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12 volt coil only has 1.6 ohms

J

Jason1Pa

Member
So I got another 12 volt (front mount) coil because the one on the tractor bit the dust. Just for curiosity I checked the ohms on it with my meter. Came out 1.6 ohms. That's odd since a 12 volt coil normally has 2.5 to 3 ohms. Even the bad coil was still reading 2.8 ohms. It's clearly marked 12 volt on the box AND coil. I'm still thinking I got a 6 volt coil. Anyone have this issue from the Chinese coils?
 
Zero your meter if it has an adjustment.

Touch the leads together.

Press really, really hard with those leads on the coil.

Might be the meter or the technique.

But it might be the coil.

" Even the bad coil was still reading 2.8 ohms."

What did you expect it to read? Unless it's got a dead short, coil resistance isn't a reliable method to determine if a coil is defective.
75 Tips
 
"That's odd since a 12 volt coil normally has 2.5 to 3 ohms. "

Yes, that's correct for a true" 12 Volt coil, however the coil you have is intended to work on a 12 Volt converted tractor WITH the OEM ballast resistor left in place!
 
"Unless it's got a dead short, coil resistance isn't a reliable method to determine if a coil is defective."

I think the most common failure mode is an open primary due to it having drawn too much current, and an "open" would definitely show up on an ohmmeter or a test light.

The coil primary circuit is a series resistance circuit having two series resistors across the battery: the ballast and the coil primary; and there is a different voltage drop across each of them. You may need to figure the voltage drop across each resistor in order to determine if you have the correct ballast; i.e. if the voltage drop across your coil primary is its recommended operating voltage. There are websites that tell you how to calculate voltage drops across series resistors.
 
BTW, a 1.6-ohm ballast used to be a common value for older 12-volt cars that had points-type ignitions, so it could be the correct value if you are using a standard automotive coil.
 
1.6 ohms was never used on point type 12 volt cars. Ford used 1.35, G.M. used 1.85 and Chrysler used .5. Each manufacturer also had their own proprietary coils with different primary resistance.
 
I generally concur with your comments regarding a standard automotive type coil. However, the specific question has to do with the N tractor front coil. From my experience, they tend to fail when hot & under load, i.e., the secondary circuit. This type of coil was standard on V-8 Ford engines from 1932 to 1948. are you familiar with it?
75 Tips
 
" if you are using a standard automotive coil. "


Once again, no!

He is not using a "standard automotive coil".

All he needs is the tractors OEM ballast resistor which is .3 ohms cold and .7 ohms hot.

That's a big difference from 1.6 ohms.

See tip # 30 also.
75 Tips
 
All of the front mount coils marked 12V that I have measured have been within the 2.5-3.0 range, most very close to 2.5 Ohms. All of the OEM style terminal block with resistor I have measured have been 0.6 Ohm cold. 2.5 + 0.6 = 3.1 which is where you want to be on 12V.

I would consider a square coil for a front mount N tractor marked 12V but measuring only 1.6 Ohms defective and return it to where I got it. These days when I go to buy a coil I go armed with a part number of the coil I want and my multimeter.

later
deano
 
Chrysler used a 1.6-ohm ballast with their points ignition systems, and only went to a .5-ohm ballast with the advent of the Mopar transistorized EI.
 
(quoted from post at 07:38:29 09/27/17) "That's odd since a 12 volt coil normally has 2.5 to 3 ohms. "

Yes, that's correct for a true" 12 Volt coil, however the coil you have is intended to work on a 12 Volt converted tractor WITH the OEM ballast resistor left in place!
Click to expand...
I'm experiencing the exact same issue with a coil that is supposed to be for a 12 volt conversation. The kit that I purchased came with a resistor so I will just install it.
 
(quoted from post at 20:53:01 09/27/17)
(quoted from post at 07:38:29 09/27/17) "That's odd since a 12 volt coil normally has 2.5 to 3 ohms. "

Yes, that's correct for a true" 12 Volt coil, however the coil you have is intended to work on a 12 Volt converted tractor WITH the OEM ballast resistor left in place!
Click to expand...
I'm experiencing the exact same issue with a coil that is supposed to be for a 12 volt conversation. The kit that I purchased came with a resistor so I will just install it.
Click to expand...
ou might get lucky! I do not know why folks are so eat up with volts & Ohms! What you are searching for is 4 amperes steady state current. Just forget the volts & Ohms & select the coil & resistor pair that yields 4 amperes SS. You will be done! Yes, it is really that simple!
 
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