Water Pump Controls

[laketime]

I have a customer who is now controlling a small water system for his neighborhood. They have two pumps; one for the well that pumps to a reservoir and another that is in the reservoir that pressurizes the system. The issue is that we are installing a back up generator system that is undersized for both pumps to kick on at the same time (a rare case). They want a 3 minute lag from when the reservoir tank kicks on until the well pump starts. I had planned to use a time delay relay to comtrol the well pump. Reservoir turns on...three minutes later well pump turns on. I have limited exeprience designing these systems but my concern is this: reservoir pump turns on, three minutes later well pump turns on, then reservoir pump turns off, will well pump keep running or will my idea to use to reservoir pump power to control time delay relay shut off well pump? I could use come help with design obviously and I am sure there is a way to keep well pump running until reservoir is full. I have also thought about using the float in the reservoir as control for the well pump, as it is already, but put the time delay in the middle of that circuit. My concern there is that it does not address the reservoir pump starting at the same time. In short....help!

 

[synchro]

Are the pumps on VFD's or soft starters? If not, then they might help reduce the peak level of the starting current.

 

[laketime]

Are the pumps on VFD's or soft starters? If not, then they might help reduce the peak level of the starting current.

Neither are soft start nor VFD's. I agree but they are wanting a "cost effective" solution with a time delay. I am hoping for guidance on the controls idea.

 

[drcampbell]

Try asking yourself the mirror-image of this question: "When do I want to inhibit each motor from starting?"
At first glance, it seems like using the normally-closed contacts of a delay-on relay should do the trick.
(which will be open during the three minutes after each motor starts)

How big a genset are we contemplating? Something big enough to be custom-ordered?
If so, another possible solution is a genset with a smaller engine that will handle the continuous load, a bigger (or lower-impedance) alternator that will handle the combined starting load, and a bigger flywheel.

 

[ptonsparky]

A CLICK from AD would work great for this.

Otherwise each starter on its own control interlocked with a delay timer on the other.

Res Pump sensor is LOW and Press Pump is not On, RP starts, along with a Delay timer that prevents PP from coming on for XXX time.
Pres is low PP starts after delay of the Res Pump Timer if the RP is On, If not the PP starts and begins a Delay before RP can come on.

Use same logic in both control.

 

[laketime]

A CLICK from AD would work great for this.

Otherwise each starter on its own control interlocked with a delay timer on the other.

Res Pump sensor is LOW and Press Pump is not On, RP starts, along with a Delay timer that prevents PP from coming on for XXX time.
Pres is low PP starts after delay of the Res Pump Timer if the RP is On, If not the PP starts and begins a Delay before RP can come on.

Use same logic in both control.

Whats does "click from AD" mean?

 

[ptonsparky]

Small PLC from Automation Direct.

 

[zbang]

Small PLC from Automation Direct

Exactly what I was thinking- a small PLC gives a lot more flexibility than a simple relay and in the end might be cheaper than the relays.

 

[ptonsparky]

For the money those small PLCs cost anybody that tinkers with control, or wants to, should get one. A low end HMI is the next step.

 

[tom baker]

But does the OP have a laptop and programming software, and the time to learn to program. I agree a small PLC is ideal, but what if the OP is not around, and the person called to work does not know how to troubleshoot the PLC
What I would suggest is find a panel shop, tell them what you want, they can wire up a control panel with some adjustable timers (I would have an on delay for each pump), the time delay for the well pump, etc. All inputs and outputs are wired to a terminal strip for OP to wire to, and to land a 15A 120 volt power circuit, all listed and labeled, drawings, ready to go. Can add a few pilot lights, reservoir hi level, HOA switch, power on...
Are the well pump and booster pump in the same building? If so that makes this pretty simple.

 

[ptonsparky]

Even the simple stuff won’t happen overnight when you start.

 

[laketime]

But does the OP have a laptop and programming software, and the time to learn to program. I agree a small PLC is ideal, but what if the OP is not around, and the person called to work does not know how to troubleshoot the PLC
What I would suggest is find a panel shop, tell them what you want, they can wire up a control panel with some adjustable timers (I would have an on delay for each pump), the time delay for the well pump, etc. All inputs and outputs are wired to a terminal strip for OP to wire to, and to land a 15A 120 volt power circuit, all listed and labeled, drawings, ready to go. Can add a few pilot lights, reservoir hi level, HOA switch, power on...
Are the well pump and booster pump in the same building? If so that makes this pretty simple.

Both pumps are located or fed from the same location. I am in rural Idaho and I am not sure about a panel shop but I like the idea.

Edit: Found a panel shop about 1 hour from here lol...gotta love the internet!

 

[tom baker]

The advantage of the panel shop is you get a set of drawings for you or the next person. Get the panel shop the motor voltages, phase, amps, take pictures of the motor controllers, they will need to know how to interface to the contactor.

 

[low-wattage]

I thought this was an interesting question and thinking about it, I couldn't see going straight to a PLC, seems like it could be done with just a couple control relays. I made a diagram, maybe it's more complicated than I think but here's what I got:



The first rung of the diagram wouldn't be part of the actual controls, I just put it there for reference, a standard motor control circuit with momentary switches for stop and start.

The second rung shows that basic motor control circuit adapted so that floats do the starting and stopping of the well pump instead of the momentary switches. It also interlocks the well pump with the pressure pump.

The third rung shows the pressure switch that starts and stops the pressure pump, interlocked by the low float and the reservoir pump control relay.

With ordinary relays, there's no delay - if there's a call for pressure and the reservoir is filling, as soon as the well pump finishes, the pressure pump will start. If you want a delay, you could use time delay relays.

It would be easy to add HOA switches, or in this case maybe a switch that lets you select well pump, pressure pump, auto, or off.

A PLC would be great and offer unlimited flexibility, but I don't know it's over the bar for where it's worth the trouble. Relays would be very simple and inexpensive to maintain, troubleshoot, etc. over the long term. With a PLC you might have a headache in five years. If you use a PLC you have to keep that code backed up and any time there's troubleshooting there's probably going to be a laptop with the correct software and the correct connection cable etc. involved, and the software for that model PLC might not be available for your current version of Windows, the PLC itself might go discontinued, etc. With relays, you could keep a spare in the cabinet along with the diagram and you can probably come back to this in 20 years and fix it quick and easy.

 

[drcampbell]

Is the intent to prevent them from starting simultaneously, or to prevent them from running simultaneously?
I think you've implemented the latter.

 

[ptonsparky]

Is the intent to prevent them from starting simultaneously, or to prevent them from running simultaneously?
I think you've implemented the latter.

I thought he did both. If ones running, the other won't. A horse race at times to see which one starts first.

 

[ptonsparky]

Rung two has an issue we dealt with a couple years ago. The low level switch stuck closed, always calling for water. It cycled via the high level switch and wave action in the holding pit. IDK why the motor lasted longer than the starter contacts, other than maintenance continually reset the overloads before finally calling. A TDR now requires a minimum Off time.

 

[low-wattage]

I think I misunderstood the post originally, I guess they want to avoid the case that they both try to start at the very same time - I guess the thinking is the generator can start one while the other is running just can't handle both inrush.

I don't think that's too hard to deal with, I think you could use two one-shot relays, one for the well pump, one for the pressure pump.

For the well pump, you could put the pressure one-shot in series with the low float to start - if the pressure switch started within the last three minutes, the one-shot will still be on, and it will wait out the one-shot interval to start the well pump.

For the pressure pump, you could just put the one-shot in series with the pressure switch, but then the well pump could interrupt the running pressure switch for three minutes when it starts. But you can get around that by sealing around it.

 

[zbang]

A TDR now requires a minimum Off time.

This is one of many places where some hysteresis (delayed start) is a good idea. Perhaps one could view it not as minimum off time but as a minimum time "start request" time (if you don't hold the button for 10 seconds, it's not gonna start).

 

[paulengr]

This is really simple to solve.

The first detail to get out of the way is that startup on an across the line motor should be under 10 seconds. So that’s plenty of delay to where starting current is down to under FLA. Typical is 2-4 seconds so 10 seconds is plenty.

Moving on when you don’t want two motors to start simultaneously the common strategy is to use a timer that only opens contacts (NC contacts) while it is timing that is controlled by the other motor. Then place a normally open aux contact of the same motor in parallel so that once it is running it stays running. The timer only blocks the motor from starting simultaneously with the other one. Use this scheme on BOTH pumps because you need to block either one from starting simultaneously.

You can extend the same scheme with more motors by placing all the timer contacts in series as long as you have extra timer contacts.