Re: 6 volt change to 12v

Posted by John T on September 20, 2017 at 15:28:44 from (216.249.81.101):

In Reply to: Re: 6 volt change to 12v posted by craig45 on September 20, 2017 at 14:33:14:

Hi again Craig, I thought I had this question already answered below??? but to your question here my answer remains the same:

1) "Ok if I use the old coil I can put a ballast resistor in line to drop the 12v down to 6"

MY ANSWER SAME AS BELOW : You can EITHER use the existing 6 volt coil but add ahead in series between the IGN switch and the coils input a discrete bathtub style voltage dropping (12 down to 6, many in the 1.2 to near 2 or so ohms resistance) ballast resistor, that's the cheapest method

2) If I buy a new 12v coil do I need to still buy a ballast resistor to keep from burning the points?

NOOOOOOOOO IFFFFFFFFFFFF the new coil is a full true 12 volt rated unit IE NO BALLAST REQUIRED, and if so its LV primary resistance + to - is around 2.5 to 3.5 or so ohms. I = E/R ,,,,,,,,,,12 volts/3 ohms = 4 amps and that's about all the points need to switch so they don't burn prematurely

HOWEVER BEWARE If the coil is labeled "12 volts for use with ballast resistor" its more like a 6 volt coil and needs the external ballast just like it says or the points will burn prematurely !!!!!!!!!!!!!!! You need a "12 Volt" coil orrrrrrrrrr one labeled "12 Volts NOT for use with ballast resistor"

Got it ??? If not post back any questions

NOTE since this is an old TRACTOR forum NOT and old CAR forum, I'm talking about typical old farm tractor coils NOT automotive coils, some of which American made cars n trucks used 6 volts coil others used 12 volt coils.

NOTE most all typical old farm tractor coils DO NOTTTTTTTTTTTT have an internal stand alone discrete ballast resistor tucked away and hidden inside the can (like a few older cars did, see my post to Old below), even though some refer to them as having an internal ballast. Typical old farm tractor 6 volt coils have around 1.2 to under 2 ohms LV primary resistance while a typical old farm tractor 12 volt coil will have more like 2.5 to under 4 ohms.

NAPA or O Reillys or Tractor Supply or Rural King etc etc stock BOTH 6 and 12 volt rated coils

John T

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