I guess its "possible" in translation and in labeling things might? get confusing if different countries are involved ? Another important and limiting factor when it comes to deciding how much total (coil + ballast) ignition circuit resistance is required is to consider the current the ignition points much pass and switch. Typically on many old tractors (sure depends on points design and construction) the current the points must switch is limited to around 3 to 4 max amps, otherwise they will burn prematurely.
THEREFORE at 12 volts if there's 3 ohms of total (coil + ballast) resistance the points current would be 12/3 = 4 amps, while if at 12 volts the total (coil + ballast) resistance were 4 ohms, the current would be 12/4 = 3 amps. As far as ballast resistance, if you wanted a 50/50 voltage divider and used 12 volts as the baseline (higher if charged) and wanted to drop 6 volts across a 6 volt coil and 6 across a ballast, the coils LV primary resistance would be the same as the ballast resistance. However duty cycle and points dwell all play into this equation, and battery voltage will vary subject to temperature, load and state of charge, and charging parameters etc. etc.
Coils (design, voltage and resistance etc) for certain cars or tractors or motorcycles or lawn mowers are certainly NOT all the same...…...
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Today's Featured Article - Third Brush Generators - by Chris Pratt. While I love straightening sheet metal, cleaning, and painting old tractors, I use every excuse to avoid working on the on the electrics. I find the whole process sheer mystery. I have picked up and attempted to read every auto and farm electrics book with no improvement in the situation. They all seem to start with a chapter entitled "Theory of Electricity". After a few paragraphs I usually close the book and go back to banging out dents. A good friend and I were recently discussing our tractor electrical systems when he stated "I figure it all comes back to applying Ohms Law". At this point
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