ballast resistor in electronic ignition cars

[str12-340]

So over the years I have been led to believe that the reason there is a ballast resistor and a low volt start feed, as well as a full voltage run lead is that back in the days of points ignition, reduced voltage to the points when the engine is cranking at a low RPM made the points last significantly longer. So why is there still a ballast resistor on cars after the advent of electronic ignition?

A couple years ago I rebuilt the engine in my 318 Dart and among the updates was a rebuild/recurve of my Mopar electronic distributor and installation of a box made by FBO. As a part of the installation directions, they had me bypass my ballast resistor. On my 340 Dart with an MSD 6AL box (old school), and billet distributor, the ballast resistor is also bypassed.

So, Magicians of Ignitions, what gives???

 

[1969383S]

DC still relied on this with the early offerings of upgrade systems. MSD and others did not. I still have one for the factory look but bypassed on the backside with a piece of solid 12AWg. I use Pertronix III.

 

[toolmanmike]

Chrysler electronics didn't run off of 12volt like GM HEI and other systems. I don't know why, they just didn't.

 

[69DodgeMan]

The ballast still functions to reduce the current through the coil, which allows it to run cooler and prolongs its life.

Btw, the START feed is the full voltage and the RUN feed is the reduced voltage, and yes, the points would last longer with this setup.

 

[67Dart273]

Chrysler electronics didn't run off of 12volt like GM HEI and other systems. I don't know why, they just didn't.

It is only PART of the electronics. Most any ECU you run into nowadays for Mopar does not use the "other half" of the ballast.

 

[1969383S]

Matched components is everything. Read the instructions for each and be sure! My system is matched and wants full 12V.

 

[1969383S]

The Chrysler ECU needs 12V, the coil used is the issue. It was designed on the upgrades to use the factory coil and thus the drop to it. Think about it. The box still required full voltage and If installed correctly did get it. Only the coil voltage was dropped through the ballast.

 

[67Dart273]

So over the years I have been led to believe that the reason there is a ballast resistor and a low volt start feed, as well as a full voltage run lead is that back in the days of points ignition, reduced voltage to the points when the engine is cranking at a low RPM made the points last significantly longer. So why is there still a ballast resistor on cars after the advent of electronic ignition?

A couple years ago I rebuilt the engine in my 318 Dart and among the updates was a rebuild/recurve of my Mopar electronic distributor and installation of a box made by FBO. As a part of the installation directions, they had me bypass my ballast resistor. On my 340 Dart with an MSD 6AL box (old school), and billet distributor, the ballast resistor is also bypassed.

So, Magicians of Ignitions, what gives???

I've always thought it was reverse logic, that is for starting. That is, runs low during running, so you can boost it back up during cranking and compensate for the battery sagging

 

[Daves69]

Any alternator output affect to that 12V in run mode?

 

[67Dart273]

Sure. The coil + varies, and that is why they call it a ballast. When running down the road with the system at 14V the coil runs perhaps 10-11-12.

Remember there is a HUGE difference between 12 and 14V. Think about your home electrical. 120V vs 140 LOL. Light bulbs would not last long.

 

[Mattax]

I've always thought it was reverse logic, that is for starting. That is, runs low during running, so you can boost it back up during cranking and compensate for the battery sagging

Yes. In fact I've seen spec that a battery drawn down to 10 Volts during starting is basically OK.

The ballast still functions to reduce the current through the coil, which allows it to run cooler and prolongs its life.

Btw, the START feed is the full voltage and the RUN feed is the reduced voltage, and yes, the points would last longer with this setup.

And Chrysler used a ballast resistor placed so it would run a little cooler at highway speeds. At least that was the threory.
page 5 Ignition System Analysis (Session 259) from the Master Technician's Service Conference

As a part of the installation directions, they had me bypass my ballast resistor. On my 340 Dart with an MSD 6AL box (old school), and billet distributor, the ballast resistor is also bypassed.

Both of these systems, along with GM's HEI, incorporate a current limiting control internally in the box.

The MSD is a little different than the others because the coil is sent power in a large pulse.