# Baldor drive overload set point



## KennyW (Aug 31, 2013)

Are you talking about P1508? 
If so, that's literally just the setpoint for when a digital output assigned to the function of "overload" will switch at. Do you have such an output configured? If so, what is it wired to?


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## Matt2318 (Jan 31, 2008)

yes, im talking about p1508, I know it is just a set point for a digital output. It is assigned to an input on the plc in the cabinet. I don't know the program for the plc but I did try lowing the set point to 1% and it did cause a failure to start. 

Obviously the idea is that when the set point is reached that a failure to start will occur. What I am looking for is a reason that someone would have set it so low? other then the fact that every time the pump fails to start that he would have got a call out to reset it. I also did try lowering the set point from 46 to 40% and at that point the drive would fail to start the pump about 50% of the time. Its right at the threshold.... pretty smart if you are the guy getting a 3 hour min at double OT call each time it happens. 

Apparently the pump station has been an issue for 2 years and has countless dollars thrown at it without a solution being found, I would love to be the guy to have solved it in 2 hours. Going to find out tomorrow when I can test the fault under auto conditions.


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## KennyW (Aug 31, 2013)

What I'm trying to say is there's not going to be a procedure for calculating it. It's application specific. "Overload" implies protection but it's a poorly named parameter- it's really just "current above setpoint" (as you know). It's not actually linked to any of the drive's I2t calcs so you could put any value in it depending on what sort of logic you are using it to engage. 

I'd go online to the PLC and see what's happening. With it set that low, I'd wonder if their intent is to use it to detect some sort of steady state condition, but the time delay in the PLC is a bit too short, so it false trips on startup. 

I agree if it's really meant to reflect "overload" then that's way too low, but sinc eit is set so crazy low, I would ensure it's not meant to serve as some other sort of process alarm before changing it.


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## dronai (Apr 11, 2011)

Kenny, wouldn't that O/L setpoint typically just open the seal in circuit on the PLC ladder ? After looking at the PLC ladder, and seeing that it is not triggering anything else in the process, would you just re set the drive overload setting ?


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## JRaef (Mar 23, 2009)

Often times something like this is used in lift stations as an indirect way to detect open flow, i.e. a broken seal, flange or pipe, which can be very costly in a wastewater application (fines etc.). In a centrifugal pump, load = flow so if the pipe breaks and there is less back pressure on the pump, more "stuff" flows and the load on the pump motor increases. So you program a set point that is just above the measured operating current of the pump at normal flow. That way if the pipe breaks and current spikes above that, you trip off line and set off alarms to get someone out there to find the leak immediately before it gets into a creek somewhere.

The thing is, you must ALSO allow for an increase in current when starting the motor. With a VFD, you can theoretically accelerate a motor with 100% of FLC, maybe less if the motor is over sized. But I seriously doubt you can accelerate it consistently at 46% of FLC ( if that's what you meant). So there would need to be a time delay in the VFD, or in the PLC program to avoid having nuisance trips. Also, if someone shortened the ramp time on the drive after it was initially set up, that can affect the acceleration time and cause this. Also a change in viscosity, or "suspended solids" in the fluid will affect that too. So right after a big Mexican food dinner party for instance? Either way, this is likely just an issue of getting the trip delay timing coordinated with the acceleration requirements.

Or, you DO have a leak somewhere!

Meh, just re-read the OP and saw that this is fresh water, not wastewater. Waste of a good Mexican food joke...

But still, it is likely there for open flow detection, because a leak in an underground pipe can result in a sink hole or something else destructive, let alone the wasting of water. So all the rest of the issues still apply.


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