Interesting to find out

[Gym]

I had a few Old School backend relays to rebuild for my 6700 Elco's, and the builds were going fine until I started bench testing them.

I hooked them up one by one to check my contact throw, and to make sure I had good contact when I came to one that just stuck after a few times that I energized the coil.

Now I had just cleaned the points, so I was a bit confused. So I tested the same relay again, and sure enough it stuck. Instead of giving it a little flick I unplugged it, and it stayed closed.

Now wait a minute, I'm thinkin, when you remove power from an electromagnet the field collapses.

Do I have a partially magnetized coil core? When we have a backend relay stick I just clean the points because that's what I thought was the cause, and now this. Damned interesting.

Any thoughts would be appreciated.

Thanks,

Jim

[rivmike]

They should slide alittle while making contact so they don't weld together. Tweak the contact lever and see if it will test ok.

[Gym]

They should slide alittle while making contact so they don't weld together. Tweak the contact lever and see if it will test ok.

Interesting thought, but I did not have any power going thru the contacts, just the coil. That's what got me to thinkin.

[Pietenpol]

I would think that if the points get worn enough they are thin enough to weld together and stick. You can clean them to a certain extent but once they get worn too thin it's time to replace.

[rivmike]

Interesting thought, but I did not have any power going thru the contacts, just the coil. That's what got me to thinkin.

Return spring tention?

[Tablejam]

They should slide alittle while making contact so they don't weld together. Tweak the contact lever and see if it will test ok.

I have saved many relays that were sticking doing this. No sense in tossing an otherwise perfectly good relay. I just slightly bend the contacts in a little so that when they close and open they slide on each other and the bent contacts also provide a little extra springiness so when it shuts off they can push away a little better. In all my years I have only replaced three of these that failed, but have adjusted several that were sticking and they are still running just fine.

[seanm]

Tightening the spring normally works for me.

[Gym]

Thanks all, but I'm still pondering on why the contacts stayed closed when I was only providing power to the coil. Just a thought, could the coil core or the contactor plate become partially magnatized?

Spring tension, Hmmmm. Great thought, I'll check that. Tks!

[Tablejam]

Well since they are old and have closed and opened probably thousands of times, its reasonable to assume that over time the spring can get weak and where the armature pivots can wear, which may cause it to get stuck. Just an idea but it makes sense.

[Gym]

Thanks. Weak spring and mechanical binding make a lot more sense. Sometimes I tend to go off on an odd track.

[Tablejam]

The magnetism idea is fascinating. Is it possible that could be happening? If you magnetize that coil several thousand times can it possibly magnetize the armature or the contacts themselves? .....hmm....

[Gym]

After I got here and finished doing the lanes and approaches, I started puttering. Just for S & G's I took that relay apart and picked up a nail with the coil. When I diconnected power the nail stayed. This is just damed interesting. Am I seeing a coil starting to break down, or as you said, TJ, maybe after all these years it is getting magnatized. Things that make you go Hmmmmmm.

[wb8yjf]

If the coil was magnatized, you should be able to manually close the contacts w/o power and it would still 'stick'.

[Gym]

/\ You're absolutely right. I did try that, and it did not stick. Then why is the field not collapsing? There is no current. I checked the relay I was mucking with, and one off the shelf (that had had no power applied to it prior to my checking) and got .0001 vac for both. Thinking about it after looking at the configuration of the core, it looks to be 2 piece. Solid center with an outer ring of 2 arches something like this ( | ). Would contact from outer to inner not allow the field to collapse?

[AmfPro]

You ever heard of a degaussing coil?? - I used to put all my questionble relays in a cardboard box, on an outside concrete wall, and wave a degaussing coil over them for 2 minutes or so, removing all magnetism from the coils. A degaussing coil is really used to clean phosphorous discoloration on the inside of overhead auto scoring monitors. I love this tool on old TV type glass monitors, for clearing up colors on monitors thaty some might think are going bad!! Something to think about. Never failed me in 20 years!!

The trick Gym is stand to 90 degrees from the coil - the degaussing coil looks like a round hoop about 12-15 inches diameter. Ya have to stand to the side of the loop and wave the circle in a circular motion over what you are degaussing/demagnetizing. Standing in front or behind of the circle can actually cause your heart to skip beatws, the magnetism is that strong. I posted this as an addedum & warning!!