Thread: what's this please?

G'day All,

As stated in earlier posts an Ignition coil with a ballast resistor on a 12 volt system is actually a 6 to 8 volt coil.
(So a coil with a ballast can be used on a 6 volt ignition system without the ballast resistor.)
The coil and Ballast resistor form a simple series voltage divider. The coils I have used have a resistance of 1.6 ohm with a 1.5 ohm ballast resistor.

During the 1970's car manufacturers realized by shorting out this ballast resistor during starting enhanced "cold starting".

A simple way was to use a relay with the coil winding connected to the starter motor terminal and the relay contacts providing the starting volts ( approx as low as 8 volts) direct to the coil during starting only.

Happy New Year to you all.

Chris

I suspect the use of shorting the ballast resistor for starting may date to a little earlier than that.

And a quick look found an article in Dykes Automotive encyclopedia from 1929 describing the use of a resistor with very low cold resistance that would provide higher voltage for starting, but would heat up and drop voltage to the coil after the engine was running or if the ignition was left on while the engine was stopped, enabling the use of a coil designed for a lower voltage.

It seems to me unlikely that the idea of shorting the resistor for starting would have not been used until the 1970s - although there may have been a burst in popularity then.

John

G'day All,

I have attached the circuit diagram of the ignition system I made up for my 2A. using the Bosch GT40RT coil. Worked well for many years.

However, have since fitted an MSD 6T electronic ignition system with a rev limiter to limit the engine top road speed when using the overdrive.

Chris

" If I ditch it - would I notice?"

I meant to say "If I ditch the coil with the ballast resistor in favour of a coil without a ballast resistor, would I notice the difference". Currently hissing down here - will try the test lamp etc when it clears up.
Thanks for all the comments.
cheers,
D

The Ballast Resistor also reduces the wear on ignition components - namely Points...

Hence why solid state ignitions didn't require it any longer..

The bypass is to enable full voltage for starting and cuts out once the starter cuts out..

Removing it and fitting a 12v coil will have your points burning out in short order.

Originally Posted by vnx205

I can tell you what happens if you have the wrong coil with no resistor.

I can also tell you what happens if the ballast resistor fails. That was on a different vehicle.

I'm sure that if I had known beforehand what the effect was, it would have taken me a lot less time to diagnose the strange behaviour my 1969 Crown was exhibiting.

The reason for the Ballast resistor & 8v coil is actually because of the power drain when cranking the starter motor. You will no longer get a full 12V to the coil. Hence the 6-8v coil is working at better efficiency whilst cranking than a 12v coil would be.

If you fit a 12v coil with no ballast you wont have as good a spark whilst cranking & may be harder to start.

If you have an electronic module in your distributor it wont matter.

I was under the impression that the ballast resistor coils were designed to handle 10 volts, not the 6-8 volts that people have mentioned.