Ballast Resistors in the Ignition System

[SafeAirOne]

An explanation of balast resistors in the coil/ignition system (Carried over from an unrelated thread):

Under "Electrical Ballast (http://en.wikipedia.org/wiki/Ballast_(electrical))," Wikipedia says:

"...The term also refers to an automobile engine component that lowers the supply voltage to the ignition system after the engine has been started. Because cranking the engine causes a very heavy load on the battery, the system voltage can drop quite low during cranking. To allow the engine to start, the ignition system must be designed to operate on this lower voltage. But once cranking is completed, the normal operating voltage is regained; this voltage would overload the ignition system. To avoid this problem, a ballast resistor is inserted in series with the supply voltage feeding the ignition system. Occasionally, this ballast resistor will fail and the classic symptom of this failure is that the engine runs while being cranked (while the resistor is bypassed) but stalls immediately when cranking ceases (and the resistor is re-connected in the circuit).
Modern electronic ignition systems do not require a ballast resistor as they are flexible enough to operate on the low cranking voltage or the ordinary operating voltage."

Without a functioning ballast resistor, the points will fry due to an over voltage at the points, with electrical arcing across the face of the points.

[thixon]

Sho nuff.

Its worth noting here that the points don't usally (in my experience on other vehicles) fry right away. Okay, maybe it was'nt worth noting, but thanks for answering his question for me anyway Mark. Sorry you had to take up my slack!:thumb-up:

It probably is worth noting that should you need one, it can be had at any auto parts store, or even radio shack. Any of you that do a wiring update similar to mine (with an ez wiring or painless) harness, new coil, alt conversion, and still want to run points will need to put one in.

[SafeAirOne]

Also worth noting is that some coils have the ballast resistor built in and some don't and require an external ballast resistor. Use the wrong type of coil and you will end up frying your points with regularity.

[scott]

I have these two ceramic things on either side of the coil. Is this what you guys are talking about? Do I need em? I've an alt, new wiring harness, electronic ign, and an autozone coil

[Apis Mellifera]

I find the "you'll shoot yer points out" thing a bit odd. I have a SIII, MGA, MGB, three Spridgets, a Bonneville, and a BMW R60. Over the last 25 years I've had a host of other old, mostly English vehicles. They all have/had a host of different coils, ignition parts, etc. Not one has ever had a ballast resistor. The only time I ever had an ignition failure was on an MGA Coupe I was racing. It had an MSD 6AL feeding a points 25D4 distributor. The battery was jarred loose and the resulting electrical hyjinx allowed the MSD to cook the points. There was no visual damage, just a loss of continuity.

I've driven a Midget 10s of thousands of miles on stock Lucas parts with the resistor removed and never had a problem. I find it hard to believe that I've been lucky all the years.

[SafeAirOne]

I don't know about Rover ignition systems...It's been two decades since I've owned a rover with a distributor. The last gas-powered, points-ignition truck I had was a 1967 J**p M-715 with an obvous ballast resistor wired into the coil primary circuit. When this resistor failed, the points quickly followed due to the excessive voltage and resultant arcing across the points in the coil primary circuit.

Most ballast resistors are not as obvious however, since most of the ballast resistors are built internally into the coil assembly itself.

I THINK I remember somebody saying that Rover coils have the ballast resistor built in, but I could very well be wrong. Somebody with spark-plug engine can confirm this (or not).

[yorker]

Every LR I've had has had an internally ballast resister type coil- the only time I've used an external one is when I've had to swap a coil in from another vehicle for some reason.

[thixon]

Hi guys, sorry I did'nt weigh in sooner. I guess I"m responsible for this post by mentioning these things in the other post. Sorry Safeairone. I've been building a fence all weekend, and havn't had time to check the board. Wife project. What can I say.

Anyway,

Scott, most likely the two ceramic blocks sound as if they are ballast resistors. Its odd that you have one on each side of the coil, but I don't know your setup. Could be an attempt to regulate voltage to the coil, and then to the points. I'll have to think about why you'd do that.

Apis, I've owned or worked on everything you listed except the bimmer (cool bike). Everything you listed either has a coil with one built in, or an external voltage regulating device. The A you had/have should be pos ground, and was a six volt coil if I remember right (if not, feel free to tear into me). That healey in my garage appears to be wired similarly.

Yorker, correct as usual. Dude, how do you keep up with all this stuff.

If you're doing a rewire similar to mine, where the harness is designed to be adaptable (hotrod harness), and you want to keep the points, you most likely will end up needing one. In my case, If I didn't run one, my points would receive full current from the sytem at all times. This would result in burnt point quick. If I decide to swith to an electric ignition, I probably won't run one unless the brand of ignition I buy recommends it. All that said, I have bypassed the resitor on at least two vehicles running point, and after several hundred miles, the points had not failed yet. Don't know how long it would have taken.

Now that I've bored everyone to tears with another long post, I'm going to retire now and recover from a long weekend of obeying.....her.

[scott]

correction, they're not both ceramic. there's is one that looks like bakelight. the bakelight has the wire in then goes out to the ceramic which then goes to the coil (a cheap autozone coil) then to the points. i didn't set this up. it's the way it came. i've got a petronix electric ignition now. do i need this bulkhead clutter?

[greenmeanie]

Scott,
With a Pertronix you do not have points to wear. This simplifies your ignition system. You need a coil that has an internal resistance of about 3 ohms. Hook the pertornix trigger directly to that as described in their instructions. Get rid of everything else.

You can play with your spark gap to deliver a bigger, fatter spark more reliably.