6 volt change to 12v

Been nursing my 47 cub elec system for years. It finally failed at the same time I need a new battery. Looked in the archives and found lots of good info and wiring diagrams. One part I am confused on is, do I need a new coil or just a resistor? There is a new coil on eBay 12 v with an internal resistor of .03 ohms. Would this work? Don't know how old the coil on there now is.

As long as you are at it, why not change to a Pertronix kit and get rid of the points and condensers, but no matter what route you take you will need a coil with at least three ohms resistance to keep things cool.

NO such thing as a coil with an internal resister!!!!!!!!!!!!!! All a true 12 volt coil is, is simply wound different to have a high resistance.
That said you can use a ballast resister like say the O'Reilly's auto part number VR-1 or VR-2
As for buying e-bay why when I am sure there are local auto parts store close to you and that keeps the $$ in your area which helps the area

Head to NAPA. Tell the guys what you're doing, and get a new coil. Probably will be needing one some time in the near future anyway. The resistor pack is OK, but that's just something else to go wrong.

Did this to my Jubilee a few years ago and never looked back !

Pete

Craig, good question "do I need a new coil or just a resistor"

ANSWER : 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 ORRRRRRRRRRRRRRRRR you can get a new full true 12 volt rated coil (NO ballast required) many typical old farm tractor 12 volt coils have somewhere around 2.5 to 3.5 LV primary ohms as measured between the 2 small + and - terminals.

NOTE since this is an old tractor forum NOT an old car forum, I'm talkin "typical" old farm tractor coils NOT old American car or truck coils, some of which used 6 volt others used 12 volt, and some had different resistances then above and also different ballast resistances to match the particular coil and ballast together.

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, 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.

Wire whichever coil to match the tractors polarity

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

John T

Oh, yes there was. Virtually all American cars and trucks used external resistors. And, because all kinds of part numbers have been combined, you can't get a tractor/vehicle specific coil any more. You have to know what you're getting. Easy to measure with an ohm meter, although I've never seen a 12 volt coil that, if it has an internal resistor, that does not have it stamped on the coil. With large engines, back in the 50s/60s when 12 volt systems became common, they needed an external resistor with a ignition by pass circuit. Starter solenoids of that era have 2 small studs, one from the ignition to energize the solenoid and one going from the 2nd stud to the coil. GM used a resistor wire and Ford/Chrysler a porcelain type. Voltage drop while cranking is significant, especially in the winter. If you were running only 9 volts thru your resistor there would only be around 6 available for the primary circuit. Even today, a lot of your solenoid replacements have the 2 studs. Again this only relevant because of the rampant part number combinations the bookkeepers have foisted on us. You must have a resistor in a 12 circuit or you will destroy your points in very short order. I taught automotive ag mechanics in the post secondary school system here in MN since 1970 and feel comfortable with what I'm talking about.

I would leave a Cub on six volts. I know four guys that have Cubs. They crank right over on six. One guy uses his to move snow and starts fine.

A 47 Cub should have a J4 magneto unless it's been changed. If it does have a distributor with an IH six volt coil. I would get a resister and keep the old coil. Those old IH coils are a lot better than any thing being made today.

My 47 Cub was changed to 12 v when I got it. I have a mag. Old alternator was no good so I bought a 1 wire self energizing alternator and that tractor cranks over about 100 mph. If you have a distributor then there is a bit more to it.

I've never seen a 12 volt coil that, if it has an internal resistor, that does not have it stamped on the coil.

Click to expand...

So you are saying you have seen a coil actually labeled "Internal Resistor"?

WOW!

Rich, Regarding your statement "NO such thing as a coil with an internal resister!!!!!!!!!!!!!!"

I believe that to be true on old farm tractor coils HOWEVER as far as some old automotive coils, Mr DeMaris was kind enough to post these two pictures a long time ago of coils THAT DO INDEED CONTAIN AN INTERNAL RESISTOR.

I recall yearssssss ago seeing a few of these (on cars not tractors) and they had like a ring or seam near the bottom and that was where there was a separate little compartment for the internal resistor.

Hope this helps, hope your high n dry down there, take care now and best wishes

John T

Thanks all for the reply, still have a question. Ok if I use the old coil I can put a ballast resistor in line to drop the 12v down to 6. If I buy a new 12v coil do I need to still buy a ballast resistor to keep from burning the points?

You can either use a ballast resister with the coil you have now of buy a TRUE 12 volt coil that should say right on it no ballast resister needed

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

Thank you all for the rereply. I think I got it now. So glad there is this much knowledge here.may need you all again before this is over.

That resistor is in a separate compartment attached to the bottom of the steel coil can, not actually inside the coil with the windings and oil, it's a seperate add on.