Constant Power To Xenon Hid Lights

[bombastic]

I will be installing Xenon headlights shortly, and will probably follow this guide so that the Xenon's stay on when high beams are on, as Xenon's don't like being switched off then on again without being allowed to cool down.

However, this method would still mean the low beams switch off for a fraction of a second when switching between low and high beams. I'm assuming this would not be good for them, but I'd be interested to hear from someone who knows for sure.

As yet I haven't heard of a way to keep them on during the switching time, so I put on my robe and wizard hat thinking cap...

My idea is to connect a capacitor in parallel with the ballast supply, so that the ballast draws power from the capacitor during the switching period. I did some calculations and came up with a required capacitance of about 150mF (assuming 200ms switching time). This would require 3X 5.5V supercapacitors in series, but I don't know if supercapacitors can discharge quickly enough to power such a low impedance load (around 4 ohms) at high current (3A).

You guys reckon it'll work? Or have any better ideas? I can go into more detail if I haven't made myself clear.

Update: I've since had another idea, which is easier and more practical than big capacitors. It would also be separate from the original guide on how to have hi+lo beams on at once.

It would involve two relays. The first relay's control is the power which normally goes to the low beams. This relay will switch battery +12V. The second relay's control is the accessory wire (which I believe comes on when you turn the ignition to just before "ON"). This second relay switches the output of the first relay. The output of the second relay is then connected to the ballast supply, and also back to the input of the first relay.

So when you turn the low beams on, it connects +12V to the second relay. Then, if the key is turned to the right position, it connects the +12V to the ballast input, and back to the control of the first relay. So, when you switch to high beams, the first relay remains switched on. So the only way to get your lights to turn off again is to turn off the car.

With my bad terminology, the above explanation is probably difficult to understand... if there is any interest then I can elaborate/do a sketch.

Downsides of this method... the key has to be in the ignition to turn the lights on, and you can't turn the lights off without turning off the car. Personally, I don't sit in my car without the keys and turn the lights on... and, I have a turbo timer so if I really have to switch the lights off I can do it without turning off the engine, I would just toggle the key off, and back on. Also... have to find the accessory wire somewhere and run it through.

Advantages... no need for expensive capacitors. Possibly easier than original tutorial...

Update 2: Oops... just thought of something else, kind of a hybrid of the two ideas. Fixes the downsides of the second idea. Involves small capacitors on the relay controls to hold them closed during switching from low to high beams. Anyway I probably shouldn't be using the forum to brainstorm, I didn't mean to initially but seems to be what I'm doing

Edited August 6, 2007 by bombastic