Coil temperature

[torque2me]

Just a thought,
if you have a balasted 1.5 ohm coil which is
re wired to run on 12volts you will get overheated as you have doubled the
current , burn points and have very high HT
which blows rotors and caps
a 12v coild has a 3ohm resistance

just a idea
Pete

Pete,

I was always under the impression that 12v coil's were standard on the mk.2 and a ballast resister was wired into the HT circuit. Those who know please post!

Kev

[Vox]

Can't speak for face light cars but pre facelift mark 2s have a 6v coil with a ballast resisitor in series with it on the low tension side, hanging off the alternator pivot bolt in my case. Both should be about 1.5 Ohm. The ballast resistor is shorted out when the starter is operated so the coil gets full battery voltage (actually more like 8v on mine when cranking) so the 6v coil puts out a much better spark than a 12v one would with 8v on it!
Hope that makes sense.
Chris

[Mike Stevens]

As far as I know, all the Mk2 cars had a ballasted coil. The resistor is either a whiteish block bolted to the coil (earlier cars) or part of the loom itself (later cars).

The resistor is wired in series with the coil from the IGN +12V. It's use is to drop the +12V to about 6-8V for normal running.

However, during start (when cranking the engine) the full battery volts is applied direct to the coil via a wire from the starter motor. The theory is that while cranking, the battery volts will drop to maybe 8V under extreme conditions. Applying this (lower) battery voltage direct to the coil will help create a better spark to start the engine. Once started (and you let go the key from the start position!) The ballast resistor is now used to drop the volts to the coil!

I hope this helps.

Cheers,
Mike.

[pete lewis]

my 74 Mk2 was ballasted built in harness the usual white/ pink trace ,cut this out and rewired from the fuse box to 12v and 3 ohm coil when I fitted lumenition to simplifiy the lecy having a 12v feed , its been fine and coil doesnt fry eggs

getting it all mix and mis matched is more common on the small chassis cars ....well i thought .

Pete

[sprint95m]

This topic is something I pondered but never did I actually ever have problems with the ignition coil on a big six,
but, if I may, I have a question......

does the make of coil make a difference here or, to put it another way, are some coils more prone to overheat?




thanks,

[Dazzer]

Ive not had a problem on my rally 2000 mk1 either. Coil in the usual spot with a spare coil also attached next to it for a quick change over just in case. The coil i use is a blue bosch type with the old lucas sports coil as back up. Hot, yes but not detrimental after seven years and 50k and numerous events. Perhaps also the heat is good to dry off the coil after some serious deep water exploits!

[torque2me]

Ive not had a problem on my rally 2000 mk1 either. Coil in the usual spot with a spare coil also attached next to it for a quick change over just in case. The coil i use is a blue bosch type with the old lucas sports coil as back up. Hot, yes but not detrimental after seven years and 50k and numerous events. Perhaps also the heat is good to dry off the coil after some serious deep water exploits!

The trouble with being doo-lally is that I can see fuzzy pictures in my mind of pottery type ballast blocks and another with something wired in before the LT spade. The problem is I can't remember when and which car the fuzzies relate to. My present car seems to be fitted with a 12v coil but I cannot see any ballast resister.

Kev

[harveycoppock]

The trouble with being doo-lally is that I can see fuzzy pictures in my mind of pottery type ballast blocks and another with something wired in before the LT spade. The problem is I can't remember when and which car the fuzzies relate to. My present car seems to be fitted with a 12v coil but I cannot see any ballast resister.

Kev

Some have the ballast resistor as a wire in the loom, think if ballasted and the points closed you should get 6V on the LT coil connections. There is a connection off the solenoid labelled IGN that gives the LT wire a full temporary 12V feed when cranking - and points still closed though, adjust them so they don't open. I assume they changed to a wire in the loom as that was more reliable than the pot resistor? I ran a TR for yonks with the lead off the starter, as there was no obvious ballast resistor, and the workshop manual wiring diagrams didn't feature a ballasted system as the earlier cars didn't have them, wondered what the lead was for....

[torque2me]

The trouble with being doo-lally is that I can see fuzzy pictures in my mind of pottery type ballast blocks and another with something wired in before the LT spade. The problem is I can't remember when and which car the fuzzies relate to. My present car seems to be fitted with a 12v coil but I cannot see any ballast resister.

Kev

Some have the ballast resistor as a wire in the loom, think if ballasted and the points closed you should get 6V on the LT coil connections. There is a connection off the solenoid labelled IGN that gives the LT wire a full temporary 12V feed when cranking - and points still closed though, adjust them so they don't open. I assume they changed to a wire in the loom as that was more reliable than the pot resistor? I ran a TR for yonks with the lead off the starter, as there was no obvious ballast resistor, and the workshop manual wiring diagrams didn't feature a ballasted system as the earlier cars didn't have them, wondered what the lead was for....

Thanks for that Harvey, I guess mine must be the wire type.

With regard to "ooops moments, best to bluff it out.

Kev

[pete lewis]

most makes of coils carry a similar specification

lucas dlb 102 may be marked as 12v but its a 1.5ohm ballasted 6v feed coil

lucas dlb101 is a straight 12v non ballasted 3 ohm coil

if you have a meter check the resistance across the two blade terminals 6v = 1.5 ohm 12v = 3 ohms

if you stick 12v through a 6v 1.5ohm coil you have excessive HT voltage and a doubled amperage at the points
hence why many blown rotors and burnt points and extra hot coils

like wise 6v into a 3 ohm 12v coil gives very low HT

and to help confusion some 6v coils are marked as 12v (being the base supply)

my mk2 74 had the white pink resistive wire in the harness not a seperate ceramic unit.

all ballast systems have a white yellow coil feed which is the feed from the solenoid to boost to 12v just when cranking


Pete