12 volt vs. 6 volt coil

[Kurtb]

The old tractor still won't start,

I'm attempting to find whether I have a 6V or 12V coil so...

While troubleshooting the resistor near the start relay on my 2N (12 volt) I decided to jump directly from the coil to the ignition switch side of the resistor where there was power, the tractor started and ran as well as it normally does. Dare I ask the obvious, but should I now assume the coil is 12V since it has a 12V battery?

 

[Bob]

2N's DID NOT originally have a start relay, so WHO KNOWS what else has been changed or cobbled up.

If the coil is a 6-Volt unit, it needs about 1.8 Ohms ahead of it, IN ADDITION to the OEM ballast resistor.

If the coil is a "so-called" 12-Volt square can coil, it STILL needs either "DELL's trick current limiting resistor of about 1/2 Ohm ahead of it (if it is an older production "12-Volt" coil).

It seems some of the later "12-Volt" coils are happy if the OEM ballast resistor from the 6-Volt system in left in place with the "12-Volt" coil.

 

[Kurtb]

OK so it's not a 6V coil if it started with 12 volts running to the coil straight from the battery correct?

KB

 

[Bob]

A "6-Volt" coil WILL work on 12-Volts, FOR A WHILE!

What you MAY have is a 6-Volt coil that has gone bad, and the extra "juice" you are giving it by eliminating the resistor is forcing it to produce enough spark to allow the engine to start.
This will be short-lived, 'til the coil finishes burning out and/or the points burn.

OR, you may have a bad reistor(s) or weak ignition switch, or poor connection in the primary circuit.

 

[MikeT]

KB -

Do you have a meter that reads amps? IF so, put it in series with the ignition wire to the coil and see how many amps it reads with the ignition switch on but the tractor not running. You may have to turn the engine over by hand till the points make contact.

You should see 3.0-3.5 amps. If you have more than that then add resistors till you get it down into the 3.5 amp range. If you need resistors, then start with the OEM ballast resistor and work from there. If you see 4.0 amps with the ballast resistor, then stop there. When the ballast resistor warms up, the resistance will go up and the amps will go down approximately to the 3.0-3.5 range.

 

[Dell (WA)]

Kurt........for a "MOMENTARY" 12-volt jolt can start a 6-volt coil. The key word is "momentary" and once started you MUST use the "infamous ballast resistor" plus a 12-to-6 volt converting resistor or you will BURN out yer 6-volt coil. Its the LAW; thermodynamics heat-sink law.

Unfortunately, the modern 12-volt squarecan ignition coil has NO identify part numbers or voltages, but they can "engrave" the country of manufacture. Go figger.

While I can quote resistance reading values, unless you have a "lab-grade" ohmmeter, they're not too helpful in identifying 6-or-12 volt squarecan coils.

But for the record, 6-volt coil primary = 1.2-ohms, about 7000-ohm for sparkies; and modern 12-volt coil primary = 2.5-ohms, about 7000-ohms for sparkies. The "infamous ballast resistor" can vary from about 0.4-ohm when COLD to about 1.7-ohms when HOT, use a nominal value of 1.2-ohms. The 12-to-6 volt converting resistor should be 2.5-ohms 50-watts (NTE 50W2D5 or eqv).

The 8NE10306 is listed as 0.5-ohms and NOT a 12-to-6 volt converter for the 6-volt frontmount coil. (unless you use 5-resistors in series like hotdog weenies) The early 12-volt squarecan coils needed a "current limiting" resistor of about 1/2-ohm. Radio-Shack no long lists their 1-ohm 10-watt 271-131 2-pack resistor to make what is commonly referred to as "Dells Trick Resistor". Use the 8NE10306 instead........Dell, yer self-appointed sparkie meister

 

[Bruce (VA)]

You asked this same question on January 29 & got plenty of answers; perhaps you didn't see them? Here is the link:
Resistor Question

 

[Hobo,NC]

what amp reading should you git when the alternator puts 14.5vs to the coil