Ignition coil question

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Ignition coil question

Post by Truckedup » Tue Apr 09, 2019 11:21 am

Let's say you have two coils....both having the same primary and secondary resistance....Is it possible for one coil to have more spark energy or a longer spark duration?...Or is it just manufacturer hype?
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Re: Ignition coil question

Post by Tuner » Tue Apr 09, 2019 11:42 am

It will be interesting to understand the core influence in the answer to this question. :roll:

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Re: Ignition coil question

Post by Schurkey » Tue Apr 09, 2019 1:04 pm

As with anything involving electrons, "resistance" (R) is important. But so is capacitance (C) and inductance, (L) and nobody is providing specs for C and L. I heard that GM designed the HEI in-cap coil to have a "high" inductance, but I don't have specs or enough background in electronics to know why. [Edit:] Reminded in another post--high inductance limits inrush current when the module grounds the coil circuit
viewtopic.php?f=1&t=56012[/Edit]


As far as "resistance", the DC resistance you measure with an ohmmeter is important. But pulsed DC acts a lot like AC if the pulsing is fast enough. So now we've got to deal with AC "impedance" at least as much--or more--than DC "resistance".

My limited understanding of circuits tells me that the circuit is defined by L, C, R, + noise; but I have no idea how many ways noise affects the ignition. (I don't necessarily mean the RFI noise generated by the ignition, which you hear on a radio or TV--I mean the noise within the system.)

I bet you could have a pair of ignition coils with the same primary and secondary DC resistances, but different C and L, and they'd perform very differently in actual use.

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Re: Ignition coil question

Post by Truckedup » Tue Apr 09, 2019 1:23 pm

Ok...I thinking that the gauge of the wiring windings can have influence even though the ohms is the same ? I have a situation where I would like more spark energy without increasing the current draw due to limitations on a vintage electronic bike ignition...I'm assuming, perhaps incorrectly, that all coils with the same resistance draw the same current...
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Re: Ignition coil question

Post by Walter R. Malik » Tue Apr 09, 2019 3:33 pm

Truckedup wrote:
Tue Apr 09, 2019 11:21 am
Let's say you have two coils....both having the same primary and secondary resistance....Is it possible for one coil to have more spark energy or a longer spark duration?...Or is it just manufacturer hype?
Of course ... actual wire size, (gauge), and length, (turns), can be different and still have the same resistance.

Induction, capacitance and amperage will be different with those changes even though the ohm resistance can remain the same.

Those will allow the same amount of WATTS to pass; (amps times volts).
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Re: Ignition coil question

Post by Geoff2 » Wed Apr 10, 2019 6:43 am

A most important part of the ign coil is the laminated metal core & it's magnetic properties.

Yes, the current produced in the secondary winding & the spark duration varies between coils.

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Re: Ignition coil question

Post by Circlotron » Wed Apr 10, 2019 8:47 am

Truckedup wrote:
Tue Apr 09, 2019 11:21 am
Let's say you have two coils....both having the same primary and secondary resistance....Is it possible for one coil to have more spark energy or a longer spark duration?
Yes.
Provided the iron core doesn't magnetically saturate, the coil with the higher primary inductance will store proportionally more energy for the same amount of amps in the primary. But this greater inductance will also take longer to run up the amps.

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Re: Ignition coil question

Post by modok » Wed Apr 10, 2019 7:55 pm

The resistance is not telling you the whole story. there are other simple tests you can do, to get an idea of the turns ratio and inductance, and of course you can also just test them at making sparks and see what they put out.
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Re: Ignition coil question

Post by Truckedup » Wed Apr 10, 2019 8:37 pm

I make up a crude testing rig from a battery, ignition condenser, jumper wires, coil and spark plug..I keep opening the gap until the spark fails..But this doesn't tell me much about what's going on in a running engine.. The waste spark on the 2 cylinder bike means the coil(s) fire every 360 degrees...That a lot of dwell time compared to single coil V8...
What goes on is this bike has a slight attestation off idle that won't tune out except for using a .035 plug gap instead of the typical .025...But at high speed full load the the ignition gets a bit weak...I moved some stuff around to make room for a pair of full side canister coils...
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Re: Ignition coil question

Post by Schurkey » Wed Apr 10, 2019 9:48 pm

Two coils, two cylinders, waste spark (four stroke)??? Is this a pair of twin-plug cylinder heads? Or is one plug lead on each coil grounded to the head?

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Re: Ignition coil question

Post by Truckedup » Thu Apr 11, 2019 6:36 am

Schurkey wrote:
Wed Apr 10, 2019 9:48 pm
Two coils, two cylinders, waste spark (four stroke)??? Is this a pair of twin-plug cylinder heads? Or is one plug lead on each coil grounded to the head?
Yes two cylinder 4 stroke one plug per cylinder....Two coils wired in series with a combined 3.6 ohms across the primary...This is in lieu of a twin output coil like used on many Japanese bikes and Harley...
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Re: Ignition coil question

Post by Schurkey » Thu Apr 11, 2019 2:09 pm

Truckedup wrote:
Thu Apr 11, 2019 6:36 am
Schurkey wrote:
Wed Apr 10, 2019 9:48 pm
Two coils, two cylinders, waste spark (four stroke)??? Is this a pair of twin-plug cylinder heads? Or is one plug lead on each coil grounded to the head?
Yes two cylinder 4 stroke one plug per cylinder....Two coils wired in series with a combined 3.6 ohms across the primary...This is in lieu of a twin output coil like used on many Japanese bikes and Harley...
Parallel twin with a 360 degree crank?

3.6 ohms through the primary is going to be a low-energy ignition system. Is there a ballast resistor? A ballast resistor would make it even worse. To my way of thinking, this thing is crying out for lower primary resistance to get more current (amperage) flow and more spark energy. What is the amperage capacity of the trigger system? For that matter, what is the trigger system? Points? Points controlling a spark-box? Magnetic pickup and some sort of module? Something else?

What is the ground path from the side electrode/cylinder head back to the coil?

If I was locked-into a single pickup/single trigger with waste spark, I would be looking for an ignition system that could survive a distributorless double-output ignition coil of about half-an-ohm, with no ballast resistor. This puts you in HEI territory, 5+ ampere primary circuit draw, perhaps more. (HEI modules are not always suitable for motorcycle use--they can go wonky due to the low rate of firing impulses during cranking. If you can get the engine running, the module may work OK--but cranking/starting can be an issue. I learned this from folks who have converted 4-cylinder motorcycles using two HEI modules and two waste-spark coils. There's ways around this problem--but it's been so long since I've encountered this that I've lost track of how to rectify it. I think it involves diodes in the wire harness, and it may disable the adaptive dwell circuit in the 4-pin HEI module. I can direct you to more info if you care. (at least, the forum posts were still there last I looked...))

https://www.summitracing.com/parts/ado-d555/overview/
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(I get these coils from the Treasure Yard, they're dirt-cheap and thick on the ground on all sorts of older 4- and 6-cylinder GMs. For all I know, you could adapt the entire coil-driver/ignition module from, let's say, a 4-cylinder application, and just trigger and install one coil. If the ICM will accept your existing trigger, you're good-to-go in terms of amperage load and such.)

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Re: Ignition coil question

Post by Krooser » Thu Apr 11, 2019 4:27 pm

Guys I know use Ford TFI coils right out of the junque yard...seem to work good.
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Re: Ignition coil question

Post by kirkwoodken » Thu Apr 11, 2019 5:06 pm

Quote: I make up a crude testing rig from a battery, ignition condenser, jumper wires, coil and spark plug..I keep opening the gap until the spark fails..But this doesn't tell me much about what's going on in a running engine..Unquote

The problem with this testing method relates to an induction coil's ability to keep raising voltage until a gap is found. If it can't find a gap outside the coil, it will find a gap inside the coil. I once got a 2 1/4" spark from an old Delco coil. Problem was that was the last spark the coil made. Had I known the coil was that good, I would have used it on my engine. Life and learn!
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Re: Ignition coil question

Post by Truckedup » Thu Apr 11, 2019 5:40 pm

Schurkey wrote:
Thu Apr 11, 2019 2:09 pm



3.6 ohms through the primary is going to be a low-energy ignition system. Is there a ballast resistor? A ballast resistor would make it even worse. To my way of thinking, this thing is crying out for lower primary resistance to get more current (amperage) flow and more spark energy. What is the amperage capacity of the trigger system? For that matter, what is the trigger system? Points? Points controlling a spark-box? Magnetic pickup and some sort of module? Something else?

What is the ground path from the side electrode/cylinder head back to the coil?

If I was locked-into a single pickup/single trigger with waste spark, I would be looking for an ignition system that could survive a distributorless double-output ignition coil of about half-an-ohm, with no ballast resistor. This puts you in HEI territory, 5+ ampere primary circuit draw, perhaps more. (HEI modules are not always suitable for motorcycle use--they can go wonky due to the low rate of firing impulses during cranking. If you can get the engine running, the module may work OK--but cranking/starting can be an issue. I learned this from folks who have converted 4-cylinder motorcycles using two HEI modules and two waste-spark coils. There's ways around this problem--but it's been so long since I've encountered this that I've lost track of how to rectify it. I think it involves diodes in the wire harness, and it may disable the adaptive dwell circuit in the 4-pin HEI module. I can direct you to more info if you care. (at least, the forum posts were still there last I looked...))

https://www.summitracing.com/parts/ado-d555/overview/
Image
(I get these coils from the Treasure Yard, they're dirt-cheap and thick on the ground on all sorts of older 4- and 6-cylinder GMs. For all I know, you could adapt the entire coil-driver/ignition module from, let's say, a 4-cylinder application, and just trigger and install one coil. If the ICM will accept your existing trigger, you're good-to-go in terms of amperage load and such.)
Yes parallel or 360 degree twin...No ballast..Magnetic pick up trigger.The engine is bolted directly to the frame ith the battery being grounded to the frame and various electrical stuff. In addition there's a 12 gauge wire from the engine to the battery negative terminal.No electric starter.. ...I did mention the system I use is a vintage Lucas Rita electronic designed in 1975.The main power transistor has been replaced but it's marginal at 10 amps.. ...I use far more modern ignitions on my vintage Triumph race bikes using .6 ohm coils with dwell control. ... The stuff you mention, what's doing the advance curve? The ignition must retard for kick starting the engine and have an advance increase compatible with detonation prone deep hemi chambers...You have to dance with the devil to make these old turds run well...That's the fun part...
Low energy maybe with 3.5 ohms...My modified Ducati 900cc V twin street bike uses the stock ignition... two 3.5 ohm coils, two pick ups, each cylinder has it's own waste spark...with 10-1 compression in a 3.8 inch bore the ignition has no problem firing a .035 gap at 8500 rpm..
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