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09-27-2021, 07:02 AM | #1 |
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Join Date: May 2010
Posts: 2,871
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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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09-27-2021, 07:15 AM | #2 |
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Join Date: Jul 2010
Location: 36 miles north of Albany NY
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Re: Variable coil ballast resistor
Hey Russ, does anything twist or slide, I can’t tell from the pictures.
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09-27-2021, 07:42 AM | #3 |
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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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09-27-2021, 10:44 AM | #4 |
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Location: Minnesota, Florida Keys
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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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09-27-2021, 11:59 AM | #5 |
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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. |
09-27-2021, 12:14 PM | #6 |
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Re: Variable coil ballast resistor
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09-27-2021, 04:24 PM | #7 |
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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. |
09-27-2021, 05:34 PM | #8 |
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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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09-27-2021, 06:31 PM | #9 |
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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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09-27-2021, 08:26 PM | #10 |
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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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