Ignition coil very hot, not "boiling" hot but...

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1966DartConvertible

1966DartConvertible

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My coil get really hot and I've been told the coil should only be "warm" to touch and if its not, there must be some short somewhere in the wiring.

Is this true? should I be concern?

Thanks

Syed
 
Have you made any modifications to the car recently? Did you bypass the ballast resistor for some reason?
 
jabdusty57 said:
Have you made any modifications to the car recently? Did you bypass the ballast resistor for some reason?
Click to expand...

Yes, upgraded to Electronic Ignition using a DIY J-Cars Australia module and the points as the "trigger" only. Car ran fine for the last couple of months or so, still does. But I never really touch the coil when the engine is warm until sometime last week when a friend pointed out that the coil shouldn't be that hot.

Engine ran smooth as silk though, no prob with misfiring or anything like that.

Syed

PS: No ballast resistor now, I figured the electronic ignition wont need it.
 
1968FormulaS340 said:
That may or may not be correct. What did the instructions say?

Where is the coil mounted? If it's mounted on the engine, it will get hot.
Click to expand...

Coil is already on the inner fender

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I would say that type of oil-filled coil always needs a ballast resistor. I have a somewhat similar (older design) Crane XR700 on 2 of my cars. The manual says to keep the ballast. What it doesn't detail is if the ballast is required to protect the factory coil or the module itself.

On my slant, I installed a Mopar electronic distributor and a GM 8-pin HEI module and GM "external coil". That setup does not need a ballast resistor. See posts by several people.

Since your module is a fairly new design, I expect it can run without a ballast, if you use the right coil. Best might be to install a better E-core type coil - Mopar Magnum, GM "external", or a new after-market. For later, search "ready to run distributor" on ebay and the link to their $20 coil (stevewhiteperformance and others). Too bad they don't make that distributor for the slant or BB engines yet. When they do, you might replace your points distributor since I expect that doesn't give the most repeatable trigger signal. You could also add a Crane XR700 optical trigger to your distributor (sometimes cheap on ebay).

Not sure why your ignition wasn't missing when the coil got hot. I had to bypass my ignition switch to drive my 64 Valiant slant home. I first just jumpered +12 V to the coil, but after 5 min it started missing above 40 mph and I found the coil was very hot. Wired in the ballast and it ran home fine.

Your Jaycar box looks like fun. I wonder if you can input a manifold pressure signal. Maybe all you need is to have it add to the advance in your factory distributor, with back-off for knock. I put a GM knock sensor in my slant. It mounts in the block drain, using a 3/8" NPT to 1/4" NPT bushing. In the U.S., we can get those parts off junkyard trucks real cheap.
 
I would repostion that coil to vertical postion, read somewhere they need to be vertical due to the oil inside and the way the oil cooled the wires in the coil, forgot the specific details.
 
1966DartConvertible said:
My coil get really hot and I've been told the coil should only be "warm" to touch and if its not, there must be some short somewhere in the wiring.

Is this true? should I be concern?

Thanks

Syed
Click to expand...

My advice would be to spend the three dollars (or, whatever,) buy a ballast resistor and wire it into the system and see what happens.

Let us know if the coil still gets hot...


Inquiring minds want to know....
 
that happened to me, I had a accidental ground to the negative side of the coil. it blew it apart and the oil stained my paint. might want to check that out, that was my issue. I was using 440 sources distributor with the ignition box in it w/o a ballast resistor.
 
It has to do with dwell. It looks like the unit has adjustable dwell control, that setting may be too high.

About dwell control:
The amount of dwell time is determined by the coil primary inductance, the current rating and the series resistance. OEM mopar box does not have dwell control, so coil current is limited by the ballast resistor. Other electronic ignitions like HEI use an analog mode of prediction to charge the coil prior to the ignition event, then current limit if necessary for the brief interval prior to ignition. The current limit is similar to the ballast resistor, however it is only for a brief interval of time, so energy dissipated is reduced. It needs the extra time to provide enough for rpm variations, that mess with the prediction.
An example of a typical dwell is 3mS, in that time the current ramps from 0 to 5A. If it is energized longer it continues to increase, only limited by resistance or current limit. The series primary resistance of high energy coils may be 0.5 Ohms, so without limit at 12V supply the current could max at ~24A without dwell control. This could be bad.

The moral of the story: Coil current grows quickly with time. Coil current ratings are often hard to find. A scope with current probe and voltage probe can sort out what is happening.
 
There are really only 2 options in coils, those that can operate on a constant 12 volts and those that cannot. If your stock coil required ballast resistor protection it always will.
 
Syed,

Do you have the jaycar programmer (KC5386 and cable WC7502)? If so, what is the dwell time setting?
 
berlins said:
I would repostion that coil to vertical postion, read somewhere they need to be vertical due to the oil inside and the way the oil cooled the wires in the coil, forgot the specific details.
Click to expand...

X2 - my replacement coil specifically stated that in it's instructions, for that reason.
 
Here is a current screen shot for an electronic ignition with electronic dwell control. I used a 0.1 Ohm resistor to view the current with a scope. 0.1 V = 1 amp. The waveform shows the current ramp to 5.5A then holds, when the current drops ignition happens. The dwell time ramp should stay nearly consistent in time, the hold time will reduce with RPM, and at very high RPM the dwell is also reduced. At high RPM the pulses get closer together.

Power loss in the coil is current squared times the coil resistance. Then power is integrated with time for the energy loss (heat). Proper dwell control greatly aids in keeping coil cool at lower RPMs. It reduce the hold current time At high RPM, it is all about getting the coil charged in the available time.
 

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And for comparison here is a point with ballast resistor using the same ignition coil. The ballast limited the current to about 6.5A, a bit too much, but OK for the short test. The RPM is not the same as the prior test. The EMI of the ignition was messing with the speed control on the portable drill, making it cut out. The scope time scale was also different. What is important is that the total dwell time was 17mS vs the 5mS so the coil heating effect is about 3 times more than the electronic. The extra dwell at low RPM does not buy performance, just adds heat.
 

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KitCarlson explains it well. The early electronic ignitions, like Mopar factory, and early after-market like Crane XR700 and Pertronix Ignitor, used simply a transistor switch. The curved charging plot Kit shows is the classic "LR circuit" in physics texts.

Later ignitions like GM HEI, Ford TFI, and after-market Ignitor II, MSD, ... use smart electronics to limit the current once the coil becomes magnetically saturated. As Kit says, more current than that just adds unneeded heat. Mopar did the same in the 80's, but you can't retrofit it because the ignition is integral to the "spark control computer" or "engine controller" (vacuum advance diaphragm sticking out the side).

What many of us can't figure out is why people spend a lot and hack up their wiring to add the sub-standard 70's Mopar factory ignition to their points cars.

Finally, it seems I was wrong in saying that the oil-filled coil syed has always requires a ballast. It seems he can run it without a ballast by setting the dwell limit properly. However, I understand that a more modern E-core coil would allow a more powerful spark.
 
berlins said:
I would repostion that coil to vertical postion, read somewhere they need to be vertical due to the oil inside and the way the oil cooled the wires in the coil, forgot the specific details.
Click to expand...

x2. Mount it vertically and it won't get hot.
 
Bill,

2x in the E-core coils. They are very efficient, the E-core design reduces leakage inductance. I will never go back to a can coil.
 
Sounds like a nightmare... shoulda just gone with what most others do and done a MSD box+ electronic dist or the factory Mopar electronic ignition conversion kit.... and ran a ballast on the coil (I still do with a MSD blaster 2 coil and Mopar electronic conversion)
 
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