coil

danmcdonald · Jun 15, 2014

How do I check if a coil has a built in resister? The coil has been on my shelf for years and is only marked 12 volts. Thanks

charlieu · Jun 15, 2014

A 12 volt coil does not have a built in resistor, When a 12v coil is made it is made with many turns of very fine wire giving it a resistance of 3-4 ohms in the primary circuit. This can be checked with an ohm meter, connected to the neg (-) and (+) pos terminals of the coil. A 12v coil should read 3-4 ohms and a 6v coil will have about 1.5 ohm reading. This should be done with no wires connected to the coil if mounted on the tractor. keep-em-crankin Charlie U

John T · Jun 15, 2014

There's most likely NOT any discrete stand alone "resistor" hidden away somewhere inside the can. A low voltage low energy ohm meter test can tell you if a coil is definitely BAD (either winding open) but it can NOT tell if its GOOD as many failures are due to HV breakdown when operating at the high voltage and/or only once warmed up.

A typical old farm tractor coil (NOT talkin high voltage or high energy or after market or racing coils like Accell or Mallory etc etc so don't have a calf Billy Bob) designed and labeled for "12 Volt" (or 12 volt NOT for use with ballast) operation will have a LV winding of approximately 2.5 to 4 ohms.

You need a real coil tester to perform a more complete true test, while an ohm meter can show if its definitely bad.

John T

coil

danmcdonald

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charlieu

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John T

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