Lotus Elan

led lights for high beam and ignition?

PostPost by: gjz30075 » Tue Mar 20, 2018 6:18 pm

So, I changed my tach on my S3 to a modern one by simply (not really) changing out the guts
from a new tachometer. However the circuit board of the new tach is in the way of the light tubes
for the high beam indicator and ignition light.

I think by changing the indicator lights to leds with pigtail wires, I can fix this. However, I don't
think this will work for the ignition light (alternator). Would this be true?
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PostPost by: Elanman68 » Tue Mar 20, 2018 6:39 pm

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.
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PostPost by: gjz30075 » Tue Mar 20, 2018 6:43 pm

As I suspected. Thanks
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PostPost by: nmauduit » Tue Mar 20, 2018 7:32 pm

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 560Ω 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.
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PostPost by: gjz30075 » Tue Mar 20, 2018 7:46 pm

Excellent writeups! Thanks
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PostPost by: bob_rich » Tue Mar 20, 2018 8:09 pm

Hi

I agree with the post above. I sketched out a simple circuit and my values differ slightly but thought it may help to have a sketch of the circuit. It assumes -ve earth as standard alternator option in elans would be -ve earth.

to test it wire it up and the put the circuit across a 12V battery. Whichever way lights it up then the battery +ve will be the one that goes to the ignition and the -ve battery terminal should be the one that goes to the alternator field.

hope it helps best of luck

Bob
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PostPost by: gjz30075 » Tue Mar 20, 2018 10:47 pm

Thanks Bob. That helps.
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PostPost by: gherlt » Wed Mar 21, 2018 8:10 am

1964 S1 (engine ready, awainting body repair)
1967 S3 DHC (now adjusted by Brian Buckland, totally calm idle)
1969 S4 FHC (finishing interior, changing wiring loom)
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