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Lathe breaker main switch repair - contact material

G

GibsonI

Aluminum
Joined
Jul 8, 2010
Location
Australia QLD
Hi Guys,

I have an okuma LB15 ii.

I have finally found a long niggling problem - the contactor pads on the main breaker have worn our and one has fallen of the actuating arm.

Rather than spend $500 on a new one I am wondering what material I can use to braze onto the arms as a replacement and where to get this.

I read a lot of about copper - tungsten and silver alloys.

This one is little square of material maybe 6-8mm (1/4-5/16) square and 2mm thick presumably once brazed onto the contactor arm.

Copper would probably weld together and have poor spark erosion resistance.

Thanks so much for any input.

Iain.
 
Didn't realize Australia was 216 hours behind.

This is a really bad idea.
Expensive machine, high voltage, and you want to home brew the breaker?

A new one costs $500, but it's worth the same as your machine.
Seems like a pretty good deal to me.
 
Hard to see why a new contact arm would cost $500, even in Australian dollars.

You could go to an old coin dealer and buy an old shilling or half crown or whatever they have that was made of real .925 silver. A worn one should be quite cheap.

I have some old motor starters with good contacts in them It would be easy enough to do a contact transplant from a surplus relay or motor starter if you have a source of such. There may be some magic alloy in them in addition to the silver that would make them better than .925 silver coins (I think the rest is .075 copper).

Larry
 
Almost always silver plated copper or silver plated phos bronze. Occasionally solid silver. Do you have the brand and model/catalog number of the breaker? I've got contacts with many breaker surplus dealers and breaker rebuilders. I'm sure I can find you one in your price range. It makes the hair on the back of my neck stand up when I think about a DIY breaker repair.
 
In desperation I have silver brazed up the contact area and filed to fit. The transplant idea is better though. Got a thermo gun to keep track of hot spots?

Ed.
 
This is an All Around Bad Idea!!! Fire Hazard, Shock Hazard, Short Circuit through controls.. All
can cost a lot more then a new proper replacement part..
At least PM mdshunk and see what He can find You..

Be Safe and Careful
Steve
 
Really, really, really bad idea!

The silver metals suggested ARE NOT for electrical contacts! They can WELD TOGETHER rather easily. Electrical metals for breakers are combinations of silver for electrical conductivity and other materials designed to prevent contact welding and resist arc erosion.

Copper was and can be used for electrical contacts but NOT WITHOUT heavy contact forces. Improperly designed copper contacts can go into thermal runaway and cause a fire.

If you don't know what you are doing in this area, DO NOT LEARN THE HARD WAY! Modifying a circuit breaker can and probably will nullify any insurance.

I don't say these things lightly. I have witnessed a lot of short circuit tests. The results can be spectacular if you are behind 2" thick safely glass.

Tom
 
Most contacts in motor starters and breakers are a silver alloy with cadmium oxide added to prevent welding together.

Ebay is a good source of breakers and contactors.
 
mdshunk said:
Almost always silver plated copper or silver plated phos bronze. Occasionally solid silver. Do you have the brand and model/catalog number of the breaker? I've got contacts with many breaker surplus dealers and breaker rebuilders. I'm sure I can find you one in your price range. It makes the hair on the back of my neck stand up when I think about a DIY breaker repair.
Click to expand...

Guys thanks so much for all your comments.

mdshunk: thanks for your offer. It is a Fuji EA103B 75A.
 
OK, the OEM part costs about $500. But have you looked into buying it from another source, like your local electrical wholesaler? Or can you get a replacement breaker with the same ratings that will fit or can be made to fit in the machine?

Look up the original breaker to see what the specs are. It is not rocket science; current, Voltage, time delay (if any), etc.
 
Yeah, holy cow. I'm not even sure I'd try a surplus breaker broker since ordinary sources are so populated with new ones for 75 bucks.
 
Gary E said:
Do you value your LIFE ???

BUY a NEW one... and NOT just new to you.
Click to expand...
Steady on. Who's it going to kill.??? (Triple question marks added for more hysteria).

Its on an Okuma LB 15. 75 amps it will be the main cabinet breaker. Its been turned on and off 200 time's per year for the past 25 years.It will be mechanically shagged, but likely to have never tripped on electrical over-current.

Down here, The machine will still be Earthed / grounded, and will have protection upstream at the service panel. The fucking thing has failed by a set of contacts falling off, so NO current is passing through that contact set. The machine isn't suddenly going to come "Live". Remind me again how that's going to kill someone??? (Even More triple Q's)

Do you even know how stupid you sound? 99.99% of the time, hot nasty volts should be passing through a breaker like that. When they fault, and don't pass the nasty shocky things, that's gonna kill you. Good one guru.
 
Bill (9100) has done contact replacement on bigger stuff than that, he might have an idea, but also may not have seen this thread.
 
If all you want to do is use the breaker as a switch, wire around it to a 100 amp breaker or fusible disconnect outside the enclosure. Not the best idea, but its not the first to have the main disconnect seperate from the control cabinet. Circuit breakers by their very nature are not designed for simple mechanical switching.

Tom
 
Gordon Heaton said:
Almost correct. Some breakers are indeed designed to perform both functions. The closest example to me is the one on my Hypertherm plasma cutter.
Click to expand...

If you are referring to breakers with out trip elements that are used only for switching, The basic mechanism, springs, contacts, ect are the same as a thermal mag or mag only. They just leave out the overcurrent sensing.

Tom
 
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