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Old September 1st, 2009, 10:42 PM   #1
Adam303
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Contactor chatter

Hi to all. I have been called to take a look at a intdustrial type control panel that gets hot about 98 F at 80 ambient. The panle has a 200 amp main and only draws about 50 amps. Panel has about 30 contactors and a small type of a siemens plc aprox. 5 cards. after a short diagnose i saw that practycly all the cable connections wore loose and i went on with tighting all connections about 4 solid turns on every one.

Problem: after making sure that all connections wore tight i went on and powerd up the panel and the componets motors, valves etc. What i experianced was that 4 of the 30 contactors started chattering execevly. I waent on and replaced the contactors and the four stoped but another 2 or 3 started the chattering again i replaced the contactors and another two started the same problem. Can anyone explain? mesured the coil vboltage at 120 volts ac . what would cause this weird chattering. Thanks to all for your help.
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Old September 2nd, 2009, 12:13 AM   #2
leitmotif
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OK lessee if I understand correctly
Initial trouble call was for cabinet overheating.

you found loose wires and tightened all connections.
On energize you had relays A B C D chattering.
You replace them and on retest they are OK
BUT
E and F start
You replace them and on retest they are OK
BUT
G and H start chattering.

Most interesting. I have a hard time with idea you have some contagous disease causing death of relays one after another.

The coils on relays are 120 VAC?
Did you check voltage on the chattering coils themselves?
Are you getting a voltage drop across the control switches and you checked both coil terminals?
What is source of 120 VAC control power? Is it large enough?
I think I would check for a lifted neutral also.

Dan Bentler
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Old September 2nd, 2009, 12:26 AM   #3
Kev77
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any chance that the panel was cleaned? I had the same type of issue after blowing compressed air in a panel (first and last time doing that!).
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Old September 2nd, 2009, 01:11 AM   #4
Mickey
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Here's another thread on the subject.

http://www.plctalk.net/qanda/showthr...highlight=coil
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Old September 2nd, 2009, 02:42 AM   #5
jingo
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possible of carbonized auxilary contacts that causes the chattering, on this contacts one of the supply line is connected before it reaches the coil,it sometimes sparks before the contactor energized....
hope this will help..
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Old September 2nd, 2009, 02:57 AM   #6
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From experience there are two separate problems you can get with contactors that have an AC coil: chattering and buzzing.

A low hum to a buzz is quite normal, these things are after all working on an AC supply. Went to a job in a bank where they were complaining about a 'buzz', they had specified AC, lapped up the facing of the magnetics and they were then whisper quiet.

A chatter to a clatter generally has two causes: first is a wrong voltage or frequency on the coil, second is major dirt or magnetic swarf inside the contactor. Went to a job up in Scotland where they were complaining of chattering. Their contractors who had installed the job had cut holes in the top of the enclosure without protecting the contactors, they were full of metal swarf and cuttings.

You often find that as you fix one noise another seems to start, I tend to find that it isn't so much that another starts, more that as you stop one source of noise you can hear slightly quieter ones.

Bryan
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Old September 2nd, 2009, 05:12 AM   #7
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The main 2 things that I have seen over the years to cause chattering are dirty pole faces and wear and tear.
A break in the shading coil usually causes the contactor to 'stick' in.
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Old September 2nd, 2009, 05:27 AM   #8
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While the above are most likely the causes (summed up nicely by BobB), some other gotchas to look out for:

1) If the neutrals (commons) are daisy-chained, an upstream problem can cause difficult to find downstream faults.

2) If any of the contactors have an internal DC coil, the holding resistor and/or contacts might have a problem.

3) If they rely on aux decks to seal in, the mechanical mounting of the aux deck may have degraded, making them function improperly.
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Old September 2nd, 2009, 10:38 PM   #9
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I would suspect the voltage at the coil terminals (What is the coil rated voltage) .

What is the control voltage? I have seen this happening with loose neutrals. (at the incomer)

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Old September 2nd, 2009, 10:49 PM   #10
Adam303
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Yes I did blow the contactors with air.
120 volt coil mesured voltage is 119 volt
i took apat the rest of chattering contacots cleaned the contacts with a wire brush and contact cleaner seemed to help a lot thanks for all your help.
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