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Old 09-27-2021, 07:02 AM   #1
russcc
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Default Variable coil ballast resistor

Using a Skip re-built, converted to 12V, negative ground !GA coil on the 59 in the roadster. The ballast resistor is a round, adjustable unit. Photo. I am getting 8V at the Ignition side of the coil while the engine is running, and I would like to get down to 3.8 to 4.2 volts to the coil. Anyone know how to change the resistance in this type of resistor ? Thank you.
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Old 09-27-2021, 07:15 AM   #2
corvette8n
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Default Re: Variable coil ballast resistor

Hey Russ, does anything twist or slide, I canít tell from the pictures.
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Old 09-27-2021, 07:42 AM   #3
russcc
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Default Re: Variable coil ballast resistor

I believe you may change the stud position. My mistake, I have 8V at the coil, and would like to get it around 5.5V at the coil, because the coil should drop it to 4.0 volts to the points. Please correct me if I am off base.
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Old 09-27-2021, 10:44 AM   #4
tubman
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Default Re: Variable coil ballast resistor

It think you are right about different stud locations having different resistances. It would be easy to check out if you have a multi-meter (set to ohms).
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Old 09-27-2021, 11:59 AM   #5
russcc
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Default Re: Variable coil ballast resistor

I do have multi-m, and I get aprox. 3-0hms at the lowest post where it is market 3 volts.
I have other ballast resistors of which I will post a photo later. They seem to all be around 3 ohms.
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Old 09-27-2021, 12:14 PM   #6
russcc
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Default Re: Variable coil ballast resistor

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These 3 ballast resistors all read about 3 OHMS.
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Old 09-27-2021, 04:24 PM   #7
Jack E/NJ
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Default Re: Variable coil ballast resistor

>>>Using a Skip re-built, converted to 12V, negative ground !GA coil on the 59 in the roadster.>>>


Prolly ~1.5 ohm primary. I'm using a ~2 ohm chrysler ballast with mine. No bypass. It's fine.
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Old 09-27-2021, 05:34 PM   #8
russcc
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Default Re: Variable coil ballast resistor

So if the coil has 1.5 ohms resistance, and ballast resistor 2 ohms what would the current in amps be in 12V circuit ? How do I measure the voltage to see if I have 3.8 to 4.2 volts at the points ? Thank you.
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Old 09-27-2021, 06:31 PM   #9
JSeery
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Default Re: Variable coil ballast resistor

To some extent these numbers/ calculations are just appropriations. The operating voltage is more like 14+, not 12. The resistance changes with temperature. There are other factors involved besides just the ballast resistor and coil, such as wire size and length and any other current paths in the circuit. And etc, etc, etc. So 3.0 ohms resistance and 12 volts are just ballpark talking points.
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Old 09-27-2021, 08:26 PM   #10
Jack E/NJ
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Default Re: Variable coil ballast resistor

>>>So if the coil has 1.5 ohms resistance, and ballast resistor 2 ohms what would the current in amps be in 12V circuit ? How do I measure the voltage to see if I have 3.8 to 4.2 volts at the points ? Thank you.>>>




Ohm's law calculations
Points closed, engine not running = 0 volts at the ungrounded point, 3.6 amps.

Points open. engine not running = 12.6 volts at the ungrounded point, 0 amps.


Ohm's law conclusions
Ignition switch left on, engine not running = good chance of fried coil and dead battery. 8^)
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