farmall H 12volt resistor for coil

Narrowfarm · May 29, 2008

what is the value of the resistor in ohms and wattage at the coil? thanks john

Anonymous-0 · May 29, 2008

$18 will buy a 12 volt coil with internal resistance, same price as non resistor. Then just throw resistor out of the circuit.

KEB1 · May 29, 2008

Most of them are in the 1.5 to 1.8 ohm range. Typical current draw is around 3 - 4 amps, which would translate to something on the order of 20 - 25 watts dissipation. Note that these numbers are with the engine stopped and the points closed; when the engine is running, the points are open a good part of the time and the average current draw is somewhat less.

The resistance and current numbers come from an old Motor's repair manual.

Easiest approach is to go to a good auto parts store and buy a ballast resistor for a 60's or 70's vintage car. NAPA has a universal one, part number SME 185450.

By the way, the reason for cars having external resistors instead of simply using a 12 volt coil was to provide a hotter spark for starting. There would be an extra contact on either the ignition switch or starter selenoid that would bypass the resistor and apply full battery voltage to the coil for starting. Once the engine started, this contact would open, putting the resistor back in line, and reducing current through the points to a value that wouldn't destroy them quickly.

Keith

John T · May 30, 2008

On that 12 volt tractor you can EITHER use a full true (some call internally ballasted) coil or else a 6 volt coil with an external series voltage dropping (12 to 6) Ballast Resistor.

Take note on coil labels, a 12 volt may read "12 volts" or "12 volts NOT for use with external ballast" while a 6 volt may read "6 volts" or "12 volts requires external ballast" which is in reality only a 6 volt coil and requires the ballast just like it says.

If you alrerady have a good 6 volt coil n wanna use it the ballast (Keith has ya covered in ohms n watts values) is a cheap addition but if you dont have any coil at all prob cheaper to just buy a 12 volt coil no ballast required

John T

El Toro · May 30, 2008

Napa has a 12 volt coil P/N IC14SB with a built-in resistor for about $18.00. Their ballast resistor is P/N ECHICR13 for $14.00. Hal

TheDurk · May 30, 2008

(quoted from post at 11:45:20 05/30/08) Napa has a 12 volt coil P/N IC14SB with a built-in resistor for about $18.00. Their ballast resistor is P/N ECHICR13 for $14.00. Hal

And the coil you use WITH the external resistor is P/N IC13.

farmall H 12volt resistor for coil

Narrowfarm

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Anonymous-0

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KEB1

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John T

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El Toro

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TheDurk

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