Coil Resistor Very Hot!

[starkizer]

So I was messing around under the hood and noticed that the little ballast / coil resistor was all cracked and broken. So I figured I would go ahead and replace it.

 

 

 

So I went ahead and replaced the thing. made sure I got one with same Ohm's etc. Actually Original as you can see is 1.1... new one is 1.2, but with variables and such it shouldnt make any difference.... I think.

 

So as the title states, this thing is getting very very hot. like hot enough you can't touch it for more then a second.

 

 

 

Theres a pic of the new one. I have been told that heat is normal at idle but once at speed electrons get to move and it is cooler etc. At least that's what I read on a dodge forum. Wasn't sure if it would be true for an MJ. Was also wondering if it makes a difference which wire is on which side. They both look the same to me. In case it helps. I bought a BWD (Borge Warner) RU12 resister.

[mvusse]

Resistors are not directional, so it doesn't matter which wire goes on which terminal. And getting hot is how they work. They add resistance to the circuit causing a voltage drop, generating heat in the process. The circuit as a whole consumes less power as a whole, though.

 

Maximum power dissipated as heat for a single comonent is when it's impedance matches the rest of the circuit. So assuming the rest of the circuit amount to 1.2 ohms as well, and 14.4V at the battery, it would be dissipating 43.2 watts., or roughly the same total heat as a 40 watt light bulb through a much smaller surface area.

 

The entire thought behind the resistor was to quiet down the fuel pump so customers wouldn't complain about it being too loud. It is bypassed on start up and during wide open throttle. The 1987 model year did not have it at all. Easiest solution is to go back to the 1987 engineering and just bypass it.

[NotMatt]

Resistors are not directional, so it doesn't matter which wire goes on which terminal. And getting hot is how they work. They add resistance to the circuit causing a voltage drop, generating heat in the process. The circuit as a whole consumes less power as a whole, though.

 

Maximum power dissipated as heat for a single comonent is when it's impedance matches the rest of the circuit. So assuming the rest of the circuit amount to 1.2 ohms as well, and 14.4V at the battery, it would be dissipating 43.2 watts., or roughly the same total heat as a 40 watt light bulb through a much smaller surface area.

 

The entire thought behind the resistor was to quiet down the fuel pump so customers wouldn't complain about it being too loud. It is bypassed on start up and during wide open throttle. The 1987 model year did not have it at all. Easiest solution is to go back to the 1987 engineering and just bypass it.

 

Dead on. I've removed it from every Renix-era XJ/MJ i've ever owned and never had a problem. Just tie the two wires together (solder and heatshrink, no butt connectors or electrical tape!) and tuck them back into the harness.

[starkizer]

Ok, That's what I was thinking. Just wasnt sure if it had a positive and a negitive side. Good info. I can always count on the Comanche Club. Thanks!