LED Brake Light Bulbs
01-11-03, 06:09 PM
#52
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Originally posted by Manntis
Je suis trés désolé, mon ami.
Je suis trés désolé, mon ami.
Perhaps I misspoke when saying that a burnt out bulb drops the rezistance to zero. It does drop the flow to zero, as the circuit is open. But for whatever reason, the drop caused by swapping in LEDs can create an annoying dash light problem for which adding a resistor to restore the original resistance is the cure.
It's the "whatever reason" I was looking for information on.
I realize that it's a common problem and adding a resistance works in practice. As you may have noticed, I get hung up on the details of why. Can't help myself.
But, enough! Happy New Year!
-John.
02-21-03, 11:03 AM
#54
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From Manntis
from FJ
The led lamp consumes less current than the incandescent one, so when you switch to a led, the resistance of the component increases (V=RI), causing the idiot light.
Now, you have to reduce the resistance of the component to get rid of the idiot light, by putting a resistance in parallel to the led lamp.
If R1 is resistance of led and R2 is resistance of added resistor, then 1/R=1/R1+1/R2, where R is the resistance of the "parallel light circuit (led + resistor)". You want R to be smaller than R1, remember, that's why you put the resistor in parallel (R<R1 or 1/R > 1/R1)
Hugues -
Perhaps I misspoke when saying that a burnt out bulb drops the rezistance to zero. It does drop the flow to zero, as the circuit is open. But for whatever reason, the drop caused by swapping in LEDs can create an annoying dash light problem for which adding a resistor to restore the original resistance is the cure.
I'm hesitant to bring it up, but that's what I was getting at on the previous page. A burnt bulb does drop the flow of current to zero, but only in one of four branches of the parallel circuit. It increases the resistance in the brake bulb circuit as a whole, which is what the stop light checker sees.
The led lamp consumes less current than the incandescent one, so when you switch to a led, the resistance of the component increases (V=RI), causing the idiot light.
Now, you have to reduce the resistance of the component to get rid of the idiot light, by putting a resistance in parallel to the led lamp.
If R1 is resistance of led and R2 is resistance of added resistor, then 1/R=1/R1+1/R2, where R is the resistance of the "parallel light circuit (led + resistor)". You want R to be smaller than R1, remember, that's why you put the resistor in parallel (R<R1 or 1/R > 1/R1)
Hugues -
02-21-03, 11:29 AM
#55
Airflow is my life
Can you get these in just plain bright white LED replacement lights? 1157/1156? If you have a reflector why does it hve to be red? I just want a nice really bright light thatll last longer than a bulb.
02-22-03, 05:23 PM
#56
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Thanks to FATBOY7 from the 1st page of this thread.
I cut the green w/blue stripe wire as he suggested and no more dummy das light yelling at me that my brake light bulb is out!
Just figured I would give am update. It took long enough
I cut the green w/blue stripe wire as he suggested and no more dummy das light yelling at me that my brake light bulb is out!
Just figured I would give am update. It took long enough
01-18-07, 07:33 AM
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Guys, I just want to chime in with a couple things. Yes, I am an electrical engineer. Mantis, I'm also in the Canadian Forces, so I have experience with how stuff gets wrapped around by military instructors too. (Sometimes I are one)
Power consumed is P=VI
In a linear resistor, V=IR
The idiot light turns on when the current gets too low, when the resistance goes to infinity when the wire in the incandescent bulb breaks.
The problem in the discussion started with 'what is the resistance of the LED'. The LED'd are a non-linear semi-conductor device. They do not follow V=IR.
Generally, they have a forward voltage ~2 V, but that can be all over the place depending on the specific diode. The big thing is, they draw a specific amount of current, most high-intensity LED's in the neighborhood of 200mA. That is MUCH less than an incandescent bulb draws, which then turns on the idiot light.
The EASY way to deal with this is to just fool the idiot light. It's probably the only way to do it and make it 'plug and play' as mantis calls it. Definitely the only way to do something to the bulb itself.
Adding the resistor in parallel draws more current, making the idiot light think there's a bulb there.
Anyway, just trying to help out.
Power consumed is P=VI
In a linear resistor, V=IR
The idiot light turns on when the current gets too low, when the resistance goes to infinity when the wire in the incandescent bulb breaks.
The problem in the discussion started with 'what is the resistance of the LED'. The LED'd are a non-linear semi-conductor device. They do not follow V=IR.
Generally, they have a forward voltage ~2 V, but that can be all over the place depending on the specific diode. The big thing is, they draw a specific amount of current, most high-intensity LED's in the neighborhood of 200mA. That is MUCH less than an incandescent bulb draws, which then turns on the idiot light.
The EASY way to deal with this is to just fool the idiot light. It's probably the only way to do it and make it 'plug and play' as mantis calls it. Definitely the only way to do something to the bulb itself.
Adding the resistor in parallel draws more current, making the idiot light think there's a bulb there.
Anyway, just trying to help out.
01-18-07, 10:13 AM
#60
One question though just reading this, lets get some points jotted down
LED's use less power, and "might be brighter"
Adding resistance to the point of making it almost stock, to compensate for the current draw needed for the other light not to come on. So really instead of conserving energy, we're using a resistor to lose energy through heat which is probably one of the worst ways.
EDIT: Just read the thing about cutting the GL wire, but won't cutting that mean that if the light goes out you won't know anymore?
LED's use less power, and "might be brighter"
Adding resistance to the point of making it almost stock, to compensate for the current draw needed for the other light not to come on. So really instead of conserving energy, we're using a resistor to lose energy through heat which is probably one of the worst ways.
EDIT: Just read the thing about cutting the GL wire, but won't cutting that mean that if the light goes out you won't know anymore?
01-18-07, 10:22 AM
#61
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Originally Posted by Viich
Guys, I just want to chime in with a couple things. Yes, I am an electrical engineer. Mantis, I'm also in the Canadian Forces, so I have experience with how stuff gets wrapped around by military instructors too. (Sometimes I are one).
01-18-07, 10:45 AM
#62
Hmm... thread brought back from the dead, though interesting nonetheless.
Does anybody else know where to find replacement side marker and rear lights done with LEDs (since Manntis isn't doing it anymore)? Ones with the resistors? I've got clear corners (thanks to Dan Atkins) and I'm going to be doing clear tails (thanks to IoTus) so coloured replacement bulbs are a must, and having LEDs would be nice
I would think that the point wouldn't be to "conserve energy" (how much could it possibly save anyway?), but rather to have the longevity of the LEDs. Quality LEDs last a heckuva lot longer than regular bulbs. Plus the colour as I mentioned, for those of us with clear lenses.
Jon
Does anybody else know where to find replacement side marker and rear lights done with LEDs (since Manntis isn't doing it anymore)? Ones with the resistors? I've got clear corners (thanks to Dan Atkins) and I'm going to be doing clear tails (thanks to IoTus) so coloured replacement bulbs are a must, and having LEDs would be nice
I would think that the point wouldn't be to "conserve energy" (how much could it possibly save anyway?), but rather to have the longevity of the LEDs. Quality LEDs last a heckuva lot longer than regular bulbs. Plus the colour as I mentioned, for those of us with clear lenses.
Jon
01-18-07, 10:53 AM
#63
