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#1 |
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Join Date: Jul 2017
Posts: 40
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What potential problems can this cause?
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#2 |
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Join Date: Aug 2011
Location: Eagle Bend, MN
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I have done the same thing before, although not on an A. Would throw a 1/2 inch spark. I figure if it throws a good spark, why not?
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#3 |
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Join Date: May 2012
Location: Chillicothe, Missouri
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If the 12 volt coil doesn't have an Internal Resistor it will be fine.
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"If I asked people what they wanted they would have said faster horses." -Henry Ford "Primitive technology is not a design flaw" 1928 Ford Model A Roadster Pickup 1930 Gordon Smith Air Compressor 1941 Willy's Pickup 1960 Thunderbird-For Sale 1964 Buick Riviera 2x4 425 1965 Pontiac GTO, 455 Super Duty 2004 Dodge Ram SRT-10, V-10 Viper 1977 Charger Jet Boat,460 Ford,Jacuzzi Jet Front Engine Nostalgia Dragster,Supercharged 296 "Fullrace Flathead" Ford Engine Build up on DVD ask |
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#4 |
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Join Date: Jun 2015
Posts: 1,414
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Good question johnr.
How about a car with a 12 volt system (12volt coil , electronic ignition, etc.) and reverting back to points/condensor distributor. Assume no issues? |
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#5 | |
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Join Date: Jul 2017
Posts: 40
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That should work. The reason for using the Nappa 12 volt coil is that they don’t break down due to heat. This is for touring A’s. Sent from my iPhone using Tapatalk |
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#6 |
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Join Date: May 2010
Location: Eastern Tennessee
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#7 | |
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Join Date: Jul 2017
Posts: 40
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I don’t know. What would happen if you use a 6 volt coil for a 12 volt system? I’m using the 12 volt with a 6 volt system. It works but there are some strange things happening. When I start the car the lights and horn work. After I take a nice ride, the lights and horn don’t work. Later, say the next day, the lights and horn work again. This has happened several times. The engine is not affected. Sent from my iPhone using Tapatalk |
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#8 |
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Join Date: May 2010
Location: Largo Florida
Posts: 7,225
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Its about the internal resistor, does it have one or not ? Automotive coils are either 1.5 or 3.0 ohms. If it has a resistor, it'll generally say so.
As long as yours is a 1.5 ohm and is epoxy filled it'll be fine. I'm thinking your light and horn issue are probably steering column/light switch/ wiring issues. |
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#9 | |
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Join Date: May 2010
Location: Eastern Tennessee
Posts: 11,519
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Yes, that is correct. There really is not a 6v or 12v coil, but more about the ohms. John's comments about other peculiar wiring issues leads me to believe the wiring has issues, one of which may be the culprit why the original coil is getting warm and breaking down. |
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#10 |
Senior Member
Join Date: Jun 2015
Posts: 1,414
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Yes concur; our car came with a 12 volt coil installed with the FS system. We haven't checked the coil resistance yet. What ohms value is desired with a stock distributor ?
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#11 |
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Join Date: Oct 2014
Location: Collingwood,Ontario,Canada
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Keep in mind that in a 12 volt system the 12 volts from the battery (or more like 14 volts ) is only used to operate the starter and then when you release the key a ballast resister reduces the voltage to 8 volts to be used for running. So by using a 12 volt coil without a resister in a 6 volt system your battery would only provide about 7 volts. not much difference !
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#12 |
Senior Member
Join Date: Aug 2011
Location: Eagle Bend, MN
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I have used the 3 ohm coil on 6 volt and it throws a nice hot spark.
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"There are some that can destroy an anvil with a teaspoon and shouldn't be allowed to touch anything resembling a tool." |
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#13 |
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Join Date: Jul 2017
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No resistor.
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#14 | |
Senior Member
Join Date: May 2010
Location: Mpls, MN
Posts: 27,582
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The Model A coil feed wire was moved to the opposite terminal, in the firewall terminal box, in late 1929, so the coil draw would show on the ammeter. On my 1928, I moved the black feed wire to the other side, so it also shows on the ammeter. This makes a good diagnostic tool to check for current draw while cranking the engine. |
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#15 |
Senior Member
Join Date: Jun 2015
Posts: 1,414
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OK in summary, for 12 volt system with stock distributor, a 3 ohm primary coil will yield 4 amps. For 6 volt applications, a 1.5 ohm reading would produce 4 amps.
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#16 | |
Senior Member
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![]() Quote:
12/3 = 4 6/1.5 = 4
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#17 |
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Join Date: Jul 2017
Posts: 40
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Very good info. Thanks Mike
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#18 |
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Join Date: May 2012
Location: Chillicothe, Missouri
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A 12 volt coil is actually a 6 volt coil with the intention of using a Ballast resistor.
If the 12 volt coil doesn't have an internal resistor then its basically a 6 volt coil but in a 12 volt application it is intended to be used with a external ballast resistor.
__________________
"If I asked people what they wanted they would have said faster horses." -Henry Ford "Primitive technology is not a design flaw" 1928 Ford Model A Roadster Pickup 1930 Gordon Smith Air Compressor 1941 Willy's Pickup 1960 Thunderbird-For Sale 1964 Buick Riviera 2x4 425 1965 Pontiac GTO, 455 Super Duty 2004 Dodge Ram SRT-10, V-10 Viper 1977 Charger Jet Boat,460 Ford,Jacuzzi Jet Front Engine Nostalgia Dragster,Supercharged 296 "Fullrace Flathead" Ford Engine Build up on DVD ask |
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#19 |
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Join Date: Jun 2015
Posts: 1,414
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We checked our (12v coil ) that came with the FS zipper we're removing in favor of points and it reads about 3 ohms. Appears to be oil filled. We assume it is internally regulated. We also assume it's OK to reuse with modern points. I guess we could check the output voltage..
Further research from our supplier: For epoxy filled coils that can be placed with leads down, etc. Pertronix 40611 black (origin?) 3ohm Bosch 022 1119 027 (Brazil) 3ohm Would appreciate any other products or feedback re; the above. Last edited by duke36; 10-31-2017 at 12:49 PM. Reason: supplier suggested products |
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