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Does anyone on here understand or can point us to and idiots guide to coils?

As regards factory fit , there are three basic types:
Standard 12v from 59-82(ish)
Ballast resistor type 82 on
Electronic ignition type

We were going to change the coil on my racer as it may have been the cause of my retirement from my last race. We then started to look at resistance of them ; they seem to vary one type to another and one age to another and we have had instances where an old stock Lucas sports coil would work with electronic converted dizzy and a modern one would'nt.

I know that if you fit a ballast resistor one in place of a 12V one (and vice versa) it will burn out the points but that's about the limit of my technical expertise.

I don't understand the reason for a factory fitted electronic dizzy having a special electronic coil , whereas you can keep a standard coil with the cheap electronic conversions that are about

I can give you my simple understanding.

Ballast resistor setup allows the coil to basically run at low voltage so its good when cranking over and the whole car's voltage dips.

The way a coil works it generates a HT voltage based upon the collapse of the current field inside it, this current field is generated by the points opening and closing.

Why would it be different with Electronic ignition? Hmm, the only thing that makes sense is that the effective dwell of the electronic ignition isn't the same as points therefore you need a coil the is wound to produce HT from a presumably much shorter / longer dwell period.

Presumably some of the kits behave closer to a points rig and therefore they work.


Nick

I created a PDF as an overview of points ignition systems. The document includes an overview of basic coil functions. You can get a copy of it by visiting the link below and viewing or downloading the document "LucasPointsIgnitions.PDF"
https://www.sites.google.com/site/purlawson/home/files

As Nick said above, the "standard" coil was replaced by the ballast system to allow easier starts in cold weather when the system voltage can drop pretty low while cranking. Standard coils typically fall in the range of 3-4 Ohms. Ballast coils typically measure 1-2 Ohms. All resistance measurements are made across the coil's low-tension terminals with the low-tension wires removed.

The OEM electronic ignition coil is a different item. On first glance it appears to be a low-resistance ballast coil. However, it typically has a resistance less than or close to 1 Ohm. I have no first-hand experience with them or with the factory electronic ignition. However, it is my understanding that using the wrong coil with the factory electronic ignitions will result to premature failure of the ignition module.

Aftermarket electronic ignitions can typically run with any coil you want as long as the current flow is not excessive. That means running a ballast coil with ballast wiring and electronic ignition is possible... but don't leave the ballast out. However, the aftermarket ignition modules typically need a full 12V supply so if you want to retain ballast wiring and a ballast coil, the ignition module must be supplied power from a full 12V source... not coil (+).

Thanks for your help. Running in and testing at Blyton follows

Thanks for that.

A very interesting article.

Thanks, Doug.

dklawson wrote: However, it is my understanding that using the wrong coil with the factory electronic ignitions will result to premature failure of the ignition module.

this is certainly the case - they don't fail to start, but you get a very hesitant misfire higher up the rev range that's really noticeable under load - once they do this the module doesn't ever get any better, even if the correct coil is then fitted.

the very early 'two spade teminal' type seemed to get the hesitant misfire at the lower end of the revs, which would clear at higher rpm