Limiting Flow on AC voltage - Grundfos 11 SQF 2 pump

cdm755 · January 2019

Hello,
I currently have a Grundfos 11SQF2 pump that I need to limit the RPMs on. Static water height is ~145'. When my storage gets behind and I need to catch up, I try to run a generator on the AC input of the IO101 module. Problem is, the pump pumps more water than my well's recharge rate and the pump begins to draw air.

There are two ideas that I have thought of to limit the pump speed.

1.) Utilize a 8.4A minimum DC power supply to convert 110VAC to ~48VDC and at that condition, the pump will pump ~8.5 gpm. I am afraid if I try to utilize a power supply smaller than 8.4A, the pump will attempt to draw more current than the power supply is rated for and go into an over current shutdown?

Here is the power supply that I had in mind. Problem with this idea is that I don't think that my well will keep up with 8.5gpm.

https://www.automationdirect.com/adc/shopping/catalog/power_products_(electrical)/dc_power_supplies/5vdc,_12vdc,_48vdc,_din_rail_mount/psh-48-480

2.) My other idea is to utilize a DC drive (VFD) to provide DC power to the CU 200. I have been told that the SQF pump has an internal VFD and that I cannot supply DC power via a VFD to the CU200 in lieu of the solar panels. I don't understand why this wouldn't work. Could someone please explain why this DC drive would not work to limit the current draw/speed of my SQF pump.

Here is the DC drive that I had in mind:

https://www.automationdirect.com/adc/shopping/catalog/drives/dc_drives/high_voltage_(>_50v)_enclosed/gsd5-240-10n4

I really hope to do this without a re-circulation line dumping water back in the well. Any input or advise on slowing the SQF down utilizing an AC input would be very much appreciated.

Thanks!

mike95490 · January 2019

PV panels are a current source, and the pump's internal controller is likely to apply load till the voltage starts to sag. That will burn up a power supply or battery bank, which are Voltage Source.

mike95490 · January 2019

To slow it with an AC input, I think a Variac transformer might work. Maybe. I have no idea what goes on in the internals of the controller.
If 48V works, would 36V or 24v also work ??

mcgivor · January 2019

Using a water level controller to only allow the pump to work between certain levels would be a simple solution with more predictable results.

jonr · January 2019

The pump has run-dry protection, so it might be OK if you did nothing. Why do you want to avoid returning water to the well?

cdm755 · January 2019

Thank you all for your replies.

Mike,
The pump's rated current is only 8.4A so, I wouldn't burn up a 10A power supply since the pump is unable to exceed the current draw rating? I would just run full speed at whatever voltage is being supplied? Would this thinking be correct? I will look into the Variac transformer that you mentioned. I am not familiar with this product. 36VDC would work, but not 24VDC. 30VDC is listed as the minimum supply voltage on the pump specs. Ideally, a 30VDC power supply would be best as the pump would run slower at 30VDC, 8.4A instead of 48VDC, 8.4A. A 30VDC power supply just does not look to be readily available like that of a 48VDC power supply.

Pump specs: https://product-selection.grundfos.com/product-detail.catalogue.product families.sqflex.html?from_suid=15470511055940040350568669013986&pumpsystemid=492170801&qcid=465390758

Mcgivor,
Using a water level controller/switch would not work so well for me as the storage tank that I am pumping into is 20' in diameter. It requires hundreds of gallons to raise the water level only an inch or two. When I hook my generator up and run full steam, I am pumping air in a matter of minutes. Also, the 100VAC generator is not available all of the time. I generally run the pump on PV panels. I am using the pump to water livestock in an agriculture application. When I have several days in a row of clouds, the water level gets behind. This well/pump is in a remote location on a cattle ranch. When this happens and my water storage gets behind, I would like to be able to haul my portable generator to the site, fire it up and drive off letting the generator run until it runs out of fuel to re-fill my water storage. (possibly as long as ~24 hours depending on flowrate).

Jonr,
The dry-run protection does not appear to function properly on this pump. Never has since it was new. These are high quality pumps but I have read of others having this same issue with the dry-run protection not cutting the pump off. Since the pump is over $2000, I really don't want to just let it run full steam pumping air because I know that drawing air is very hard on the mechanical components of this helical rotor, corkscrew design. I could return water to the well, just want to avoid lugging around a hose and fittings to plumb up the re-circulaiton line every time. Also, it will be running unattended, and I can't think of a good way to keep the flow correctly split between how much is going into the storage tank and how much is going back to the well. Anything messes up and the pump will be drawing air until the generator runs out of fuel or the pump burns up. Just thought that there would be a better/safer way to do it through the current/voltage source.

Thank you all so much for your replies, keep them coming!!
Clayton

Aguarancher · January 2019

The old school way we do this is with a gate valve on the pump outlet. With a little bit of experimenting you should be able to set the flow so you don't run the well dry.

mcnutt13579 · January 2019

You can't gate an SQ Flex, it has a positive displacement pump.

mcgivor · January 2019

@cdm755 said

Mcgivor,
Using a water level controller/switch would not work so well for me as the storage tank that I am pumping into is 20' in diameter. It requires hundreds of gallons to raise the water level only an inch or two. When I hook my generator up and run full steam, I am pumping air in a matter of minutes. Also, the 100VAC generator is not available all of the time. I generally run the pump on PV panels. I am using the pump to water livestock in an agriculture application. When I have several days in a row of clouds, the water level gets behind. This well/pump is in a remote location on a cattle ranch. When this happens and my water storage gets behind, I would like to be able to haul my portable generator to the site, fire it up and drive off letting the generator run until it runs out of fuel to re-fill my water storage. (possibly as long as ~24 hours depending on flowrate).

My idea was to use a level controller in the well itself, not the storage tank, I've used this a safeguard to protect my pump, amongst other protection, flow, pressure and time, for when I'm not present. An attempt to make something idiot proof, if there is such a thing.

Aguarancher · January 2019

..You can't gate an SQ Flex, it has a positive displacement pump..

I didn't say close it off, just use the gate to throttle it back a bit.

cdm755 · January 2019

Mcgivor,
Ahh, I understand your thinking. Yes, several of the other solar control boxes that I have ran in the past have a "well float" input. However, since the Grundfos is made to have it's own "dry well sensor" (which is wired into the factory pump leads), the Grundfos CU 200 controller does not have a well float input. Any idea how to wire up a "stand alone" well float?

Aguarancher,
Lol, yeah I'm familiar with the old school ways. We do it on irrigation wells but I just hate it. It's hard on the pumps and difficult to keep adjusted to keep from pumping air. Also, have a look at the pump curve shown in this link.

https://product-selection.grundfos.com/product-detail.catalogue.product families.sqflex.html?from_suid=15470511055940040350568669013986&pumpsystemid=492170801&qcid=465390758

If I crank the gate valve down to increase the head pressure, I really don't decrease the flow much when utilizing an AC input. With an AC input, the pump is going to be running full steam. For instance, if I gate valve the flow off, I would say for comparison sake, move from the 131' head pressure curve to the 394' curve. Max potential on the 131' curve is 12.4 gpm and max potential on the 394' curve is 10.3 gpm. If I cranked the gate valve down to cut flow down to ~6gpm, I'll over pressure and trash the pump.....

mcnutt13579 · January 2019

Aguarancher said:

..You can't gate an SQ Flex, it has a positive displacement pump..

I didn't say close it off, just use the gate to throttle it back a bit.

But if you throttle it back, at first the current just goes higher and the GPM stays the same. So you would be wasting energy, if that is a factor.

Eventually if you throttled it far enough back the rotors would start to turn slower, still at max power, but I don't know what it would do to the $$$$ pump/motor assy.

cdm755 · January 2019

mike95490 said:

To slow it with an AC input, I think a Variac transformer might work. Maybe. I have no idea what goes on in the internals of the controller.
If 48V works, would 36V or 24v also work ??

Mike,
I looked into the Variac transformers. I didn't see one that fits the bill for this scenario. Problem is that my minimum AC input voltage for the pump is 90 volts. At 90VAC and 8.3A, the pump is still running at max potential (on the 131' TDH flow curve). The advantage of converting to Ac over to DC is that the pump can accept down to 30 volts DC.....

Dave Angelini · January 2019

I had something like this a ways back. We switched in and out a string or 2 of panels for poor/good solar conditions.

Aguarancher · January 2019

You are right about old school not always being the best school. lol Looked at the pump curve.

Looks like you need a variable DC power supply to dial your pump in to your needs when running off a genny.

jonr · January 2019

The pump has a built-in buck-boost DC-DC converter. So as you drop voltage, it draws more amps to compensate. Same watts - so no effect on output.

As far as I can tell, 8.4 A rating is what goes to the motor - not the input to the DC-DC converter.

It's not clear to me what will happen if you further current or voltage limit the input. Does it continue at full output down to 30V and then shut off? Or produce less output below some voltage?

In any case, this isn't a simple brushed DC motor where less voltage clearly slows it down.

cdm755 · January 2019

My understanding is that maximum amperage drawn by the pump is 8.4A. If this is the case, @ 30VDC the pump is only drawing 252 watts. If voltage drops below 30, the controller shuts the pump off. But at 30VDC and max current draw of 8.4A (252 watts), looks to me like I could slow the discharge volume down to right around ~4gpm (assuming the 131'TDH flow curve). Perfect. IF I could locate a minimum 8.3A, 30VDC power supply.......... I think this would work.

jonr · January 2019

That's possible, but I would think that they would disclose that at anything less than ~120VDC, the pump will have reduced output (not efficiency).

Only $30 to try. Let us know if it works.

Search ebay for: DC-32V10A-Switching-Power-Supply-32V-320W-LED-Lamp-Industrial-Control-Equipment

Dave Angelini · January 2019

The strings of solar are different voltages. As the voltage goes up the output increases or the depth from where you are pumping increases output. Forget the current as long as it is enough, for limiting output that you want.

If this is a new ap, make sure you have good surge protection and grounding. This controller has a history of easily being damaged.

mcnutt13579 · January 2019

My understanding is that the pump runs slower and slower the less voltage you give it, down to 50 or 30 volts or something.

It is designed to take advantage of opportunity even if the solar is not that great, it will still pump some water, better than none.

But when you feed it higher voltage it reaches its max RPM limit, and then when the voltage gets higher than that it just backs off current to keep the power level the higher the voltage goes.

jonr · January 2019

How much power you can draw from a solar panel is a quite different subject - it's mostly independent of voltage.

mcnutt13579 · January 2019

jonr said:

How much power you can draw from a solar panel is a quite different subject - it's mostly independent of voltage.

I believe you are correct, actually, I think the SQ Flex has MPPT in itself so the panel voltage probably stays up but it works across the knee of the curve to find the max power that the panel is capable of producing for that particular irradiation.

Dave Angelini · January 2019

You guys have this wrong. What is your panel arrangement? How many and what voltage panels in series? I did not have time to read the previous posts. It would help if you summed it up.

cdm755 · January 2019

My pump setup is a Grundfos 11 SQF 2 with a CU200 controller. Power can be supplied to this pump as 90-300 WAC or 30-300 VDC. (My understanding is that the pump itself has an internal rectifier). Normally, I utilize my PV panels to supply the controller with DC current on a daily basis. I have three panels wired in series. They are 240W, 30.2A panels. The Total Dynamic Head of my well is 145'. For whatever reason, when my water storage gets low, I need to be able to utilize a generator to pump all hours of the day/night.

The issue I have is that when providing 120V @ 8.4A, the pump pumps more water than my well can provide. I am looking for a solution to limit the pumping rate when utilizing an AC generator. I need a method to limit current output to the pump.

jonr · January 2019

Gotta love people who say that you are wrong without bothering to learn what was said.

cdm755 · January 2019

They are 240W, 30.2V panels.**** Sorry for the typo. They are 30.2V panels not 30.2A.

Dave Angelini · January 2019

How are they wired? My point is if you have 4 in series and need to lower pump output, you need to try 3 in series or 2 in series.

Dave Angelini · January 2019

I gotta love people who try to help but have never installed grundfos. A pretty expensive mistake is in alot of the previous posts.

cdm755 · January 2019

My three panels are wired in series. I do not need to lower output when utilizing the PV panels. I need to lower output when I get in a pinch and have to use a generator AC input as the power source. Utilizing a generator, the pump runs full steam and pumps air. (110 VAC, 8.4A). I am looking for a solution to lower pump output/speed when I use my generator.

Dave Angelini · January 2019

Have you tried adding a 4th solar panel for that, or a second string of 3?

cdm755 · January 2019

If I cannot find a way to run at a lower speed using my generator, I guess that will have to be my solution. I just really would like to be able to use a generator in case of emergencies. My solar pumps water livestock in remote locations. Sometimes I don't see the cows for several days in a row. Every so often when I find that I have an issue (storage tank sprung a leak, pipeline sprung a leak, cows from a neighboring pasture tore the fence up and all showed up at the wrong water tank and drained it, etc.), I need the water NOW. I cant afford to wait for tomorrows sun (assuming that tomorrow is sunny enough to pump). Under these circumstances I could run the generator continuously instead of hauling water or moving livestock. Secondly, this specific pump is in a remote location, a difficult location to haul water to.

Limiting Flow on AC voltage - Grundfos 11 SQF 2 pump

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