Feasable? 50 GPM @ 40 PSI?

theobilltheobill Registered Users Posts: 4
I have a question that I'm still wrestling with and think it's possible. I have an old AG well (3 phase) that used to run this property with huge overhead sprinklers. It used to put out 180 GPM on 12 acres. We're going to try this year to scale back a bit and only do 1/5 of that acerage but we need water this year.
PG&E took out the transformers years ago for the 3 phase and left only the one. Now, if we want to use that old pump, we're looking at at least $5k, probably about $7-10k AND monthly payments.
We're still a little in the dark, but the dawn is breaking!
My requirements are this: 50GPM (the more the better tho) at 40 PSI. The well never ran dry and is at the very bottom 125', but our water table is at 11' (I understand from locals that 30' well's several years ago nearly ran dry during a drought). Friction loss is negligible as the supply pipe is 6".

Here's what I've been talking with folks about - if I got an SQ Grunfos pump that got the water from 80' up to the surface to a 5,000 gallon tank, then an A/C (I have 220v at the well) booster pump thereafter to give us the PSI requirements, with a float switch on the pump. That Grundfos would have to refill that tank probably all the way every hour and a half during daylight hours.
Two questions -
Does the water requirements sound feasible?
And, am I missing any big ticket items into the cost? The solar requirements on that would be around 1.5 KW, so that's not too bad (can get panels for around $1.25/watt), the well's already dug, the pump should be about $2k, and the tank will be the same I hope - so for the same $$ as getting two transformers, I'll get water free forever! Granted, it's not the same GPM, but it's also not a monthly bill.
Thanks in advance - lots of great info here!


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    You know 50 GPM is five times what a standard pump delivers? The old system was likely one of those massive 15 HP 3 phase irrigation pumps.

    But your plan is to fill a 5,000 gallon tank over time with the Grundfos pump and draw from that through the pressure pump.
    So this comes down to a question of the total volume of water you'll use vs. the Grundfos's ability to supply it over the time it is able to run. The 40 SQFl-5 can do 70 GPM from 90', so which model do you have?
  • theobilltheobill Registered Users Posts: 4
    Re: Feasable? 50 GPM @ 40 PSI?

    yep - that's the model I've been looking at. I don't have it yet - just trying to get my options set understood. Do the other calculations compute? If my sprinklers "eat" 50 GPM, the grundfos would be able to deliver (assuming the pressure is boosted in between)?
  • theobilltheobill Registered Users Posts: 4
    Re: Feasable? 50 GPM @ 40 PSI?

    Oh, and the former owner said it was a 10HP 3-phase. But I guess I'd be looking to replace the needs of more along the lines of a 4-5 HP a/c model.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    5,000 gallons in 90 minutes is 56 GPM so in theory the pump could do it.

    The problem is the Grundfos isn't designed to run full out all day long so its over-all lifespan would probably be shortened. Compared to trying to power a 10 HP 3-phase from solar replacing the pump would be simple and cheap.

    This should work. Maybe someone else sees a flaw?
    There's a few forum members who have similar irrigation systems; hopefully they'll chime in with some first-hand insight.
  • theobilltheobill Registered Users Posts: 4
    Re: Feasable? 50 GPM @ 40 PSI?

    Thanks for the help on this - anyone else have a suggestion of way the water their crops using solar?
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    I've got about an acre of hazels, they get water every other day. I pump from a pond, up to several 3,000 gal tanks, for gravity feed. Pump is conventional 240V deep well pump, properly sized for the lift/flow I need, and is on a timer, to limit it to the sunny hours of the day.
    I pump about 9gpm @ 160' . So you need to carefully size the system for your needs, it's really easy to get sold a much larger pump than needed.

    Of course, your scale is much larger than mine, but to move that much water, will cost a lot of power.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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  • Ken MarshKen Marsh Solar Expert Posts: 114 ✭✭✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    Here is a different approach, I guess I am just unconventional but have had good luck with this stuff.
    Use a VFD drive and your installed 10 Hp pump.
    With a Variable Frequency drive you don't have to run at full power.
    You could run the 10 Hp pump at 5 Hp if you want.
    Just crank the frequency down till you get the water you want at the pressure you need.

    Don't mess with an intermediate tank. Run the sprinkler heads right off the primary pump.

    You could power it with your existing single phase service but input voltage does have to match the pump motor voltage.
    Your pump could be 220 or 440 Volt. This would have to be determined before you get equipment.
    If you have a single transformer on your electric service, you probably have 220 V.
    A 440 V motor would require a step up transformer when powered by a 220 V Service.
    Or you might get the electric Co. to cooperate and install a 440 v Transformer but it would be costly.
    440 Volt VFDs usually have to be derated if you are powering them with single phase.
    220 V VFDs usually do not have to be derated.

    For examples of VFDs search ebay for "VFD drive".
    As you can see they could be your least expensive option by far

    If you decide to go solar, a VFD will allow you to start your pump with no high current inrush.
    This is much more agreeable to a solar system.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    Ken, I don't think a VFD is the answer, the motor still needs 3 phase input unless it is reconfigurable. OP - if you know the manufacturer and model, or can pull the pump to find out, it is possible the motor is reconfigurable for split-phase service (which is what you have now). It will have a lower output but since that's what you want anyway it may be a win-win situation. Call them and find out.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Ken MarshKen Marsh Solar Expert Posts: 114 ✭✭✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    A VFD receives its power as either single phase or three phase and rectifies it to DC.
    It then chops the DC into three phase.
    The nice thing is that it lets you set the output frequency.
    You can control the speed of the motor.
    The Grundfos and the Minisplit air conditioners work the same way.

    You are correct, it would not be wise to use a capacitor to run the motor off single phase.
    Lightly loaded motors can be run this way but it is far from ideal.
    The capacitor gives you 90 deg phase shift.
    The motor is expecting 120 deg shift.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    The VFDs I've seen operate by modifying/chopping the waveform, but not converting from split phase to 3 phase, or vice-versa. What you describe is closer to an online UPS with AC to DC to AC stages. I'm not saying the VFD you describe doesn't exist, I just haven't seen that, which is why I suggested seeing if the motor could be field modified.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Ken MarshKen Marsh Solar Expert Posts: 114 ✭✭✭✭
    Re: Feasable? 50 GPM @ 40 PSI?

    My apologies, I re-read my last post and can see that it is not very clear.
    You are correct the Variable Frequency Drive (VFD) is similar to the UPS.
    They both start with AC, rectify it to DC then re-chop it back to AC.
    But the VFD has two significant differences.
    1. The VFD has three outputs spaced at 120 electrical degrees.
    2. The VFD allows you to control the frequency of the output.

    The three outputs go to a three phase motor's three windings.
    The variable frequency allows you to control motor speed.

    It has other things going on too.
    An on board microprocessor keeps tab on the motor and changes the pulse width
    such that motor delivers needed torque without saturating the core.
    But this occurs with no operator intervention.
    They use bridge type choppers so are what the solar types call Modified Sine Wave.
    You have to be careful that the output has no connection to ground or neut.

    VFDs have been around for many years.
    I have installed dozens of them over the last 30 years in industry and as engineering consultant.
    What is new is, while they used to cost thousands of $,
    now since the Chinese and Japanese have gotten into it, 2-5 Hp versions can be purchased in the $100 range.
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