HID Wiring (Headlight on ONLY when engine is running)

My motorcycle headlight turns on whenever the key is on, regardless of whether the engine is running. There's a momentary cut when the starter button is depressed but other than that, they're always on. This kind of power cycling is hard in HID lights.

I haven't actually done this yet. It's just an idea that I plan to execute on my CBR600F4i when my HID projectors arrive next week. If anyone out there knows anything about electronics please don't hesitate to leave feedback. Thanks.

By the way, "IGN (+)" is power supplied only when the key is in the "ON" position

This should have been posted in the Automotive Electronics Forum.


Here is how I would do it. This circuit turns on the HID relay about 1 second after the oil pressure switch opens. You can increase the delay to ~10sec easily by changing the R1C1 time constant. This provides a nice delay, and saves one relay.



We could also do it with no relays, where a PMOS transistor switches the HID directly.

Wow that sounds good. I have to admit, though, that I don't really understand that diagram. My knowledge of electrical circuits doesn't extend much past simple analog devices (i.e. relays), ohm's law, and basic semiconductors (diodes, resistors, and capacitors). How would I do it with a transistor? Would it be simpler, and would I need to use a circuit board?

The circuit is simple enough that no PCB is required. I would use some perf. board. The IRF540 (or any of hundreds of similar NFETs) can be mounted on any metallic surface with a TO220 mounting kit.

The no-relay version would have a few more electronic parts. How much current does your HID draw during startup and while operating?

Probably no more than 20 amps but I'd say 30 just to be safe.

Here is a simulation of the posted circuit. Note that the Ignition switch is operated at 1sec, then the oil pressure switch opens at 3 sec, followed by the HID relay coming on at 5.4sec, for a delay of about 2.4sec. If the Ignition switch is opened, the HID goes off instantly, resetting the timer for a new cycle...

romoses4 said:

Probably no more than 20 amps but I'd say 30 just to be safe.

Click to expand...

I doubt that. Some of my friends have installed HID landing and taxi lights on their airplanes, and the selling point is that it about halves the current that a standard 100W sealed beam 4509 lamp would pull. The 4509 draws 8A at 14V, so the HID should be only 4 or 5A