Coil Question

Here is a picture I posted not too long ago showing where I mounted a round can coil on my '48 front mount.

I gutted my square can coil much like the other pictures in this post show.

You're correct, you MELTED yer squarecan coil insulative tars and that is the reason it will run for about 1-hr and QUIT, 'cuz the tar melts. It will solidify in about 4-hrs and re-start and run for about 1-hr again.

Me? I'd use the squarecan 12-volt 2.5-ohm ignition coil with "infamous ballast resistor". Replace yer points and re-gap for WIDER 0.017" gap. Your call..... .Dell, a 12-volt advocate for the right reasons

The "secret trick resistor" from RatShak is only 0.5-ohms for eariler versions of the 12-volt squarecan ignition coil. Wanna guess what would happen iff'n you used the secret trick 0.5-ohm resistor with the latest 2.5-ohm 12-volt coil??? Iff'n you guessed 'nuttin', yer guessin' ability exceeds yer readin' ablility.

DO NOT USE the secret trick 0.5-ohm resistor with the latest 2.5-ohm coil 'cuz you'll MELT THE GUTTS.....UNDERSTAND???..... ..respectfully, Dell

Yes, Dell, thank you for your response. I can appreciate the fact that time seems to be changing parts. In June, I bought a Chi/com 6v sq coil from a local parts place and it measured about the same as you quoted, 1.2 ohms (I measure these low resistances by running a fixed/known current thru the device & measuring the voltage across it). The one I took off the tractor measured 0.55 ohms, and I found this part of some old Ford manual (see attachment photo)I think, which shows about 0.5, so I guess the 6v coils are-a-changing too?

I have read many of your "official self designated sparkie meister" posts with great interest & am about to glean that your scheme is to insert whatever resistance it takes with any given coil to get about 3 amps. Am I correct?
I recently measured what I believe to be an original late '40's ballast and it was about 0.35 cold and 1.0 at paper scorching hot & 4.2 amps.
Do you know the difference between the A8NN12250B ('39-'47) and the A8NN12250A ('48-'50) ballasts?

I really appreciate your collection of knowledge and sharing it. I can appreciate the fustration you have, too, in that there are so many variables in both parts and people's background.
Thanks!

3-amps for coil is nominal design current for either 6-volt or 12-volt coils. Roundcan or squarecan. Why? 'cuz the "area-rule" of electrical contact sez that is about "optimum amps" for the size of the points contacts.

As fer 6-volt coil primary resistance; until you use "LAB grade" measuring equipment, most commonly available ohm-meters are inacurate at low ohms. (its a technical thing) For accurate low resistance measurement you need a "Wheatstone Bridge" and Galvanometer detector.

I'm kinda surprized that the "official" 6-volt coil primary resistance is listed at about 0.5-ohm. Why? 'cuz simple circuit analysis sez that inorder to get about 3-volts at the coil top terminal, you have a simple series circuit of coil primary and infamous ballast resistor; and therefore the resistance of BOTH must be the SAME to equally divide 6-volts down to 3-volts. Which is nominal coil operating volts.

I was under the impression the "infamous ballast resistor" resistance ranged from about 0.4-ohms COLD (but it could be 0.35-ohms) to 1.7-ohms HOT; with a nominal operating resistance of about 1.2-1.4 ohms. Therefore, the nominal coil resistance should be about 1.2-1.4 ohms to DIVIDE the 6-volts in half for 3-volts at the coil terminal (points closed) Yer spec of coil primary resistance of 0.5-ohms won't DIVIDE 6-volts to 3-volts, closer 2-volts and WEAK SPARKIES..... NOT GOOD..... ..Dell, yer self-appointed sparkie-meister

If you like to play, you can probably do it. I've done it twice, once on a very old unit where the epoxy like filler was all hard, cracked, such that some of it just chipped out easily. BUT, the next one was almost new, filled with good, hard, fresh epoxy...really wasn't worth all the cutting, drilling, die-grinding, chiseling, etc. but once committed, what do you do? A real BEAR! The pictures are of the 1st one & the white wire was replaced with HV spark plug wire before I sealed it up.

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Final pic