Motor controller contacts

[Plastikosmd]

Any clue as to what material is used for the “points” on a motor controller?

Burnt one in front , ok one on table

Some are so fried the points are gone. The current issue has been addressed but the contacts are bad.

 

[Gozo]

Often beryllium copper alloy. It’s a hard material, has some “give” without creep, somewhat corrosion resistant, and conducts well.

 

[fitter30]

Measure voltage across contacts more than 3 volts time to replace to or the contractor. Either filing or sanding contacts aren't recommended makes things worse.

 

[manwithtools]

Just replace the entire contactor...

 

[dogdog]

the contact point itself uses tungsten or something... just that round piece. the body of that is some sort of copper.
clean it up with a brush and see how much is left... if it have a lot, then put it back and reuse, knowing that it would fail any time. I did that to my craftsman table saw and a jet drill press , work fine so far.... I applied electrical grease a bit also. but some say its a no, no thing to do.

or replace it, its burn and arc.

 

[TurnipTruck]

We were always told that the contacts in the 480v breakers we occasionally scrapped were silver. I guess we never got around to PMI nuking the parts to see what they actually were.

 

[wyliesdiesels]

clean it up with a brush and see how much is left

make sure it isnt an abrasive brush

 

[RPH]

Actually, using anything more abrasive than clean paper or a dollar bill will to rough. The contacts don’t require a file or sandpaper. Doing this will cause the points not to sit flat. It may look like but electrically it arc out quickly. Also arcing builds up carbon. This carbon is conductive. This tracking can cause a fire or continue to push current through. I had a certain contactor that I replaced completely instead of the contacts do to carbon build up.

 

[dogdog]

make sure it isnt an abrasive brush

at home, I used anything I can find, like a 1000 grit sand paper and a wire brush. It’s already arc and pitted, that is where you are at, needing to fix to hope it last a bit longer cause those platinum and gold plated pieces are just too dam expensive or I am too dam cheap. At the expense of my own risk of cause. Use your best judgement what you can handle and do.

In a work setting…. You probably won’t even go that far to disassemble, just replacing it, cause it’s not on your dime and your neck is on the line, besides that there is just dam too many monkeys flocking around.

 

[wyliesdiesels]

I used anything I can find, like a 1000 grit sand paper and a wire brush.

not a good idea....

 

[dogdog]

not a good idea....

For work yes I agree, for home…. Dependents on how much cost and your comfort level.
The table saw and drill press still working good but that is not a 480v 3ph thing. Means not that high power amp watt thing


This is the old thread still works fine, of cause ymmv on these things. It’s not high power or high frequency on that table saw. So it only arc when breaking contact probably from back EMF.

https://www.garagejournal.com/forum/threads/arcing-inside-a-tablesaw-switch.332512/post-5828253

 

[marinusdees]

Any clue as to what material is used for the “points” on a motor controller?

Burnt one in front , ok one on table

Some are so fried the points are gone. The current issue has been addressed but the contacts are bad.

Arguably, gold is the best conductor. I used to coat the contacts in the rheostat on my Lab (think, sewing machine) belt engine in the dental lab with 450 fine gold solder, seemed to hold up well. 450 fine is not pure gold and has a lower melting point than pure gold.

 

[Stuart in MN]

We were always told that the contacts in the 480v breakers we occasionally scrapped were silver. I guess we never got around to PMI nuking the parts to see what they actually were.

Silver plate, at least.

A soft pencil eraser can work pretty well for shining up relay or switch contacts, but I agree that using abrasives or scraping is not a long term solution - once they're burnt, they're burnt.

 

[nadogail]

I have seen forklift contacts rebuilt with Silver Solder.