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Old 02-27-2011, 11:10 AM   #1 (permalink)
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How to keep automagic LED DRLs on during EO(ff)C



I recently got a kit of LED DRLs to save power while driving during the day. This will be particularly useful while engine off coasting, however, the fact that they are entirely automatic poses a problem if i coast for longer than 20 seconds, since that seems to be their timeout time.

After some thinking and testing i built this device, it consists of some diodes and a small electric motor wired in parallel, when connected in series with thr DRLs it keeps them thinking that the engine is on!

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Old 02-27-2011, 12:31 PM   #2 (permalink)
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Could you explain how and why that works?
How are your DRL's wired to the car's electrical system?
Do you turn your engine off with a kill switch, or by turning the key in the ignition?

Here is how I wired my LED DRLs:
The (-) is just from mass (chassis), the (+) is from the cabin's cigarette lighter socket, which is energized whenever the key is turned, independent of whether the engine is on or off (*). From there it goes through an ON-OFF-ON switch, so that they can be manually forced ON or OFF, or in AUTO mode (the other ON). Auto mode means that the DRLs turn off when the car's headlights turn on (this was done with a relay getting a signal from one of the headlights).

If I turn the engine off with the key, then the headlights (and sometimes other electrical stuff) goes off after 0, 15, or 30 seconds (so-called 'walk home' function, this can be programmed in the computer). But if I use the kill switch, then the headlights and most other electrical accessories stay on for at least 10-15 minutes (they do turn off after a while). But the ECU knows that the engine is off, since a few things do go off, like the ventilation fan.

I think in your case you need to find a wire which does not power down when the engine stops.

(*) My car has a so-called "economy mode" in which the power to all accessories is turned off after 30 minutes of use if the engine is off. This means that if I've used the radio, or the key has been turned in the ignition, for more than 30 minutes after the last engine-off, then my DRLs won't turn on until the engine is on. This is almost never a problem, though.
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Old 02-27-2011, 02:36 PM   #3 (permalink)
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...just an educated guess, but:

...it looks like an "inductive" load (the DC motor) that's "clamped" by three paralleled diodes, ie: an inductive "discharge" delaying load.

...when power is suddenly removed, the motor inductance tries to continue current flow for a short period (ie: LR-time constant).
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Old 02-28-2011, 04:21 PM   #4 (permalink)
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The kit is just connected to the battery, it senses that the engine is on from high frequency components in the battery voltage(i assume). The brushed DC-motor generates an HF voltage ripple and the diodes keep the voltage across the motor down. (without them the motor spins really fast and the light dim)

The kit also has a wire that connects to your normal light that dim the LEDs when your other lights are on.

I turn the engine off with the ignition switch.
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Old 02-28-2011, 04:52 PM   #5 (permalink)
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weird. I would probably look at a crank or cam sensor if I wanted to know if the engine was turning (or the system voltage). I wonder if a plain coil would work instead of the motor.

Reminds me of a story about magic

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