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Ballast resistor

A

Anonymous-0

Well-known Member
What would cause a ballast resistor to get hot and smoke? Its between the ignition swith and the coil on a SH. Just bought the tractor (not running) guy said would not start. I put a new battery in, filed the point becouse it wasnt sparking, then it started right up and ran for about 20 seconds and died and the resistor started smoking and melted the core that the wire is wraped around. Are all these the same? What should I ask for at parts store? All wiring lookes good. THANKS!
 
Whisky, On NAPA's web site they have ballast resistors listed. I would think that you have a bad coil that shorted or the resistor was shorted. If you are running 12 volt to 6 volt coil they should beable to tell you what resistor you need. Oldiron29
 
(quoted from post at 20:37:59 01/31/10) What would cause a ballast resistor to get hot and smoke? Its between the ignition swith and the coil on a SH. Just bought the tractor (not running) guy said would not start. I put a new battery in, filed the point becouse it wasnt sparking, then it started right up and ran for about 20 seconds and died and the resistor started smoking and melted the core that the wire is wraped around. Are all these the same? What should I ask for at parts store? All wiring lookes good. THANKS!
Click to expand...

i have always thrown those coils that need external resistors away and replace them with one that has the built in resistors
 
The way you wrote that it sounds like the ballast resistor became hot and began to smoke AFTER the engine "died".

WHY did you leave the ignition switch "ON" after the engine had stopped???

If the engine stopped at a position where the points were closed it is NORMAL for the resistor to get quite hot if the switch is left on.

It SHOULDN'T have burned out, though.

Sounds like the coil may have shorted out, also check for a shorted wire from the resistor to the coil.

The NAPA # for a REAL 12 Volt coil needing NO resistor is IC14SB. Should be under $20.00.

(The core the resistor is wound on is a heat-resistant glass or mineral fiber core and it seems odd that that would have melted!)
 
Bob, the coil you talk about has a built in resistor? I have some 12v coils, but then I would still need a resistor between the coil and the points correct?
 
Generally, the TRUE 12 Volt coils such as the IC14SB are simply wound with enough wire in the primary to work on 12 Volts, rather than having an INTERNAL resistor. (There MAY be exceptions, but I don't know of any.)

ANYHOW, a TRUE 12 Volt coil needs NO external ballast resistor.

So-called "12 Volt" coils that DO need an external resistor are generally marked "Use with external resistor". Of course, there exceptions to that, as well, and you need to know the part number and be able to look up "specs" or accurately measure the primary Ohms.

A 6 Volt coil or 12 Volt "use with external resistor" coil will generally have about 1.75 to 2.5 Ohms of primary resistance and a "true" 12 Volt coil will probably have 3.5 to 4.5 Ohms of primary resistance, or thereabouts.
 
Any good ballast resistor will smoke and heat up if you leave the ignition on, without the engine running, and the points happen to be closed. At it heats, its resistance also increases. Ballast resistor is designed to get hot under a high current load. It won't do that with the engine actually running. It works as a varible load-sensing current regulator, and to a degree, adjusts to engine spark demands.
 
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