6 volt system, has a 12 volt coil

My 1948 farmall H will not start, so I dug into the ignition system. The condenser was bad, but before I put back together, I noticed that the Coil is a 12volt. The system is a 6 volt, the tractor ran but I only started it 10 times after I bought it, before I started to restore it.

Will this 12 volt coil be ok, or is this the reason my condenser is fried?

Thanks for your help

"12 Volts NOT for use with external ballast resistor" which are indeed full true 12 volt coils

"12 volts for use with (or requires) external ballast resistor" They are indeed actually 6 volt coils and such will work fine on a 6 volt tractor. They are used on 12 volt tractors that use a 6 volt coil and most have the start by pass feature which allows for a hotter start up spark, They sort of start on 12 volts and run on 6 volts.

Theres a common misperception (old wives tale) out there that all coils are 6 volt coils simply NOT true. A full true 12 volt coil has a primary winding resistance (measured between its lil + and - terminals) of around 2.5 to 3.5 ohms or so while a 6 volt coils is more like 1.25 to 2 ohms. ALSO some people refer to 12 volt coils as "internally ballasted" which some think have a built in discrete ballast resistor wired in series before the coil winding HOWEVER most achieve the added primary winding resistance simply either by having more primary wire/winding length or else use wire having a higher resistance per unit of measurement.

One limiting factor and the reason 6 and 12 volt coils are indeed different concerns the life of the ignition contact points which is limiting the current they are required to switch unde load to around 3 to 4 amps or so..... Thats why a 6 volt coil has say 1.5 ohms or primary resistance 6/1.5 = 4 amps) and a 12 volt coil say 3 ohms (12/3 = 4 amps)..... AND THEY ARE NOT ALL THE SAME 6 VOLT COIL..... ..

BOTTOM LINE you need a 6 volt coil on a 6 volt tractor cuz a 12 volt coil will produce a weak spark. All coils are NOT 6 volt coils, see the explanation and reasons why above

Yall take care now

John T

Thanks for all the help! I checked the coil and it is running avout 1.7-1.9 ohms. So it must be a 6 volt coil, with 12v on the side.

Again thanks for the help. I hope to try this out this week.

Another factor you must consider is for some weird reason some 12 volt coils are labled 12 volt coil no external resistor required, while others are labled 12 volt coil requiring a added resistor. As I see it the first one is a true 12 volt coil, while the second example is nothing more than a 6 volt coil requiring a resistor when used as 12 volt. Why industry doesn't just call them 12 and 6 volt coils, beats me.

The resistor bypass wire (that was connected to a terminal often labeled "I" on the solenoid or relay) allowed the 10 volts, of the remaining battery volts, to power the coil above the normal run voltage of the coil 10 volts on what is essentially a 6v coil. this raised the output at a time it was most needed, starting.

Another method of doing this is to use a thermal resistor that starts out cold and has low resistance, then gets hot and resists down to the 6v range. These can be internal (most) or external, allowing a simplified wiring system and about the same results. Seasons greetings from central MN Jim

As you well explained, that feature could really improve cold weather starting cuz when its cold the battery is less efficient PLUS the engine is harder to crank and the high starter current draw drops battery voltage drastically causing a weak spark WHEN YOU NEED IT THE MOST

Yall take care now

John T

John T

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