Re: 12 volt coil without resistor

Posted by John T on January 14, 2006 at 18:55:08 from (66.244.90.98):

In Reply to: 12 volt coil without resistor posted by deene on January 14, 2006 at 17:46:57:

Deene, First of all if you bought a true full 12 volt (what some call an internally ballasted) rated coil and are using it on a 12 volt tractor. YOU DONT USE ANY EXTRA SERIES BALLAST RESISTOR. It takes the full unballasted 12 volts.

HOWEVER if its labeled "12 volts for use with an external ballast resistor" then its in reality a 6 volt coil and does indeed need the external series voltage dropping (12 to 6) Ballast Resistor

The more typical use of the external series voltage dropping (12 to 6) Ballast Resistor is when youre using a 6 volt coil on a 12 volt tractor. It drops 6 volts across it leaving the remaining 6 across the 6 volt coil so it runs at its designed current and voltage and resultant heat.

A typical 6 volt coil will have around 1.25 to 2 ohms primary resistance measured between its lil + and - terminal while a true full 12 volt coil will have around 2.5 to 3 and over.

NOTE; If you use an external series ballast, it should be wired after the ignition switch and before the coil NOT between the coil and distributor. After the points open the condensor is in series with the coil and some ringing occurs.

Hope this helps, post back any questions, good luck and God Bless

John T

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