C1 Ballast Resistor

[Bob Malone]

What is the function of the ballast resistor? My '60 doesn't have one and it seems to run just fine. Could it be that it isn't needed because I'm running an MSD solid state ignition?

[Ed Jennings]

Re: C1 Ballast Resistor

The function of the ballast resistor is to cut the voltage going to the coil down to around 8V. This helps to preserve the points. The resistor is by-passed during starting. I know nothing about MSD ignitions, but I suppose it's reasonable that they operate off a full 12V, since there are no points to burn up.

[Duke W.]

Re: C1 Ballast Resistor

The TI and HEI operate off full system voltage, and I expect aftermarket electronic systems are the same. Any required resistors are in the box or, in the case of the TI, the harness. As Ed said, the function of the ballast is to limit point current. Otherwise, the points would have a very short life.

duke

[Bob Malone]

Re: C1 Ballast Resistor

Thanks. That explains why I was burning up points before I put the MSD ignition in. Bob

[Dale Pearman]

It Isn't A Simple Job

that the ballast resistor does. By passing current, it's resistance converts electrical energy to heat which is liberated into the air in your engine compartment. The net virtual resistance at any time is dependent on the temperature of the element. Energy liberated = current squared times the resistance times time. Since current is a variable, as is power (heat) AND resistance, then a balance will be struck between resistance and current dependent on liberated energy (heat).

Another way to say this is the ballast resistor adjusts itself to regulate current. By choosing ohmic values as a function of temperature carefully, current can be regulated over rpm to always approach coil saturation. (desirable for maximum spark energy)

In this sense, the ballast resistor is an analog computer. Mathematically it is a function with a variable coefficient which is in itself a function of another variable.

So if ya ain't got one, the points burn! Also, MSD multiple spark capacitor discharge ignition systems require a direct connection to +13 or so volts. That's why the dude putting yours in removed the resistor!

Original-appearing ballast resistors have been discontinued for quite a while now in both the 0.3 ohm and 1.4 ohm versions (at 75 degrees F). They are getting scarce and commanding prices as high as $75.00!

Dale.

[Jim T.]

Re: It Isn't A Simple Job

Dale I have a new unused ballast resistor that came with a high performance coil that I purchased new in 72. I didn't use the resistor because my car had resistor wiring to the original coil. Are non original resistors still manufactured?