Coil input information

[Kelly]

Just fishing for comments here.

I am in the population of people who have fried multiple coils with minimal use (two that I purchased plus one that was already on the engine when I bought it). I have just recently lined up my ducks by eliminating possibly mis-matched parts in the ignition circuit: new plugs and wires from Moyer Marine, new Pertronix Flamethrower coil (oil-filled; 40,000V; 3.0Ohm) to go with my Pertronix electronic ignition.

I made a few measurements today with my basic digital volt-meter. Positive was taken from the + on the coil and ground was a near-by head nut.

Results:

1)Everything off: 0.25V
2)Ignition switch on: 11.12V
3)Cranking engine: 9.3V
4)Engine started at idle, cold (no alternator): 11.7V
5)Engine idling at 1000RPM w/ alternator excited: fluctuating from 5.4V to 13.5V
6)Engine warm at 1400RPM w/ alternator : settled at 14.04V
7)Engine warm at 800RPM: 13.0V

5, 6 and 7 are with the engine in gear.

I am way over my head here so any comments? Missing information?

[hanleyclifford]

Oddly enough it seems that the members most diligent about ignition systems are the ones burning coils (right, Shawn?). I don't like #6, 14.04 volts but I'm not able to explain exactly why. I still run points and condenser with automotive type (cheapo) coils. Usually I test less than 10 volts at coil+ (no external resistor), BUT, I run my electric raw water pump and fuel pump on the same circuit. I'm afraid this thread could empty the barracks (again).

[Kelly]

Oddly enough it seems that the members most diligent about ignition systems are the ones burning coils (right, Shawn?). I don't like #6, 14.04 volts but I'm not able to explain exactly why. I still run points and condenser with automotive type (cheapo) coils. Usually I test less than 10 volts at coil+ (no external resistor), BUT, I run my electric raw water pump and fuel pump on the same circuit. I'm afraid this thread could empty the barracks (again).

That's a virtual risk I'm willing to take in order to understand why I can't dial-in a consistent performer with my A4.

All hands on deck!

[Mark Millbauer]

From a WEB article on ignition systems:
"The coil is designed to operate on 9 volts. Battery voltage (12 volts) is reduced to 9 volts by the Ballast Resistor. When the ignition switch is in the run position, the coil is powered through the Ballast Resistor feeding it 9 volts; but when the ignition switch is turned to "start", the Ballast Resistor gets by-passed. This feeds full battery voltage to the coil for better starting. The starter motor is drawing battery voltage down to about 10 volts at this time."

We must either run a ballast resistor of the correct resistance for the volts our system is feeding it or, as Moyer states, a coil with internal resistance. It too must have the correct resistance for the voltage our system is trying to shove through it.

The type, operation and condition of the ignition switch is a key component here as well. As is the output of the charging system.


mark

[sastanley]

Yay - coils!

Hi Kelly, Just for grins, can you measure the static resistance of the coil before you turn on the key? How many hours do you have on the new Flamethrower?

My 'dead' Flamethrower was in the 3.3 ohm range (I have to check my notes to confirm) at rest (cold), and 4.2 or 4.3 ohms when it would fail 25 minutes later. However, the voltage at the coil as the engine sputtered to a slow death never faltered from 13.94volts. No real way that I can tell to measure the secondary output voltage while the coil is active...except for a visibly weak spark that wouldn't start the motor again when I cranked it.

I need to measure my new coil after I've run the engine, with the key off, to see if the resistance stays constant or is the same as it was cold..which I think it should. I think the resistance went up and caused the bad coil to fail...or rather, the higher resistance at failure is a symptom of a 'fried' coil...I am purely guessing here that the resistance gets high enough that the coil can no longer produce a reliable secondary spark (to the plugs) and it dies. I would expect a good coil's resistance to stay constant.

[hanleyclifford]

From a WEB article on ignition systems:
"The coil is designed to operate on 9 volts. Battery voltage (12 volts) is reduced to 9 volts by the Ballast Resistor. When the ignition switch is in the run position, the coil is powered through the Ballast Resistor feeding it 9 volts; but when the ignition switch is turned to "start", the Ballast Resistor gets by-passed. This feeds full battery voltage to the coil for better starting. The starter motor is drawing battery voltage down to about 10 volts at this time."

We must either run a ballast resistor of the correct resistance for the volts our system is feeding it or, as Moyer states, a coil with internal resistance. It too must have the correct resistance for the voltage our system is trying to shove through it.

The type, operation and condition of the ignition switch is a key component here as well. As is the output of the charging system.


mark

Thank you, Mark; your post represents the conventional wisdom and still merits our attention.

[Kelly]

Yay- coil comments!

Shawn,

I'll make the measurements the next time I can make it down to the boat- should be tonight or tomorrow at lunch at the latest.

My Flamethrower is less than an hour old. Measured Volts at the coil + seem to reflect yours (13-14V). Taking into account Mark's response, I would like to think that my internal resistance coil is the perfect match for my electronic ignition (both Pertronix). My installation is very basic...I've just "upgraded" to the electronic ignition in the hopes of having fewer parts to adjust.

[smosher]

I don't know what a coil is rated for in watts, but here's the calculations
based upon a 3.3 ohm coil.

14.2 volts / 3.3 ohms = 4 amps

4 x 4 x 3.3 = 61 watts

12 vdc / 3.3 ohms = 3.6 amps

3.6 x 3.6 x 3.3 = 47 watts

61 / 47 = 130 percent

We know heat kills coils and at 14.2 volts the coil has to sink 30% more heat.

To decrease the amps in a 14.2 system to the draw in a 12 volt system you would add a ballast resistor to the coil.

14.2 / 3.6 = 4 ohms - 3.3 coil = .7 ballast.

So to me this means that if we add a ballast resistor we can reduce the heat
in the coil by 30% and still provide the 14.2 to the battery.

knock on wood, as I have an electronic ignition and I have used both a pertronix and an autozone coil, both oil filled and for 5 years I haven't had a problem. My Alt charges at 14.2 volts. The pertronix coil moyer sells is epoxy which is for vibration area's, oil coils have better cooling.

The question is what coil and where are they mounted ?

Steve

[sastanley]

do as I say, not as I do

Kelly, you essentially have the same setup as I had which just failed, however, seems to work just fine for everybody else. To remedy the problem I had this summer of running from storms in 15 minute chunks until the coil would die, I've gone to a redundant coil system: I have a (identical to the recently failed one) 3 ohm oil filled Flamethrower as my backup, and I am currently running a 1.5ohm (Accel brand) oil filled coil with a 1.5 ohm resistor in front of it, as recommended by Pertronix. I figured after burning up the 3 ohm coil, why not?

Full disclosure - I've screwed up my 'testing grounds' too by dialing down the voltage a little bit..Those numbers reported above were in the "as failed" running conditions..I am seeing something in the 10v range at the externally resisted coil now. I'll have to do further testing (sorry, going cruising this weekend!) on the readings of the new 3 ohm coil to compare to my dead 3 ohm coil with the updated voltage settings. So, essentially, I've changed three things...a new externally resisted coil, an internally resisted coil as backup, and the voltage I am sending to the coil.

So much for following my own suggestions for a methodical approach.

[JOHN COOKSON]

I Run Points

But here goes anyway R\E electronic ignitions.

I don't think burned out coils are the problem. They are a symptom of a bigger problem.

To me burned out coils mean the electronic ignition is acting up. Why do some EIs work fine and others fry coils? (as others have noted)

Maybe some dwell readings would be helpful. Dwell with engine (and EI) at idle cold, and dwell with cold engine reved up. Then dwell with engine (and EI ) warmed up at idle and then dwell with a throughly warmed engine (and EI) reved up.

Just an idea. My $0.01 for the day.

TRUE GRIT

[hanleyclifford]

But here goes anyway R\E electronic ignitions.

I don't think burned out coils are the problem. They are a symptom of a bigger problem.

To me burned out coils mean the electronic ignition is acting up. Why do some EIs work fine and others fry coils? (as others have noted)

Maybe some dwell readings would be helpful. Dwell with engine (and EI) at idle cold, and dwell with cold engine reved up. Then dwell with engine (and EI ) warmed up at idle and then dwell with a throughly warmed engine (and EI) reved up.

Just an idea. My $0.01 for the day.

TRUE GRIT

Interesting questions raised here. I would like to see some dwell data from the EI crowd. We know that the EI has greater dwell than the point ignition and that greater dwell imposes a greater heat burden on the coil. The fact that some EI systems work and others don't might be related to actual, effective, cruising voltage at coil+ which can reflect dozens of electrical system differences on our boats. Coil+ is where "the rubber meets the road", so to speak.

[smosher]

The ei does have a larger dwell than the points, larger dwell more heat in the coil.

All comes back to more heat in the coil.

Mine is installed on the engine in the original location. I wonder if someone
has remoted the coil and it had failed.

I think this we though I'll hook up a 1/2 ohm ballast to the 3.3 ohm coil and see if it works.

The primary side resistance is 3 ohms, while the secondary side is in the 1000's of ohms.

[sastanley]

I am guessing my regular run-of-the-mill multi-meter doesn't do dwell.

edit - steve, sorry I missed your post until now. Yes, my failed coil was remotely mounted, as shown in this picture taken earlier this spring. That is actually the dead coil, and the location where it lived the last 26 months since it was new in 2009. My original bracket rusted off, and the mounting bolts are solid in the block, so I just left them there. It would be a bear to remove them to re-mount a coil to the engine.

[JOHN COOKSON]

A Bit More Explicit

My theory is that it is a heat related problem with some EIs that is manifesting itself through the dwell angle.

By proving or disproving this theory hopefully some light will be shed on the final answer to the problem.

TRUE GRIT

[ndutton]

As part of my ongoing testing of another theory I have already measured EI dwell. My Pertronix dwell is 62 degrees and this is pretty much in line with an email exchange I recently had with Hot Spark, another Hall effect electronic ignition manufacturer who specifies a particular unit for the A-4. Theirs is 50 degrees.