Repairing contactors, welded contacts?
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  1. #1
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    Default Repairing contactors, welded contacts?

    I've discovered why my mill's motor comes straight on when power's connected, and why I can't stop the spindle motor or put the spindle into reverse...

    Contacts on the forward contactor are welded closed (well, just one or two, the main motor contacts), enough to hold it in the "on" state and operate the aux contacts to prevent the reverse contactor pulling in (luckily...)

    The contactors date from the early 60's, Italian, no maker's marks visible and unusually complicated with multiple aux contacts to enable / disable other functions like the feed motor, fed and spindle clutches etc. and fairly low profile (current available contactors with aux contacts would be poking out through the cast-aluminium cabinet cover...)

    So... I'm looking at a major rewire, additional contactors to manage clutches etc., new cover if I change 'em out. Not good, and wouldn't look right!

    I'm considering stripping the existing contactors and repairing instead, this will require separating the welded contacts, fitting new contact tips, so a few questions!

    Separating - any method less destructive than a Dremelloid with the thinnest possible cutting disc? I've tried prying with the contacts in situ, no dice

    Contacts / materials - silver/cadmium-oxide was the go-to until Europe came up with the COSHH regulations, would a silver/nickel or copper/nickel alloy be usable? Would I be better stripping a modern contactor or three and silver-soldering their points into the old relay? Could I even get away with building up new contacts with silver solder?

    Any suggestions very welcome!

    (Yes, it's always been like it since I got it, and no, I don't yet know why they welded closed...)

    Dave H. (the other one)

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    Last time I looked I found a company in Los Angeles or near their. They rebuild contacts. The look was started because of something on this forum.
    A rebuild would just be removing the old points and punching in new ones. I don't see why there shouldn't be a service for that in England.

    Custom Manufacturing – WES
    Last edited by rons; 08-04-2019 at 01:23 AM.

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    There may be, but if there is... after an evening of looking I can't find one - that's why I'm asking the questions!
    I'll try a local motor shop next week and see whether they'll divulge their secrets (if they have any)

    Dave H. (the other one)

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    I would not attempt to fix welded contacts. Even if you get it working for a while, the contact surfaces will probably continue to cause you trouble indefinitely.

    You can probably put together an equivalent contactor with all the necessary auxiliary contacts if you spend some time with a catalog. I think I put Siemens contactors into my VN mill electrical rebuild, and I was able to buy the basic contactors, reversing interlock, safety circuit contacts, and a couple of sets of aux contacts a la carte. The non-power contacts "stack" onto the body of the basic contactor, and you can easily get 4-pole units.

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    We need a little more information. Horsepower, voltage, current, wiring diagram, machine. A few photos.

    Can you replace the reversing contactors with a VFD and an aux relay?

    Firstly, DO NOT USE SILVER SOLDER to build up the contacts. That material is intended for joining. It would do a really good job of joining the contacts permanently.

    The silver nickel alloys are only good up to about 25 amp. I haven't heard of anyone using copper nickel. That may be a specialty alloy for resistance welding electrodes. Member 9100 has/had a business of replacing contacts for GE locomotives, so he would be equipped to braze replacement contacts. I would go for old, as in 1970 and earlier, contacts as these would be silver cad. Later ones may or may no be Cd as this is about the time silver tin oxide was starting to make noises. I know the GE 300 line was AgCd at least through 1985, I don't know about A-B or Cutler Hammer. Stay away from SqD. The GE size 1 through size 4 were percussion welded as I believe CH so these would have to have the backing machined away to salvage the silver. Rebuilding what you have will be a challenge.

    Can you replace the aux contacts with an aux relay?

    Tom

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    I liked Arthur C. Clarke's directive in Diaspar AKA The City and the Stars;

    "No machine may have any moving parts"

    Crydom SSR's have been my go-to since the dawn of the 1970's.

    Those for AC circuits inherently switch at the zero-cross. No arky-sparky. No contacts. No wear. No fire hazard even where solvents are about.

    No drama at all, generally. Even the control loop is internally opto-isolated and tolerates a wide voltage range.

    Fifty-plus years on, they are even cheap, extensively documented with application notes, copied by everyone from major EU legends to Asian El Cheapo no-names, and widely stocked.

    You have wot? About 5 HP to control? Not all that hard.

    Have a recce.

    Buy Solid State Relays at Wolf Automation

    Lots of them cheap, NOS, NNB, at "the usual suspects" of remaindermen as well. Used ones off ebay "may" be OK, too. Mostly, anyway.

    and.. have you REALLy exhausted all sources for drop-in new "mechancial" contactors to Euro/IEC or japanese specs?

    Basic Construction & Sizing for Contactors | Wolf Automation

    Contactors 3-pole - Eaton Europe - Switching, Protecting & Driving Motors

    IEC Contactors, Starters & Overloads |AutomationDirect

    [ZOB] Japan Fuji Fe SC 2S/G 50 DC24V 80A genuine original DC contactor-in Contactors from Home Improvement on Aliexpress.com | Alibaba Group
    Last edited by thermite; 08-04-2019 at 01:01 AM.

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    First, we need pictures. I can't make any kind of a statement without seeing them. Tom is correct about silver brazing. Not only is silver solder made up of all sorts of alloying metals, there are countless different compositions. A contactor that old will probably do with silver with a few percent copper. Another issue is that brazing anneals the copper base. If they have thin fingers, as many do, annealing the finger can make it unuseable. The Riverview Water Works that supplies a large part of St. Louis had me make replacement contacts for the controllers on the large gate valves that let in the Mssissippi water. These were dime sized silver contacts on copper strips about 3/32" thick and 5/8" wide. I got them all brazed on and found to my horror that even the pressure of the contactor would bend them, meaning that the entire run was scrap. After drying the puddle of tears on the floor, it occurred to me that peening the surfaces might stiffen them enough. Shot peening was preferable but what I had was glass beads, so I tried that. That had an effect like case hardening, making a soft core with rigid surfaces. That was a long time ago and they are still working.

    Bill

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    Quote Originally Posted by Hopefuldave View Post
    There may be, but if there is... after an evening of looking I can't find one - that's why I'm asking the questions!
    I'll try a local motor shop next week and see whether they'll divulge their secrets (if they have any)

    Dave H. (the other one)
    You can search for your contactor's rebuild kit. The kit would have new points on whatever metal arms that were original.

    I hate to use Grainger but it is only for the picture.

    GE Replacement Contact Kit, Contacts per Kit':' 4, Starter Size':' 0 - 3HXX6'|'546A300G002 - Grainger

    Another one. Easy to look up.

    Electrical Contact Kits - Replacement Parts and Surplus Electrical Equipment

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    Thanks all, first a pic of the contactors in situ - the sharp-eyed may even spot the welded contacts, the lower pair are forward on the left, reverse on the right with the overload (set at 10A). Excuse the filth, before I started cleaning, honest!

    Rons
    - there are no makers marks on the contactors, so unless someone recognises them it's unlikely I can order t he right contacts off the shelf (where they will have been gathering dust for 50+ years)...

    9100 Bill, excellent info, so it is possible - the contact points are riveted into the moving bridges and all looks demountable so I'd go with new contacts on the bridges, which appear to be plated steel (according to a magnetised screwdriver) and are carried by springs, not springs themselves, no worries about annealing copper parts.

    Thermite - SSRs would be t he way to go if I were designing it from scratch, but knowing how long a complete redesign/rebuild took me on my lathe and that I'd wind up adding all kinds of features I don't really need, I'd rather get what's there working! The existing contactors are pretty unusual, have 36vac coils, which I've not seen listed anywhere

    Tom - lovely Idea the VFD, but I'm aware how long I took doing the same to my Holbrook lathe... I'd like to use the mill (can as it is, but I'd like it to be right) and such a conversion would involve repowering a pair of magnetic clutch/brake units, currently fed 110v from existing contactors - and going with a VFD I'd no longer have 110 if I tore out the original 415v to 36v & 110v transformer. Lots of work I don't need to do if I repair t he contactors.

    Wiring diagram? What wiring diagram? This is an Italian Test 2U from about 1960 - 1965, the company doesn't appear to exist any more (I even read through a local business directory in Milan where they were based when I was there a few months ago, great way to spend a holiday ), I've seen one other in captivity, another member on PM who sent the diagram for his - rather different, a later model with 2-speed motor, different switchgear. I've made notes while buzzing out the existing wiring / contactors etc and found SOME similarities, e.g the use of very odd contactors...

    I think I'm going to have to go with repairs to the originals, form factor, voltage and functionality appear to be mutually exclusive, 9100 Bill's suggestions are the most useful so far, but thanks all!

    Dave H. (the other one)
    Attached Thumbnails Attached Thumbnails 20190715_215912.jpg  

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    Quote Originally Posted by Hopefuldave View Post
    I think I'm going to have to go with repairs to the originals, form factor, voltage and functionality appear to be mutually exclusive, 9100 Bill's suggestions are the most useful so far, but thanks all!

    Dave H. (the other one)
    Given that electrons move too fast to much care if the switchgear is three inches away or thirty feet, I'd just leave the too-tight box empty and remote the whole lot to some other location where conventional US-spec goods bought cheap could serve. You know what the desired outcome is, design and component selection is inbuilt.

    Pondering over similar Euro-weird shenanigans, the 1970's era Cazeneuve HBX 360 - which DID at least include a good schematic, on durable plastic not paper, yet, as was glued right inside the plenty-large 'lectrical cabinet door.

    Helluva lot of pretentious trash in there for as little as is asked of it ... 7 HP final-drive motor, two electric juice pumps, (mine had originally shipped as a hydraulic tracer..) the main juicers being direct-drive off the motor tailshaft. For now.

    Classing it as noisey as a ce-ment mixer ful of stove bolts is insulting to the mixer. Cross between an bicycle siren and a plate tamper on hard pavement is closer.


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    I would look at the welded contact and compare it to one of the auxiliary contacts. If they are similar in size and weight I'd simply clean up the welded one and swap it for an auxiliary. The auxiliaries carry very little load usually. You might even be able to soft solder a new tip on just for auxiliary duty.

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    Quote Originally Posted by thermite View Post
    Given that electrons move too fast to much care if the switchgear is three inches away or thirty feet, I'd just leave the too-tight box empty and remote the whole lot to some other location where conventional US-spec goods bought cheap could serve. You know what the desired outcome is, design and component selection is inbuilt.

    Pondering over similar Euro-weird shenanigans, the 1970's era Cazeneuve HBX 360 - which DID at least include a good schematic, on durable plastic not paper, yet, as was glued right inside the plenty-large 'lectrical cabinet door.

    Helluva lot of pretentious trash in there for as little as is asked of it ... 7 HP final-drive motor, two electric juice pumps, (mine had originally shipped as a hydraulic tracer..) the main juicers being direct-drive off the motor tailshaft. For now.

    Classing it as noisey as a ce-ment mixer ful of stove bolts is insulting to the mixer. Cross between an bicycle siren and a plate tamper on hard pavement is closer.

    If your Cazeneuve is really that noisy, we have a saying in Britain: "Sold a pig in a poke", they're good machines unless they've been neglected / buggered about with!

    So, what you propose is effectively a complete electrical rebuild, something I made it pretty clear I DON'T want to do: it works as-is and the electrics (apart from three welded contacts) are what's needed to do the job and no more.
    No "Euro-weird" to it, well-designed, well-specified system showing the effects of nearly 60 years use and possible abuse.

    And... an external box would look like what it would be, a bodge.

    Dave H. (the other one)

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    Quote Originally Posted by Peter. View Post
    I would look at the welded contact and compare it to one of the auxiliary contacts. If they are similar in size and weight I'd simply clean up the welded one and swap it for an auxiliary. The auxiliaries carry very little load usually. You might even be able to soft solder a new tip on just for auxiliary duty.
    Thanks Peter, a very constructive suggestion - I'll see whether there are enough of the right contacts to juggle, the contactors look fairly simple to dismantle and assemble (inside a large plastic bag, lots of Pingf*ckits in 'em)

    Dave H. (the other one)

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    Quote Originally Posted by Hopefuldave View Post
    If your Cazeneuve is really that noisy, we have a saying in Britain: "Sold a pig in a poke", they're good machines unless they've been neglected / buggered about with!
    Not just "good". Great. Perhaps the best manual single-point threaders ever built as well.

    Milacron doesn't deal in pigs in pokes. Certainly not in his used machinery biz, anyway! I thot he was actually trying to breed Deckels and Schaublins at the time I picked it up.




    Also noisy as Hell. Combination of mechanical Variator driving into a geared-head, hydraulic and coolant pumps, cooling fins on the earlier mechanical external band brake's hub (later ones used a solid disk, electro-hydraulic "spot" caliper).

    Plenty of 'em on You Tube vids, one here on PM just recently as well. All much the same sound, save PM member JHolland's "silent" conversion. Of which I am downright envious! Especially as the "inch" lathes here are really, really quiet Dinosaur Current 10EE.




    So, what you propose is effectively a complete electrical rebuild, something I made it pretty clear I DON'T want to do:
    I DON'T want .... to eat Broccoli, either, to be clear. But it is good for my health. And for my grocery bill, relatively.

    A "from clean-sheet" can be faster and less costly. It is only ordinary electricity, after all. There are hundreds of contactors out there than can manage it, many of them cheap as dirt.

    Fair warning.. if you DOO this tedious rebuild of contactor contacts & such?

    You may be expected to report back that it was actually bit of FUN! No grumbling..


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    Replacing the contacts would be simple, drill them off and make new ones to rivet on. I cast a silver rod and turn them out. I may even have some that would work. OTOH, you should be able to buy a contactor that would fit in the same space. The biggest concern is finding what welded the contact in the first place. I only have what used to be called coin silver, with a few percent copper. The large contacts I repaired were not switched under load. They are used in the -7 and -8 GE locomotives where they shut the field down on the main generator, throw the switches, then bring it back up.

    Tom, what is your objection to Square D? I just replaced a Cutler Hammer manual starter on a little Harig grinder. The C-H was a very cheaply made size 0 with tiny contacts, one of which was completely burned away. I had a similar Square D starter in my junk collection which was much better built with larger contacts. It has only been in service a few days, so there is no feedback yet.

    Bill

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    The contactors shown often had the same rating for all poles, making changing to the use of an aux practical. I would do that and repair as best you can the welded contacts for use as aux contacts. Contact kits for this size contactor were not available, at least not in the US. The devices were considered throw away. Don't bother trying to use silver out of a US switch, they would be much too large. Try to use the welded contact as an aux. If the welded contact is completely unserviceable, turn a rivet from pure copper or silver (not brass).
    I did not not recommend SqD because at the time I though we were talking a size 2 or 3 device. SqD had come out with SilCdQ contacts that were large in diameter and made of powder metallurgy. The powder metallurgy contacts were brittle and being thin would be difficult to salvage.

    A picture of the contact assembly would help.

    Tom


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