# Used contactors... how do I test them



## MechanicalDVR (Dec 29, 2007)

Hook up an ohm meter to the contacts points and then energize the coils. A good set of contacts with have no resistance. If you make the contacts manually they could make better contact than being energized normally.


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## John Valdes (May 17, 2007)

I would test each device or control on the bench, then mark it used and put it into your inventory.
The drives are a little different especially if they have been idle for long periods.
You may have to apply voltage to them in stages (soaking). I understand the capacitors can dry up or blow if you apply full power to old ones?


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## JRaef (Mar 23, 2009)

John Valdes said:


> I would test each device or control on the bench, then mark it used and put it into your inventory.
> The drives are a little different especially if they have been idle for long periods.
> You may have to apply voltage to them in stages (soaking). I understand the capacitors can dry up or blow if you apply full power to old ones?


Electrolytic capacitors don't "dry out", but yes, they have to be "re-formed" after sitting with no power applied for a year or more. Caps are made from layers of aluminum film separated by an electrolyte "gel" material and when the poles are energized originally, a thin layer of aluminum oxide forms on the surface, acting as an insulator between the layers, which is what makes it a capacitor. Whenever the caps are not powered, that layer is slowly dissolving back into the electrolyte, but every time it is energized, it re-forms. If left with no power applied for too long though, the layer dissolves completely and needs to be "re-formed" by applying a low voltage to it and slowly increasing it over time. Not doing that means that when energized at full bore, the current flows unrestricted straight through the layers and burns holes in them, permanently, before the oxide layers can form. By using low voltage, you are engaging the oxide forming process but keeping the current very low so that the layers don't burn.


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## Flyingsod (Jul 11, 2013)

If you are not in a critical situation environment I would just shelf them and try em out when ya need em. Unless you really have a lot off time on your hands. Most likely they will be ok unless someone at the other plant suffers from "saving it because it's bad" syndrome. Hmmmm now that I'm thinking about it if you are in a critical situation you shouldn't even have used parts as spares. If you do save the drives be sure to add then to your PM routines.

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## Cow (Jan 16, 2008)

If they are NEMA starters I open them up and give the contacts a visual. Then test the coil operation if possible to make sure the contactor cycles properly. Verify the N/C overload contacts have continuity.

If it's crates full of crap that doesn't fit any of your electrical equipment, then I'd just toss it. I like replacing parts with "like" parts, not some jerry rigged piece of crap somebody wanted to save just because "we had it."

I've been there before, it's not fun.


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## JRaef (Mar 23, 2009)

There was a time when people used to steal the contacts out of starters for the silver content...


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## telsa (May 22, 2015)

I thought this thread was supposed to be about used contractors... and how to test them.

My bad. :001_unsure:


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## Missouri Bound (Aug 30, 2009)

telsa said:


> I thought this thread was supposed to be about used contractors... and how to test them.
> 
> My bad. :001_unsure:


The difference is simple.....used contractors test you.
Your patience, your wallet, your sanity.


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## micromind (Aug 11, 2007)

The best way to test mechanical contacts is by measuring voltage drop across them (fall of potential) while they're under load.


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## Flyingsod (Jul 11, 2013)

micromind said:


> The best way to test mechanical contacts is by measuring voltage drop across them (fall of potential) while they're under load.


Feh. If they carry a load walk away and let them operate says I

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## Zog (Apr 15, 2009)

micromind said:


> The best way to test mechanical contacts is by measuring voltage drop across them (fall of potential) while they're under load.


Or use the proper test equipment and test them on the bench. a 10A DLRO should be good enough. 

To the OP, I suggest you download the ANSI/NETA MTS test procedures to properly test this equipment. Otherwise toss it all.


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