Eaton soft start and thermal cutout

Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I installed a replacement motor run off an existing Eaton S811+ soft starter. The new motor has an internal thermal cutout whereas the old one did not. There are a couple of ways I could tie in the cutout to the general control circuit, but it seems like it may be easier and better to use the options (I/Os) on the soft starter. Is there a standard way of doing this?
I could just have the cutout open either the RUN or ENABLE signal. There are input options for "external trip" or "external e-stop" but the manual says those disable the ramp to stop feature. This is a pump application, and a diaphragm valve needs to close as the motor ramps down.
I'm probably making this more complicated than it needs to be, so I thought I'd ask here for some clarity.
TIA
 
Sure, there are lots of ways to do this. I use DOM/DOB (delay on make, delay on break) timers a lot with soft starters and drive for all kinds of applications. This might be one of them. You can delay the stop after the cut-out of whatever method. You mentioned internal cutout as opposed to external cutout. Are you sure you can access the internal cut out? Is it buried in the windings?

General rules: never interrupt the output of a drive or SS. Cut out the enable or discrete. Can you send me a schematic of what you have? I can take it from there. Thanks.
 
If the motor thermal cutout trips, you do NOT want to ramp to a stop! You will smoke the motor. Decel ramp on a soft starter keeps more energy ON the motor as it decelerates, to lengthen the stopping time. That is already hard on the motor and the soft starter. The motor thermal sensors are a last resort to prevent harm to the motor.

Using an “external trip” input to shut it down then displays that as the reason it is shut down. Interrupting the Enable does not give the user a simple way to diagnose the reason it isn’t running.
 
Thanks for the feedback!
The main concern at this site is whether a diaphragm valve will be able to close on a sudden stop of the pump. Nobody at our operation is quite sure. However, the motor is currently wired so that a fault from the soft starter will actually shut the entire motor cabinet off via a shunt trip. Not to say that's desirable, but how it is.
This cabinet has been through many iterations before I got here. I came up with the schematic below. There is a separate control panel and SCADA involved external to the starter cabinet.
I agree that running 24V through the thermal to an external trip input is the way to go--and easy. I'll have to see if someone can figure out the valve situation.

Highland WATK P1_existing.png
 
I agree with the prior comment that any fault in winding equates to immediate shutdown of motor; and it will if it’s internally attached and not “tapped” into, unfortunately it cannot time out. It needs to shut down instantly.

Thanks for the schematic I’ll give it a review later today.
 
So there are different types of back flow check valves used, but when you say “hydraulic”, that narrows it down to two. A Pump Control Valve, mainly championed by a company called “Cla-Val” where that name is used generically, and a hydraulically dampened check valve. In EITHER case, they are ALWAYS made to still function correctly when power is cut off, because if you think about it, that happens whenever you lose utility power too. The only time you have to worry about that is when someone uses a motorized valve. No power, no motor.
 
Thanks, @Jraef. The valve is a Cla-Val. Your mention of a power failure is a good point as far as circumstances making the pump eventually having to stop without ramping. And as I mentioned, the existing wiring has the starter completely kill the cabinet on a fault anyway.
Now I just hope I can navigate the DIM menus to set up an external trip input. (The Eaton manual isn't that great!)
 
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