Posted by John T on December 16, 2012 at 06:07:26 from (216.249.82.117):
In Reply to: Ignition Resistors posted by K-Mo on December 16, 2012 at 04:19:16:
You are correct!!!!!!! The ballast resistor should be the proper match with the coil, if you have a 12 volt tractor but are using a 6 volt coil, it should be sized such that it drops "approximately" 6 volts so 6 remains on the 6 volt coil. Thats like a 50 50 Voltge Divider and if pure resistance is all that matters, its DC resistance would be approximately the same as the DC resistance of the coils LV primary i.e. 1/2 the voltage dropped across ballast and remaining 1/2 across the coil, 6 + 6 = 12.
HOWEVER as little as 0.2 ohms difference (2 versus 1.8) shoudnt make a huge significant difference???? but I cant argue with your results, you were there not me........Perhaps there was a resisitve connection causing part of the problem which was cured when you installed a new ballast???? Also, some ohm meters arent all that accurate at such low ohms readings...
On many tractors that are 12 volts but use a 6 volt coil plus an external ballast resistor, they are equipped with a ballast by pass system such that ONLY while the engine is cranking over (starter motor engaged) the ballast is temporarily by passed so the coil sees the full unballasted battery voltage which really helps improve cold weatehr starting. I WOULD SEE IF YOUR TRACTOR HAS SUCH AND IF ITS WORKING. If so you need to measure the coils voltage when the starter motor is engaged and if the ballast by pass is functioning Id expect it to be near the battery voltage (maybe 10 to 12 depends on battery and current draw) versus the only 5 or 6 normal when shes not cranking over!!!!!!! If it has a by pass system theres an extra wire to the coil or low output side of the ballast which feeds unballasted battery voltage to the coil ONLY WHILE CRANKING
Good observation and post on your part, perhaps this discussion will help others understand the system better....
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