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

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.

jraef said:

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.

Click to expand...

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

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.

ASF said:

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.

Click to expand...

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.

Can get you 39kW in an Moeller/Eaton DILM65(RDC24) with a 24watt pick up.

BryanG said:

Can get you 39kW in an Moeller/Eaton DILM65(RDC24) with a 24watt pick up.

Click to expand...

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

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.

Originally posted by BryanG:

...if you want it to look prettier paint a flower on it.

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Or an octagon, as the case may be.

Keith

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

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

kamenges said:

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

Click to expand...

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

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

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