System for intermittent well pump

johnny84 Registered Users Posts: 7 ✭✭
I have a friend that wants to have backup power for his well pump.
The pump is a 10gs05412 Goulds pump, 3 wire 230 volt that runs intermittently for a pressure tank. He is on grid and and wants the system to charge from the grid and then charge from his generator that he runs periodically during outages. I know this system may cost a bit but this is what he is looking for.

Any recommended configurations would be most appreciated, thanks
40 years, I was solar/off grid before solar was cool


  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Welcome to the forum Johnny,

    It looks like a 1/2 hp 230 VAC 3 wire pump (starting capacitor in the control box at top of well):

    Those are easier to start (lower surge current). 

    Mike has posted well motor specifications here (I suggest you read the whole thread--It is pretty short):

    Another Mike posted in the same thread for a 2 wire pump:

    And the problem with induction motor based well pumps... They are are real monsters to run. They tend to have high starting surge current, and poor Power Factor (they draw 120/240 VAC current "inefficiently"). So, unless there is a VFD on the pump (variable frequency drive--basically a 2 or 3 phase AC inverter with variable frequency output--VFDs "correct" many induction motor issues like high starting surge current and poor power factor--There can be other issues with VFDs... The wrong VFD on the wrong motor can cause dramatically shorted motor life).

    Anyway... If looking for a simple genset (not an inverter-genset--very nice stable AC output, but not really needed for a typical well pump)--Then very roughly, I would be looking these numbers
    • 230 VAC input
    • 6.0 amps maximum load
    • 960 Watts maximum load
    • 6 amps * 230 VAC = 1,380 VA maximum load
    • 960 Watts load / 1,380 VA = 0.70 Power Factor (about average)
    So, for the running rating of the genset (note most residential generators are rated in Watts and VA where Watts=VA rating...):
    • 6 amps * 230 Volts * 1/0.80 genset derating (better life, don't push limits) = 1,725 Watt (VA) minimum 230 VAC genset
    Then there is the starting surge... Can easily be upwards of 5x running load:
    • 6 amps running * 5x starting surge * 230 VAC = 6,900 VA starting
    • 6,900 VA starting / 2 (assuming genset can surge 2x rating) = 3,450 Watts (VA) minimum
    Note that fuel consumption wise, the genset will be supporting ~960 Watts (full load) of fuel consumption. VA wise (the power power factor) the wiring will be supporting ~6 amps and 1,380 VA worst case running.

    The genset itself suggest 80% rating (to keep from overheating motor and alternator and genset wiring).

    If for some reason, he wants to use an inverter genset--They typically do not have the high surge current support (browning out output, "ride through" surge/voltage drop). And inverter genset will (many times) simply shutdown its output because of the high surge current. So, and inverter genset will typically need to be larger to support high surge current vs standard "cheapo" alternator based generator.

    The above is just some math and guesses on my part.. Could a 2 kWatt genset run the well pump--Possibly.

    And before I purchased a genset, I would suggest renting a genset and trying it for a day on the well pump if trying for the smallest working unit. This is a good idea anyway, large gensets consume lots of fuel--And when running at low output power (670 to 960 Watts), the typical gasoline/propane genset does not drop much below 50% fuel flow when the electrical load drops below 50% of rated output (big/oversized genset, lots of fuel, lots of fuel storage/trips to the gas station).

    Alternative fuels like natural gas, propane, diesel have their pluses and minuses.

    Gensets are pretty cheap these days (comparatively speaking). And even getting two--A smaller unit (like the Honda eu2000i or similar family) to run the home, and a cheap/bigger 3.5 kWatt to run the well pump when needed.

    And alternatives for pumping... Pumping to a cistern (once every day or two) and use a smaller AC or even 12 or 24 volt RV water pump for house pressure. Replacing the present pump with a Grundfos pump (much more genset and even solar/off grid friendly pumps--But very expensive).

    Hopefully somebody else will answer here that has experience... I am out of my depth on well pump genset/AC inverter power needs. Just trying to get the conversation going and some idea of what you are looking at.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    If I'm reading right, the friend already has a genny, and is looking for a battery based backup? 

    I'm guessing the generator has trouble starting the pump during an outage?

    The idea would be to run the pump and other loads during the outage from a battery based system, and use the generator to charge batteries as needed?
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • johnny84
    johnny84 Registered Users Posts: 7 ✭✭
    He basicly wants a dedicated electric storage system just for the well pump that will be kept charged by the grid and charge maintained by periodic running of his generator that he only runs a bit every day, for the fridge and such.
    40 years, I was solar/off grid before solar was cool
  • johnny84
    johnny84 Registered Users Posts: 7 ✭✭
    Thanks for the welcome and info. I'll tell him his options and costs.

    The last time I was there and looking at his set up I noticed a capacitor set up that wasn't connected to any thing. Next time Ill look at it more closely and get any info on it. From what I've gathered it will be a required factor in his options. 
    40 years, I was solar/off grid before solar was cool
  • johnny84
    johnny84 Registered Users Posts: 7 ✭✭
    Oh, I'm not sure if he has tried running his pump off his gen. He was looking for options during power outages and wanted to have a nice balance of cost, efficiency, long term planning and environmentally friendly. But he would like to avoid his gen cycling repeatedly through out the day/evening.  
    40 years, I was solar/off grid before solar was cool