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#1
IP: 193.253.220.149
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Coil input information
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?
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Kelly 1964 Cheoy Lee Bermuda Ketch, Wind and Atomic powered Last edited by Kelly; 09-22-2011 at 09:15 AM. |
#2
IP: 107.0.6.242
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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).
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#3
IP: 193.253.220.149
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Quote:
All hands on deck!
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Kelly 1964 Cheoy Lee Bermuda Ketch, Wind and Atomic powered |
#4
IP: 134.39.100.70
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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
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Mark C30 "Kismet" |
#5
IP: 206.125.176.3
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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.
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-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) Last edited by sastanley; 09-22-2011 at 10:14 AM. |
#6
IP: 208.89.140.11
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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 |
The Following User Says Thank You to smosher For This Useful Post: | ||
TimBSmith (12-01-2020) |
#7
IP: 107.0.6.242
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Quote:
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#8
IP: 193.253.220.149
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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.
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Kelly 1964 Cheoy Lee Bermuda Ketch, Wind and Atomic powered |
#9
IP: 199.173.226.236
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See my notes:
Quote:
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#10
IP: 24.152.131.220
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A word of caution
Before we start piling on a bunch of resistance on the input side of the coil we need to consider the output as well. Having a cool running coil that puts out a weak spark is not a solution. Accordingly, not any random resistor will do.
I can speak only to my system and how I intend to approach this new strategy:
Regarding coil spark output, as I recall the standard points type coils were 28K volt. The Pertronix Flamethrower I installed as part of the conversion to electronic ignition is a 40K volt coil so I'm thinking I could tolerate a 30% output reduction and still run as well as when I had the old points ignition and original coil. Dang this is interesting. edit: To repeat, I eventually lowered the target amperage to 3.4 amps for a wider margin of safety.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others Last edited by ndutton; 10-05-2011 at 12:01 AM. |
#11
IP: 173.166.26.241
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This has turned out to be one of the more interesting and informative threads in a while thanks in large part to Neil and Mark and others. Good shot Kelly! Since the coil (automotive type) is designed to run on 9 volts it seems we have a large voltage cushion to work with. I will do the math as recommended by Neil to see where I fit in the equation. 40K volts? Are we headed back to the Drags?
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#12
IP: 206.125.176.3
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Yup....flying down the creek at 2,000 RPM!
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-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) |
#13
IP: 24.152.131.220
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Quote:
I think but as yet cannot prove a big part of what is aggravating our coils is the dwell common in electronic ignition. What's our A-4 specified dwell, 31 degrees? Well, my Pertronix measured at 62 degrees and there ain't nuthin' I can do about it. I can't see any other difference between the two (points and EI) but this difference is significant.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#14
IP: 75.68.130.228
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More dwell means more amps is flowing through the coil, generating more heat.
If we knew the minimum amps needed to create the spark needed then we can calculate the total resistance needed to stay below the 4 amps The other solution is maybe there's another coil that can take the higher amps Steve Last edited by smosher; 09-23-2011 at 04:32 PM. |
#15
IP: 174.65.54.224
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This is an excerpt from Wikipedia on Resistors:
"The term also refers to an automobile engine component that lowers the supply voltage to the ignition system after the engine has been started. Because cranking the engine causes a very heavy load on the battery, the system voltage can drop quite low during cranking. To allow the engine to start, the ignition system must be designed to operate on this lower voltage. But once cranking is completed, the normal operating voltage is regained; this voltage would overload the ignition system. To avoid this problem, a ballast resistor is inserted in series with the supply voltage feeding the ignition system. Occasionally, this ballast resistor will fail and the classic symptom of this failure is that the engine runs while being cranked (while the resistor is bypassed) but stalls immediately when cranking ceases (and the resistor is re-connected in the circuit)." I thought it was interesting as to "why" our coils are designed to operate at the lower voltage.
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"Jim" S/V "Ahoi" 1967 Islander 29 Harbor Island, San Diego 2/7/67 A4 Engine Block date |
#16
IP: 151.200.21.32
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Jim...my understanding is that coils were originally built at 6 volts & they supplied sufficient voltage for spark plugs to work. the coil technology hasn't kept up with the shift to 12v apparently..This is an entirely layman's answer and I don't really know...just my own personal theory. You'd think a slight change in the number of wraps on one side or the other of the coil would fix the issue.
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-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) |
#17
IP: 174.94.23.187
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Quote:
Actually...it does sort of remind me of a drag race Hanley and Shawn. You know that part of the race I mean Hanley - where you look on one side and the guardrails are flashing by at light speed...and then you look at your closely matched opponent and it seems he is gaining/losing on you by a snails pace. I think they call it a paradox...or something like that! |
#18
IP: 50.104.123.38
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Hot Coil
Thanks much Maurice for pointing this out. I now remember reading this FAQ sometime ago. I've been through all the major systems on my A4(Tartan 30) and it is running extremely well. Smooth idling, easy starting, steady 160 deg temp. 115 compression. On a recent 100 mi trip, had to motor part way and got about 0.55 gal per hour at 5.25 kt. To keep it that way I try to keep up on small improvements such as external ballast resistor if making system more fail safe. With 4 ohm coil, seems the safety factor is already built in. This thread has provided a great learning experience.
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#19
IP: 76.247.170.139
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Boy am I glad I don't have any coil issues.
dvd |
#20
IP: 71.181.37.6
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One item arises my curiosity. No one has mentioned the reactance, or AC
resistance of the coil, and what part this will play in the load and power dissipation. inductive reactance = xL =2 pi times f or frequeny times L Inductance of the coil . Or xL = 2 (3.14 ) f L As RPM goes up, the AC resistance (reactance) goes up and dissipation should therefore go down. Just some thoughts Regards |
#21
IP: 199.173.226.236
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I think I did mention that Ohm's law is an approximation at best for what is really an inductive AC circuit. That said, a lot of empirical evidence and testing went into these calculations and the resistors seem to do the trick. I also decided thanks to this thread the next EI system I get will be CD and not use the coil to store energy.
Quote:
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#22
IP: 96.48.9.106
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Confused on Coil
I have an A4 installed in a 27" C&C Sailboat. The engine has consitantly run for hours without problems until last week when it began to run rough and then died. I was unable to restart.
I suspected it was a coil problem and began research on this site which has provided some great info however I am now confused. The engine has an electronics ignition package and I assumed from the info here that the coil would have a ballast resistor or an internal resistance type coil. I removed the old coil #407, manufacturer unknown, other labeling unreadlable except the words "use ...R...", however could not locate any resistors in the circuit. I measured the primary coil resistance at 3.9 ohms but no sure if this would be accurate on a failed coil. I am not sure I can find a replacement coil based just on the part number. Will I damage anything if I replace the unit with a new coil with internal resistor or should I replace with a normal external resistor type coil. Any help would be greatly appreciated. |
#23
IP: 98.82.114.31
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egmonster,
some of us are using both an internally resisted coil AND and external inline resistor to assist the internal ballast coil...edit- what the in-line resistor is really doing is reducing the input voltage to the coil to hopefully keep it from burning up. What I think is most important is the input voltage the coil is seeing..This is measured on the (+) on the coil post, and the ground on your meter to a good ground like the engine block (the (-) on the coil is NOT ground.) - this needs to be checked while the engine is running, and while the alternator is charging (i.e., normal cruise RPM) Then you can use Neil's calculator somewhere in this thread to determine if you think you need an external resistor. 3.9 Ω is pretty good, and higher internal resistance than most. But, if your input voltage to the coil is too high, it may not be enough to keep from frying the coil. Hope that helps clear the muddy water a bit..I think we need more info from your set up for further diagnosis. Just for a reference point..I have a 3.3Ω internally resisted coil, and a 1.63Ω external resistor in-line in front of the coil (if my memory serves me..) This gives me somewhere in the 10v range of input voltage to the coil.
__________________
-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) Last edited by sastanley; 07-04-2013 at 05:30 PM. |
#24
IP: 67.235.27.130
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Quote:
A really simple answer would be to buy the coil sold on this very site by our sponsor. It already has the proper resistance. No fussing with an external resistor. Just a straight R&R and you're done! Give Ken a call (610.421.4436) in parts and he'll get you all set up.
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-Jerry 'Lone Ranger' 1978 RANGER 30 |
#25
IP: 71.178.85.108
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Jerry..of course you are correct. I think the coil sold by Moyer is over 4 ohms of internal resistance.
__________________
-Shawn "Holiday" - '89 Alura 35 #109 "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!) |
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