How do you tell a 6 volt coil from a 12?

Just wondering if any one knows how to test a coil to tell if its 6 or 12 volt. The H tractor I just got has a larger coil than my 6 volt original international Coil on my other H. I just want to make sure that this tractor wasn't converted to 12 volt or something.

Well finding out id it is 6 or 12 is easier than testing the coil.

If the battery has 3 cell fill caps/holes, it is 6v.
if 6 it is 12 v.
With a volt meter it can be checked (across the two terminals)
If it is running and charging use it until you decide to put it to original or leave it alone.
the coil should draw about 3 amps. if drawing 6 amps it is the wrong one. If drawing 1.5 amps it could be a 12v on 6 volt battery.

There wasn't a battery on it when I got it and the wiring is old and not in good shape right now. I'm hoping i can figure out how to test the generator and see if its charging as well. Been searching around right now and haven't come up with anything.

Does everything else look the same on the wiring harness? Same generator and so forth?

The first step I would do is figure out what type battery and if it should be negative or positive ground.

I have little experience working with generators but there have been discussions here before about Gen/regulator problems so maybe you can find some info there

If the generator has a black tag it was originally 6V (could have been rewired as 12 volt but not too likely) if red tag was 12 volt.
The bulbs would have been changed to 12 volt!
The regulator will likely have a voltage stamp on its back side. These should help. Thanks to bob.
Jim
Bob Ms Superlative Wiring diagrams

QUESTION

Just wondering if any one knows how to test a coil to tell if its 6 or 12 volt.

ANSWER: Many original coils designed for use at 6 volts have a primary winding resistance as measured between their small + and - terminals around 1.25 to under 2 ohms (1.5 ohms typical)......THEY ARE LABELED 6 VOLTS

Many original coils designed for use at 12 volts have a primary winding resistance around 2.5 to 3.5 ohms (3 ohms typical)... THEY ARE LABELED 12 VOLTS

One reason being is so the points dont draw and have to switch too much over 4 amps so they dont burn up too quick. If you use a coil designed for 6 volts on a 12 volt tractor unballasted it can overheat badly, while if you use a coil designed for 12 volts on a 6 volt system the spark will be weak

NOTE Im NOT talking about high performance (Mallory and Accel etc) or elec ignition coils, Im talking many older original stock farm tractor coils for points and condensor ignitions THIS IS NOT A PERFECT TEST but when I was a used tractor dealer I used this method many many times AND IT WAS ALWAYS CORRECT. They could make a coil that would work at 6 or 12 volts but my best guess is its ohms would be well over 2. Still when you walk into NAPA they will ask if you want a 6 or 12 volt and will sell you one or the other more likely then they will sell you a UNIVERSAL coil for either 6 or 12 volts (I doubt they will have one)

NEXT does the tractor have a 6 or 12 volt battery?????????????

Is the genny a 6 or 12 volt??? Many 6 volt are black labeled while many 12 are red labeled

John T

(quoted from post at 19:26:07 03/06/10)
ANSWER: Many original coils designed for use at 6 volts have a primary winding resistance as measured between their small + and - terminals around 1.25 to under 2 ohms (1.5 ohms typical)......THEY ARE LABELED 6 VOLTS

Click to expand...

Thanks John, This is excactly what I was looking for.

There wasn't a battery on the tractor when I got it. I've basically been using my 12 volt lawn mower battery to hear it run. The wiring on the tractor is mostly original, missing its loom, and very ratty/broken up. The one and only battery cable that should have been connected from the starter button to the starter was only connected to the starter and was almost completly bare of its insulation.

The center post on the regulator is unhooked and I think thats the supposed to be the charging wire back to the amp meter.The wire was still there and hanging but has been disconnected from the amp meter as well. I tried connecting it to the terminals to see if anything would happen but I didnt get anything to register on the amp meter. May not be charging or it could be to much rust on the contact of the regulator. I havn't cleaned them yet.

The regulator is pretty rusty. I've seen where it has ink marking underneath the regulator that says 12v or 6v on aftermarket ones. I was wondering if IH put it on the OEM ones or not. I'll have to take a look at this.

Basically I would like to know what the charging system should be so that I can get a battery for it in the future. I figure I'll leave it the way it is, 12v or 6v, whatever it is.

I'm going to have to check out the generator for that tag today. Hopefully there is some paint left to it. It seems some one installed an upper mount off a car so that the alternator would swing further to tighten up the belt instead of tighting up the pulley. The hood hits against the mount and won't fully close.

Thanks for the wiring diagrams Jim, these will help and keep me from having to take other H part to see where the wires are supposed to run.

If it has an alternator (or had one), its likely 12 volt and its likely Negative Ground. DO NOT wire ANY alternator at reverse polarity. Also if it has a Delco 10SI Alternator or any other, a DC genny type of Voltage Regulator WILL NOT BE USED. What you have would be easy to diagnose if we were there but tougher based on tid bits we get off the net

If it were mine Id start all over and take it back to original which is likely 6 volts and Positive ground. You can get a new complete wiring harness from Jim at Agri Services in New York www.wiringharnesses.com and Jim gave you a URL link to Bob M"s Wiring Diagrams

Best wishes

John T
Agri Services

Generally speaking with post-1940s coils, there is no such thing as a "6 volt system" or "12 volt system" coil. That because many systems, regardless if 6 or 12 volt, feed the same voltage to the coil under normal running.

What you need to determine is IF that coil needs an external resistor hooked to it when used on a 12 volt system.

You also need to know if it was designed for a system WITH ignition points, or for a more modern high-energy breakerless system. Such coils will have very low resistance across the primaries; often only 6/10ths of an ohm.

A typical OEM coil on an H that had 6 volts fed directly to it is checked as thus with an ohm-meter.

2.6 ohms across the primaries and 7000 ohms across one primary to the secondary.

Same coil was also used in 12 volt systems along with an external 1.8 to 2.2 ohm resistor.

A coil that has a built-in resistor is only good for use in a 12 volt system. It will measure around 4 ohms between the primaries.

Then you've also got the many "hot spark" coils made for older tractors. Often 1.4 ohms on the primaries and 10,000 ohms between one primary and the secondary. Can make 40,000 volts instead of the standard 20,000, but also can be hard on ignition points.