Originally Posted by slartidbartfast
These HID lamps were an eBay purchase. The seller was kassabian9898
It's probably hidden under the tangle of wiring in this photo but there is an igniter (I assume that's what it is - it's a small black box in appearance) in-line with the cable from the ballast to the capsule. I'm not sure of the exact reason (probably has to do with the inductance or capacitance of the cable) but I have heard that the length of the cable is important to the proper operation of the lamp and should not be adjusted.
Thanks, Philip. The 'igniter' is a coil of wire, a large inductor. The HID controller, together with the coil, form a boost-type switching power supply.
The controller sends a low voltage switched voltage to the coil, and 'flyback' from the coil creates a high voltage to strike the plasma arc in the lamp. Once the arc is formed within the lamp 'envelope', the voltage drops to a very low DC level. That voltage level is set by the physics of the elements in the plasma arc. With some gas/metal mixtures the 'arc voltage' is as low as 6 volts.
After the plasma arc is formed, the controller becomes a DC current supply. The current through the plasma can be varied to adjust the brightness of the lamp. I haven't seen any automotive controllers that do this.
The wire lengths are not too important, especially on the low voltage side of the coil. Some lamps have the inductor coil built into their base. Those type of lamps use typical light gauge PVC-insulated automotive wire running between the controller and the lamp.
If you decide to make a change to the high voltage side of the coil, between the inductor coil and the lamp, a teflon or silicon insulated wire would not be a bad idea. It isn't too critical, it's only high voltage for the short time before the arc is struck. Some 10s of milliseconds.