Posted by John T on December 16, 2009 at 17:41:08 from (66.244.97.31):
In Reply to: IH 454 coil issue posted by N8terry on December 16, 2009 at 15:34:25:
I will take your questions one at a time:
QUESTION: Why did they use a 6 volt coil on a 12 volt tractor?
ANSWER: One possible advantage is to improve starting at cold temperatures when battery voltage can be drastically reduced while cranking. Its quite common to use a 6 volt coil on a 12 volt tractor and add an external series voltage dropping (12 to 6) Ballast Resistor after the switch and before and ahead of the coil, that way the 6 volt coil operates at its designed intended 6 volts to avoid overheating and over current, plus the points only have to switch around 4 amps so they dont burn prematurely... HOWEVER during cranking when battery voltage drops which can reduce spark energy, THE BALLAST IS (or can be) BY PASSED resulting in a hotter starting spark that would occur if it were a 12 volt coil with no ballast capable of being by passed during cranking. They run on 6 volts but start on 12 (as reduced by cranking amps)
QUESTION Is it ok for me to use a 12 volt coil instead?
ANSWER YES INDEED you can use a full true (some call internally ballasted) 12 volt coil NO BALLAST REQUIRED. You would loose the benefit available if it was equipped with a 6 volt coil and external ballast and had the start by pass system, however.
QUESTION: Would I need to use a resistor with either coil?
ANSWER: Yes you need an external series voltage dropping (12 to 6) ballast resistor if its a 12 volt tractor and you use a 6 volt coil WELL DUH.. HOWEVER YOU DO NOT need an external ballast resistor if its a 12 volt tractor AND YOU USE A FULL TRUE 12 VOTL COIL. NOTE some of the Older Fords still require an external series ballast
THE DIFFERENCE IN 6 AND 12 VOLT COILS
a) A typical 6 volt coil has around 1.25 to 1.75 or so ohms LV primary winding resistance and it and the points draw and switch around 4 amps on a 6 volt system... b) A typical full true 12 volt (some call internally ballasted) coil has around twice that (2.5 to 3.5) ohms primary and draws around 4 amps on a 12 volt system (as does a 6 volt coil + ballast).
Some coils are labeled "12 volts" and they are indeed designed to operate at 12 volts WELL DUH.......Some coils are labeled "6 volts" and they are desigend for 6 volT use WELL DUH....Some coils are labeled "12 volts NOT for use with external ballast resistor" that means just what it says......Some coils are labeled "12 volts requires (or for use with) external ballast resistor" again it means what it says.
I hope this explains all the 6 volt versus 12 volt coil and external ballast resistor thing, if I missed anything I'm sure the other fine gents can add to this......
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