Bench test square coils

DAS

New User
Hi again. I searched the archives and really didn't find an answer.
I know checking on the tractor works but my old stiff hands find it painful and difficult. I have accumulated through the years a lot of coils. Is there a way to bench test them and pitch the bad? If the answer is no then that's the way it is.
 
You can, with a power source (battery, power supply) and a condenser, spark gap (spark plug or spark tester to measure magnitude) do some testing. What you can't determine is whether or not it is good over the high temperatures that it will see in operation. So, I say, yes & no.
 
The latest edition of N News has a great article on this very topic. And heat is the only thing that you can't test for.

Wondering if you can stick the coil in an oven to replicate a hot environment ?
 
Get a power supply (the battery is a good place to start - be sure to use 6v for 6v coils and 12 for 12), ask that annoying little neighbor kid to come over and hold something for you.......

You put your 6v neg to the threaded post on top of the coil, have the punk, I mean helper, hold the coil while touching that brass or steel tang near the rounded side. Brush a jumper wire from the positive side of your battery against the coiled spring contact. If the kid jumps and screams, it's a good coil. :)
 
awe yes, the mysterious square coil. It don't look like the 2-terminal round coil so it must be BAD when I can't start my N-Tractor. I would guess it's bad about 5-percent of the time. Most of yer sparkie problems is in the points.

You do know the 4-nipple squarecan dizzy was designed to have the points (0.015) replaced on the kitchen table, don't you? Since ittza 2-bolt device, you can NOT install outta time without breakin' sumptin'. Just finger start the 2-bolts and then install the rotor. Now twist the rotor until the tang fits into the camshaft slot. Now tighten the 2-bolts and re-snapple the capple. Simple, eh?

While it true, heat is the enemy of the squarecan coil, that is due to the insulative tar that hold the coil inplace inside the squarecan.

Remember: BOTH the original 6-volt and the modern 12-volt squarecan coil require the "infamous" ballast resistor. NO ARGUE!!!

And while the N-tractor came from the factory, 6-volt positive (+) ground, it will work just fine with negative (-) ground as long at the generator and roundcan cut-out relay are polarized fer negative ground. .......electrical Dell
 
(quoted from post at 17:55:18 10/23/14) The latest edition of N News has a great article on this very topic. And heat is the only thing that you can't test for.

Wondering if you can stick the coil in an oven to replicate a hot environment ?
ertainly. All kinds of electronics for military, space, etc. are placed in environmental chambers and tested at desert temperatures, arctic, deep space, etc. Done it many times, including explosive gas atmosphere, vacuum, high pressure, vibration, shock, EMP, you name it.
 

Hhmm... As a test im going to hook up an ohm meter to a square coil and stick it in a toster oven and slowley raise the heat to about 175 degrees and watch the ohm reading. i think that this will give me a bench mark in case i ever have coil problems and need to troubleshoot.
 
The only bench test that I have found (FOR A COLD), square front mount coil, is to test them with a digital ohm meter. 1.5 ohms for a 6 volt coil, and about 3.25 ohms for a 12 volt.
However the only (HOT LOAD)test is on the tractor (like bush hogging at 80 degrees outside). This is when the insulation breaks down and the engine stumbles and dies, but restarts when the coil cools down. Then putting on a known good one and the engine doesn't die.
I have seen other problems, not related to the coil effectiveness, that can mimic the above not starting. One is the failure to put in the right (new gaskets) two is the spring like connection, not making good contact with the distributor.
3. is the not having the correct ballast resistor, or reducing resistor, or the wrong coil ohms (IE 6 volt coil on a 12 volt conversion.

Charles Krammin SW MI
 
He doesn't come around anymore. Sumtin' about the Model T coil...
Any way I have a bunch of coils, Some have ohms, some do not.
Jumper from battery to coil terminal.
jumper from front tab to in-line spark tester other end of spark tester to.....
I'm expecting to do momentary contacts but need resistor to protect the coil? Condenser?
 
(quoted from post at 22:09:02 10/23/14) He doesn't come around anymore. Sumtin' about the Model T coil...
Any way I have a bunch of coils, Some have ohms, some do not.
Jumper from battery to coil terminal.
jumper from front tab to in-line spark tester other end of spark tester to.....
I'm expecting to do momentary contacts but need resistor to protect the coil? Condenser?
f you do not use the condenser, your spark will be weak! You can get by without the resistor. Test more realistic/pure with it.

or if you don't want to do all that hand work touching the jumper, substitute this "buzzer" relay connection & it will spark repeatedly until the cows come home!
 
I've sold all my front mounts tractors,
but I think I still have my 'front mount necessities' box
in the shop somewhere.
I snagged front mount distributors whenever I saw one cheap.
One beater in the box for testing stuff like coils.
One good one, complete with a good coil and cap, all assembled and ready to go.

Damp, corroded no start, or poof into a snow drift in freezing weather....swap the whole thing out..took minutes
Then fix the one on the bench and throw it in the box for next time.
dang front mounts :D

ps the only testing I do on square coils now for other people is to look for a tar-filled one, so it will be easy to soak/gut it out and run a round coil....
 
There is a good article in the latest issue of the N-News by Bruce Haynes on Ford coils. It may surprise you that most ignition problems are not due to a bad coil. As stated by Dell, a coil will melt the internal protective tar if the key switch is left on and points burn up. But it will start the engine when cold. Once it reaches ambient temperature, it will short out and shut the engine down. That is really the only way a coil can go bad. The 1.5 ohm reading from top post to pigtail connector on a square can is correct. Tune-up at least once a year is recommended depending on usage and always keep 6-volt system clean, bright, and tight.

Tim 'PloughNman' Daley(MI)
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top