RE: Electrician has optional way to hook up HID's for Gen 1
Here is the post, minus pictures:
Ok, it looks like I may have finally stopped the first generation computer from whining about HID lights. I installed the Abel shunt and the following computer fix in both HOTLNC and Theologian’s car. So far, with about 20 car-nights of running, there have been NO computer complaints.
The parts:
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The parts are fairly common except for the power resistors. These resistors are from Allied electronics, stock number 795-0322. They are ARCOL brand and the ARCOL part number is HS25-7.5. Any other brand (Dale, etc) of resistor would work, but they MUST be 7.5 ohm, 25 watt, “chassis mount” resistors.
The wire is 16 to 18 gauge wire, automotive grade. The black rod above is heat shrink tubing. Radio Shack sells the heat sink grease for $1.99 (catalog number 276-1372.) I’m running one resistor without and the other with the grease. I have not found any heat related problems with the resistor that is running without the heat sink grease. The metal-to-metal contact is good and resistor heat is passing to the car’s frame efficiently.
Installation:
To install the fix, pre-solder a foot of wire to each resistor terminal. Use shrink tubing to insulate one or both solder connections. Find a position under the lamp access doors that has a flat, smooth area on the metal cross member of the car. You will be mounting the resistors on a vertical surface. There should be enough wire on the resistors to stretch between the mounted resistors and the LOW beam lamp connections on either side. This is where you connected the input power cable for the HID ballast. Connect the terminal with the heat shrink insulation to the RED lead. Connect the un-insulated resistor wire to the black lead. I made the connection with twist caps – the kind that electricians use to connect ceiling fans and electrical outlets. You can use in-line splices, since you will not need to disconnect the connections.
Position the resistors under the door and against the metal rail. Make sure you will be able to close the door (hatch) with the resistor mounted. Mark holes for the resistor. Drill holes for whatever sheet metal screw you use. You make have to ream out the resistor mounting holes to fit the screws. If you have to do this, only one screw need be used per resistor. You will want a firm connection between the rail and the resistor – especially if you do not use heat sink grease. These resistors get too hot to hold your finger on it for any length of time. Theologian complains that we mounted one resistor too close to his outside sensor – the outside temperature now reads about 2 degrees higher when the lights are on! Opps!
The picture below shows a bead of heat sink grease applied to the resistor just prior to mounting the resistor to the rail.
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The picture below shows the mounted resistor.
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Notice here that the heat shrink tubing is only on the HOT side of the resistor (connected to the RED light bulb wire.) Since the other side (with the purple wire) is ground, it can touch metal and there would be no problem. Not true on the green wire side – I would blow my headlamp fuse! The split jacket where the wires are going in is the feed cable for the HID ballast. I just added the resistor wires to the jacket and taped it closed.
The math behind the “fix:”
Second generation cars uses a shunt to determine if there is a problem with the HID lamps. This shunt has a higher resistance than the shunt used in a first generation car. This higher value is needed because the HIDs pull a lower average amount of current than the halogen bulb. Ed98Mark looked up the values for me and he supplied me with the following:
First generation Halogen system uses an 0.0500 +/- 0.0029 ohm shunt
Second generation HID system uses an 0.0778 +/- 0.0028 ohm shunt.
Assuming a 60 watt halogen bulb, each bulb would pull 60/12Volts = 5 amps. For two bulbs, that is 10 amps through the shunt: 0.05 times 10 amps = 0.5 volts. The shunt drops ½ volts, which tell the first generation computer that both lamps are OK.
The second generation computers will more than likely keep that same ½ volt drop as the “good level.” This is an assumption that seems to have panned out. Now we can calculate the HID total current, using the above as a known fact: 0.5V/0.0778 ohms = 6.43 amps. HIDs pull slightly over 64% of halogen lamp total current. When this current flows through the first generation shunts, the computer measures only 0.322 volts, so it whines about a lamp being out.
The Fix:
Make the first generation computer think that there are still two operating halogen lamps instead of the brighter HID lamps.
To do this, we must add a “fake lamp.” To drop ½ volt on a first generation shunt, we will need 10 amps going through it. If the HIDs is supplying 6.43 amps, all we need to do is select a load that pulls the remaining 3.6 amps. A 7.5 ohm resistor will pull 1.6 amps. Two of them in parallel will pull 3.2 amps. That is close enough to our required 3.6 amps to try them. Each resistor will dissipate slightly over 19 watts at 12 volts. The actual voltage getting to the resistor will be less than 12 volts, due to the shunt and wire losses.
