You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old March 25th, 2020, 02:21 PM   #1
rQx
Member
Sweden

rQx is offline
 
Join Date: Oct 2010
Location: Trelleborg
Posts: 783
Allen Bradley contactor control - high pick up current

Hi,

We normally use the Allen Bradley 100-c contactors with electronic coil wich has low pick up current. These range up to 27,5kW.

Now I need bigger but here's my issue:
The pickup current for a DC coil is 200W.

1. We control this through a SMC-3 soft start and the output from it is rated:

Rated Operational Current (max.) 0.6 A @ 120V AC and 0.3 A @ 240V AC
Make/Break VA 432/72

Am I correct in assuming that I can use this contactor with this soft start? The operational current is only 4W for the contactor. But the pickup is 200W, the Make for the soft start is 432VA. I think that it's a large load on a small relay in the soft start and since we can start this motor up to 40 times an hour the stress for the relay is significant. But it seems like overkill to have a interface relay wich in this case should be an interface contactor to handle the current.

2. It is also connected to an safety relay as emergency stop contactor, the output from the safety relay is rated DC-13: 3A / 24 V DC.

I struggle to get my mind about how these large contactors are controlled when there aren't many output that can handle the load. Or shouln't I look at the rated current when I try to dimension for pick up?

Thankfull for any input

/Tim
  Reply With Quote
Old March 25th, 2020, 02:46 PM   #2
jraef
Member
United States

jraef is offline
 
jraef's Avatar
 
Join Date: May 2006
Location: Northern California
Posts: 1,898
If it were me, I would use an interposing relay, preferably a plug-in style. If you are unfamiliar with the term "interposing relay", you have the contact on the Soft Starter turn on a small relay, then the contacts of that small relay turns on the contactor coil. If the coil inrush damages or shortens the life of the small relay, you replace it quickly and cheaply. Even if the contacts on that PCB are rated for 1 million operations (typical), at 40/hour, 24/7/365, that's less than 3 years.


Side note:
40 starts per hour on a Soft Starter is something worthy of careful study of the soft starter's ratings to be able to handle that, not to mention the motor. I hope you considered those issues.

Last edited by jraef; March 25th, 2020 at 02:50 PM.
  Reply With Quote
Old March 25th, 2020, 02:53 PM   #3
rQx
Member
Sweden

rQx is offline
 
Join Date: Oct 2010
Location: Trelleborg
Posts: 783
Quote:
Originally Posted by jraef View Post
If it were me, I would use an interposing relay, preferably a plug-in style. If you are unfamiliar with the term "interposing relay". you have the contact on the Soft Starter turn on a small relay, then the contacts of that small relay turns on the contactor coil. If the coil inrush damages or shortens the life of the small relay, you replace it quickly and cheaply. Even if the contacts on that PCB are rated for 1 million operations (typical), at 40/hour, 24/7/365, that's less than 3 years.


Side note:
40 starts per hour on a Soft Starter is something worthy of careful study of the soft starter's ratings to be able to handle that, not to mention the motor. I hope you considered those issues.
Yes, that is what I thought of aswell but the technical specs get to me. For instance a 700-HK relay we regularry use is only 5Amps and when I search for other we use such as 700-HC it is stated: inductive 240VAC 7.5Amp, 120VAC 15amp. But not DC loads, is inductive DC loads to compare with AC loads so that I can use those values?

I'm aware , thanks for the thoughtful input
  Reply With Quote
Old March 25th, 2020, 04:40 PM   #4
ASF
Lifetime Supporting Member
Australia

ASF is offline
 
Join Date: Jun 2012
Location: Australia
Posts: 3,071
Use a 240VAC coil with a 100-JE coil interface module. 240VAC is applied to the interface at all times, and it does the actual pulling in, but won't pass the power through to the contactor coil until you apply a 24VDC signal to the interface as well. It's basically like having an interface relay built into your contactor.

Or, if when you say "bigger" you mean "55kW or above", you can use the new 100-E contactors which have this 240VAC/24VDC interface built in already.
  Reply With Quote
Old March 26th, 2020, 01:40 AM   #5
rQx
Member
Sweden

rQx is offline
 
Join Date: Oct 2010
Location: Trelleborg
Posts: 783
Quote:
Originally Posted by ASF View Post
Use a 240VAC coil with a 100-JE coil interface module. 240VAC is applied to the interface at all times, and it does the actual pulling in, but won't pass the power through to the contactor coil until you apply a 24VDC signal to the interface as well. It's basically like having an interface relay built into your contactor.

Or, if when you say "bigger" you mean "55kW or above", you can use the new 100-E contactors which have this 240VAC/24VDC interface built in already.
Thanks I know, but then I have to put in a transformer in the panel wich I'm trying to avoid. Otherways the interface is the way to go or I just put a 230V contactor in there since it's controlled from the soft start and the emergency stop relay

The contactor is a 37kW contactor, I saw the D and E variants but those are unneccessary big.
  Reply With Quote
Old March 26th, 2020, 04:00 AM   #6
BryanG
Member
United Kingdom

BryanG is offline
 
Join Date: Feb 2005
Location: Manchester
Posts: 1,467
Can get you 39kW in an Moeller/Eaton DILM65(RDC24) with a 24watt pick up.
__________________
Knowledge is power, share the knowledge.
  Reply With Quote
Old March 26th, 2020, 11:17 AM   #7
rQx
Member
Sweden

rQx is offline
 
Join Date: Oct 2010
Location: Trelleborg
Posts: 783
Quote:
Originally Posted by BryanG View Post
Can get you 39kW in an Moeller/Eaton DILM65(RDC24) with a 24watt pick up.
Thanks for the tips! I'm sure there are other brands but I'd like to stick with Allen Bradley since almost all equipment is from them
  Reply With Quote
Old March 26th, 2020, 11:34 AM   #8
BryanG
Member
United Kingdom

BryanG is offline
 
Join Date: Feb 2005
Location: Manchester
Posts: 1,467
It might be nice to stick to Alan Bradley but don't let your need for a neat solution get in the way of a better solution. In the big brands a contactor is a contactor is a contactor, if you want it to look prettier paint a flower on it. :-)
__________________
Knowledge is power, share the knowledge.
  Reply With Quote
Old March 26th, 2020, 02:19 PM   #9
kamenges
Member
United States

kamenges is offline
 
kamenges's Avatar
 
Join Date: Nov 2002
Location: Brillion, WI
Posts: 3,958
Quote:
Originally posted by BryanG:

...if you want it to look prettier paint a flower on it. :-)
Or an octagon, as the case may be.

Keith
  Reply With Quote
Old March 26th, 2020, 02:32 PM   #10
rQx
Member
Sweden

rQx is offline
 
Join Date: Oct 2010
Location: Trelleborg
Posts: 783
We have connected components deal with Allen Bradley so not a fan of choosing other products but as you said I might be forced to. Looking around I see that Siemens is also having contactors with lower pickup.

But the question about how you use these contactors with large pickup is still bothering me. Many products like relays doesn't specify make/break capability and if they do they often doesn't have inductive DC specified
  Reply With Quote
Old March 26th, 2020, 02:41 PM   #11
kamenges
Member
United States

kamenges is offline
 
kamenges's Avatar
 
Join Date: Nov 2002
Location: Brillion, WI
Posts: 3,958
DC coils aren't subject to inrush current the way that AC coils are because the resistance of the coil (which is what concerns us in static DC circuits) isn't dependent on the location of the armature relative to the solenoid like an AC coil is. So you don't need to worry about inrush.

You do, however, need to worry about the inductive kick resulting from the collapse of the coil magnetic field when the contactor turns off. So make sure you install a flyback diode across the coil of the contactor or that the contactor comes with a flyback diode as part of the coil assembly, which I believe most do these days.

Keith
  Reply With Quote
Old March 26th, 2020, 03:00 PM   #12
rQx
Member
Sweden

rQx is offline
 
Join Date: Oct 2010
Location: Trelleborg
Posts: 783
Quote:
Originally Posted by kamenges View Post
DC coils aren't subject to inrush current the way that AC coils are because the resistance of the coil (which is what concerns us in static DC circuits) isn't dependent on the location of the armature relative to the solenoid like an AC coil is. So you don't need to worry about inrush.

You do, however, need to worry about the inductive kick resulting from the collapse of the coil magnetic field when the contactor turns off. So make sure you install a flyback diode across the coil of the contactor or that the contactor comes with a flyback diode as part of the coil assembly, which I believe most do these days.

Keith
But the specifications say 200W pick-up, that is around 8Amp. You meen that I don't need to take that into account when I start it through say a relay that is rated for 5Amp?
/Tim
  Reply With Quote
Old March 26th, 2020, 03:42 PM   #13
kamenges
Member
United States

kamenges is offline
 
kamenges's Avatar
 
Join Date: Nov 2002
Location: Brillion, WI
Posts: 3,958
To the best of my knowledge you need additional control components to take advantage of the difference.

When a contactor is in the open state the armature (which the contact carrier is attached to) is largely disengaged from the solenoid. This significantly decreases the magnetic coupling between the armature and the solenoid. In order to get the armature to start travelling toward the solenoid the user must apply at least the pick-up current through the coil.

When the contactor is closed the armature is fully engaged into the solenoid and the magnetic coupling between the armature and solenoid is increased. This means a much weaker magnetic field is needed to keep the armature engages with the solenoid, meaning much less solenoid current is required.

I don't use too many contactors in the size range you are using and when I have I have designed assuming the pick-up current will always be required. Others may say differently but to the best of my knowledge the AB 100C conventional coils do not contain any type of switching components that would result in lower holding current through the solenoid when the contactor is closed. The coil itself is designed to pass pick-up current when 24VDC is applied to it.

You as a user can add a coil current controller that would apply the 8 amp required pick-up current for some time and then reduce the current to as little as 0.16A after the contactor is pulled in. However, that would require control outside of the contactor itself.

Keith
  Reply With Quote
Old March 26th, 2020, 04:15 PM   #14
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 314
Can't resist

1 of 4
Attached Images
File Type: jpg IMG_5648.JPG (250.0 KB, 30 views)
  Reply With Quote
Old March 26th, 2020, 04:15 PM   #15
drbitboy
Lifetime Supporting Member
United States

drbitboy is offline
 
drbitboy's Avatar
 
Join Date: Dec 2019
Location: Rochester, NY
Posts: 314
Can't resist

2 of 4
Attached Images
File Type: jpg IMG_5649.JPG (638.4 KB, 29 views)
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Weird Allen Bradley coil issue... Matchu04 LIVE PLC Questions And Answers 3 February 10th, 2014 04:01 AM
Allen Bradley for temperature control again irondesk40 LIVE PLC Questions And Answers 12 November 15th, 2013 02:01 PM
Help! DeviceNet for SLC500 Allen Bradley Buscom LIVE PLC Questions And Answers 7 October 7th, 2013 07:33 AM
Learning Allen Bradley mbferrari LIVE PLC Questions And Answers 9 March 11th, 2009 12:25 PM
allen bradley 1746 high speed counter andy fearne LIVE PLC Questions And Answers 1 March 29th, 2005 12:05 PM


All times are GMT -5. The time now is 04:06 AM.


.