What coil..?

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318willrun said:
then I guess the question is, what coil (part number, brand, link etc etc) could be used with the factory electronic ignition that would allow bypassing the ballast resistor. I think Andover Coils bragged about this, but I cannot find a dealer.
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Pertronix Flamethrower with the 3 ohm coil resistance is an option. PN 40511.... or 40501 if you want chrome! LOL
 
My Petronix distributor lasted about 2,000 miles.

I replaced it with an electronic unit from the Dodge dealer.

The Petronix coil lasted about another 300 miles.

I put the stock coil back in & no problems since.

Left stranded miles from home & walking back twice due to Petronix products.
 
In order to understand all this coil swapping stuff, it is much easier to talk in terms of current rather than voltage. Folks talk about voltage because that is what is easily measured.

The higher the current in the coil, the more energy is available for the spark. There are other factors, but we are just working on coil swapping for this discussion.

In the stock mopar system, you have a 1.5 ohm resistor and a 1.5 ohm coil, those add for a total of 3 ohms. Using Ohms law, 12 volts divided by 3 ohms is 4 amps. This is what the system is designed for.

If you take the ballast resistor out, then 12 volts divided by 1.5 ohm coil is 8 amps, doubling the current in both the ECU and the coil. One or both of them are likely to be damaged. This is why my car kept burning out coils. The previous owner had it wired so that the ballast resistor was in the start circuit, not the run circuit.

So, if you want to swap coils with a mopar ecu, you need to keep the current about the same, at 4 amps, to keep from damaging the ecu.

This all means if you buy a 3 ohm coil, the current would be 12 volts divided by 3 ohms = 4 amps, so you would be fine without a ballast resistor.

If you buy a 1.5 ohm coil, then you would need a ballast resistor of about 1.5 ohms to keep the current correct.

Disclaimer: I have used nominal values for illustration. Some will say that the 12 volts is really 14, and the 1.5 ohms may really be 1.6. While all that is true, I just picked numbers for easy math for demonstration of the concept.
14 volts divided by 3 ohms is 4.7 amps.

Electronic systems are designed to operate in a range, so 4 or 4.7 amps probably doesn’t matter, and certainly 1.4 to 1.6 ohms really doesn’t matter. Doubling the current from 4 to 8 amps does matter.

If you understand what current you ecu is rated for (whatever brand it is) Then you can make an intelligent decision about the coil you choose.
 
Mike69cuda said:
In order to understand all this coil swapping stuff, it is much easier to talk in terms of current rather than voltage. Folks talk about voltage because that is what is easily measured.

The higher the current in the coil, the more energy is available for the spark. There are other factors, but we are just working on coil swapping for this discussion.

In the stock mopar system, you have a 1.5 ohm resistor and a 1.5 ohm coil, those add for a total of 3 ohms. Using Ohms law, 12 volts divided by 3 ohms is 4 amps. This is what the system is designed for.

If you take the ballast resistor out, then 12 volts divided by 1.5 ohm coil is 8 amps, doubling the current in both the ECU and the coil. One or both of them are likely to be damaged. This is why my car kept burning out coils. The previous owner had it wired so that the ballast resistor was in the start circuit, not the run circuit.

So, if you want to swap coils with a mopar ecu, you need to keep the current about the same, at 4 amps, to keep from damaging the ecu.

This all means if you buy a 3 ohm coil, the current would be 12 volts divided by 3 ohms = 4 amps, so you would be fine without a ballast resistor.

If you buy a 1.5 ohm coil, then you would need a ballast resistor of about 1.5 ohms to keep the current correct.

Disclaimer: I have used nominal values for illustration. Some will say that the 12 volts is really 14, and the 1.5 ohms may really be 1.6. While all that is true, I just picked numbers for easy math for demonstration of the concept.
14 volts divided by 3 ohms is 4.7 amps.

Electronic systems are designed to operate in a range, so 4 or 4.7 amps probably doesn’t matter, and certainly 1.4 to 1.6 ohms really doesn’t matter. Doubling the current from 4 to 8 amps does matter.

If you understand what current you ecu is rated for (whatever brand it is) Then you can make an intelligent decision about the coil you choose.
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This helped a lot, thanks!
 
I like the MSD Blaster 2 coil for factory ignition systems.
I usually paint it black to look more factory.
 
So again: What would happen if I put a "no-needing-resistor" coil in while the resistor is still there & connected..? Would the spark be to weak or would something else happen?
 
Moparbaker said:
So again: What would happen if I put a "no-needing-resistor" coil in while the resistor is still there & connected..? Would the spark be to weak or would something else happen?
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Using the ballast in series with a 3 ohm coil would reduce the coil current and thus spark energy, cold and hot, so you'll just end up with a weak spark if you try that.
 
Moparbaker said:
So again: What would happen if I put a "no-needing-resistor" coil in while the resistor is still there & connected..? Would the spark be to weak or would something else happen?
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What are the specs of the coil? Resistance?
 
Moparbaker said:
I'm not throwing away the resistor, but I wonder what would happen if I use one that's supposed to be used without one..?
& by now I also wonder if many has had problems with the round high performance ones but not with the square ones?
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I have had no problems with the round ones, I actually have one on each of my Mopars, please note there are two different part numbers, one for ballast resistor and one without.
 
Mike69cuda said:
Interesting, looks good. I wonder how they get that much voltage with a 60:1 turns ratio?
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Because the flyback voltage at the primary side rises to - several hundred volts peak. Put an oscilloscope at the coil + connection and you will see this.
 
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nm9stheham said:
Because the flyback voltage at the primary side rises to -several hundred volts peak. Put an oscilloscope at the coil - connection where the points or ECU connects, and you will see this.
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Theoretically true, but don’t the ECUs have snubbers that limit the primary voltage peak to a few hundred volts to prevent breakdown of the switching transistor? That would seem to be a limiting factor no matter what coil is used. Seems to me the only way of increasing the peak voltage would be a higher turns ratio or more inductance.

I am always a little skeptical of advertised specs, as they are often derived using “best case” conditions which may not achievable in a normal application.
 
Mike69cuda said:
Theoretically true, but don’t the ECUs have snubbers that limit the primary voltage peak to a few hundred volts to prevent breakdown of the switching transistor? That would seem to be a limiting factor no matter what coil is used. Seems to me the only way of increasing the peak voltage would be a higher turns ratio or more inductance.

I am always a little skeptical of advertised specs, as they are often derived using “best case” conditions which may not achievable in a normal application.
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I've put an o-scope voltage probe on the coil + and measured this. This voltage at coil + is going several hundred volts minus relative to ground [rest of sentence deleted]. I thought I had some pix of this on the 'scope display, but I only got pix of the details after the arc was fired, when the voltages collapse everwhere. (Once the spark arc is established, it's a short on the system, and the voltages drop like a rock.)

-400 volts x 60 = 24000 volts.... And yes, the 60:1 OR the 46,000 volts may be some nominal value or some special conditions... who knows what the marketing dept did with what numbers LOL.
 
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nm9stheham said:
I've put an o-scope voltage probe on the coil - and measured this. This voltage at coil - is going several hundred volts minus relative to ground, so all that is needed for output device protection is a high voltage diode in series with the ECU drive xtr output (not a snubber in shunt/parallel) and it is easy to get a 1000v reverse breakdown diode even 'back in the day' (as I am sure you know). I thought I had some pix of this on the 'scope display, but I only got pix of the details after the arc was fired, when the voltages collapse everwhere. (Once the spark arc is established, it's a short on the system, and the voltages drop like a rock.)

-400 volts x 60 = 24000 volts.... And yes, the 60:1 OR the 46,000 volts may be some nominal value or some special conditions... who knows what the marketing dept did with what numbers LOL.
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Good info. Seems like there are a lot of exaggerated claims about coil performance in the high performance business. I suspect they feel they have plenty of wiggle room since most cant really measure or maybe even understand all the details.
 
Exactly. All you need is enough voltage to break down the fuel-air mixture in the gap and start an arc, with enough stored energy to maintain that arc hot enough for long enough.....but more volts looks good. Canister coils of the typical size are physically limited to how much voltage you can get out and how much magnetic field energy you can store. They are not really all that different versus what they were in 1960.... That is why I'll just get a reliable canister coil for a standard points or ECU systems and leave it at that.

You need to change the coil/coil size and configuration and how the coil charging is managed (CD, MSD, HEI) to move beyond that.
 
BTW.. .one thing I realized is that I did my coil voltage testing (to see that large - voltage excursion) on a points ignition. So I am wrong to make a solid conclusion on the ECU's output protection; the shunt snubber diode across the ECU output is possible. If is has one, then you can put a VM in diode test mode and will see the output just 1 diode drop from the ground (case) with the - lead on the output and the + lead on the case.
 
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And I have to correct one more thing I said wrong: The - several hundred volts appears at the coil + terminal, not the coil -. (I fixed my posts above.) Took me a while to recall that. The condensor keeps the coil - pegged near to 0 volts (ground). Seems counter-intuitive but there are 'laws of physics' reasons for this to happen.
 
Got the coil installed today & found I had to change the wire cuz the one I had had an angled connection that was to short for MSD's deep holi in its neck.
So I kinda wonder if anyone knows why it's such a high neck/deep hole & if it would hurt to take off a piece?
 
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