Coil input information

[joe_db]

Probably would, but it doesn't do the same thing. A current limiter would vary the overall resistance up and down to keep the current at a set-point. They are made by combining a voltage regulator and a power transistor to keep a voltage drop though a sensing resistor constant. It was more a though-experiment than something I would actually build. It can also be done by using a voltage regulator followed by a ballast resistor set to precisely that voltage.

Wouldn't the ballast resistor be more reliable than a current limit circuit ?

Steve

[sastanley]

Neil, just to throw a monkey wrench in the mix..my failed coil never got hotter than 135 F degrees. - I do not know if it got hotter than that when it wasn't failing.

I'll take some temp readings of the current set up & some more voltage readings for Kelly too. Didn't have time to run the motor yesterday, just a few extra minutes to turn the key on and grab some voltage numbers before heading home to cook dinner.

[ndutton]

Picture time

Unfortunately my most accurate digital tester would not give meaningful voltage readings while the engine was running, they were jumping all over the place. My dumber tester that rounds voltage to the nearest integer works but the readings aren't precise at all. Oh well, here's what I have anyway:

Static unloaded battery voltage = 13.6 VDC
Ignition on, engine not running = 12.5 VDC ahead of the resistor, 10.3 VDC at the coil post

Resistances
coil alone = 3.5 ohms
coil + resistor = 4.3 ohms

Here's the bracket. 3/4" x 3/4" aluminum angle


Bracket and resistor


View from the port side


View from behind

[ndutton]

Neil, just to throw a monkey wrench in the mix..my failed coil never got hotter than 135 F degrees. - I do not know if it got hotter than that when it wasn't failing.

I suspect it did. I'd also suspect the internal damage from previous overheating left it in a condition where all it took was 135 degrees to cause the subsequent failures. 135 is well within Pertronix's published temperature range.

It reminds me of the advice on another thread from the alternator shop who cautioned against alt temps beyond 200F. Damage to the winding insulation was their reasoning.

[hanleyclifford]

Neil - Nice installation! The spiral lead, resistor to coil+ is a nice touch for a little extra resistance. BTW, regarding your digital meter fluctuations--do you have a suppressor in your alternator output circuit? They can cure a lot of fluctuation issues all over the system.

[ndutton]

--do you have a suppressor in your alternator output circuit? They can cure a lot of fluctuation issues all over the system.

Not unless there's one internally that I don't know about. Remember, I have a single wire internally regulated alternator. The only wire attached is a #4 cable to the starter post, less than 6" in length. With a history of trouble free and reliable performance I'm thinking I don't need or want a supplemental suppressor either.

Nice installation!

Thank you. When it comes to boat building and maintenance, a polishing wheel is one of my more essential tools. I was a little embarrassed that I didn't polish the button head resistor bolt before installation too.

[hanleyclifford]

Yes, that button head is a little substandard for you - not quite STRAK. As for suppressors, you might be pleasantly surprised how they help performance of sounders, autopilots, televisions etc. They are nothing but a big capacitor in the output circuit (actually interrupting alt + to batt+); also a big ground cable. As far as I know they can be had in 70 and 150 amp configurations.

[ILikeRust]

I was a little embarrassed that I didn't polish the button head resistor bolt before installation too.

Yeah, I didn't want to point that out and embarrass you, but now that you have - what the hell is up with that? Slacker.

[ndutton]

Re: polishing, presentation is everything. Really though, it's the little things that make a difference. If installing a track on deck, align the slots in the machine screw heads with the length of the track. If countersinking and plugging a piece of teak, try to align the holes. If making a new wood accessory that will be "finished bright", align the grain in the panels vertically even if it results in more offall (waste). It really makes a difference.

Okay, enough of that. Here's a graph of my coil temperature testing.

[smosher]

Its not stabilizing I would expect the temp to at one point level off and remain constant assuming nothing else changes

[ndutton]

I arbitrarily tested for only 30 minutes. As I use the boat I'll keep the temp gun handy. The rate of change (acceleration if you will) approaching the 30 minute mark was markedly different between the two. The no-resistor temp rose 10 degrees over the last 4 minutes while the with-resistor temp rose 2 degrees over the same final time interval. That's a 5:1 difference. Over the final 2 minutes the ratio was 4:1.

I think this implies the resistor setup was closer to reaching it's plateau than the no-resistor setup was. We'll see. I'll post more as I learn more.

As it stands though, I'm a lot more comfortable at somewhere between 18% - 20% less coil heat even if it is at only the 30 minute mark. I'm careful not to suggest conclusions based on extrapolation. All I can say for now is 30 minute's worth.

[thatch]

Another approach

I just returned from the boat after doing some "parallel" tests to Neil's.
To set the stage, I will say, at the outset, that my wiring condition is at the
opposite end of the spectrum from Neil's. Most of my wiring looks to be over 30 years old and has been repaired numerous times. My approach to the tests was to try to find out just how low of a plug voltage an A4 would tolerate before performance would begin to drop. For the "doomsday" test I used an adjustable, ceramic resistor that would allow me to adjust down from my already low (11.6 volt) running coil voltage. For the record, my A4 cold starts very quickly despite this low voltage. After a brief warmup (about 5 minutes) I began adjusting the resistor down gradually and at just under 9 volts she began to stumble. At this voltage performance would certainly be affected and after shutting the engine down completely, it would not start at all, most likely because of the the additional starter induced voltage drop. After these tests, I installed a 2 ohm resistor (similar to Neil's) and despite now having a coil voltage of 10.2 volts, my engine started and ran the same as without the resistor. My coil temps were 120 degrees without a resistor and 105 degrees with the 2 ohm resistor, which seems to fall in line with Neil's findings. What is the reason for all of my testing?, simply to prove that many of us are quite likely "over volting" our ignition systems at the cost of early coil burnouts and shortened point or ignition module life.
Tom

[hanleyclifford]

I just returned from the boat after doing some "parallel" tests to Neil's.
To set the stage, I will say, at the outset, that my wiring condition is at the
opposite end of the spectrum from Neil's. Most of my wiring looks to be over 30 years old and has been repaired numerous times. My approach to the tests was to try to find out just how low of a plug voltage an A4 would tolerate before performance would begin to drop. For the "doomsday" test I used an adjustable, ceramic resistor that would allow me to adjust down from my already low (11.6 volt) running coil voltage. For the record, my A4 cold starts very quickly despite this low voltage. After a brief warmup (about 5 minutes) I began adjusting the resistor down gradually and at just under 9 volts she began to stumble. At this voltage performance would certainly be affected and after shutting the engine down completely, it would not start at all, most likely because of the the additional starter induced voltage drop. After these tests, I installed a 2 ohm resistor (similar to Neil's) and despite now having a coil voltage of 10.2 volts, my engine started and ran the same as without the resistor. My coil temps were 120 degrees without a resistor and 105 degrees with the 2 ohm resistor, which seems to fall in line with Neil's findings. What is the reason for all of my testing?, simply to prove that many of us are quite likely "over volting" our ignition systems at the cost of early coil burnouts and shortened point or ignition module life.
Tom

Hear, Hear.

[sastanley]

Roger...temp gauge in hand the next time i run the engine. My wife loves it when we are motoring somewhere and I have my head in the engine compartment.

[thatch]

On the cool side

Shawn,
I have been taking my coil temp readings on the water pump side of the coil. First, on a Catalina 30, the access door makes taking that reading easy and secondly, the heat coming off of the exhaust has a tendancy to heat the port side of the coil up considerably more than the other side.
Tom