Coil overheating

[robshepherd]

Hello All,

In a previous post last month I thought I had resolved my intermittent stall issues by replacing my ignition switch. That thread is here:

http://www.moyermarine.com/forums/showthread.php?t=7371

The problem persists, and now it seems that the coil is overheating and causing a shutdown after about 15-20 minutes. Motor runs wonderfully up to this point, then misses a few times, then gets really rough and dies. The coil will be almost too hot to touch after this event.

Right now I can't get it started, though I've got spark at the points -- but the spark from the coil wire when tested on the block appears very, very weak. Yesterday I replaced the coil AND condenser, but may have already damaged them to the point that one or both won't work.

Before I solicit help on the coil issue (and assuming I can somehow get her started again...) I have a couple of basic questions for you all. My goal is to get it started again and see if the coil overheats with the alternator disconnected from the coil, since I think I've ruled most everything else out.

1. How do I check the alternator's voltage output while running?
2. How do I check voltage while cranking?

I do have a multi tester. Just not so good (yet!) with this piece of equipment.

I'm ready for EI, but want to resolve this overheating coil issue before introducing more issues.

Thank you for any help! Kind regards, Rob

[hanleyclifford]

Sounds like you have fried the new coil most likely thru excessive voltage at coil +. The alternator is probably putting out 14 volts+ and if that is being delivered to coil+ the coil won't last long. If you can get the engine started you should immediately check voltage at coil +. If it exceeds 12 volts be prepared to put resistors in front of that terminal to bring that voltage down. Resistors can be found at Radio Shack cheap in 1, 2 and 6 ohm. If possible get a coil with internal resistance of 3 to 4 ohms. The alternator output should not go to coil +, nor the sensing wire

[robshepherd]

Originally Posted by hanleyclifford

Sounds like you have fried the new coil most likely thru excessive voltage at coil +. The alternator is probably putting out 14 volts+ and if that is being delivered to coil+ the coil won't last long. If you can get the engine started you should immediately check voltage at coil +. If it exceeds 12 volts be prepared to put resistors in front of that terminal to bring that voltage down.

Thank you! Two questions for you:

1. If the alternator is putting out more than 12 volts, shouldn't I have it looked at and corrected?

2. How do I check voltage at the coil+ while running? Do I simply put the positive side of the multi tester on the coil+ and ground the multi tester to the battery- ? Apologies for such a basic question!

Regards, Rob

[hanleyclifford]

Originally Posted by robshepherd

Thank you! Two questions for you:

1. If the alternator is putting out more than 12 volts, shouldn't I have it looked at and corrected?

2. How do I check voltage at the coil+ while running? Do I simply put the positive side of the multi tester on the coil+ and ground the multi tester to the battery- ? Apologies for such a basic question!

Regards, Rob

Once the engine is running you can test alternator output voltage by putting ther meter + lead on the output terminal and grounding the negative anywhere on the block where you get a good connection. Alternator voltage of 14.1 to 14.3 is considered ideal by most but that much voltage will fry a coil. You are correct on #2. If you are running alternator output to coil+ that should be changed. Alternator output should go to the main buss bar or batt switch. Try testing voltages around the engine and it's components and you will see that voltage is not uniform throughout the dynamic system.

[romantic comedy]

Rob, alternators charge at about 14.3 volts. 12 volts would not charge a battery to full. A fully charged battery should read 12.6. The voltage to the coil (or resister) should be battery voltage.

Yes you measure voltage at the coil the same way all the time. One lead to the + side of the coil, and the other lead to ground.

[sastanley]

rob,
even though you may get the engine started again, it is possible the coil is no good. Likely, the heat caused an internal short that comes back to haunt you as the coil heats up and then it shorts out and the engine dies after running for 30-45 minutes. After the coil cools off the engine will often run again for a little while before the cycle repeats.

I highly recommend the "coil input information" thread --> here

It may help to answer some of your questions and then we can answer the remaining ones.

[robshepherd]

Originally Posted by sastanley

I highly recommend the "coil input information" thread --> here

Whoa.... Just spent the morning reading that thread/tome. I can see I need to take some readings today and figure out how much resistance I need to add, as well as get the alternator output off the coil +.

Kind of scratching my head though why I haven't had these kind of problems over the past few years with this boat. If anything we motor less than we used to.

I will be back with questions I'm sure. I also need to research how to wire alt. output to my 3 position battery selector. It's not obvious to me.

Thank you for the input! Regards, Rob

[sastanley]

Rob, There are a couple different ways to wire the charging circuit.

The simplest is to run a sufficient gauge wire (I think my boat had #8 for 35amp alt., but bigger is always better) from the output post on the alt. to the big terminal on the starter. The other end of that big cable should be connected to the common post on the battery switch. This will charge whichever battery you have selected on the switch.

One caution..when charging in "ALL" or "BOTH", a bad battery can suck the juice out of the other good battery, so I generally do not recommend that you run in that configuration..I would charge one battery at a time..if you set the throttle all the way to idle the alt. usually isn't putting out any charging amps and it is safe to shift between batteries but NEVER EVER thru "OFF", or you will blow the diodes on the alternator...

If you added in isolators or electronic charge controllers, etc. things would be connected differently, so we'll leave those out for now.

[robshepherd]

Boy, what a learning experience. I want to write up what I learned because it seems possible that my coil was overheating for a reason that was not mentioned in the 12-page thread on "coil input".

A couple of "bookkeeping" items first. What I thought was a coil output wire on the + terminal of my coil was actually the exciter wire. Ignorance is bliss... I learned this because I took my alternator in for a bench test. It's generating 14 to 14.1 volts, and the gent even checked the amperage draw on the exciter wire when I explained what I was working on. That wire is drawing 0.1 amps from the coil. He gave my alternator a clean bill of health.

After frying a brand new coil with 15 minutes of run time, and also after reading the coil input thread, I purchased another coil with the intent of getting the motor started so I could take the appropriate measurements so I could determine the size of additional resistor to add. I expected the motor to fire immediately with the new coil, but she didn't. Back to checking for spark, etc. All good in the primary ignition, but I could not get a spark from the coil wire to the block, when the day before I could. After much head scratching I finally noticed that the end of the coil wire was charred black. I thought "ah ha!", and immediately tried the test by substituting a spark plug wire for the apparently bad coil wire. HOLY SPARK from the coil, and now I know that the spark I was previously observing was very, very anemic. Again, ignorance is bliss. I fashioned a new coil wire from extra length of a plug wire, put it all together and she fired immediately and ran very smoothly. I should also note that I decreased the points gap from .019 to .017.

Is it possible that I had a damaged, or slowly failing wire between the center of my coil and center of distributor? Could this be the cause of my coil overheating and failure? I didn't suspect this because the wire set is a good one and only 1 year old. Before replacing this wire the motor seemed to run "fair", but now it's running perfectly. No occasional misses, AND it has a LOT more power. I can only estimate, but I would say 40% or more power than previously. It's dramatic.

Ok. The MEASUREMENTS

3 ohm internally resisted coil
Coil voltage w/ key in on pos: 12V at coil +
Coil voltage at cruise RPM: 14V at coil +
This yields a 4.66 amp system at cruise--higher than recommended, it seems

THEN

3 ohm int. resisted coil, with .85 ohm resistor ahead of coil + (multi meter indicates 1 ohm of resistance here)
Coil voltage w/ key in on pos: 9V at coil +
Coil voltage at cruise RPM: 12V at coil +
This yields a 3 amp system at cruise, nicely below the 4 amp maximum

So, with all this being said, and the motor running perfectly for a couple of 45-minute sessions, the coil is still VERY hot to the touch. I don't have a heat gun like some members, so I can't provide better data.

Would it be worth trying more resistance ahead of coil + now, or wait for a while to see how the coil fares? Any thoughts?

Thank you for taking the time to read this, and I look forward to comments!

Regards, Rob

[ndutton]

Nice progress.

I'd like to see some heat measurements before we get all excited. Please check out Harbor Freight Tools and pick up an infrared thermometer.
http://www.harborfreight.com/automot...ing-60725.html

I have a theory about that coil wire and its relationship to the subsequent overheating coil but it's entirely speculative, not worthy of this forum.

[hanleyclifford]

If you are cranking at 9 volts and the engine starts you are about as low as can be achieved and still start the engine. Your cruising voltage of 12 volts does leave some room for additional resistance. However, if you do this you may get cranking voltage below 9 volts and not be able to start. The solution may be an override or bypass circuit via the "R" terminal on the starter which is only energized when the key is all the way over to "start". A coil that is too hot to touch does not augur well for the long term if you plan on cruising.

[robshepherd]

Originally Posted by ndutton

Nice progress.

I'd like to see some heat measurements before we get all excited. Please check out Harbor Freight Tools and pick up an infrared thermometer.

Oh boy... but I kind of knew this would be coming. I'll pick up a thermometer. After I'm done with the coil I suppose I could use it to calibrate the oven temp dial to the actual oven temperature. Haha.

I notice that my coil bracket is metal, and attached to the block. That HAS to transmit heat from the block to the coil through the bracket. If it's a problem now, why wasn't it (presumably) over the past 40 years?

I think that I'd like to try moving the coil to an alternate position away from the block and give it the "touch test" tomorrow. It was on the list for today, but the weather was so darn nice we just HAD to get out for a bit! Picture below with Yuki at the helm and the tall ship Lady Washington in the background. They got into irons shortly after this picture!

[robshepherd]

Originally Posted by hanleyclifford

If you are cranking at 9 volts and the engine starts you are about as low as can be achieved and still start the engine.

Thank you. The only measurement I don't have is voltage at the coil + while cranking. My 9v measurement is just with the key in "on" pos, but engine not running nor cranking.

I can get some help tomorrow by using a "cranker" (friend) and "measurer" (me).

If I understand correctly, the measured voltage should be higher when cranking than it is with key in "on" pos. -Rob

________________________________________________

Ok. Misunderstanding on my part. I read the following by Hanley and missed the whole bypass concept. Yes, it makes intuitive sense that voltage should be lower while the starter is doing its job.

"Kelly - Sometimes, especially in cold weather, engines can have trouble starting because cranking voltage can be as low as 9 or 10 volts. If ignition voltage is being further reduced by resistors ahead of the coil it is possible that insufficient voltage will be available to fire the coil. The remedy? Bypass the coil resistor during the cranking cycle by running a wire from solenoid "R" which is activated only when cranking. Once the key (or button) is released "R" goes dead and the coil must draw thru the resistors."

[robshepherd]

Guys,

It occurs to me that my voltage readings may not be as good as they could be. I'm using an older analog multimeter--the type where you select a range (ex X1, X25, X100), and as such, it's not easy to get a perfectly accurate reading due to the shared scales for the different ranges.

Is this important? It seems like it probably is since the percentage difference between these small numbers (before adding resistance and after) can be rather large.

Would I be better served by a digital unit? I really love analog stuff. Just a disclaimer there...

Thanks, Rob

[hanleyclifford]

I liked analog cell phones.....but seriously, you need a good digital meter to do this exercise properly.

[hanleyclifford]

If you are only getting 9 volts on a meter, key "on" but not cranking, something is amiss.

[robshepherd]

Originally Posted by hanleyclifford

If you are only getting 9 volts on a meter, key "on" but not cranking, something is amiss.

OK. Thanks for the input. Give me a few days and I'll get a proper/more accurate meter and report results!

Thank you kindly. -Rob

[romantic comedy]

This coil voltage question has me fascinated.

Hopefully I will get around to some experiments soon. Until then, let me share this.

Yesturday, I opened a spare coil that I took out of the boat, because I dont need to carry 3 of them.

It is a Ford Motorcraft part # DG-5 says ford 1960-74

I dont know the exact age of the coil, but the package has a REV 3/89 on it, so I know it is at least that young.

The marking on the coil are as follows:

E8TF-12029-BA
6/12 VOLTS MOTORCRAFT 9JA

FOR 12 VOLTS
USE WITH EXTERNAL RESISTOR
MADE IN USA


What does all this mean? Does this mean that this coil can be run on 6 volts. And that it should be run on 6 volts?

I played with a lot of Volkswagens, and VW dune buggies. Some were 12 volts and some were 6 volts. As far as i could tell, they all used the same coil. We used to just use whatever one was handy, with no concern about the voltage. I admit that i was barely a teen back then, so I did not know as much as I think I do now.

I remember the old timers saying that coils worked on 6 volts. They would point out the resistor on a car, and say that it reduced the voltage to 6 volts. No one had a multi meter, so who knows what the voltage was. I do know that the coils ran on cars and boats.

Anyone remember the Capacitor Discharge Ignitions? The new ignitions are much different, and many fore on the build up of the field, so saturation is not an issue. Neither is dwell, or current thru the primary.

My guess is that these coils are running on way too much current, but have been built tough, so they last. For instance the coil on my engine, with points, is the origainal. It runs hot to the touch, but still keeps going. I have been waiting for it to fail, but no luck.

The question is, what is the ideal voltage for it to receive, and how much current is ideal. Of course they are related.

My guess is that our coils would run fine on 6 volts. This is what I would like to bench test. I plan in hooking up a coil to a VW distributor, hooked to a drill to spin it. Then see if i can play with the voltage, to see how it effects spark.

[robshepherd]

Today I purchased a digital multi tester, and rented an IR heat sensor. Before I share results, I also wanted to mention that when I'd hear my alternator "kick on" periodically while motoring in the slip I was able to measure alt. output. 18.1 volts!!! At that time I could measure 16.4 V at coil +. When the alt would shut down its output was 14.5 V, and I could measure 13.6 at coil +. My tech at the electric shop could not duplicate this with a bench test today, even with a load tester in the mix. He had a used motorola 55 amp on the shelf (I had a 35) and let me install it for test purposes. It had normal output very close to 14 V. I bought it from him for $50. Now that issue is solved.

OK, on to the data, again with my 1 ohm resistor ahead of the coil. 10.12 V at coil + with key "on". 12.82 V at coil + while running. Without presenting all of the temp data, I can tell you that over 45 minutes of motoring in the slip coil temp went from 78 degrees to 119. In the last 10 minutes readings were similar, so I'd call that a plateau. Temps were taken at 2-minute intervals and went up pretty linear fashion.

That 119 was quite hot to the touch though, and everyone I talk to says "it should only get warm". Hmmm.

So I replaced the 1 ohm resistor with a 2 ohm resistor ahead of the coil. That gives me 8.45 V at coil + with key "on". 11.70 V at coil + while running.

I ran the motor again for 30 minutes and the coil temp seemed to plateau around 112 degrees. Still quite hot to the touch, but a bit better than the earlier test. With the additional resistance the motor started just as easy as before.

Now these numbers certainly get me WELL below the 4 amp maximum discussed in the coil input thread. Starting is fine, and she runs like a top.

My question.... Are these coil temps still too high? What do you all think?

I should also mention that for these tests I unmounted the coil and set it on a piece of wood so as not to conduct heat from the block. Oh, and one last thing. I bought a new battery and am conducting these tests with a single known good cell. I've know that one bat. in my 2-bank system was a little "punky", so I wanted to rule that out... especially with the excessive voltage coming off the alt.

Thank you for your consideration! Regards, Rob

[hanleyclifford]

You are definitely on the right track but the first thing you need to do is get that alternator voltage under control not to exceed 14.3 volts. Sounds like you have no regulator. Do whatever it takes; only then will you be able to determine what resistors you need.

[ndutton]

18.1V?? No wonder.

The new temps sound a little on the high side to me but just a little. You're in the ball park. Here is a graph of my coil temps @ 14.7V alternator output before and after the addition of a resistor (0.885Ω) and a spot check after taming down the alternator output to 14V (with resistor).

One question though: is this the same coil that was subjected to 18.1V? If yes I wouldn't trust it.

[robshepherd]

Originally Posted by hanleyclifford

You are definitely on the right track but the first thing you need to do is get that alternator voltage under control not to exceed 14.3 volts. Sounds like you have no regulator. Do whatever it takes; only then will you be able to determine what resistors you need.

Thanks, guys. Hanley, indeed. The "new" 55amp alt has output below 14.3, AND I never hear the motor change pitch or slightly bog down when the alt kicks on and off.

Originally Posted by ndutton

18.1V?? No wonder.

The new temps sound a little on the high side to me but just a little. You're in the ball park.
One question though: is this the same coil that was subjected to 18.1V? If yes I wouldn't trust it.

Neil, yes, this coil was subject to the higher voltage of the faulty alternator. Agreed, I don't trust it. That said do you think that it may be overheating because it was damaged? I am going to replace it, but thought I would do so after I get the temps down. Maybe the coil temps WON'T come down if this coil has already been damaged. Again though, the motor does not miss a beat, and it certainly did before as the coil temp came up, and ultimately stalled out when coil got hot.

What temps are you getting now with your coil? Steady 95-ish? My alternator output now runs between 13.61 and 13.78. Have not seen it hit 14V yet.

Thanks, Rob

[ndutton]

Originally Posted by robshepherd

That said do you think that it may be overheating because it was damaged?

Indeed I do. It would be very interesting to replace the coil, measure again and report the difference if any.

Originally Posted by robshepherd

What temps are you getting now with your coil?

Can't say with certainty. I haven't measured it beyond 20 minutes from cold start. The measurements presented were taken to determine a trend and once the trend was established I was satisfied. No need to look further.

[robshepherd]

Originally Posted by ndutton

Indeed I do. It would be very interesting to replace the coil, measure again and report the difference if any.

Ok. Very interesting. I'll pick up a new coil in the morning. As previously mentioned, when that old alt would go into is 18.1V rage, the Voltage measured at the coil + was 16.4.

Here's a thought. Knowing that the P.O. didn't have these issues in 25 or so years of ownership, it's possible that the alternator recently went haywire and introduced these problems, AND that the new alternator with its correct output voltage in concert with a brand new good coil will solve these issues -- regardless of the coil heat measurement. By that I mean that I've never checked coil temp when I was previously able to motor for a duration -- and I have motored for a 4 hour stretch a couple of times over the past 4 years of ownership. Maybe the coil was in the 110 - 120 degree range and did fine with normal alternator output.

I do understand and respect the calculations to get below a 4 amp system though, and I'm well below that with my new resistor.

I feel like the only way I'll really know for sure is to replace the coil and take my resistor and new alternator for a 4-5 hour motor. Terribly boring. Does anybody want to go for a boat ride?

Best, Rob

[ndutton]

Originally Posted by robshepherd

. . . . when that old alt would go into is 18.1V rage . . .

I take it that was a typo but I like the description better than what I think you meant to type.

Here's a thought. Knowing that the P.O. didn't have these issues in 25 or so years of ownership, it's possible that the alternator recently went haywire and introduced these problems,

These things seldom improve with age.

AND that the new alternator with its correct output voltage in concert with a brand new good coil will solve these issues -- regardless of the coil heat measurement.

I suspect they will result in a rock solid ignition system that will give you many years of reliable service if you keep an eye on connections and the ignition switch (regularly replaced on Kalina as a routine maintenance item just like an impeller).