Elanman68 wrote:Have changed all my lights except headlamps and ignition warning light to LEDs. The reason I didn't change the ignition was because the LED supplier advised against it. I understand this is because the circuit requires a level of resistance which a filament bulb provides but a LED doesn't. I was happy to accept the advice. I haven't changed the headlamps as I've not convinced myself that I have the clearance for the heatsinks typically found on the back of the LEDs or if I have whether there is sufficient air flow to cool them, I don't want to damage the headlamp pods.
I have not done a headlight conversion yet, so maybe I should let someone who has done it comment first, but my gut feeling is that leds being more efficient than halogen at producing light there should be less heat dissipated from a led system than from a halogen bulb to obtain the same amount of light (measured, say, in Cd). The heat issue may rather be a concern for the leds themselves, which are very small hence have a very small heat capacitance, while their lifetime is greatly reduced after a certain temperature thresold: in a isolated closed area their temperature would rise to destructive level, hence the need for a heat sink for increasing the led lifetime - but I would think such a heat sink is likely to dissipate less than the equivalent halogen bulb.
As for replacing a bulb by a led where there is no room for a bulb, I would think this is possible, either by keeping the bulb somewhere while pulling the signal (bulb on/bulb off) to a led interface (to be defined), or possibly by replacing the bulb by a led interface altogether.
some sources of inspirations found randomly below, to be checked and tested carefully ...
https://www.electro-tech-online.com/thr ... led.88735/_____________ for option 1 or similar
Hi, most alternators in cars I have worked on, seem to have a 12 Volt 3 Watt indicator lamp on the dash, to assist in exciting the armature of the alternator.
That equates to around 250 mA, which yields a 48 Ohm resistor.
Get a 47 Ohm, 5 or 10 watt resistor to replace the lamp and put the led in parrallel with it and have a series R to limit the current through the led to 20 mA or less.
_____________for option 2
The field current bypasses the light, so you shouldn't need the power resistor. When the alternator fails, the isolation diodes can't keep the field at a voltage higher than the battery - so at that point the current runs from the battery runs through the light to the field windings, yes.
But when that happens, it doesn't matter, because the alternator is dead anyway.
So add a 560? current limiting resistor on the anode of the LED, so these two components are in series. Place a 1N4004 diode backwards across the led to protect it from the reverse voltages - these two components are in parallel. This circuit will replace the light.
Tricky part is determining which way to put it in - it won't work backwards. Take the old light out. Switch on the ignition without starting (not "acc", but "on"). Measure in the lamp socket to ground on each side. One side will be +12V, the other near 0V. The resistor hooks to the +12V, the cathode of the LED (and anode of the 1N4004) hooks to 0V.
To test it, take the belt off so the alternator doesn't turn when you start it. Start it, verify the light came on, measure about +12V on the battery. Stop, put the belt on, start again, light should be out. Measure about +14V to verify the alternator is charging the battery.
Posted: Tue Mar 20, 2018 6:18 pm