Re: resistor smoking!

Posted by John T on January 12, 2006 at 14:52:21 from (66.244.90.98):

In Reply to: resistor smoking! posted by Nebraska Kirk on January 12, 2006 at 14:03:19:

Kirk, if it continues to smoke even after any oil or residue or moisture have had a chance to burn off, thats usually a sign of a) Its conducting excess current or b) Its of insufficient power rating, and overheating.

A Excess Current:

The coil (if its good and is one labeled for use with external ballast resistor) ought to measure somewhere around 1.25 to 2 ohms in the primary as measured between its lil + and - terminals.

The Ballast should be around 1.4 to 1.85 ohms.

If the coil and ballast are good and of the approximate ohms listed above, the current ought to be within spec and it shouldnt continue to smoke, provided its rated to handle the power.

B. Insufficient Power Rating.

Most of the Ballast are wirewound power resistors encased an a ceramic bakelite type bathtub housing and rated around 25 to 30 watts. Is yours a typical looking power ballast resistor??? i.e. a 5 watt 1.5 ohms resistor would fry.

When the ignitions on and the points are closed and if the wiring and coil and all else is okay, there ought to be around a 6 volt drop across the ballast and around 6 volts across the coil. Whats yours measure???????

Another slight factor causing overheating may be the physical mount of the ballast, a good secure connection on its metal holder to the tractor ought to help transfer and dissipate some of its heat by conduction, but I have seen them hung in free air (no condustive heat transfer of them) and they were fine, so thats likely not an issue.

I guess the ballast or coil is bad (too low ohms/shorted) or underrated if she keeps on smoking. THIS ASSUMES THERES NO OTHER SHORT which would reduce the net resistance of around 3 ohms total in the ignition circuit. i.e. if the wire from the ballast to the coil were shorted or the coil shorted and 12 volts were applied to the ballast, it could smoke.

Insure the wirings all good and in place and theres NO SHORTS. The series ignition circuit is from the switch to and thru the ballast to and thru the coil to the distributor and its points (when closed) to ground. Check the circuit!!!

Let us know, Best wishes n God Bless, maybe shes just wet or oil coated!!!!!!!

John T

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