Posted by John T on November 20, 2010 at 09:49:14 from (66.244.97.31):
In Reply to: 210 IH Swather Coil posted by greyfoxxca on November 20, 2010 at 09:27:27:
What you describe as a resistor that increases in ohms resistance value as it gets physically hotter I would call as a "Thermistor". Im NOT aware typical tractor coils have a built in thermistor but hey Im never too old to learn. (Maybe only Swathers use them???)
Some manufacturers used a piece of thermistor wire as the ballast on 12 volt tractors that used a 6 volt coil, that was so there would be a hotter spark for starting but once the thermistor warmed up and its resistance increased, it acted as a normal series voltage dropping (12 to 6) ballst resistor so the 6 volt coil only got 6 volts to avoid overheating
What many folks call an "internally ballasted" coil ACTUALLY DO NOTTTTTTTTTT HAVE ANY DISCRETE STAND ALONE RESISTOR TUCKED AWAY INSIDE THE CAN. Their primaty winding/coil has sufficient length and/or ohms per unit length such that they have a total primary winding in the 2.5 to 4 ohms range making them suitable for use on 12 volt tractors with no other series external ballast needed. They are labeled something like "12 volts" or "12 volts NOT for use with ballast resistor" but most DO NOT have any actual internal resistor. Yep some were made like that but I believe that was more for older autos in the twenties n thirties.
Very generally speaking, a coil should run warm but not so hot you cant lay your hand on it
Anyway I was not aware they made coils with internal thermistors so maybe we can all learn something here today if that be the case??? Of course Im more familair with tractor coils NOT Swathers so if you have any more tech info on that family of coils id appreciate it
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