Coil input information

[ndutton]

Reference the bottom picture in post #78
I took all my temp readings with the laser centered on the Flamethrower label.

[jpian0923]

New MMI catalogue item, "Dutton" coil resistor and mounting bracket!

With shipping and handling: $Priceless

Sweet looking Neil. Thanks.

[Kelly]

Coil+ vs. RPM graph

Oooooh, graphs!

Here's a go with my data. Sadly, I don't have temperature data.

In parentheses I've calculated maximum amperage according to the formulas in this thread.

My two resistors (0.22ohm x 2) are on the small side as I would like the maximum amperage to be a bit lower. In searching for a local solution, I struck out in the French auto parts stores, electric generator repair shop etc. and was forced to try electronic components. They look undersized to me and a bit fragile for my application...but at least I'm seeing the effects of added resistance before ordering a resistor from the U.S.

[hanleyclifford]

Kelly - Your numbers are still a bit high even with the small resistors. If you are having trouble finding suitable resistors you can substitute 12 volt light bulbs. For ignition I'm guessing two 10 watt bulbs in parallel might give the right voltage. Better yet, order stock # 271-131 from Radio Shack (package of two, 1 ohm wirewound resistors).

[Kelly]

Hanley,

Hmmmm...thanks for the reference but I'm puzzled here. Shouldn't we be concerned by Watts in our application?

When I look at the Radio-Shack product I see they label it as "10W" but it seems to be clearly marked with "2W" on the product picture. Which is true? And in our application, are we not likely to see values of near 50W (Volts x Amps = Watts; 12V * 4A = 48W) Feel free to correct me if I'm way off base here.

The components I found locally are rated for 50W.

Anyone want to jump in here to help clear things up??

[Dave Neptune]

Wow!

You guys amaze me with all the info you have compiled here, what a wealth of knowledge.
I think it may be time for a pole of sorts. There have to be more than a few like me who have had absolutely no trouble with the electronic ignition or the 'flame thrower" coils. It is obvious that some are having trouble and I just don't understand how it is problematic for so many.
Perhaps a pole for both types and whether or not you are having trouble with your coils.
I do have the Indigo and have used it for about 7~8 years now I think with absolutely no trouble. I have installed many pertronic units in dune buggies and had almost no trouble with them and seldom hear of anyone having trouble either. Is this problem a unit problem or a common issue found in OLD boats? This leads me to think wiring may be weak.
There have to be many othere also having no trouble~~what say ya'?

Heading out for Buccaneer Days at the Isthmus back tuesday.

Dave Neptune

[ndutton]

Kelly,
You're in the neighborhood of 60 watts (rounded up) on the system so you'd best select a resistor capable of handling it.

Dave,
I have a response but late for work so I can't get into it now in any detail. The Cliff Notes version is wiring system condition and voltage drop are huge contributors and vary boat to boat. Shawn's the recent poster child for this one.

Outta here

[Kelly]

Just for the record, here's what I found locally (but at .22ohms). I could move up to a 100W version but they're not called the same thing: "charge resistor" in a direct translation.

[smosher]

I think what happened is the pertronix design doesn't take into account the change of alternator voltage from 13.5 to 14.2. This is an automotive product we are using in a marine environment.

Steve

[hanleyclifford]

Kelly - Somebody put the wrong picture out. Here is what comes out of the package.

[joe_db]

Things to consider:

1. Cars routinely run over 14 volts. My BMW is about 14.4 for one example.
2. My original A4 coil lasted from 1973 to about 1989 and we ran the engine thousands of hours in that time.

I have wondered if maybe since these types of ignition coils are no longer used in new cars if they are still as good as they used to be. Maybe production has shifted to second or third tier manufacturers and they just can't hold up like they used to. I am surprised if a Pertronix coil is being killed by a Pertronix ignition!

I also recall being told I was nuts to get rid of my Indigo electronic ignition, but I got tired of having my wife make me show her a replacement coil before we left the dock. She knew we'd need it! The last straw for the Indigo was when the coil died headed towards a closed bridge with 15 knots of wind and 2 knots of current on our stern

[hanleyclifford]

I also recall being told I was nuts to get rid of my Indigo electronic ignition, but I got tired of having my wife make me show her a replacement coil before we left the dock. She knew we'd need it! The last straw for the Indigo was when the coil died headed towards a closed bridge with 15 knots of wind and 2 knots of current on our stern

I can relate - I have learned to have anchor at the ready when approaching bridges. Can be a scary experience.

[smosher]

Same here on the anchoring. mine is the Agawam River and the engine died going from idle to power. Later found out I have used a 1/4" barb instead of 5/16 and the pump doesn't like air in the system.

Steve

[sastanley]

A quick, fun & easy excursion (I hope)

So...tomorrow, off we go...and take powerboat friends as guests....I am gonna put my 1.82 ohm resistor on the 1.5 ohm coil & the 1.2 ohm resistor on the 3.0 ohm coil (nominal readings, actual a little higher) for testing & field reliability purposes. The male half of our guest(s) is a retired Air Force pilot...he'll love to be tinkering with the motor while the ladies are on deck.

[ndutton]

Things we've learned along the way

During this process I've learned or realized a few basic facts as they pertain to coil heat.

Fact 1
Energy stored by the coil heats it up. The more energy or the longer it's in the coil, the more heat is produced and regardless of age, brand, configuration or resistance it can heat itself to the point of destruction. To prove this, what temperature is the coil when the engine has not been run for a week? See, no energy = no heat. At the other extreme, try turning on your ignition without starting your engine and let it sit that way for a couple of days. You know the outcome, it will cook off. Therefore we need to find the sweet spot between the amount of energy stored and how long it's held in the coil.

Fact 2
The energy is held in our coils for a looong time because our engine is only 4 cylinders and it runs at very low RPM. This means fewer coil discharges (dumping stored energy from the coil) per minute compared to other engines.

An eight cylinder engine running at 2000 RPM discharges it's coil twice as much as a 4 cylinder engine at the same RPM. This means our coil is holding a charge twice as long. Comparing a 4 cylinder automotive engine running at 3000 RPM to our engine cruising along at 1800 RPM and again, we're holding charge 2/3 longer. And remember, the longer the charge is held by the coil, the hotter it gets.

Fact 3
Electronic ignition provides around twice the dwell than specified for our engine. In terms of what the coil receives, dwell is the amount of time energy is being delivered so our coil is getting far more energy with electronic ignition than with points. More heat again.

Fact 4
Resistance in the coil circuit is there specifically to balance the charge/discharge/heat dynamic. If it weren't, all coils would be the same. Since we are charging the coil for a longer time and discharging the energy at a slower rate, we need to reduce the charge going in but only to a point. Too much reduction and the coil won't function and the engine won't run (thanks Tom, great testing).

Fact 5
Pertronix, the manufacturer of most of our electronic ignition systems, has provided us with a recommended maximum ignition circuit parameter of 4 amps. I want to emphasize their recommendation is in amps, not volts and is a maximum, i.e., not to exceed.

Fact 6
Volts = current times resistance, V=IR. If current (I) is fixed at 4 amps by design, higher voltage requires higher resistance to maintain the balance. Lower voltage requires less resistance. See how this last statement pertains to the next fact.

Fact 7
Our boats are aging and many if not most have electrical wiring, connections and decades of repairs in varying stages of decay. The result of this decay is voltage drop (it doesn't get higher). Other factors affecting voltage drop are at play too like wire gauge and circuit length. As a result, no two of our boats are the same in terms of voltage applied to the coil circuit.

Example for Fact 7 or why our coil has run fine for years
Let's say your ignition wiring is deteriorated and/or Heaven forbid you have a Catalina 30 with 2 corroded rubber trailer plugs in the circuit all of which imparts enough voltage drop to reduce your 14VDC alternator output to deliver 11.3VDC to your 3 ohm coil. Using V=IR, V= 11.3, R=3 so the current (I) = 3.8 amps, well within the recommended maximum of 4 amps. Life is good.

Then one day you can't stand looking at all the spaghetti any longer. Perhaps you've been inspired by Msauntry's or Rust's or that PITA ndutton's pics and decide the time has come to clean the mess up. So you rip out the old and install all new wiring using the proper gauge, new corrosion free and tight terminations and no more butt splice repairs everywhere. There, she looks great and functions much better. So much better that the voltage drop is now reduced to a point where you're delivering 13.2VDC to your coil, the same 3 ohm coil that has worked fine for years.

Again, V=IR, V=13.2, R=3 so the current (I) is now 4.4 amps and there's trouble in your future.

Okay, I've blabbed long enough. Hope all this helps.