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Old 06-19-2013, 12:02 PM   #1
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Default 120v ac relay chattering

We use a bagger system that puts product in the bag, seals, cuts and drops the bag onto an outfeed conveyor with a metal detector, which should turn off the conveyor if metal is detected. One reset is located on the door of the bagger to reset the metal detector and allow the conveyor to continue running after the product has been removed. After wiring the relay the metal detector will stop, but will sometimes latchin and sometimes if the metal is removed will just keep running. I really need this to stay down until the reset it pressed.

The way that the panel is setup involves a 120v feed from a transformer
feeding;
-a momentary pushbutton with a ka5 (nc contact) which runs back to a n.o. contact on the relay. The other side is jumped to the coil. used as a latching circuit.
-a run of 18-2 that goes to the metal detector and feeds a set of NO contacts and returns to the coil. (contacts close the 120v circuit when metal is detected)

I've used my fluke multimeter to see if the voltage is dropping, but I don't have a high end multimeter and mine can't see the voltage dropping out.
Adjusted the metal detector to leave the contacts closed for a longer period of time, no change.
Tried another relay as I read that trash, or a weak coil could be the culprits.
Any insight would be greatly appreciated.

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Old 06-19-2013, 02:08 PM   #2
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I am not sure exactly what you have.
Here is a a very basic drawing using one contact from the metal detector.
Use this as a guide and change what you like.

In this drawing, the metal detector opens the motor circuit. And can be reset by pushing either the start or the reset button.
You can change this to any arrangement you want.

You can move the reset button over to the left, so the motor cannot start if metal is present.
Attached Images
File Type: jpg Metal Det 2.jpg (56.7 KB, 13 views)


Last edited by John Valdes; 06-20-2013 at 02:37 PM.
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Old 06-19-2013, 02:27 PM   #3
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Ron. My memory has resurfaced and I wanted to add something I missed.
The metal detector has the reset button on it? Right?

If that is the case, ignore the one I drew. The metal detector should close that contact when you reset the detector.
If the detector does not allow the conveyor to stop and wait for reset to function, you have an issue inside the detector.

The metal detector opens and closes contacts. You need to look at the detectors instructions to be sure how these contacts behave.
If the detector is set to open a set of contacts and drop the motor for the conveyor, my drawing above will work.

But check and see if they reset themselves after you clear the detector.
Just keep in mind you are opening up the motor circuit. Nothing more.
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Old 06-19-2013, 04:18 PM   #4
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Quote:
Originally Posted by John Valdes View Post
Ron. My memory has resurfaced and I wanted to add something I missed.
The metal detector has the reset button on it? Right?

If that is the case, ignore the one I drew. The metal detector should close that contact when you reset the detector.
If the detector does not allow the conveyor to stop and wait for reset to function, you have an issue inside the detector.

The metal detector opens and closes contacts. You need to look at the detectors instructions to be sure how these contacts behave.
If the detector is set to open a set of contacts and drop the motor for the conveyor, my drawing above will work.

But check and see if they reset themselves after you clear the detector.
Just keep in mind you are opening up the motor circuit. Nothing more.

Like your EZ Schematics John ! No relay in that drawing ? and your numbering stopped
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Old 06-19-2013, 06:30 PM   #5
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pretty sure i see a coil and some relay contacts there.
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Old 06-19-2013, 06:38 PM   #6
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Quote:
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pretty sure i see a coil and some relay contacts there.
Transformer
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Old 06-19-2013, 06:42 PM   #7
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I see M for motor, and a seal-in contact with M on it. CR would be the relay. John knows this and has a reason.
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Old 06-19-2013, 07:09 PM   #8
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For some reason the F U 1 jumped out at me.

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Old 06-19-2013, 07:15 PM   #9
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I think he left the contactor out and wanted the OP to adjust the schematic to fit his needs. No telling how big the motor is or if the metal detector contacts can handle the current. What's confusing, it looks like a motor starter control circuit but the motor shouldn't be part of the control circuit.

Oh wait.....Maybe M1 is the contactor coil and he isn't showing the contacts.
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Old 06-19-2013, 07:22 PM   #10
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Looks like M1 is a contactor coil for the n.o. M1 contact
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Old 06-19-2013, 07:27 PM   #11
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M1 would have to be the holding contact for the coil. If that contact wasn't there you would have to hold the start switch down to make things happen.

Last edited by 8V71; 06-19-2013 at 07:33 PM.
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Old 06-19-2013, 08:47 PM   #12
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You have a bad overload. I did get outsmarted by a loose fu1 fuseholder, once.

Last edited by bobelectric; 06-19-2013 at 08:53 PM.
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Old 06-20-2013, 12:56 PM   #13
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M1 is the seal for M1 motor starter coil.
M1 coil, closes M1 NO contact holding the circuit.

Reset (momentary) just restarts the motor. This is why I asked him about the detector. The detector has its own relay and I am certain the detector logic can be played with.

So the metal detector contact is located in the detector, that is why you see no coil for it. Some call it a dry contact.

Dorian. I left out the numbers because he has a functioning circuit and equipment.
Had I used my numbers, he might have taken those to mean literal numbers which they do not.

If the drawing worked for him, he could easily use his own numbers. The right ones for his application.
If he was building this. I would have numbered every single wire.

Note. There is one mistake on the drawing. A process mistake. Can you tell me what should be changed?
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Old 06-20-2013, 01:15 PM   #14
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Quote:
Originally Posted by John Valdes View Post
M1 is the seal for M1 motor starter coil.
M1 coil, closes M1 NO contact holding the circuit.

Reset (momentary) just restarts the motor. This is why I asked him about the detector. The detector has its own relay and I am certain the detector logic can be played with.

So the metal detector contact is located in the detector, that is why you see no coil for it. Some call it a dry contact.

Dorian. I left out the numbers because he has a functioning circuit and equipment.
Had I used my numbers, he might have taken those to mean literal numbers which they do not.

If the drawing worked for him, he could easily use his own numbers. The right ones for his application.
If he was building this. I would have numbered every single wire.

Note. There is one mistake on the drawing. A process mistake. Can you tell me what should be changed?

Mistake is; your Overload should be a N/C contact ?

So when drawing a motor starter combo where the coil is built in, you don't need the schematic to show the CR on a different rung ?
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Old 06-20-2013, 01:23 PM   #15
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Quote:
Originally Posted by John Valdes View Post
M1 is the seal for M1 motor starter coil.
M1 coil, closes M1 NO contact holding the circuit.

Reset (momentary) just restarts the motor. This is why I asked him about the detector. The detector has its own relay and I am certain the detector logic can be played with.

So the metal detector contact is located in the detector, that is why you see no coil for it. Some call it a dry contact.

Dorian. I left out the numbers because he has a functioning circuit and equipment.
Had I used my numbers, he might have taken those to mean literal numbers which they do not.

If the drawing worked for him, he could easily use his own numbers. The right ones for his application.
If he was building this. I would have numbered every single wire.

Note. There is one mistake on the drawing. A process mistake. Can you tell me what should be changed?

If the detector opens up the latching relay, I don't see how your reset button would re-latch it.

Edit: Wait, maybe I do!

Last edited by A Little Short; 06-20-2013 at 01:26 PM.
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Old 06-20-2013, 01:27 PM   #16
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Quote:
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Mistake is; your Overload should be a N/C contact ?
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Old 06-20-2013, 01:30 PM   #17
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Quote:
Originally Posted by Little-Lectric View Post
If the detector opens up the latching relay, I don't see how your reset button would re-latch it.

Edit: Wait, maybe I do!

You see that by bypassing the switch with the reset, and energizing M coil closes those contacts on the seal in or latching circuit again.
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Old 06-20-2013, 01:30 PM   #18
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Thank you all of the help. The relay is breaking a 24v signal that comes from a plc output through the relay and back to a powerflex 4 as the run enable.

The reset was an afterthought to the metal detector and so it was a quick fix by some of my predecessors. Unfortunately we don't have any schematics and three different machines wired three different ways.

The signal from the metal detector back is just a momentary 120v signal and that's why I'm trying to make it latch on using NO contacts on the relay itself. When the metal detector closes the contacts the 120v feed will no longer be from the metal detector but from the reset button. Thus far I've seen it chatter a little and I'm trying to get it wired correctly.
I'm sorry my breakdown wasn't better, I tried ez schematics and had a bit of trouble I will try to figure it out for future use.
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Old 06-20-2013, 01:35 PM   #19
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You see that by bypassing the switch with the reset, and energizing M coil closes those contacts on the seal in or latching circuit again.
Yep, I saw that after I posted. That's why I edited it.
The drawing is backwards/different to what I'm used to seeing.
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Old 06-20-2013, 02:34 PM   #20
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Mistake is; your Overload should be a N/C contact ?

So when drawing a motor starter combo where the coil is built in, you don't need the schematic to show the CR on a different rung ?
Yep. But that is not what I was thinking. I missed the OL contact. I will fix the contact, but you still need to tell me why the production manager has an issue with this operation.

The starter coil, and the OL relay are one device in this drawing. Regardless of physical location.
Never use any more than you need to accomplish the objective.
No additional relay is required in this drawing.
The motor starter can accept auxiliary contacts if required. We only needed one on board aux contact to hold the motor starter in.

Quote:
Originally Posted by Little-Lectric View Post
Yep, I saw that after I posted. That's why I edited it.
The drawing is backwards/different to what I'm used to seeing.
Backwards?
How do you mean?
You are using American logic?


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