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Thread: Small cabin DC water pump set-up?

  1. #1

    Default Small cabin DC water pump set-up?

    Greetings,

    I've read this link, but still had some questions:
    http://www.windsun.com/Solar_Water_Pumps/pumpinfo1.htm

    Details:
    Small off-grid cabin.
    2800 gal. water storage container (above ground and 3 feet away from the cabin)
    80 gallon (30 gallon water capacity with bladder) pre-pressurized tank

    As it stands I'm using an AC flotec pump (1/2hp - 115v - 9.4A). I'm still in the construction phase (and don't have solar installed yet) so I power the AC pump with a 5k generator. This is plenty for the pump with a surge of 3300.

    Eventually, I plan to use a DC pump with my system. The DC pump only has to pull water from 4 feet away into a pressure tank that is two feet away. The water is already stored above ground which should be easier on the DC pump because it doesn't have to draw from a well. I would like to have water pressure of 45-50 lbs.

    Based on my specs, I was hoping for a recommendation on a DC pump with a built-in pressure switch that will fill my pressure tank to 45-50lbs and run off of a 12v battery bank (recharged by 1000k of PV). Hopefully something moderately priced. Sureflo?

    Lastly, I would still like to keep the AC pump in line for emergencies. Can I have two pumps in line? Anyone else have a set up like this, with two pump types (AC & DC) in the same line?

    thanks,

    Hairfarm

  2. #2
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    20,520

    Default Re: Small cabin DC water pump set-up?

    Should not be a problem... You probably would want to plumb in a pair of ball valves per pump (or similar) to isolate each pump from the common water pipes (or at least check valves to prevent back flow through one or the other pumps)... That way you can still have pressurized water while the other pump is being serviced.

    If you have freezing conditions, adding a drain valve will be a help too.

    Regarding what kind of pump... There are simple DC pumps that will last a couple years between overhauls (new diaphragms and motor brushes)... If you will be pumping a fair amount of water, a brushless (PM type) motor with electronic control would be nice for a longer service life.

    Also understanding how much sand/grit you have in your water will be a help... Grit in the wrong type of pump will quickly kill them. Using filters on the water inlet can create its own problems (pump pulls a vacuum on the inlet and stops pumping).

    There is quite a range in pricing between a "simple" and a "nice" pump:

    Shurflo 8000 standard delivery pump 12 volt ($100)
    Shurflo Extreme smart sensor 5.7 RV pump 12 Volt ($340)

    Others here who have more experience with off-grid pumping can probably give you more information than I.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  3. #3

    Default Re: Small cabin DC water pump set-up?

    Thanks for the helpful response BB.

    As it is, when the 30psi cut-in switch kicks in it will take roughly 2 minutes (give or take) for my AC pump to fill my pressure tank (80 gal capacity - 30 gal water). My pressure switch settings are 30-50.

    Question: How long will it take a DC pump to fill my pressure tank? Will it be much slower than my AC pump?

    thanks!

    Hairfarm

  4. #4
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    20,520

    Default Re: Small cabin DC water pump set-up?

    Your AC pump is around 1,000 watts... The 12 VDC pumps I linked to are around 4.5-9.5 amps -- or ~114 watts maximum. So, at the very least, I would expect them to run 10x as long for otherwise identical / same efficiency pumps (the small DC pumps may actually turn out to be more efficient).

    You should find a data sheet for the pump you are interested in... For a random 12 volt pump, here is one PDF data sheet.

    At 30 PSI it runs about 2.3 GPM at 8.4 amps. At 50 PSI it is 1.8 GPM at 9.5 amps.

    So, around 2 GPM for 30-50 PSI.

    30 gallons will take around 15 minutes to fill (if I understand your setup).

    -Bill "I think" B.
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  5. #5

    Default Re: Small cabin DC water pump set-up?

    I use a Shurflo and no pressure tank for small cabin. It has pressure switch built in. Powers shower, sink and etc. They are only 2 or 3 gallons per minute - so problems with running several taps open. Our host has a cool looking one at http://store.solar-electric.com/2088-514-145.html but the less expensive models likely as good. And even cooler one at http://store.solar-electric.com/sh41potw12vo.html . I use http://store.solar-electric.com/2088-443-144.html and its fine.

    I see they have both 12v and 24v units.

    Locate below the suppy as they do not pull too well and are meant to push.

    Get a filter mounted before the unit if there is chance of junk in the line - save the pump.

    There are many places that sell these and parts are available everywhere.

    Not tried one with a pressure tank - they pump at 45 psi. Would be interested in experience of those with Shurflow and a pressure tank also - sounds complicated.

    The company product line (go for the RV units - this is the market they corner) is at http://www.shurflo.com/rv-products/r...s/default.html .

    See also

  6. #6
    Join Date
    Oct 2003
    Location
    Paradise, CA
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    369

    Default Re: Small cabin DC water pump set-up?

    I have a cistern that normally supplies an AC pump to fill two pressure tanks. I also have a 12VDC Shurflo pump as a backup to that AC pump, using (as suggested) ball valves to isolate the two.

    If the AC pump fails then two valves are shut for it, two are opened for the DC pump, and a fuse is relocated to supply the DC pump power and a breaker is switched so the AC pump doesn't get power. Less than a minute total.

    Yes, it takes longer for the DC pump to get the tanks up to pressure, but it's no big deal. On those few times we've been on the backup, we never got to a point where the DC pump couldn't keep up with demand (like a shower or washer) and still fill the pressure tanks.

    Phil
    Happily off-grid since 1977

  7. #7

    Default Re: Small cabin DC water pump set-up?

    Could you rate your shurflo pumps? Have they been durable for your usage?

  8. #8

    Default Re: Small cabin DC water pump set-up?

    train82499 -
    I use a Shurflo and no pressure tank for small cabin.
    How do you get stable water pressure? What's the shower experience like with no pressure tank? Do you get hammering in your lines?


    PhilS - What type of DC pump do you use? How many gallons is your PT?


    BB - Are all Sureflo DC pumps positive displacement? I like the ball valve set up and idea of having an AC backup running off of my generator.

    thanks!

    Hairfarm

  9. #9
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
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    20,520

    Default Re: Small cabin DC water pump set-up?

    I believe that the ones I pointed at are all positive displacement pumps.

    But they also make some other types too (like a sump pump)--and other models that NAWS does not carry.

    I have no directly knowledge of the product line--You should contact NAWS, Shurflo, or your local supplier for details.

    Otherwise, I am just searching the web for information too.

    I have a small DC pump in an old RV (may even be a very old Shurflo)--And no pressure tank... Pump simply turns on when a faucet is opened. Probably not ideal for a cabin/home where a pressure tank would be a lot nicer (and handle multiple points of use at the same time).

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  10. #10
    Join Date
    Jul 2007
    Location
    Quetico, Ontario
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    Default Re: Small cabin DC water pump set-up?

    We use small shuflos without tanks in small seasonal cabins. They work fine for one appliance at a time. Given a choice, I would instal at least a small P-tank to reduce cycling.

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

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