|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
|
11-14-2020, 12:00 PM | #1 |
Senior Member
Join Date: Oct 2010
Location: Cumberland, ON
Posts: 252
|
difference in 6 volt and 12 volt ignition ?
Is there any electrical difference between a 6 volt and a 12 volt ignition coil ?
Also is it ok to use a 6 volt coil in a 12 volt system ? keeping in mid that I would be limiting the primary current to 3 or 4 amps by using an exterior resistor if needed. Can anyone recommend a 12 volt coil that is available off the shelf at NAPA for my following specifics: - motor is a 1937 V-8 flathead with helmet distributor - motor is in a 31 Model A Ford with 12 volt alternator system - not using the original coil, using the replacement cover on the helmet dist. that requires a ingition coil - this is not a hot rod, it is simply a nostalgic conversion without high performance |
11-14-2020, 01:44 PM | #2 |
Senior Member
Join Date: May 2010
Location: Star, MS
Posts: 4,026
|
Re: difference in 6 volt and 12 volt ignition ?
I sounds like you are on the right track. The Bosch "blue coil" #00012 made in brazil is listed to have 3.4 ohms resistance. You could use any coil with 1.5 primary resistance with a 1.8 ohm ballast with the same results.
|
Sponsored Links (Register now to hide all advertisements) |
|
11-14-2020, 01:52 PM | #3 |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
|
Re: difference in 6 volt and 12 volt ignition ?
What is often called a 6v coil will work fine on 12v, positive or negative ground. As you posted, it is the current in the circuit that needs to be controlled in the 3 to 4 amp range. With a "6v" (really one in the 1.5 ohm range) you need a ballast resistor (also in the 1.5 ohm range) for use with 12v. So, you are looking for ~3.0 ohms of resistance for a 12v ignition circuit. Or, you can use what is referred to as a 12v coil, really a 3.0 ohm resistance coil, as it provides the 3.0 ohms of resistance without a ballast resistor. The polarity of the coil needs to match the polarity of the rest of the system, so a negative ground system has the negative terminal of the coil going to the distributor points & capacitor and the positive terminal of the coil connected to the ignition switch.
|
11-14-2020, 02:15 PM | #4 |
Senior Member
Join Date: Oct 2010
Location: Cumberland, ON
Posts: 252
|
Re: difference in 6 volt and 12 volt ignition ?
your reply is exactly what I wanted to know. I have always enjoyed your knowlegable input on the forum
Thanks much Tom |
11-15-2020, 05:04 PM | #5 |
Senior Member
Join Date: May 2010
Location: Northeast Pennsylvania
Posts: 1,582
|
Re: difference in 6 volt and 12 volt ignition ?
OK, so I don't want to get into the weeds of electrical theory, but a resistor doesn't limit or reduce current, it limits or reduces voltage.
You cannot use 6volt coil for 12volt system or the reverse. Well actually you can and it might work poorly or fry the coil, but that's your choice. Coils are rated in ohms, which is the measurement of resistance. Typically you want a coil around .5 ohms in a 6 volt system, and around 1.5 ohms for a 12 volt system. Ballast resistors are used to lower the voltage to the coil, and most particularly to the ignition points, because points last longer with lower voltages. In theory, you could use a 6 volt coil in a 12 volt system if you used a big enough resistor to lower the voltage from 12 to 6, but again, that 's not the best way to build an ignition system. |
11-15-2020, 05:18 PM | #6 |
Senior Member
Join Date: May 2010
Location: PRINEVILLE, OR.
Posts: 490
|
Re: difference in 6 volt and 12 volt ignition ?
Sponsored Links (Register now to hide all advertisements)
__________________
KIM KARDASHIAN ISN'T FLAT, BUT MY MOTOR IS..... http://s818.photobucket.com/home/roglehr/index |
11-15-2020, 05:44 PM | #7 |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
|
Re: difference in 6 volt and 12 volt ignition ?
|
11-15-2020, 05:19 PM | #8 |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
|
Re: difference in 6 volt and 12 volt ignition ?
Afraid your theories are not correct. Ford used what are often referred to as "6v" coils in 12 volt systems for many years after they switched to 12v systems. There are advantages to doing this. It allows the ballast resistor to be bypassed during startup making it easier to start an engine. It is the resistance of the coil that matters, "6v' coils are often in the 1.5 ohm range which works fine in a 6v system and coupled with a 1.5 ohm resistor works fine in a 12v system. Or, you can use a 3.0 ohm resistor without a ballast resistor in a 12v system.
Current, Voltage and Resistance are all related. What you are really wanting to do is limit the current in the ignition circuit to around 3 to 4 amps. 6 volts divided by 1.5 ohms equals 4 amps, so is on the high side, but works. For 12 volt systems you need around 3.0 ohms, so, a 3.0 coil or a 1.5 ohm coil coupled with a 1.5 ohm ballast resistor. May be confusing something like a GM HEI ignition system which uses a .5 ohm coil. A .5 ohm coil in a 6 volt circuit would give you around 12 amps, why to high and very short points life. Same goes for a 1.5 ohm coil in a 12 volt system. 12v / 1.5 ohms = 8 amps, still way to much current. Last edited by JSeery; 11-15-2020 at 05:37 PM. |
11-15-2020, 06:31 PM | #9 | |
Senior Member
Join Date: May 2010
Location: Northeast Pennsylvania
Posts: 1,582
|
Re: difference in 6 volt and 12 volt ignition ?
Quote:
If the systems are ballasted, a 12 volt coil would have 1.5ohms and the 6 volt coil would have less resistance (I used .5 as an example, but that would vary depending on the value of the resistor that gets added to it). Current draw (amps) will vary depending on the voltage, but it is really total wattage (Volts x Amps) that has to be limited. |
|
11-15-2020, 10:50 PM | #10 | |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
|
Re: difference in 6 volt and 12 volt ignition ?
Quote:
Another variable is the ballast resistor if one is used. The actual resistance changes with temperature. Some of the early car manufactures didn't use ballast resistor on the OEM style coils. All of the above relates primarily to "can" coils which do not require a ballast resistor (assuming it has the correct resistance). With the original Ford coils, they were a lower resistance value and coupled with a ballast resistor (I think the numbers were somewhere in the .8 ohm range). The ballast resistor had a lower resistance when cold which increased the amperage in the circuit to ad start up. As the current flowed through the resistor it would heat up and increase the resistance which lowered the current in the circuit to prolong point life. So, again, there are variables all over the place in the ignition circuit and the resistance numbers used is just guidance as to what is needed. |
|
|
|
Sponsored Links (Register now to hide all advertisements) |
|