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Tractor Talk Discussion Board

Re: Tractor coils


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Posted by John T on October 18, 2021 at 16:53:36 from (174.198.151.201):

In Reply to: Tractor coils posted by 300jk on October 18, 2021 at 15:10:35:

300 GREAT QUESTION Ive answered this probably a hundred times on here the past 20 years but Im happy to help again !!

1) A 12 Volt tractor can use EITHER:

a) A full true 12 Volt rated coil which has a LV primary winding resistance between small + and - terminals around 3 Ohms
Some mistakenly call those internal ballasted HOWEVER there's no actual discrete resistor hidden inside the can, the 3
Ohms is the resistance of the LV primary winding/coils NO EXTERNAL ADDED BALLAST RESISTANCE IS NEEDED for a full true
12 volt coil. It already has 3 ohms resistance

b) A 6 volt coil with around 1.5 ohms LV Primary PLUS an external series voltage dropping (12 down to 6) Ballast

The thing is you need to limit the coil current the points switch to not much over 4 amps else they burn too quick

THEREFORE 12 Volt /3 Ohms (6 volt 1.5 Ohm coil + 1.5 Ohm ballast orrrrrrrrr 12 volt 3 ohm coil no ballast) = 4 Amps

NOTE A coil labeled 12 Volts orrrrrrrr 12 Volts NOT for use with ballast is a full true 12 volt coil no ballast required HOWEVER A coil labeled 12 Volts for use with ballast in in reality a 6 volt coil and needs ballast as it says on a 12 volt tractor or it will overheat

DO AS PERTRONIX SAYS NOTTTTTTTTTTTTTTTTTTTT WHAT ANY OF US ON HERE GUESSES

If points burn too soon they are switching too much current so that needs to be limited to around 4 amps and on a 12 volt tractor thats a 6 volt coil plus ballast (1.5 + 1.5 total 3 ohms) orrrrrrrrr a full true 12 volt coil (3 ohms) no ballast required

NOTE these numbers may not be exact they are rough averages, Ive seen 6 volt coils 1 to 2 ohms and 12 volt 2.5 to near 4 and different accompanying ballast

Hope this helps, got it any questions ????????

John T


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