coil resistance

[jds535]

Hello all, its been a while....cuz my tractor was running good.

Sorry to drag up this topic again but searching through all of the posts is very time consuming. With all of the knowledge here I know I can get a quick correct
answer.

The motor blew in my 9N a few weeks ago so I took the opportunity to buy another 52 8N sidemount. This one has a Howard reduction gear setup in it very cool.
Soooo happy I bought it. It was a non runner but I got her going quickly. Reversed plug wires, dirty carb, and a stuck valve later she runs good and has great
oil pressure too.
I just cleaned up all of the wiring and removed 2 resistors that were tie wrapped and taped in the wiring but didnt appear to be plugged into anything. That got
me thinking about the coil.
Its a newer Napa coil. I measured the resistance across the primarys and it was 1.8ohms. I want somewhere around 3 ohms so as to not kill my coil quickly, right?
One of the resistors I removed measure 1.5 ohms. Should I wire that into the 12V feed to the + side of the coil primary?

 

[Ericp351]

Yes. Get a 1.5 Ohm resister, +- .2. Actually, you will save your Points .

 

[HFJ]

i put well over 100 hours on a 6 volt frontmount coil in a 12 volt system with no added resistor and it's still good. YMMV, but define 'quickly'

 

[lastcowboy32]

Any resistor will do the job.

But ideally...

For best performance, you want a "ballast" resistor that has low resistance cold (you'll get a little spark boost at cold start) and the resistance will go up to 1.5 (approximately) after current passes through for a while and the engine warms up... this will preserve the life of your coil.

In modern terms, what used to be called a "ballast" resistor will often be called PTC (Positive Temperature Coefficient) resistor.

(full disclaimer... almost all resistors have a positive temperature coefficient... but it is usually in the ppm (parts per million) range for regular resistors. A true PTC resistor will change ~50%, more or less, from cold to warm)

 

[JMOR]

(quoted from post at 09:10:31 07/12/23)
Any resistor will do the job.

But ideally...

For best performance, you want a "ballast" resistor that has low resistance cold (you'll get a little spark boost at cold start) and the resistance will go up to 1.5 (approximately) after current passes through for a while and the engine warms up... this will preserve the life of your coil.

In modern terms, what used to be called a "ballast" resistor will often be called PTC (Positive Temperature Coefficient) resistor.

(full disclaimer... almost all resistors have a positive temperature coefficient... but it is usually in the ppm (parts per million) range for regular resistors. A true PTC resistor will change ~50%, more or less, from cold to warm)

he coil primary winding of copper wire is in effect a PTC resistor....not as much as you might like, but it does result in lower current as it heats up.

 

[R Geiger]

I would just get a 12 volt coil and be done with the add on resistor. Ballast resistor not needed with side mount ignition system.

 

[rvirgil_KS]

You can either use the 1.5 added in series as you describe, or replace coil with NAPA IC14SB or equivalent coil with approx 3 ohm primary and eliminate need for extra resistor.

 

[Ericp351]

1- A Ballast resister is way cheaper than a coil. 2- most 12 volt point coils ARE 6v. that is why they use resister wires or bar type ballast resisters. IF
you want 12v for cold starts still, buy a start solenoid for an older Ford Car- when closed (12 V to starter, It has an I post, temporally full 12 v to
coil, via a simple 14 Ga wire. This stuff has been proven- perfected about 6 decades ago. Cheap to do correctly go for total coil resistance at 2.8- 3.2
Ohm, protect your points, enjoy + do not worry that somebody else Ductaped some do dad in to save $3.59 , et cetera.

 

[jds535]

Thank you all for your feedback, and confirming what I thought was the way to go. I used the 1.5 ohm resistor that I had. We used to call them sand resistors. ??She starts and runs good.