Smoked Ignition Coil

[hsdropout]

Got engine wired up to run in basic form similar to a test stand (see picture, less the tachometer wires). On/off switch and push button for starter. With coil unplugged from dist., turned engine over with push button, everything good. Repeated a couple time, turn engine over for several seconds each time.
Leaving switch in on position and checking with tester to coil, ok 12V+. After the switch was left on for approx. 1 minute, the coil starts sizzling and smoking! Killed power but I'm afraid I fried it.
Any clues to why this happened?
Ran red "hot" wires to positive at coil from distributor and on/off switch; black from distributor to negative on coil and grounded to firewall (not to engine as shown but tested ok).
Coil should be able to take constant 12V, correct?
Summit 850500 remote coil for HEI distributor.
Wasn't plugged in to distributor.
Anybody have this happen before? Thanks for any help or comments..........

[mr48chev]

If you grounded the - side of the coil like that diagram shows you created a dead short to ground right there and that would smoke the coil. That line to ground from the neg side of the coil absolutely should not be on the diagram. The coil grounds through the distributor and that is what creates the magnetic field in the coil that in turn creates the spark from the coil.

I don't know who drew that diagram but it is poorly done and creates several issues if you follow it 100%

[hsdropout]

Thanks mr48chev.........So take the ground off the firewall (black loop) ?
And, only need the black wire from distributor to coil neg. post?

Seems a ground is a ground whether it comes from distributor or elsewhere.........why would this be a problem?

Great..........the diagram I decide to go with is wrong!!!

see photo..........work in progress...........

[mr48chev]

When you put the Ground wire from the negative post to the firewall you created a direct short to the firewall. There is no need for the coil it's self to be grounded to anything as the ignition module or points inside the distributor are what ground the coil.

As I said before when the points are closed or the electronic module electronically closes the circuit the primary wire in the coil builds a magnetic field around the core of the coil. When the points open or the module opens the circuit that magnetic field collapses sending the high voltage current though the secondary wire to the distributor cap, rotor, plug wires and spark plugs. What you have done is create a setup where the winding in the coil was always building up a magnetic field until it got hot and fried the coil.


The other thing I didn't like on the Test engine wiring diagram was that the pushbutton to trigger the solenoid was run through the ignition (toggle) switch. That creates a situation on the test engine where you have to have the ignition on to bump the engine over with the starter when you are bumping the engine over to run the valves, run a compression test or bring the number one cylinder up on tdc to drop the distributor in. That isn't a real issue on the truck as it shuts off power to the pushbutton when the switch is turned off.

[hsdropout]

Thanks again Mr. This makes perfect sense, very basic, and not sure what I was thinking other than focusing on the diagram which is a bit misleading.

[OrrieG]

To clarify, the power from the coil to the plug is seeking ground by sparking from the isolated center electrode to the ground electrode creating combustion.

[hsdropout]

Well put Orrie.
40 bucks..........new coil.........rookie mistake.....duh.........moving on......
Thanks.

[OrrieG]

Been there, hoping I do not have any surprises when I fire mine this spring...

[hsdropout]

Yea............no surprise is good...........but inevitable.

By the way, I got that diagram off of the HoTRodders Forum.........
go figure....I coulda swore those fellas knew everything and would have caught that one.............or.........they are laughing about it right about now.