ballast resistor getting hot

Installed new in tank electric fuel pump. When running wires in engine bay (I was looking for a keyed power wire for relay) I noticed my ballast resister was getting very warm; almost too hot to touch. Is this normal? Key was in "on" position for less than 10 minutes, probably about 5 but less than 10. 6.4 volts in and 10.5 volts out if that makes any difference.

Normal operation. It's not uncommon for new ones to smoke and "burn off" contaminants on the coil.

It'll get hot enough to burn your finger after awhile.

OK thanks. Just something I never noticed before.

Perfectly normal. It functions as a heat sink for your ignition circuit. Without it, the same thermal energy would be transferred to your ECU, coil or wires cooking them in their own juices.

First time I've ever seen a resistor described as a radiator...

It's not by the way.

Resistance in an electrical circuit generates heat and depending on the components, light too.

If it says Lucas on it smoke is a given...

Kevin

The change in temperature changes the resistance. This is a design feature.

OTH. If the electric pump is drawing power from the charge/ignition circuit - then its going to be a problem. Do not want pump drawing current through the resistor.

Never said it was a radiator. A heat sink is an electrical component. The ballast is a resister that captures heat. The resister in the ballast is encapsulated by ceramic. This material can take a lot of heat and the location of it allows it to release that heat without affecting any of the other nearby electrical components.

That's so bad, it's not even wrong.

A heat sink is a radiator, it takes heat from an electrical component, like a power transistor, and radiates it out into the environment.

A ballast resistor is nothing more than an resistor that can tolerate high heat generated during it's use, as a resistor not as anything that "captures heat". A ballast resistor is NOT a heat sink. The fins on the ECU would be a heat sink, one that radiates the heat from the power transistor in the ECU.

Look up wire wound ceramic resistor, which is what a ballast resistor is.

http://www.atomic4.com/faqres.htm

Most definitely it's a heat sink. In order to read about how a resistor set in ceramic can function as a heat sink, I offer the link above to better inform you on what the resistor does in a primary ignition circuit. That is what the ceramic is all about and that is exactly what it's function is.

If the heat is of some concern for you, there are several other factory/aftermarket ballast resistors with different OHM values, determine what you have first, and what your ignition system requires,... I had the same concerns on various builds when the ballast was a little too hot and raised some concerns

WHAT IS A RESISTOR LINKY ??

Your link does not even support your statements.

I don't know where you get this from, but I can state definitely, you are wrong.

Wire wound ceramic resistors are for high heat applications. They may or may not include a heat sink in the design, but the ballast resistor does not include one and the heat sink is not part of the resistance in applications that use one, which I will once again state does not include the ballast resistor.

Rather than waste any more of my time on this thread, I'll just include a definition of what a heat sink does and then move on. You can believe what I say or not. I sleep like a baby at night regardless.

Mopar ballast resistors perform as a resistor in a circuit by virtue of their electrical properties and they perform as heat sinks because of their mechanical properties and materials used in construction.

This supports what I've been saying about dissipating heat caused by the primary ignition circuit.


A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature at optimal levels.

The reason for the ballast was to drop the voltage and amps in the ign primary circuit so the points wont burn up to soon and to limit the current flow through the coil so it last as long as it should. Mopar still uses the ballast when they went to electronic ign but not all manufactors did as some built the coils to work with a full time 12 volt feed and they can also limit the current flow by the electronics controlling the dwell. But the ballast is a resistance put in the primary ign circuit before the main load (the coil) in the circuit. It gets hot because of the electrical resistance it puts in the circuit to limit voltage and the current flow. Its not made to be a heat sink but they put it in the ceramic because they know it will get hot enough to maybe burn someone touching it when its in use. Its just like having a loose connection in an electrical circuit that can get hot because the loose connections puts more resistance in a circuit. Think of it like a crankshaft not getting enough oil to the journals. They heat up and get hot because the resistance to turn is much more with less oil and that resistance will build heat. Look at a blower motor resister as it puts resistance in the circuit before the load (blower motor) and it can get red hot on the lower speeds when it puts the most resistance in the circuit. I am sure the engineers dont want it to get red hot but it does heat up because of the electrical resistance it puts in the circuit. It only makes sense because the only reason for the ballast in the ign circuit it to limit the current flow and drop the voltage. They dont need it to get hot but thats what it does because of how much resistance it puts in the circuit. The only reason some may have ceramic on them with fins is to help disapate the heat which is why many blower motor resisters are in the housing so it blows air over the blower resister to help it disapate some of the heat. Ron

Function of Ballast Resistor with Points Ignition.
Essentially as described above (protect points) and uses temperature to increase flow at higher rpms to offset reduced dwell time.
Attachment. 1969 Dodge Service Manual, page 8-46:


Function of Dual Ballast Resistor with Magnetic Pickup Ignition.
Chrysler Master Technicians Conference, "Ignition System for 1972," page 5

FWIW, the Ford Duraspark systems I've worked with on AMC Jeeps used a resistance wire to the coil instead of ballast resistor. The wires are quite long, doubled back on themselves whe needed to keep it within the harness loom. Using a wire presumably spreads the heat created over a larger distance, and sufficiently so it doesn't degrade the carrying capacity of the otehr harness wires.

In any event, if an electric pump is drawing power through the resistor either in Start or Run, this will be a problem.

I agree with all of that Mattax. In fact most older GM and Fords (1971 and back)used the resistance wire as you described in the wire harness and not the ballast type like Mopar. But all the resister wires I have read about say they are not temp sensitive like the Mopar ballast resister which cools at higher rpm since the dwell is less with the dist turning faster so it will have a stronger spark at high rpm since it has less time for dwell and the coil to saturate at higher rpm. I like that idea but as far as I know none of the ones with the resister wire in the harness change resistance by temp like Mopars do. Most techs I worked with over the years dont even know the older GM and Fords used a resistance wire in the harness. But they should know something about it since both Ford and GM use a resister bypass when cranking from the starter solenoid that sends the 12 volts to the coil. I always wondered to myself how hot the resister wire in the wire harness gets as I have never tried to get to the wire harness and check it with the eng running. I actually worked for Ford dealers from 1974 to 1980 as their Dura Spark electronic ign came out while I worked at a Ford dealer. I was also at the Ford dealer when the pain in the butt Variable Venturi carb came out. Ron

Many moons ago my charger kept stopping randomly and then be fine after 30 mins of sitting - only found it was the Ballast when it happened at night one time and popped the hood, it was actually glowing bright red