6 or 12 v coil ???

[Kevin Mc]

1965 JD 4020 gas...
12 volt system with an Alt./ neg. ground
I've read about the by-pass starting system providing 12v to coil for starting, then 6v when starter disengages. coil is marked 6v. I've run this coil for several years.
When I turn the key to the RUN position (has a push buttton for start) I get 12v at coil, not 6v. Should I change to a 12v coil?? Internal resistor???

 

[georgeky]

Kevin, if it ain't broke it doesn't need fixing. If it has been working for years what makes you think it needs another one? I would run it until it quits, but that is just how I do things.

 

[old]

Whats the voltage when the tractor is running?? It may have a system where it puts 12 volts to the coil for starting and then when you let off the start button it then goes to the coil through a resister. I know in the old dodge cars and trucks that is how it worked. By doing that it made a hotter spark just to get them running then switched the coil to 6 volts once the engine was running. So if its set up that way you need to stay with the 6 volt coil or you may not have enough spark to run the engine you
Hobby farm

 

[kevmc]

I just added the Alt. and changed to neg. ground.
Swiching leads at coil when I noticed the 6v marking. Checked voltage. Still trying to keep plugs from fouling, wanting to insure hot spark is all.

 

[rvirgil_KS]

If you have a 12 volt system with 6 volt coil with external resistor and turn ignition switch on, but engine not running, you should see:

With POINTS OPEN - 12 volts at both + and - terminals of the coil and both sides of resistor.

With POINTS CLOSED you should see near 0 volts at distributor side of coil, 6 volts at battery side of coil and output of resistor and 12 volts at input to the resistor.

This is because with points open there is no current flow and you see battery voltage on coil, but with points closed the circuit is completed and is designed to drop 6 volts across coil and 6 volts across resistor.

Bob

 

[Anonymous-0]

My gas 4020 has that 6 volt coil and the original resistor was a part of the ignition switch. There is an S terminal on the starter solenoid and it applies 12 volts directly to the 6 volt coil for starting. And for the short time while cranking its probably only applying 10 volts anyway. Not something that will harm the coil. Going to a 12 volt coil will not have a signifcant effect on the lifetime of the coil and won't be good for strong ignition with the resistor in place.

Poor spark or fouling plugs can come from carbon instead of copper plug wires and from running Champion plugs. Seems like the modern Champion tractor plugs can't be cleaned when they get dirty either by engine operation or a spark plug cleaner.

Plugs may be fouling from oil or from running rich. The float needle and seat get worn from decades of vibration and don't seal off gas making the engine run rich.

Gerald J.

 

[Allan in NE]

Coils are like starters.

There isn't a heck of a lot of difference between 6 volt and 12 volt.

Allan

 

[John T]

Kevin, If you indeed have an external ballast resistor (regardless if part of switch or a discrete stand alone unit) and a 6 volt coil, in the RUN position but NOT while cranking iffffffff all is wired correct n functioning properly and the points closed (which they usually are) there should only be around 6 volts on the coils input (NOT to distributor) terminal. If its 12 with a good set or working points closed a 6 volt coil will run hot plus the points will burn up prematurely!!!!!!!!

Are you Sure its a 6 volt coil???????

NOTE a full true 12 volt coil will be labeled "12 volts" or "12 volts NOT for use with external ballast resistor" HOWEVER if labeled "12 volts for use with external ballast resistor" its in reality a 6 volt coil and needs external ballast!!!!!! But since yours is marked 6 volts we have to assume thats correct IN WHICH CASE I strongly suggest you add an external ballast to extend points life even if running warm hasnt harmed the coil as of yet......Id also insure any start by pass system is functioning n wired correct such as an extra lil I terminal on the starter solenoid or an extra terminal on the push to start switch used to feed hot unballasted voltage to the coil ONLY while cranking.

If it had a discrete or part of switch ballast perhaps it went bad and it was by passed?? BUT if so and you use 12 full time on a 6 volt coil it will simply run hotter and the points burn up sooner.

Until the coil overheats (if it ever does???) or the points burn up the spark ought to be plenty strong in the meantime lol

John T

 

[John T]

Allan, NOT to be a smart alek or nuttin but simply to help others, heres some info for yall:

A generic tractor starter is a series wound DC motor with the armature n field wired in series and a 6 volt starter will have different current ratings then one designed for use on 12 volt. As we all know, however, you can use 12 volts on a 6 volt starter n provided you dont let it crank too long n overheat thay can last a long time other then perhaps premature bendix wear from the higher kick in torque. HOWEWVER if you use 6 on a 12 volt starter she wont work worth a dern lol.

A 6 volt coil IS NOT same as a 12 volt coil. A typical 6 volt will have around 1.5 ohms of primary resistance as measured between its lil + and - terminals while a 12 volt coil (some call internally ballasted) will have more like 3 ohms. If you use 12 volts on a 6 volt coil it will run too hot and the points burn up soon and likewise, if you only use 6 volts on a 12 volt coil it will yield a weaker spark. There is some truth in your statement since a coil is more of a current then a voltage device. Its the current passing through the primary winding that develops a magnetic field in which energy gets stored and why (GIVEN the correct current) a 6 volt coil can develop a spark of sufficient energy just the same as a 12 volt coil can.....

Moral of story, they reallyyyyyyyy arent the same.

Hope this helps, God Bless n yall take care now

John T

 

[Bob]

Depending upon the tractor's serial number, the resistor is either on the ignition switch, or built into the wiring harness, as a length of nichrome resistance wire.

If the engine had stopped with the breaker points "open", it would be normal to have 12 Volts at the coil.

If you "jog" the engine over a bit, so the points close, and primary ignition current is flowing, about half of the battery voltage will be "dropped" across the resistance, and half across the coil's primary winding, giving you about 6 Volts at the igntion switch side of the coil.

 

[kevmc]

Thanks Guys, I had indeed checked the voltage with the points open. With points closed, voltage is 4.3v.