Coil checker?

1. Run a wire (alligator test clips) from the flat spring on bottom front of a square coil to the black battery jumper cable connected to one of the battery post.

2. Run a second wire from that same flat spring to a point that is held 1/4" from the bottom of the coiled spring on bottom (springy-thingy).

3. Run another wire from the red battery jumper cable connected from the other battery post to a simple on/off switch and then on to the connection point on top of the coil.

4. When you rapidly flip the switch on and off, you should see a spark jump the 1/4" from the coiled spring to the wire if the coil is good.

First and formost, if it works, there will be a lot of voltage as this coil (transformer transforms a relatively small voltage 6v-12v to much larger (I've heard 400v-3500v) and IT WILL SHOCK YOU. Second, you should use battery jumper cables so as to be as far away from a potentially exploding battery as possible. and thirdly, this square can coil is kinda light-weight and will not take much heat. So flip the switch quickly and only once or twice.

I haven't tried this yet, as I don't have a spare working coil, but in my mind, I don't see why it wouldn't work. Give me your opinions please. If there are reasons why it wouldn't work, we need to know up front. thanks..Ron

Zane

The biggest spark will be at the FLAT SPRING, which is the SECONDARY OUTPUT TERMINAL not at the coiled spring, which is the second PRIMARY TERMINAL.

You're making it sound difficult... simply mimic the wiring of the coil and distributor. And, since there's no ballast resistor in the circuit, to limit primary current, don't keep pressing the switch until the coil overheats internally, and may be damaged!

The trouble is, though, MANY coil problems occur after the engine has run a while, with the combined heat from the current flowing through the coil, and heat fron the engine and radiator causing the coil to "short" internally, and fail, and then work for a while again, after it has cooled. It would be tough to simulate that exact degree of heating, to absolutely verify the coil will work when it's hot.

I have a "SUN" coil tester, and recently picked up an "ALLEN" coil tester, which has a "HEAT" function, to safely heat up the coil, and verify it still functions. I haven't had time to mess around with the ALLEN unit yet, though.

The Pigtail is switched to a ground. The top of the coil is HOT Battery. Do not confuse the battery with Hi-voltage spark. The battery just provides low voltage current to "charge" the coil.

The primary resistance does have significance and can be very accurately measured. You can check the "COIL", contrary to the wisdom of others, but what you can't determine is the reliability of the coil over time.

Hope this helps,

I agree measuring the resistance of the winding will give you an idea if the winding is completely open, or shorted, yet, as little as one shorted turn will adversely affect spark output, while making only a TINY change in the resistance of the winding, not enough to detect with an Ohmmeter, unless you had it's EXACT original measurements, the temperature was constant between the before-and-after-failure measurements, and you were using a high-precision meter.

As you know, REAL coil testers RING the winding with a pulse of current, and display on a meter the length of time it takes the pulse to "decay".