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Old 06-24-2010, 04:45 PM   #1
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Default Problems with a start/stop motor control

I've been trying to figure out this kink with a 3 phase 600Vac Nema size 2 Class 8536 Series A Type SDG1 Form S starter. It was working fine for roughly 5 years with 2 120Vac start/stop stations in parallel. I got the call when the motor simply wouldnt start. After testing the contacts on the start/stop stations I realized they were behaving as expected. I can use the manual start button to close the contacts on the starter and get the motor to start, after which the stop buttons on either station will stop the motor. But the start buttons will not start it whatsoever. It obviously is something with the starting/holding part of the circuit but I replaced the coil on the starter but that didnt change anything so I'm kind of stumped as to what else it could be. I appreciate any ideas as for what to look for and can give additional info if I'm missing anything here. Thanks.

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Old 06-24-2010, 04:59 PM   #2
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Did you check the holding contact on the starter and see if it's being pulled in by the coil when the start button is pressed?

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Old 06-24-2010, 08:53 PM   #3
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Broken wire on one of the start buttons. I would start by testing for voltage present or drop across the start buttons. Holding contacts on the contactor appear to be ok because the stop buttons work.
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Old 06-24-2010, 10:41 PM   #4
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What do you mean by "Manual start button" ?
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Old 06-25-2010, 06:02 AM   #5
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What do you mean by "Manual start button" ?
Depending on the brand and model it is the contactor indicator or just a tab that can be pushed or lifted to manually activate the contactor.

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Last edited by John; 08-10-2010 at 07:22 AM.
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Old 06-25-2010, 06:52 AM   #6
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Originally Posted by John View Post
Depending on the brand and model it is the contactor indicator or just a tab that can be pushed or lifted to manually activate the contactor.

Attachment 3608

Those are not manual start buttons. The one on the left is meant to link with more contacts.

When you push it in manually, and it holds, that proves that the NC contacts in the overlod circuit are closed, and it also proves that the holding contacts are closed and working. The problem is somewhere between 1)where the control voltage originates, travel through your stop buttons, and into your start buttons, then you close start button and it travels to the 2)coil. The problem is between those two points.
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Old 06-25-2010, 06:56 AM   #7
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Quote:
Originally Posted by mcclary's electrical View Post
Those are not manual start buttons. The one on the left is meant to link with more contacts.

When you push it in manually, and it holds, that proves that the NC contacts in the overlod circuit are closed, and it also proves that the holding contacts are closed and working. The problem is somewhere between 1)where the control voltage originates, travel through your stop buttons, and into your start buttons, then you close start button and it travels to the 2)coil. The problem is between those two points.
Agreed..
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Old 06-25-2010, 09:54 AM   #8
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Quote:
Originally Posted by mcclary's electrical View Post
Those are not manual start buttons. The one on the left is meant to link with more contacts.

When you push it in manually, and it holds, that proves that the NC contacts in the overlod circuit are closed, and it also proves that the holding contacts are closed and working. The problem is somewhere between 1)where the control voltage originates, travel through your stop buttons, and into your start buttons, then you close start button and it travels to the 2)coil. The problem is between those two points.
I know that and I was just pointing out that the OP was refering to these as a manual start button....maybe. As you and I have stated there appears to be a problem in the control wiring. Now it's time to start taking a real close look at the wiring and hardware.
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Old 06-25-2010, 01:57 PM   #9
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Originally Posted by Empowered View Post
I've been trying to figure out this kink with a 3 phase 600Vac Nema size 2 Class 8536 Series A Type SDG1 Form S starter. It was working fine for roughly 5 years with 2 120Vac start/stop stations in parallel. I got the call when the motor simply wouldnt start. After testing the contacts on the start/stop stations I realized they were behaving as expected. I can use the manual start button to close the contacts on the starter and get the motor to start, after which the stop buttons on either station will stop the motor. But the start buttons will not start it whatsoever. It obviously is something with the starting/holding part of the circuit but I replaced the coil on the starter but that didnt change anything so I'm kind of stumped as to what else it could be. I appreciate any ideas as for what to look for and can give additional info if I'm missing anything here. Thanks.
If the stop buttons, as you say, will stop the motor, the control circuit is intact. Since you manually started the motor and the unit ran, your problem is most likely a faulty coil. He can no longer perform as required without assistance.

Silly me, I now see where you already replaced the coil. I am now stumped as well.

However, as others have stated, its got to be in the start circuit. You say you manually started the motor. I would try electrically energizing the contactor. If it engages and the motor starts, then it's just a matter of tracing the path to locate the open or weak connection. Problem I have with all of that though, is why does the stop button work?

I just answered my own question . The problem is not in the holding contact portion of the circuit, but in the start portion. Again, start tracing. You're losing control power somewhere.

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Old 06-25-2010, 03:16 PM   #10
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Quote:
Originally Posted by yucan2 View Post
If the stop buttons, as you say, will stop the motor, the control circuit is intact. Since you manually started the motor and the unit ran, your problem is most likely a faulty coil. He can no longer perform as required without assistance.

Silly me, I now see where you already replaced the coil. I am now stumped as well.

However, as others have stated, its got to be in the start circuit. You say you manually started the motor. I would try electrically energizing the contactor. If it engages and the motor starts, then it's just a matter of tracing the path to locate the open or weak connection. Problem I have with all of that though, is why does the stop button work?

I just answered my own question . The problem is not in the holding contact portion of the circuit, but in the start portion. Again, start tracing. You're losing control power somewhere.
I would say that the stop button interupts the holding circuit which it sounds like is independant of the start circuit. Once you engage the contactor it makes the holding circuit then the stop button breaks it.

Push the start button and verify that you have voltage at the coil. I would bet on a bad push button or a loose connection.
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Old 06-25-2010, 06:20 PM   #11
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Pushing the contactor in and having it hold proves the coil is good.. You have a open on the wire going to the start buttons coming from the holding contact.
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Old 06-25-2010, 08:35 PM   #12
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Did you check for voltage at the wire itself? You would think that if it ran well for five years it was installed correctly but I have seen contacts that were squeezed partially on the insulation and over time build up a carbon like resistance and heat and cold can loosen the connection. If it is stranded wire I have seen it break completely after a time due to improper stripping and it is hard to see until you tug on it.
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Old 06-26-2010, 07:31 AM   #13
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Check where the common control connection is made to the first start button.
Also check the contactor 'armature' (that which moves due to a magnetic field) shading rings/coil. Some contactors wont pull in far enough when the shading ring is broken, can also be the machined surfaces between the armature and stator of the contactor are not flat any more, this stops them bedding in fully. Both effects might be overcome by an initial manual push. Just guessing. But still Sirius.

Last edited by sirius0; 06-26-2010 at 07:33 AM. Reason: grammer
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Old 06-28-2010, 11:11 AM   #14
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Push the start button and hold in, check for voltage on both sides of the start contacts. You should have voltage on both sides.

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