Testing original coils: C-1, C-2

[Verne Frantz]

I have several used original ignition coils for my cars. I have the specs and know how to test them, however the specs are fairly wide, allowing for quite a variation in primary and secondary resistance readings.
What combination of low/high primary resistance and low/high secondary resistance would produce the hottest spark (highest voltage output from the coil)?
Any "EE"s out there?

Thanks
Verne.

[Duke W.]

Re: Testing original coils: C-1, C-2

A "hotter spark" means more energy and energy is primarily a function of primarly current.

The primary circuits with the highest currents would be the 0.3 ohm ballast used in conjuction with the "107" and "091" coils or any other coil that was designed to be used with the 0.3 ohms ballast.

Any coil used with the 1.8 ohm ballast will have less primary current and, therefore, less ignition energy.

If the coils fall within the specified primary and secondary resistance range, they are satisfactory for use.

Duke

[Verne Frantz]

Re: Testing original coils: C-1, C-2

Thanks Duke,
I am using the black dot ballast (.3ohm) with coils designed to be used with that, such as the 107.
I was just wondering, since I have several to choose from, if there was any advantage to picking one with a lower or higher resistance (within spec) on either of the windings.
Why settle for "satisfactory" if I can choose one which might have a better output than the others?
Verne.

[Duke W.]

Re: Testing original coils: C-1, C-2

All other things being equal the lower the resistance the higher the current, but I think you're splitting hairs.

Duke

[Mike M.]

Re: Testing original coils: C-1, C-2

vern and duke: when hitting the drags back in the early 60's, we'd attach a pigtail wire to both sides of the ballast resistor. had to remember to disconnect the pigtail on our 60 mile trip back from the strip or would weld points. mike

[Jack H.]

Danger, Will Robinson!!!!

The specs you see for primary and secondary windings (expressed in ohms) were for quick and dirty shop mechanic go/no-go evaluation. It's the actual INDUCTANCE of the primary compared to the secondary that produces transformer step-up action via mutual inductance/coupling.

Now, wire is pretty uniform so, resistance generally co-varies with inductance, and few techs have RLC meters.... But, just about everybody has an ohm meter making it simple to spec that coils this way.

What's the upshod here? Well, it IS possible for a coil to have it's primary and secondary windings intact (resistances read like they should), but because the coil lost cooling oil the core of the transformer is delaminated or melted causing a loss of magnetic coupling. Energy in doesn't correspond to energy out per the winding ratio prediction.... Hence, verifying resistances is a necessary test but it's NOT a sufficient test to guarantee the integrity of a given coil!

[Verne Frantz]

Re: Testing original coils: C-1, C-2

Gentlemen all,
Thank you for your knowledge and wisdom. I was guessing the answer to my ohm question was Low-Low. I can't perform the more adequate test Jack described, however if I can get my 1964 Sun Scope Motor Tester up and running, I'll be able to capture the coil output on the scope and choose the best one.

Duke, I've been known to split hairs with just about everything, and I'm too old to stop now. I figure if I split enough of them, I just might end up with a better running car.

Thanks again!
Verne.