Low Flow Well and Solar Pump Controller?

hpinson · December 2010

Hi. I have a low-flow, but reliable well, that I want to put back into service.

Well output is 1/2 GPM and has remained constant over the 20 year life of the well.

Static water level is 180 feet.

Well depth is 310 feet.

Casing is 6".

I would like to go with a solar pumping system, and the GrundFOS 3-SQF-2 or 3-SQF-3 looks appropriate, pumping into a 1000 gallon tank and then gravity fed to a small cabin.

A problem that I anticipate is that even at the low flow rates of these pumps, the well will pump dry and need to replenish.

The SQF Controllers have a feature that shuts the pump off when it runs dry, via a sensor.

The problem being is that after an initial pumpdown, the well will slowly replenish just enough for the pump to cycle on and off continulally, not allowing the well to fully replenish, and probably straining the pump (an assumption).

If AC power were available I could use something like a Coyote Pump Controller, which lets you set a time between dry-run power off and restart, say 3-5 hours.

http://www.coyotemfg.com/

However I can find no similar device for a DC solar pumping system.

Does anyone have any idea where I might find such a DC pump controller timing device, or perhaps could suggest an alternative idea, perhaps somehow restricting the pump output to 1/2 gallon per minute? Maybe I am looking at the wrong pump?

Any ideas are appreciatated! Thanks.

-- Harlow

bmet · December 2010

Re: Low Flow Well and Solar Pump Controller?

What is the depth of your pump? Is it all the way to the bottom of the casing?

stephendv · December 2010

Re: Low Flow Well and Solar Pump Controller?

I think the simplest solution is to use a battery based timer switch, with a relay that can handle the DC current from the PV to the pump controller. Just determine when the well will be dry for an average solar day and set the timer accordingly. Re-adjust twice a year for winter and summer.

hpinson · December 2010

Re: Low Flow Well and Solar Pump Controller?

I'm thinking that the pump should sit at 290 feet, about 20 feet above the bottom of the well.

SCharles · December 2010

Re: Low Flow Well and Solar Pump Controller?

hpinson wrote: »

I'm thinking that the pump should sit at 290 feet, about 20 feet above the bottom of the well.

Well, sure. You want the pump deep so you can draw off as much volume at a time as you can. Or, I would in a slowly-producing well. At the beginning of the draw, you won't use any more electricity than you would with the pump higher, of course, until the level of water in the column drops. [Except for a very small voltage drop due to the longer wire run.] I would think that 20 ft. from the bottom would give you adequate protection from particulate matter.

solarvic · December 2010

Re: Low Flow Well and Solar Pump Controller?

I am not an engineer or anything like that but I have an idea that could work if you can get someone to figure it out. When your well casing is full the pump requires less amps to run. As the waterlevel lowers in the well casing the pump should take more amperage to pump the well. Just thinking = Is there some kind of adjustable relay you can get that is controled by the amperage? You could adjust the amperage on it at a point that matched the amperage draw at the water level you wanted to stop the pump. Thus letting the casing fill to a certain level before the pump turns on again. :Dsolarvic:D

hpinson · December 2010

Re: Low Flow Well and Solar Pump Controller?

Those are two ideas worth exploring. I found such a timer controller sold on this site:

http://www.solar-electric.com/fldctico.html

I wonder if there is any way to restrict the output of the 3-SQF-2 to at, or near the well output. Or would that even be necessary? Looking at the GrundFOS performance curve chart for the 3-SQF-2 I see that even at 250W (which would take a boatload of PV panels), output is near or below 2GPM.

Or could a lessor pump be used, like a sureflow 9300, and be placed much higher in the water colum, and have pumping output restricted to 1/2 GPM somehow, perhaps through the use of some sort of orifice?

-- Harlow

PhilS · December 2010

Re: Low Flow Well and Solar Pump Controller?

hpinson wrote: »

Those are two ideas worth exploring. I found such a timer controller sold on this site:

http://www.solar-electric.com/fldctico.html-- Harlow

Thanks Harlow!!

I'd kill for your "low flow well". We've lived over 25 years on a well that outputs 50 gallons per day. Every four days I pump 200 gallons into our 1000 gal cistern. I have the Grundfos 6SQF-2 with the CU200 controller.

If I forget or am out of town, and pump after 10 days, I get 200 gallons. Two days yields 100 gallons. It's linear but never gives more than the 200. I try to not forget to pump. The ways I measure are three: time (horribly inaccurate, I think the pump may differ whether operating off of an inverter or off of a generator); reading on the CU200 (I usually stop at 70 but don't start pumping air until 73 or 74; cistern readings (the most accurate... if I've pumped 200 gallons, good enough).

That timer you linked to seems like it could put my system on "automatic". And under $100!!

Phil

hpinson · December 2010

Re: Low Flow Well and Solar Pump Controller?

That's good to hear that it is possible to get by with such low flow.

Here' another gadget that might do the trick in that scenario, but like the Coyote pump controller seems AC 115/230 only. Need to contact this company and see if they offer a DC solution.

http://www.deanbennett.com/bw-lh-systems.htm

Two sensors, one just above the pump and one near static level. Pump cuts out when water is below the lower sensor, and start up when it refills to the level of the upper.

-- Harlow

PhilS · December 2010

Re: Low Flow Well and Solar Pump Controller?

Something I forgot to mention about my SQFlex:

There is a low-water cutoff but it worked properly on my unit less than a year. Since it is just a couple of contacts positioned above the pump, maybe it is "slimed" now so that it always thinks there's water in the well?

If I pump my well dry, I'll start pumping air. I can hear it going through the piping. I can see it bubbling into our cistern.

I had one of the Coyote units when we first started using this well. As I remember, it worked for a few years then didn't, but it wasn't worth pulling the pump to change it.

After this long, I'm pretty good at judging how much water I can pump until the well is empty.

Phil

icarus · December 2010

Re: Low Flow Well and Solar Pump Controller?

1/2 gpm is about 700 gpd. Do you have a need for that much water? Does your static level remain constant at 1/2 gpm, or does it drop over the course of the day?

hpinson · January 2011

Re: Low Flow Well and Solar Pump Controller?

I wish I could answer your question about static pressure dropping over the day, but at this point I have no good history of the well output, other than 1/2 GPH was the logged rate when it was drilled in 1984, and an bailing output test last October (2010) that indicated similar.

I would expect much much less than 700 GPD would be our use. Perhaps 150 GPD for three users max.

mike95490 · January 2011

Re: Low Flow Well and Solar Pump Controller?

I've got a regular AC pump, but also have a "Pump Protecter" which is suppoesd to cut power if it senses the pump becomes unloaded (dry), and it has an adjustable restart timer. All mounted in the pump controller box with capacitor and wire interfaces.

tmarch · April 2011

Re: Low Flow Well and Solar Pump Controller?

hpinson wrote: »

Hi. I have a low-flow, but reliable well, that I want to put back into service.

Well output is 1/2 GPM and has remained constant over the 20 year life of the well.

Static water level is 180 feet.

Well depth is 310 feet.

Casing is 6".

I would like to go with a solar pumping system, and the GrundFOS 3-SQF-2 or 3-SQF-3 looks appropriate, pumping into a 1000 gallon tank and then gravity fed to a small cabin.

A problem that I anticipate is that even at the low flow rates of these pumps, the well will pump dry and need to replenish.

The SQF Controllers have a feature that shuts the pump off when it runs dry, via a sensor.

The problem being is that after an initial pumpdown, the well will slowly replenish just enough for the pump to cycle on and off continulally, not allowing the well to fully replenish, and probably straining the pump (an assumption).

If AC power were available I could use something like a Coyote Pump Controller, which lets you set a time between dry-run power off and restart, say 3-5 hours.

http://www.coyotemfg.com/

However I can find no similar device for a DC solar pumping system.

Does anyone have any idea where I might find such a DC pump controller timing device, or perhaps could suggest an alternative idea, perhaps somehow restricting the pump output to 1/2 gallon per minute? Maybe I am looking at the wrong pump?

Any ideas are appreciatated! Thanks.

-- Harlow

6" well casing will hold quite a bit of water between the static level and the pump. I haven't looked at the curves for that pump, but I would think with the low water probe as close to the pump as Grundfos puts them the pump shouldn't be cycling that often. JMHO

Low Flow Well and Solar Pump Controller?

Comments

Categories