Ballasted Ignition

[Tullamore]

I am looking at replacing my stock ignition coil with one of the 40,000 V models but they all warn about having a ballast resistor, where would this be and how can I tell if mine is that type or not. If you could explain the purpose of it too that would be great.

 

[lesingepsycho]

I can fully relate. I had YEARS of ignition problems due to a ballast resistor and the fact that I had no idea what they did. I replaced everything on the car including carbs, distributor, fuel pump, filters, etc etc,... even tried a handful of different coils and nothing worked. The car got parked for about 6 or 7 years because I couldn't make it run reliably. After the 7 years or so when it came back out of storage, wouldn't you know it, same problems. One day I finally narrowed it down to the coil (even though it was brand new out of the box Mallory) and went down to the local auto parts store to have them test it. He said it was hot but checked out fine and then he asked me what size ballast resistor i was using. "Ballast resistor?" I replied rather sheepishly. Turns out the ballast resistor lowers the amount of voltage going through the ignition system which keeps from burning up the coil and points etc. Once he said this I realized that in all those years of car problems, I would always stop on the side of the road to reset the points gap (my father, not knowing much more than I always told me the problem was the points "floating"). When I stopped on the side of the road and popped the cap, what was actually happening was I was venting out the distributor enough that the points would cool back down and the coil would have time to cool off a bit as well, then when I buttoned it all back up, whaddya know, it would run again, of course it would only be a matter of time before I would get the same problem but since in those days I never drove the car much more than 15 miles, it would only happen about once per trip. The guy at the auto-parts store offered to sell me the proper ballast resistor to go with the mallory but since I was stuck on the side of the road, instead I had him sell me a coil with a built in ballast resistor. That way I was able to install the new coil in the dark on the shoulder of a freeway on ramp and, wouldn't you know it, I've never had the problem since. Also, since then, I've installed an MSD-6AL box and gone back to the original Mallory which, when you run an MSD box, you don't need a ballast resistor because the box does the work for you. SO, to make a long story at least worth while, here's the info you're looking for. The ballast resistor for spridgets, according to the Haynes Manual was only fitted on later model cars with the 15C6 coil and should be 1.3 to 1.5 ohms. The LA12 coil fitted on 948 and 1048 engines had a primary resistance of 3.2 to 3.4ohms and the 11C12 and HA12 coils 3.0 to 3.ohms. Hope this helps!

 

[Tullamore]

Where is the restister located, would it be near the coil, or is it inside the dist. cap with the points. Sounds like it connects to the 12V line going to the coil?

 

[Thor]

The location depends. Some coils have built in resistors such as in my 1975. Other times it is a small rectangle shaped device which is located I believe on the positive wire going to the coil.

I just put an image of the ones i have on my website:
https://www.visn2.com/mgmidget.html Hope this helps. I point out that I have two in the engine component. Just never removed either of them but both are unused.

 

[piman]

Hello all,
I can't comment on the Spridget, but this system is common on the Triumph 2000 range and others. Early models had a cylindrical resistor which was mounted on the coil terminal with later versions having a resistor wire in the loom.
The reason for this system is to assist starting, the coil is an 8 or 9 volt rating with the system voltage being dropped to that voltage with the series resistor. When you crank the engine there is a cable from the starter solenoid which connects directly to the coil terminal. The starter motor load drags down the battery voltage and this reduced voltage directly to the coil still gives full high tension voltage to the plugs. At all other times the ballast drops the system voltage to the coil. It is a simple idea to aid starting but, it can cause a lot of confusion if it is not understood.

Alec

 

[lesingepsycho]

/ubbthreads/images/graemlins/iagree.gif You can say that again Alec!

 

[Geo Hahn]

Knowing zip-all about Sprites I do not know whether your ignition system should include a ballast resistor though my vague impression is that a 1275 engine would not. A clue is sometimes whether the coil has a screw-top (usually not ballasted) or is a push-on (usually use a ballast resistor). The resistor may be as noticable as a big ceramic thing or as discrete as a special wire... so looking for it it not necessarily going to help, better to consult a reliable wiring diagram.

FWIW the Lucas Sport coil (although it is push-on) is for non-ballast systems.

BTW, people often speak of non-ballasted coils as having an 'internal ballast' but I think these are simply coils that do not require a ballast. You don't get the higher voltage for better starting, just the same lower running voltage all the time.