Coil questions

[lolbell]

How do you test a 12v coil to see if it is internally resisted. I have a 140 that is burning points up too often. It has no external resistor so I wondering if its got a 12v coil with no resistor.

[customcutter]

Hope this helps.

https://forums.yesterdaystractors.com/v ... ?t=1485877

[lolbell]

Thanks for your response
The coil on the tractor is testing at 6.1 ohms. I went to NAPA and bought an internal resisted coil it’s testing at 6.0 ohms. What have I got?

[Gary Dotson]

Are you checking small post to small post? Are the wires disconnected? The ohm reading should be approx 1.5 ohm for non resister, and approx 3 ohm for internal resister. Have you replaced the condenser? A fault condenser can cause point failure, as well.

[JoeB]

A 6 Volt coil with a ballast resistor in line between battery and coil will provide the most life out a set of points and condenser.

A 12 volt coil that says " external resistor required" is the same as a 6 volt coil, and would work as well.

The 12 volt coils that do not require a ballast resistor do best electronic ignitions.

High performance coils have no place with points and condensers ignitions on these tractors as well.

[lolbell]

Are you checking small post to small post? Are the wires disconnected? The ohm reading should be approx 1.5 ohm for non resister, and approx 3 ohm for internal resister. Have you replaced the condenser? A fault condenser can cause point failure, as well.

Yes small post (+ to -). Checking with a Fluke 13 multi-meter. Both coils off of the tractor on the work bench.

I pulled the distributor to give it a once over and, I think, found the problem. The lobes on the shaft were very rough and the contact surface on the points would wear quickly which would narrow the gap. I dressed the roughness up with emory cloth and reassembled with all new electrical components. It now runs like a sewing machine. I’m still baffled about the resistance on the coil though.

[lolbell]

Another thought just occurred to me. Several years ago while answering a high voltage call I discovered a weak battery in the Fluke would cause a high A/C voltage reading. I need to replace batteries in the meter and take another reading. I don’t remember when I replaced the battery and I’ve been retired a while and not used it much since

[lolbell]

Put a new battery in the meter and got 3.1 ohms.

[Jim Becker]

Did you try touching the 2 meter proves together to check for 0 ohms? That is my usual quick check whenever i get the meter out to see that it is working properly. If it won't measure 0, it won't be close on any other low resistance reading.

[lolbell]

Yes Mr. Jim I did. It zeroed out. Before and after the new battery.

[Gary Dotson]

I had the same thing happen with my favorite meter, I was getting some really goofy voltage readings, on something, and thought my meter had given up. Replaced the battery and it’s worked great ever since. Glad you found the cause of the point problem, hope it works okay going forward.