coil test

hayhay5757 · May 13, 2017

12 volt coils primary side pegs ohm meter / secondary 8 ohm have 3 coils 1 on each tractor & a old 1 I had laying around all test the same to high on the secondary side / 3 ohm is what I was told / primary how high ??

Steve@Advance · May 13, 2017

I've never tried checking the secondary side, not sure what that would read.

But checking the primary side (+ terminal to - terminal) should read around 3 ohms for 12v, 1.5 ohms for 6v.

Be sure the coil is out of circuit, the meter is set for Rx1.

If the reading is infinite, there is an open primary, coil is bad.

If the reading is high, the winding is weak, coil is bad or failing.

If the reading is low, the winding is shorted internally, or the coil requires an external resistor.

Basically what you are trying to determine is the health of the coil, and the application. Since many coils are not marked, it is best to know, otherwise the coil will either under perform, or overheat and overload the points or electronic unit.

The best test of the secondary that I know is,(after determining the primary is correct) to put it in circuit and test the spark.

hayhay5757 · May 14, 2017

(quoted from post at 18:20:42 05/13/17) I've never tried checking the secondary side, not sure what that would read.

But checking the primary side (+ terminal to - terminal) should read around 3 ohms for 12v, 1.5 ohms for 6v.

Be sure the coil is out of circuit, the meter is set for Rx1.

If the reading is infinite, there is an open primary, coil is bad.

If the reading is high, the winding is weak, coil is bad or failing.

If the reading is low, the winding is shorted internally, or the coil requires an external resistor.

Basically what you are trying to determine is the health of the coil, and the application. Since many coils are not marked, it is best to know, otherwise the coil will either under perform, or overheat and overload the points or electronic unit.

The best test of the secondary that I know is,(after determining the primary is correct) to put it in circuit and test the spark.

Ok the coils on both tractors get HOT what to do to fix this

Steve@Advance · May 14, 2017

As for the coils getting hot...

Assuming you have checked the ohm reading across the primary terminals, and the reading is in the 3 ohm range, corrected with a resistor if needed.

It is normal for coils to increase in temperature in use. One big factor is heat picked up from the engine compartment.

Another is the point gap. If the points are set too close, the dwell will be too long, causing the coil to run hotter. If the points are run too close, typically you will see some heat discoloration on the contact tip. Check the distributor bushing for wear. Or consider an electronic conversion.

Any coil left under power, ignition on, points closed, engine not running, will get dangerously hot, even to the point of exploding!

But the typical test is, you should be able to hold your hand on it, maybe not for too long, but not so hot that a touch is going to burn you. Take into mind that if the surrounding parts are too hot to touch, so will the coil be.

rvirgil_KS · May 15, 2017

Sounds like your ohmmeter is set on x1000 scale, which would mean your 8 on secondary side would be 8000 ohms which would be in expected range

You need to set meter to x1 scale to read across the + to - It should be about 1.5 ohms for 6 volt, and 3 for 12 volt. If using 1.5 coil on 12 volt add a 1.5 ohm ballast resistor

coil test

hayhay5757

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Steve@Advance

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hayhay5757

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Steve@Advance

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rvirgil_KS

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