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      01-13-2009, 09:30 PM   #17
camaross305
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Drives: 2008 M3
Join Date: Jul 2008
Location: gainesville fl

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Just to show im not sure what your talking about let me give you a little back ground. First you must use the right resistor. I know id did. Trust me this wont burn up anything.



Electric current is the rate of electrons that pass by a given point in an wire or some sort of an electric circuit measured in Coulombs/second which is named Amperes. Since in DC circuits, which our cars run off of DC your house is in AC, we can say that the current in the circuit is related to voltage and resistance which is basically summed up by OHM's Law.

Basically ohms law states "Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere. "

Because resistance is measure in OHMs.

Next you have to look at the formula for resistance. Because it ties into ohms law. Just for reference the gauge wire in out car is aprox. 16 awg. Which being made of cooper has a resistance of about .00473 per foot. If you measure its only about 1 foot or so But to make calculations safe we will say 3 feet to make a factory of safety of about 3. Usually i use 2. But hey this is a BMW. So then lets say .01419 per foot after the factor of safety. If you use the formula for resistance.

Resistance (Ohms) = Voltage (v) / Current (I)

The voltage on the stock bulb halo circuit is about 4.5 volts and has a current of about 3.5 amperes or 3.5amps. This will give you the correct resistance. However divide that by the factor we figured out above (.01419) and you get about 92.

However you have to factor into account power. The stock bulbs are 35w where as the HID's are also 35 watt but Hid's actually use less power than a regular halogen with way more light output. Hid's also use a completely different concept then an incandescent bulb. They ignite inside of a xenon gas instead of heating up a tungsten element through the means of resistance.

P = I × V = R × I2 = V2 ⁄ R

So this is how you choose the correct resistor. I mean look at the stock halo bulbs or any typical incandescent bulb in your house etc. Its basically a resistor made of a special material, usually tungsten, which through resistance cause it to glow. Thats all the stock BMW computer does is measure the resistance in the stock halo circuit and if it gets to a certain point, I.E the bulb blows and there is no resistance, it trips the circuit and the computer notifies the driver. I mean yea if you were you use a huge capacitor trying to store energy like a .5 farad ot something, or use the 16 gauge halo wires to run like 1000 watt speakers or something then yea the wires might get hot lol. But choose the correct resistor via Ohm's law and use a factor of safety and youll be fine

Last edited by camaross305; 01-14-2009 at 12:07 AM..
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