Posted by John T on May 04, 2010 at 11:06:33 from (66.244.97.31):
In Reply to: Re: coils posted by mmidlam on May 04, 2010 at 09:25:28:
Id agree "basically" many (NOT all) older 6 volt tractor coils (Im NOT talking high performance or after market or electronic ignition stuff) had in the vicinity of 1.25 to 2 or a bit over ohms (good average may be 1.5) while many (NOT all) older 12 volt coils had more like 2.5 to 3.5 or so ohms (good average may be 3 ohms). That way the current that had to flow through and be switched by the points was in the neighborhod of 4 amps AND IF YOU SWITCH TOO MUCH MORE CURRENT THE POINTS WILL BURN UP PREMATURELY. (6/1.5 = 4 points amps on a 6 volt system,,, 12/3 = 4 points amps on a 12 volt system)
THEREFORE YES the ignition primary series circuit combination of COIL PLUS BALLAST was in the neighborhood of say 2.5 to 3.5 or so ohms on 12 volt systems which limited points current to the 4 amps range.
As usual Bob and I agree, most older tractor coils that some refer to as "internally ballasted" didnt actually contain an internal discrete resistor, but the higher primary resistance was made up of either higher resistive wire or simply more wire length. HOWEVER they indeed made some coils (those were truly internally ballasted) that had a seperate internal compartment with stand alone resistor but I view that more on older cars then our 40 and 50 vintage tractors
Hope this helps, we have pretty much beat this to death lol
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