TroubleShooting Hardwired Daisy Chain Controls

[Clay B.]

Sounds like grimlins

I Mov supresses voltage surges as the relay opens. It still sounds like your root cause is the relay opening.

I would confirm a voltage drop across the Relay coil itself.

Hook your meter across the relay, set your Min/Max and let the next event happen. For that relay to drop out the seal in contacts must open or something upstream has to drop the voltage.

Just keep moving upstream of this coil until the voltage drop shows itself.

You can knock a seal in contact open with vibration. The good news here is if it is a cube relay you will see some arch damage on the contacts. If you have not thrown the old realy away pop the cover off and look for this.


Don't get frustrated though. Chasing problems like this is like trying to catch smoke with a net. Just do not start jumping around, a systematic aproach will always work best.

 

[The Plc Kid]

@ Clay B

This panel is for a auxillary grinder and it is not hard piped to the eqipment but it is mounter to the floor with about 4-6 inches of space between the 2.

I am starting to think vibration also because it will stay engaged for quite some time with the motors off (fuses Pulled) but when running with a load (material being fed in) In tends to be much more frequent.

Would a 3 phase iec contactor maybe be better than a cube relay? I would thing it would be less susceptible to vibration? Anyone agree?

 

[The Plc Kid]

I hope i find something soon. This thing is really kicking my a%4.

 

[brucechase]

...
What doesn't make sense is this relay is just a standard start/stop circuit and it is a 3 pole relay using the center pole N.O contacts as the seal in. Every few minutes this relay just drops out with no change in load or anything so installed a new relay and base,checked all the wires and replaced a few and it is still doing it? I even put a jumper clip across the stop button in case the contacts on the stop button were the problem and it still happens.

...
Voltage is perfect never dips.

Text book basic. There are other permissives in the circuit but they are all jumped out and even the contacts on the stop button are jumped. So we have L1 going to one side of the stop button coming out of the stop button we next go to the start and out of the start we go to the relay coil.

The circut works correctly it is just that after a few minuites and sometimes a hour it will drop out. I know the control voltage is not the issue because it we lost the voltage other parts of the circuit would drop out but they remain running.

Don't rule out the control voltage yet. If as you describe you have L1 to the stop button (and the stop button was jumped out) and then go through the start button in parallel with the aux contact and then to the neutral and it still happens, then the voltage would be where I look at.

Other than that, I would replace the start/stop button and make sure you have the correct relay in there. Make sure the coil is rated for the voltage (120VAC) and it isn't a latching relay. You don't know what has been replaced before you got there.

 

[Clay B.]

@ Clay B

This panel is for a auxillary grinder and it is not hard piped to the eqipment but it is mounter to the floor with about 4-6 inches of space between the 2.

I am starting to think vibration also because it will stay engaged for quite some time with the motors off (fuses Pulled) but when running with a load (material being fed in) In tends to be much more frequent.

Would a 3 phase iec contactor maybe be better than a cube relay? I would thing it would be less susceptible to vibration? Anyone agree?

A larger relay is less susceptible to vibration. But before I go thru all that trouble I would measure if I actually had a voltage drop across the coil of the relay. If you susspect that vibration is the cause then measure voltage on the seal in contact after you have confirmed you did not have a voltage drop across the relay coil. Let that fancy Fluke meter do the work for you. Min/Max on a 87 series Fluke can see voltage changes in the micro seconds. If that relay is your problem I will bet a small fortune your meter can catch it.

 

[The Plc Kid]

I removed the cube relay and installed a AB Mini contactor and problem solved. Maybe it was vibration? But i tried 2 different cube relays and bases from 2 different manufacturers and had the same issue.

Go figure.

Thanks Everyone.

 

[TomekPLC]

Told ya

 

[silva.foxx]

Told ya

 

[Gil47]

I removed the cube relay and installed a AB Mini contactor and problem solved. Maybe it was vibration? But i tried 2 different cube relays and bases from 2 different manufacturers and had the same issue.

Go figure.

Thanks Everyone.

Sounds like the shading ring in the relays may not be doing their job or that DC coils instead of AC coils.
Or do you have AC voltage on top of DC, feeding to the coils

 

[The Plc Kid]

Gil47

Educate me on the "shading ring" if you will?

 

[The Plc Kid]

Doing a little lite reading before bed on relay chatter and everything points to coil voltage supply not up to snuff. But in my case i installed a larger relay ( contactor) with a larger coil which should make the problem worse but instead it fixed the problem?

Vibration is the only thing that makes sense and i a cause of relay chatter but it is rare.

 

[sthompson]

Gil47

Educate me on the "shading ring" if you will?

A Shading Ring is a usually a Copper Ring imbedded in the faces of the Contactor Laminations. It has a Current induced into it slightly out of phase with the lamination of the Contactor Coil. It helps the Contactor stay pulled in for the 120 Zero Crossings of 60HZ AC. Do a Google search, and I am sure you will find explanations of how it works.

Stu....

 

[Gil47]

Educate you well who is going to educate me first.
Here is my 2 seconds of knowledge on the subject.

Shading rings function is to keep an AC coil closed without buzzing or opening as the voltage crosses zero as STU said.
The ring is in one face or in two faces, but not in its mating face or faces.

I also agree Google is a good choice to find info.

It is quite unusual to have a cracked shading ring, but in saying that I have found it several times, it normally shows itself by louder than normal buzzing and can sound like vibration, In one case I found it chattering the contactor without actually opening the contacts was not a nice sound, it was on special interlocking contactors which I was suprised that I actually managed to repair with a home built copper ring.

Machine vibration would have been my first choice but your statements left me thinking that you were looking for something out of the ordinary.

 

[TomekPLC]

Gil47, thanks for some good tips.
Here is some more info regarding shading ring:
http://everything2.com/title/Shading+ring
Tom

 

[OkiePC]

I could be wrong, but isn't there another feature similar to the shading pole used in smaler control relays? And PLCKid went through two bases and at least two relays? I have been through hundreds of bad relays over the years, but I have not dissected the cheap ones.

I have seen broken shading coils on contactors a couple of times, and they were still functional, just irritating to listen to, and would gradually destroy the rest of the assembly if not dealt with.

I suspect there is a loose wire or semi-open neutral somewhere else in the controls causing the problem.

A fluke with peak hold could prove the voltage.

If the vibration is high, check all terminations in the panel. Loose wires in terminal blocks can do strange thing. We had a machine that wouldn't run with the main panel door closed. This went on for a month, and the techs were sure it was heat, but none of the drives or other controls seemed hot. Finally, I got sick of hearing about it, and went to isolate it with a "show me" approach with a meter on peak hold. The weight of the open door was holding a loose wire firmly connected, close the door, and the tiny flex of the well built panel caused it to go intermittent (like open a drive enable once every 60 seconds...)

Paul