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Old 09-05-2020, 06:52 AM   #21
koates
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Default Re: over heated coil

By the way you will need a good quality multi meter. Elcheapo ones tend to jump around all over the place on petrol engine electrics ,as in your voltage spiking readings. I mostly use an older analog automotove test set when working on old cars. Regards, Kevin.
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Old 09-05-2020, 10:44 AM   #22
GB SISSON
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Default Re: over heated coil

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Instead of messing around till the cows come home you need to measure the current draw (AMPS) the coil primary is drawing with the engine running. To do this set your multi meter to DC AMPS scale which on most meters with this feature is 10 amps and insert your test leads into the common and amps sockets. Remove either of the coil primary wires and connect your meter in line between the coil terminal and the removed wire. With engine running you should have something like 3 or 4 amps draw reading. It will read a bit lower with higher revs. When you have done that report back. Regards, Kevin.
When you say 'either primary wire' does that mean either the one from the ignition circuit or the one from the coil to the distributor? I would have thought they'd be different after passing through the coil. I could get a multitester at Napa and give it a try. Then I guess I'm supposed to check the ohms across the coil too. I will surely have questions once I get the meter. Thanks
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Old 09-05-2020, 07:10 PM   #23
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Default Re: over heated coil

The amps current draw will be the same on either primary wire. And YES you do need to measure the ohms primary resistance on any coil you choose to use. Depending on the coil resistance and the in line coil ballast resistor if used, then these two components dictate how many amps are flowing in the coil circuit. Too many amps flowing equals a HOT COIL. Regards, Kevin.
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Old 09-06-2020, 11:46 AM   #24
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Default Re: over heated coil

I would use the wire terminal that comes from the ballast resistor after the ignition switch to check the amps just to insure a good result every time. Kevin is correct about either wire but I don't consider them both to be primary. One side is the breaker side after the primary and the other is power in to the primary after the ignition switch. This way folks don't get confused. The main thing is to measure the current draw so as long as it gets done, that's what matters.

Just to add: One terminal of a coil is attached to both the primary and the secondary where the other terminal is attached only to the primary. This has an affect on polarity of the coil and is what makes them different.

Last edited by rotorwrench; 09-06-2020 at 11:55 AM.
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Old 09-07-2020, 01:47 PM   #25
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Default Re: over heated coil

I borrowed a meter from a friend. So at the coil wire at the ignition side I'm to check how many amps are passing through, not the voltage, correct? I have two bosch blue coils. The one sitting on the bench shows 4 ohms across the terminals. The one in the woodie shows 3 ohms. I am not running a resistor and am 12v neg ground.
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Old 09-07-2020, 06:04 PM   #26
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Took the measurement on my 49 Ford and it read 11/2 Amps and not the 3to4 Amps as stated in the prior posts. What does that indicate? Positive Ground System with original coil and distributor. Thanks! Stay safe.
Bob
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Old 09-07-2020, 06:38 PM   #27
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Old 09-07-2020, 07:37 PM   #28
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"Took the measurement on my 49 Ford and it read 11/2 Amps and not the 3to4 Amps as stated in the prior posts. What does that indicate? Positive Ground System with original coil and distributor. Thanks! "

6v or 12v doesn't make a difference with the amperage you are wanting at the points. It is controlled by the total resistance in the circuit. With 6v that is ~1.5 ohms and with 12v it is ~3.0 ohms. I just don't have the experience with the original Ford coils to provided an intelligent answer, but I would presume you are wanting the same current flow and the same amperage at the points.

What ballast resistor are you using?

Last edited by JSeery; 09-07-2020 at 08:01 PM.
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Old 09-07-2020, 07:43 PM   #29
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Took the measurement on my 49 Ford and it read 11/2 Amps and not the 3to4 Amps as stated in the prior posts. What does that indicate? Positive Ground System with original coil and distributor. Thanks! Stay safe.
Bob
teltruck, obviously by now most here will know I am certainly no electrical guru. but I think since it has the resistor and is six v, that is the correct reading for your vehicle.
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Old 09-07-2020, 10:44 PM   #30
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Default Re: over heated coil

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Originally Posted by Teltruck View Post
Took the measurement on my 49 Ford and it read 11/2 Amps and not the 3to4 Amps as stated in the prior posts. What does that indicate? Positive Ground System with original coil and distributor. Thanks! Stay safe.
Bob
Your 1 1/2 amps is OK. You should have noted I said that the amps could be a bit lower with revs up. The point here is that the amps are not too high and four amps would be on the high side. The contacts in the distributor act as a regulator of sorts and the faster they open and close with revs up then the lower the amps current draw. Many cars I have checked with engine running are in the 2 amps or so range. If the current draw is above 4 amps then the coil windings will become hotter than desired and the points life will be reduced. Of course if you test the coil current draw with the engine not running and the points are closed the the reading will be higher. Regards, Kevin.
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Old 09-08-2020, 01:44 PM   #31
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Thanks very much for the answers! Lots of great knowledge on this site! Really appreciate it! Stay safe!
Bob
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