Re: 841 Powermaster Electrical Help

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Posted by Bruce(VA) on August 31, 2022 at 06:43:55 [URL] [DELETE] :

In Reply to: Re: 841 Powermaster Electrical Help posted by jrobin1 on August 30, 2022 at 16:51:44:

No modern automotive coil has an “internal resistor”. Internal coil resistance is determined by wire gauge and the number of turns. Higher resistance is provided by smaller gauge wire with greater turns. If the coil is marked or sold with a notice “requires an external resistor” that simply means it has a low internal resistance and will be damaged by excessive voltage. It does not mean the coil has an internal resistor. Yes, plenty of coils are advertised as having an internal resistor. That’s called advertising, not electrical engineering. To be both accurate and precise, every automotive coil should simply state the internal resistance of the coil. But that would require a basic understanding of the Kettering Ignition system. So to keep it simple, ANY side coil with an internal resistance of 3.25 ohms will work fine on your 12 volt tractor w/o any external resistor. Like the NAPA coil, p/n IC14SB. Many folks just add a 12 volt coil rather than dealing with trying to find an external resistor to work with their existing 6v coil. Too much resistance gets you a weak spark; not enough and the coil melts. So, see if it's got 3.25 ohms or more. If not, you have a 6v coil. You're not going to get an accurate voltage reading w/ the tractor running. Measure the voltage points open, points closed, engine off.

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