Re: Ignition: 6v to 12V

YOUR QUESTION

Is it not true that the 12 volt coil cuts the 12 volts down to 6 in order to work 6 volt ignition systems.

NOOOOO Most (but not all) 12 volt coils are designed n rated to operate on full 12 volt input and one major design consideration that makes them 12 n NOT 6 volt is their primary resistance being enough (around 3 ohms) to limit the amount of current the points have to switch to around 4 amps or less so they dont burn up too quickly. A 12 volt coil has around 3 ohms primary resistance between its lil + and - terminals (regardless if caused by more wire or an internal seperate discrete ballast resistor) while a 6 volt coil only has around half that or 1.5 ohms. They ARE NOT THE SAME AND NOT BOTH 6 VOLT COILS

Sooooo o to get 3 ohms of primary resistance (a 6 volt coil just has 1.5 ohms) in the 12 volt coil versus only half that used on a 6 volt coil MOST (not all) simply have more length of wire or turns so they have twice the primary resistance so the points current is held to around 4 amps or less.

Nowwwww there are a few 12 volt coils that do indeed work as you suspect, they have a seperate internal compartment and a seperate discrete internal ballast resistor to reduce the 12 volts down to 6 and the current through the coil/winding portion of the coil down to that 4 amp or so figure so the points dont burn up quickly. These appear to be the fewwwww Ive seen that have a ring on the can which is that seperate compartment where the resistor is housed. jd even showed some with the ressitr on top n very seperated but those were pretty old units n NOT like ones Ive seen on most thirties thru fifties Deere n IHC n other tractors n maybe not even 12 volt coils but 6 volt units.

jd did an excellent job of posting good correct info n pics that were internal ballasted coils (actually had an internal ballast) buttttt many were real old and many were 6 volt coils and one could even make out that ring or seperated internal component I mentioned. Stilllll ll most alllll ll 12 volt coils I ovserved over manyyyyy years of a used tractor dealer were NOT internally ballasted but instead were 12 volt coils with 3 ohms of primary resistance because they had more wire length/turns of primary winding and DID NOT have the outer ring or groove or the top compartment like jd's pics indicative of any seperated internal compartment housign a resistor .

SOOOOO O again a 12 volt coil IS NOT a 6 volt coil. The 12 volt has around twice the resistance so the points current is limited to arund 4 amps or less. Anddddd it dont matter if that resistance is more wire/turns (like most)
or a seperate internal ballast resistor (like the ones jd showed) SIMILAR a 6 volt coil is designed for 6 volts n only has around half the resistance (1.5 ohms) and if you apply 12 volts it will overheat plus the points burn up quuicker.

Thats why if you convert from 6 to `12 volts you must EITHER use a full true 12 volt coil (3 ohms resistance n 4 amps current) or add a series voltage dropping (12 to 6) ballast resistor so the coil only sees the 6 volts it was designed for and it n the points carry the same 4 amps.

Finally the 4 amps and 1.5 (6 volt coil) or 3 ohms (12 volt coil) is an approximation n not every coil in the world is exactky that. I try to explain in a few sentences here what it takes books to fill and I spent years in college n the practice to learn so dont dare try n expect it perfect for all in the world.....

John T Retired Elecrical Engineer

The points and condensor dont know or care so much about voltage so long as its not so high it would cause points or condensor failure. The voltage withstand ratings of the points n condensor is wayyyyy yyyyy higher then merely 6 or 12 volts anyway. They dont make a distributor to handle only 6 volts while another one can handle 12 THEY ARE THE SAME and switch the coils approximate 4 amps REGARDLESS if its a 6 or 12 volt coil. The voltage rating of the points n condensor is more like in the hundreds of volts NOT only a mere 6 or 12. The distributor will work n dont care if you have a 6 or 12 volt tractor or coil ITS JUST A SWITCH THAT closes when points close n opens when they are open and can do that regardless if theres 1 or 6 or 12 or 50 voltsat its input terminal/stud

SO AGAIN A distributor IS NOT a 6 or 12 volt distributor THEY ARE THE SAME N DONT KNOW OR CARE. When you convert from 6 to 12 volts you for sure DO NOT have to change or convert the distributor !!!!! !!!!! Its ONLY a current switch and it and its points n condensor can withstand wayyyyy yyyyy yy higher then 6 or 12 anyway.

AGAIN a 6 volt coil is NOT a 12 volt coil, see my post above so if anyone tries to tell you different they are just plain WRONG

Hope this helps n dont be worried if you cant understand what a person does who has a lifetime od training n experience can. Great questions n I hope you understand this..... .

John T