proper resistor to use for rear window defogger

91tr thanks for that clarification

Now I know how to proceed but still dont know whether to do the 45 0r 180w method

 

I just want everything on the car to work as intended. Also driving in the rain or humid days with the a/c on can cause fog ups.

 

Last night I decided to try the 180w version and cut the right buss bar in hte middle. I then tried it out and to my surprise the heat was not all that great. Just kinda warm. I used a 14gauge wire from the negative term of the buss bar back to the left side original ground connector. I thought that this heavy wire might be adding resistance and causing lack of heat so I used a 22 gauge wire and grounded it to a point much closer to the right bus bar . Very little change in percieved heat. I then reconnected the cut between the ground and 12v on the right bus bar and put the ground back to the left side (now original configuration) and expected to get that screaming hot heat but it didnt. It was barely warm.

I tested each wire without the ground connected when I took the positive probe to each wire and the neg probe to a ground each wire showed 12v. There is continuity between each wire and when the ground was re-connected each wire had continuity to a chasis ground.

I dont understand why so little heat with 180w version and why when put back to original it does not heat up like it did before. Should I try one long surpentine route whould this give more heat.

When I measured voltage of the wires with pos probe on the 12v connector and the neg probe on the wires with the ground wire connected to the grid teh voltage was in the milliamps.

I'm stumped

Thanks

Dave

 

From your description I must have been in series measuring amps. but the meter showed in the milliamp range. Anyway I just want to determine how to get the most heat out of this thing. The wires are getting 12v when measured at the wires (pos probe) and the chasis ground (not grid ground).

I think i know just enough to be dangerous about voltage and its relation to amps etc.

Thanks again

 

Maybe this is true but its a cheap pocket RS meter. Anyway it doesnt get that hot. I would like to know if there is some configuration to have to work hotter. Maybe the ground to the grid is not perfect and causing to much resitance even though it does have continuity with chasis gound. I really dont know where to go from here other than taking all the wires off and create new copper bus bars and reapply the wires again.