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Old 07-02-2019, 08:30 PM   #21
richard instness
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Default Re: Cause of hot ignition coil?

Today's update on the coil issue.
I forgot to mention in the first post that this car also has an electronic ignition in place of the points. It was on the car when I purchased it and it has ran well so I left it there.
I am still using the Bosch 12v blue coil with a resistance of 3.3, but today I removed the external inline resister. After a long drive the coil temperature was much lower than before and everything else seems to be as it should. The coil is still slightly warmer than my other model A with modern style points, but I think the temperature now is very acceptable. I am going to monitor it for a while and if things continue to be as they should I think I will call that good.
Thanks to all who replied. A lot of good information.
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Old 07-02-2019, 09:16 PM   #22
noboD
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Default Re: Cause of hot ignition coil?

Doesn't a Bosch blue coil have an internal resistor?
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Old 07-03-2019, 10:23 AM   #23
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Default Re: Cause of hot ignition coil?

Quote:
Currently the amp meter shows a charge of about 10amps while driving.
It sounds like your voltage regulator is set too high.

Quote:
Old coils were filled with pcb’s, lilke a PG&E transformer, not oil
The coils WERE oil filled, but the oil contained PCBs.
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Old 07-03-2019, 03:24 PM   #24
Chuck Sea/Tac
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Default Re: Cause of hot ignition coil?

I took an oil field coil for Model A and cut it open. It has a spacer on the bottom so the windings are immersed in the oil when it’s upside down the spacer is what is in the air. Now if all of them are that way I don’t know I’ve only cut one open.?
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Old 07-03-2019, 03:27 PM   #25
Chuck Sea/Tac
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Default Re: Cause of hot ignition coil?

Correct me if I’m wrong, but I believe coils are made for plus or minus ground. That is, one or the other not both. If you’re running one in the opposite way it was designed, could that cause it to overheat?
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Old 07-04-2019, 08:41 AM   #26
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Originally Posted by Chuck Sea/Tac View Post
Correct me if Iím wrong, but I believe coils are made for plus or minus ground. That is, one or the other not both. If youíre running one in the opposite way it was designed, could that cause it to overheat?
It wouldn't cause it to overheat, but it doesn't give as good a HV spark.
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Old 07-04-2019, 10:12 AM   #27
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Default Re: Cause of hot ignition coil?

Thanks for cutting one open Chuck. Maybe that’s why some survive the upside down position. Was it one sold by one of the Model A vendors? Does anyone know if a Bosch blue coil is built the same way? As Dick pointed out the Bosch coils for a VW are in the down position.
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Old 07-04-2019, 11:23 AM   #28
30 Closed Cab PU
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Default Re: Cause of hot ignition coil?

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Originally Posted by Chuck Sea/Tac View Post
Correct me if I’m wrong, but I believe coils are made for plus or minus ground. That is, one or the other not both. If you’re running one in the opposite way it was designed, could that cause it to overheat?


I do not know if there are different coils for + and - 6V systems. Previously ran across this statement in a string and called a couple of vendors to see if they carried or knew of people that carried different 6V coils, they said they have never heard of this, and carry only one 6v coil.


If you have sources additional info, please post, I would be interested.


Thanks
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Old 07-04-2019, 11:26 PM   #29
Chuck Sea/Tac
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Default Re: Cause of hot ignition coil?

If you look at this diagram, the ground is the side with one end of each winding terminating. So a coil for an opposite grounding system would be labeled backwards. I suppose if you switched the primary, then it would be correct for that system regardless of labeling.
By the way,Bubba of Bubbas ignitions says that once a coil is ran wired wrong, then switched, it wonít put out full voltage because of core magnatism. Iíve never heard that before.
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Old 07-05-2019, 08:24 AM   #30
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Default Re: Cause of hot ignition coil?

Interesting about the full voltage statement. When I checked my 6 v positive ground system using the pencil flair test it was correct. Bought a spark tester that has the movable wire in it that is put in series with the dist./coil lead so you can see where the spark starts degrading. Noted this, and then switched primary connections on the coil, and did see about a 40 percent degrease in the reading. Switched the leads on the coil back to correct and got the same reading as teh 1st correct hookup reading, so did not see a decrease. Perhaps you have to run it incorrectly for a while to get the core magnetism issue.


Not familiar with ignition coil constructions - they have a conductive core the windings are wrapped around? Might be a silly question, but would like to know.
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Old 07-05-2019, 09:30 AM   #31
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Default Re: Cause of hot ignition coil?

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Bubba of Bubbas ignitions says that once a coil is ran wired wrong, then switched, it won’t put out full voltage because of core magnatism.
I doubt that, the core is made of mild steel laminations, and the residual magnetism can easily be reversed, same as a generator.
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