Originally Posted by harderkev
So we can caluculate using Ohm's Law that a Gerbing jacket liner (6.4 amp draw at 12 volts) has a resistance of 1.875 ohms?
I = V/R or V/I = R therefore 12/6.4 = 1.875 ohms.
Maybe I should have bought the 26ga wire at .041 ohms/ft. instead of the 30ga at .1 ohms/ft. to get more even heating and cover a larger area?
I think that's right. 30 feet of the 26 ga wire would give you 1.23 ohms of resistance, drawing 9.75+ amps, and 117+ watts, which would probably be too hot. To get the same wattage as the Gerbing (6.4 x 12 or about 77 watts), you'd need about 45 feet of the 26 ga wilre.
Looking at that though, it doesn't seem to make sense. If I've computed it correctly, the heat goes up as the diameter of the wire increases and resistance goes down. But that would mean your battery cable should get practically molten, which it doesn't.
By the way, I tried the electric jacket this morning with the straight hook up (no switch). It wasn't real cold, about 55 degrees, but with just a cotton work shirt, the jacket and my Road Crafter 2-piece I was fine. Apparently, electrically heated clothing works much better when there's electricity actually flowing through the wires.
Anyway, I don't think you have to get too hung up about even coverage. I'm 6'4", so I have a pretty long torso and long arms. 35 feet of wire was enough to put 6 strands of wire each in the front and back of the jacket, and 4 strands down the full length of each arm. The heat felt pretty evenly distributed to me this morning.