So, it is finally cold enough in Michigan and, sadly, too cold for my DDM HID kit. Below about 65F the low beam craps out, i.e., LAMPF! (despite the "CAN Bus cancellers" from DDM). So far the high beam has been working down to 40F. We'll see how it holds up when the winter comes.
Just to reiterate, the central control electronic measures the current to the low/high beam and disables the output if the current is either too low or too high to warn of a failed bulb or prevent circuit damage, respectively (remember, this bike does not have fuses). It does that by measuring the voltage across a shunt inside the module and only allows a certain voltage window.
After reading the recent posts I decided to do some further tests and here are the results (2008 R1200GS):
A. Forget the resistor in series. The HID module controls the power, that means if you reduce the effective input voltage by using a series resistor the HID tries to compensate by increasing the current. I confirmed this with an adjustable power resistor. Once the resistor is big enough the HID just starts to flicker. I managed to get the HID to stay on for a maximum of 250 milliseconds. That's it. So the module checks the current after 250ms after start-up (again).
B. By using an adjustable resistor instead of the HID, I also measured the thresholds (low and high current) to find the point at which the central controller shuts down the low beam. The upper threshold was at about 6.2A @14.2V. The threshold is probably somewhat lower while the alternator gets to full output. During this time the current rises (for about 2-3sec after crank). The lower threshold was at 0.86A @14.2V. So, the current must be between these two values to be acceptable for the central controller.
I didn't check the high beam as these thresholds are typically higher,
This confirms everybody's findings:
A. Some kits are just above, some below the 6.2A. Keep in mind that there is also some tolerance of the threshold from one bike to another.
B. Using a relay to switch battery directly to the lamp will work if you have a resistor in parallel to the relay coil of about 14.2V/0.86A = 16 Ohms to satisfy the minimum threshold. Maybe 15 Ohms to be on the safe side. At 14.2V this resistor "consumes" 14.2Vx14.2V/15Ohms = 13.5Watts. Make sure that the resistor has adequate cooling surface. A 50W resistor can only handle 50W with a huge heatsink!!! Consider using a 15W or 18W automotive lamp instead (you know how hot that gets! The resistor is no different).
Finally, there is one other option I am going to investigate when I have some more time (not for the faint hearted
). As mentioned earlier the central controller uses a shunt to measure the current. If I could reduce that shunt by, say 20%, the thresholds for the current would increase by 25%. But there are a bunch of "If's". I would assume that the module is sealed against water intrusion etc. - We'll see. I'll report back if this is feasible (you can really fuck up your bike if something goes wrong
). Anybody know off hand where this module is hiding??