Posted by John T on December 26, 2007 at 09:47:20 from (66.244.83.147):
In Reply to: Re: 12 volt front coil posted by georgeky on December 26, 2007 at 09:14:28:
George, Actually, there are indeed 6 VOLT COILS and then there are 12 VOLT COILS and NOT ALL coils, therefore, are 6 volt. Heres the difference:
6 VOLT COIL
Has around 1.5 ohms of low voltage primary winding resistance as measured between its lil + and - terminals.
It is engineered and designed for ONLY 6 volts use and 12 volts would cause it to overheat plus the points would burn up quickly from switching excess current!!!!
12 VOLT COIL
Has around 3 ohms of primary coil/winding resistance as measured between its lil + and - terminals and is designed to have 12 volts (NOT 6) applied across its terminals.
If you were to only use 6 volts it will have a weak spark !!!!!
Although some refer to them as being "internally ballasted" most (slight exceptions) achieve their higher 3 ohms of primary resistance by use of more turns or length of primary coil windings OR ELSE they could use higher resistance wire.
One reason for 6 volt coils to have only 1.5 ohms of low voltage primary winding resistance while a 12 volt coil has twice that (around 3 ohms) is to limit the amount of current necessary for the points to switch to around 4 amps to avoid premature burning.
If you wish to use a 6 volt coil on a 12 volt tractor you can add an external series voltage dropping (12 to 6) ballast resistor so the coil only sees 6 volts plus the current the poinst have to switch is again reduced/limited to around 4 amps to avoid premature burning. One advantage of such a system is so the externally ballasted system (NOT so if theres no external resistor as on a 12 volt coil) can by by passed during start up to improve cold weather starting.
Hope this helps yall understand the 6 volt and 12 volt coil thing.
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