent bulb back in that spot, which I would rather not do.
Last edited by Eric Buckley; 03-12-2015 at 08:08 PM. Reason: spelling
03-18-2015, 12:28 PM
#2
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Answer: install a 1k (1000 ohm) 1/4 watt resistor across (in parallel with) the offending LED. This increases the overall current drawn by the LED/resistor combo. and causes the LED to be completely extinguished when it is supposed to be off.
12-02-2017, 09:12 AM
#3
Burning Brakes
Hi,
Sorry to bring out an old thread but I found it searching for a solution to my problem.
I’ve just installed the new instrument cluster foil from Roger, with led’s, and everything fits perfectly except that I have the same issue as the OP also with the “Stop Lamp” warning light.
After the car is running and after the first press of the brake pedal the light goes out but not completely, it stays on very dim.
I’ve replaced the brake lamps with new and identical bulbs but the problem remains.
The OP mentions the installation of a resistor.
Before I get to that is it supposed to work and is that the only solution or someone have another idea, besides changing again the Led for a normal bulb?
Thanks in advance for your answers.
Regards
Sorry to bring out an old thread but I found it searching for a solution to my problem.
I’ve just installed the new instrument cluster foil from Roger, with led’s, and everything fits perfectly except that I have the same issue as the OP also with the “Stop Lamp” warning light.
After the car is running and after the first press of the brake pedal the light goes out but not completely, it stays on very dim.
I’ve replaced the brake lamps with new and identical bulbs but the problem remains.
The OP mentions the installation of a resistor.
Before I get to that is it supposed to work and is that the only solution or someone have another idea, besides changing again the Led for a normal bulb?
Thanks in advance for your answers.
Regards
12-02-2017, 09:45 AM
#4
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It was never planned to work with anything other than an incandescent lamp - there are many places where Porsche relies on the very low resistance of a filament when off & cold (~1/10 of the hot on resistance) - to provide a ground path for sensing when the filament is not powered. Swapping an LED usually breaks these cases because the LED has a much higher on resistance anyway than the incandescent filament - and has an even higher (not lower) resistance when it is not powered (in fact it is close to infinite at very low voltages).
The bias currents used for sensing or for warning monitoring are often within an order of magnitude of the normal on currents for the LED (Vs multiple orders of magnitude for incandescent) - so the LEDs can partially activate all the time.
Add the resistor - its the easiest most robust solution here.
Alan
The bias currents used for sensing or for warning monitoring are often within an order of magnitude of the normal on currents for the LED (Vs multiple orders of magnitude for incandescent) - so the LEDs can partially activate all the time.
Add the resistor - its the easiest most robust solution here.
Alan
12-02-2017, 10:30 AM
#5
Burning Brakes
It was never planned to work with anything other than an incandescent lamp - there are many places where Porsche relies on the very low resistance of a filament when off & cold (~1/10 of the hot on resistance) - to provide a ground path for sensing when the filament is not powered. Swapping an LED usually breaks these cases because the LED has a much higher on resistance anyway than the incandescent filament - and has an even higher (not lower) resistance when it is not powered (in fact it is close to infinite at very low voltages).
The bias currents used for sensing or for warning monitoring are often within an order of magnitude of the normal on currents for the LED (Vs multiple orders of magnitude for incandescent) - so the LEDs can partially activate all the time.
Add the resistor - its the easiest most robust solution here.
Alan
The bias currents used for sensing or for warning monitoring are often within an order of magnitude of the normal on currents for the LED (Vs multiple orders of magnitude for incandescent) - so the LEDs can partially activate all the time.
Add the resistor - its the easiest most robust solution here.
Alan
Thank you very much for the detailed and very usefull explanation
By the way, why this only happens (as with the OP) in the "Stop Lamp" warning? What about all the other warning lamps that were changed also to Led's? They are working as they should.
This question is only for curiosity, so I learn something new
Thanks again for your help.
Regards