On dressing contacts
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  1. #1
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    Default On dressing contacts

    A Hawacheon lathe refusing to run and making growling sounds. It didn't take long to determine that it was losing one phase. The Yaskawa contactor is still available from China with several weeks travel time. Meanwhile, the folks wanted to make parts. The contacts were all burned evenly and by the gospel according to Tom, should not be filed. Maybe so in most cases, but in this one, the contacts were in two rows of fixed ones with the moving contacts on a strip with a jiggle in it that locates in a notch in the Bakelite frame. They move straight up and down with no wipe and are only more or less positioned. You can't count on them meshing the same way twice and sometimes one set was not making an electrical connection. I filed them down to where there were a few tiny spots of pitting left, which left .030" to 040" of silver. Heresy though it may be, the bottom line is the machine runs, which is the name of the game. We will get a new contactor, but I don't expect to have to change it for a while.

    Bill

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    Whatever works. What I railed about was the sense less filing or sanding contacts because they looked dirty or black. If it takes doing what you did to make it work by all means do it. Sounds like there may be a fundamental design error in the contactor.

    Tom

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    Agree, always inspect and then do the least amount of damage (metal removal) to make things work.

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    Filing contacts shortens their life and INCREASES the RATE of decay. But to get back up and running when you are not, it's better than waiting for a replacement contactor.

    Pitting by the way is NOT a bad thing. When you see a pit on one side, there is usually a peak on the other side that matches it, which actually INCREASES the surface area of contact. That's why filing them down increases the rate of decay. The problem with old contacts is usually just dirt and carbon causing an increase in resistance. Burnishing them with some fine emery cloth is better than filing, but do so AWAY from the contactor so that the grit doesn't get in it. I have also used a pencil eraser, that works well.

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    Quote Originally Posted by 9100 View Post
    A Hawacheon lathe refusing to run and making growling sounds. It didn't take long to determine that it was losing one phase. The Yaskawa contactor is still available from China with several weeks travel time. Meanwhile, the folks wanted to make parts. The contacts were all burned evenly and by the gospel according to Tom, should not be filed. Maybe so in most cases, but in this one, the contacts were in two rows of fixed ones with the moving contacts on a strip with a jiggle in it that locates in a notch in the Bakelite frame. They move straight up and down with no wipe and are only more or less positioned. You can't count on them meshing the same way twice and sometimes one set was not making an electrical connection. I filed them down to where there were a few tiny spots of pitting left, which left .030" to 040" of silver. Heresy though it may be, the bottom line is the machine runs, which is the name of the game. We will get a new contactor, but I don't expect to have to change it for a while.

    Bill
    Ummh.... "the gospel according to Tom", I actually DID take to heart.

    Figured if one is meant to let the metal decide under the influence of un-American influences where TF it wants to be... and interfere ye not?

    That was as good an endorsement as I was likely to find to keep-on using Mercury Displacement Contactors.

    Ain't had to file one YET. Unless the world turns upside down, or I relocate to Tasmania or South Island, NZ? I do not expect to EVER have to do.

    Nor the lighter-duty Crydom SSR's either, FWIW..


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    Now I would have thought the OP....would have taken a TIG torch, and Zap.


    A little "re-puddling" of the offending tip.

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    Quote Originally Posted by digger doug View Post
    Now I would have thought the OP....would have taken a TIG torch, and Zap.


    A little "re-puddling" of the offending tip.
    9100 Bill P.?

    Doug?

    There is not ONE component in a contactor Bill cannot make from a cold start, and properly Engineered to do a specific task.

    Contacts, armature, integral and/or separate springs, frame, bobbin, coils.

    Not ONE.

    He did the common-sense thing, here. Most of us would do.

    Not as if it were a weapons system.

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    Quote Originally Posted by thermite View Post
    9100 Bill P.?

    Doug?

    There is not ONE component in a contactor Bill cannot make from a cold start, and properly Engineered to do a specific task.

    Contacts, armature, integral and/or separate springs, frame, bobbin, coils.

    Not ONE.

    He did the common-sense thing, here. Most of us would do.

    Not as if it were a weapons system.
    Yup, having read much of what 9100 has done in the past with TM contactors and smaller, and having witnessed the production of new contacts (both silver soldered, and spot/projection welded) myself, I know what goes into them
    (well, some of them at least)

    I thought maybe, just maybe Mr. 9100 had given it a try.

    You don't remove any material, just reform, and slag off the burned up bits.
    Filing requires you to remove good material to "dig out the pits".

    FWIW, I have used one of those "fiberglass pens" for polishing the contacts, but I'll bet, the OP's needed reshaping as well.

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    The problem with reforming the contacts with a TIG is that if the contact is silver cad oxide, the silver will segregate from the cadmium oxide. Pure silver on pure silver makes for a WONDERFUL weld combination. I would not do that unless the contactor is a 00 which is fine silver anyway. The other issue is not to put too much heat into the contact or the backing, usually fine silver, may be loosened or the bond damaged.

    Father Tom

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  13. #10
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    Quote Originally Posted by Jraef View Post

    Pitting by the way is NOT a bad thing. When you see a pit on one side, there is usually a peak on the other side that matches it, which actually INCREASES the surface area of contact.
    As I said in the initial post, the nature of the mechanism was that you could not count on the contacts meshing the same way each time. After taking the contactor apart, there was no chance of returning to the same alignment.

    The moving contacts are on copper strips held in place by springs and can move around. Heating them would anneal the copper, rendering them useless. The water coming into the Riverview waterworks north of the city are controlled by large valves (like 5 feet) connecting to the might Mississippi. I made replacements for the contacts controlling the motors on the valves. The moving contacts were on copper strips about 5/8" wide, 3/32" thick. I silver brazed the silver disks on them and found that all I had was a batch of the proverbial wet noodles. The copper was so soft that the contract pressure would bend them. It looked like I had scrap until it occurred to me to try work hardening them. Shot peening would have been best, but what I had was glass beads, so that was what I used. That nicely case hardened them and they have been happily supplying water to the city since.

    Re mercury displacement relays, they are fine unless you cycle them too fast. The arcing generates mercury vapor, like the old mercury rectifiers, the vapor sustains the arc and things go south in a hurry.

    As to design flaws in the contactor, it is a simple one- Cheap. They are simple units, held together by three spring clips and have rudimentary arc chutes, strips of metal that keep the arcs from burning the Bakelite. However, this lathe has been in everyday use for at least 15 years that I know of, and, like all good machine tools, has earned its purchase price back over and over, so it is hard to fault the design.

    Bill

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    Quote Originally Posted by 9100 View Post
    Re mercury displacement relays, they are fine unless you cycle them too fast. The arcing generates mercury vapor, like the old mercury rectifiers, the vapor sustains the arc and things go south in a hurry.
    Known issue, thanks for reminding the clan.

    I'm using them at conservative loads for RPC feed, plus supplementary idler drop-on.

    Idler shutdown is done after load has been shed, so even the upstream on the incoming isn't that heavily loaded comes time to break the flow.

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    Quote Originally Posted by thermite View Post
    Known issue, thanks for reminding the clan.

    I'm using them at conservative loads for RPC feed, plus supplementary idler drop-on.

    Idler shutdown is done after load has been shed, so even the upstream on the incoming isn't that heavily loaded comes time to break the flow.
    I put one ON an air compressor once...once.

    When it would shut off, it would "bounce", and restart the motor.

    Mercury relays do suffer from "jiggling".

    Could have put it on the wall, I still have the relay.

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    I have been filing contacts for 42 years and I will not stop till I am dead. I know the exact amount of years because I started doing it on ignition points when got my first car at 16. I last did it on a Furnas brand contactor on 3 phase horizontal band saw a half dozen years ago. It may have "shortened their life" but they still work after a couple minute fix 6 years ago. I have a spare contactor if it dies. My favorite tool to use is an emery board for filing finger nails.

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    Quote Originally Posted by digger doug View Post
    I put one ON an air compressor once...once.

    When it would shut off, it would "bounce", and restart the motor.

    Mercury relays do suffer from "jiggling".

    Could have put it on the wall, I still have the relay.
    RPC idler might jiggle it? Only maybe.

    But "jiggle" would have to bounce a 27 KVA EGS/Hevi-Duty Delta to Wye drive Isolation transformer as well. Dunno if the "duty' is heavy, but the transformer assuredly IS!



    Last two Earthquakes, my area, were slow-period waves, too.

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    Quote Originally Posted by thermite View Post
    RPC idler might jiggle it? Only maybe.

    But "jiggle" would have to bounce a 27 KVA EGS/Hevi-Duty Delta to Wye drive Isolation transformer as well. Dunno if the "duty' is heavy, but the transformer assuredly IS!



    Last two Earthquakes, my area, were slow-period waves, too.
    3 hp single phase 60 gallon tank.

    I put a surplus 8" x 12" hoffman cabinet on top/front, made a nice neat job of it....

    Replaced the mercury switch with a standard contactor, all is well.

  21. #16
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    Can a mercury contactor safely interrupt a stalled rotor motor? Can they pass a U/L 508 test?

    Tom

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    Quote Originally Posted by TDegenhart View Post
    Can a mercury contactor safely interrupt a stalled rotor motor? Can they pass a U/L 508 test?

    Tom
    Not on my dance card to mistake a contactor for a fuse.

    Square-D "QO" breaker supply-side, or Square-D "QO" breaker load-side never puts the question to it, so I don't see the relevance..

    If even I could stall an RPC idler double the load motor rating without tripping one breaker or t'other.

    How much wood could a woodchuck chuck if a woodchuck could chuck wood?

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    The relevance is that you keep trumpeting how great they devices are when in fact they are not suitable for the applications discussed here.

    Tom

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    Quote Originally Posted by TDegenhart View Post
    The relevance is that you keep trumpeting how great they devices are when in fact they are not suitable for the applications discussed here.

    Tom
    WTF would a "raggedy-ass is-more-better" alleged contactor mavin know about contactors as cannot GET raggedy-assed to begin with?

    Stick to what you (think you) know.


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