Problem with contactors wired in parallel

[hmmmnz]

OK I've got 2 contactors where the coils are wired in parallel.
They are sitting right next to each other,
One pulls in and holds perfectly well. The other pulls in and drops out. Pulls in again drops out. Ect. Ect. For as long as you are trying to keep the contacts closed.

I've tried swapping out contactors, I've tried swapping the wiring around,

Same thing.

This is an established system that's been working fine for probably as long as I've been alive.

Any clues on what to try.


Cheers

 

[Lucien Nunes]

Have you proven that the coils are indeed wired in parallel and that the voltage at the coil terminals is what you expect it to be, correct for the coil and constantly energised?

What is the voltage? AC or DC? What type of contactor? How rapidly does it operate & release?

 

[James]

Any pictures or wiring diagrams?

 

[snowhead]

How does the resistance of each coil compare?
What's the source of the control voltage to the coils?

 

[PEG]

Yep,more info needed,could be as simple as it's coil feed,going through it's NC switch?

 

[littlespark]

Does it work ok with the other one out of the circuit? If not, I say a dodgy contractor.
Replace both with new, identical units.

 

[James]

I have seen contactors that were originally 2 no + 2nc
changed for 3no +1nc or 4no etc, you get the idea.
can have some very strange effects on machine opperation

 

[Pete999]

maybe the first coil contactor is providing current to a latching contact which brings in the second coil has developed a fault

 

[James]

there are so many ways the 2 contactors could interact with each other it can only be speculation or suggestions of what "may be wrong" some more info from the op would be great.

 

[Lucien Nunes]

The OP does say specifically at the beginning that the coils are wired in parallel, i.e they should both energise and release at the same time regardless of anything else. This then suggests one coil is faulty or the wrong type, but he claims to have substituted them.

I recently had a head-scratcher where I had made a similar assumption that two relay coils were paralleled. They looked like it and tested like it, but when I picked the wiring loom apart it turned out they were not, there was a contact elsewhere in series with one of them that sometimes opened when I was not looking.