Generator size for submersible pump

Discussion in 'Pumps and Tanks Well Forum & Blog' started by Arky217, Oct 19, 2013.

  1. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas
    What's the minimum size generator (surge watts/continuous watts) that I would need
    to start and run a 1/2 hp, 240 volt, 4 amp (FLA) submersible pump ?

    I'm looking at the Harbor Freight 4000 watt surge/3200 watt continuous model
    and was wondering if it would do the job.

    Thanks,
    Arky
  2. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    It should. Are you using a 3-wire pump? FYI a Franklin 3 wire uses about 1/2 the starting power of a Franklin 2-wire.

    Faradyne motors have the capacitor in the motor so there is no difference between 2-wire and 3 wire I'm told.

  3. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas

    Well, I've tossed it back and forth a dozen times or more on 2 wire vs 3 wire and
    after reading pros and cons till my eyes crossed, I'm leaning toward the 2 wire.
    Can't really give a definitive reason why; there's good arguments on both sides.
    The actual pump I've decided on is a Gould, 7gpm, 230v, 4amp, 2 wire, model # 7GS05422C.

    I want to go as cheap as possible on the generator since it's main use will be to power the pump during power outages.
    I'll just be running it only long enough to refill the pressure tank (about 15 gal. of water) and then off again til I've emptied the tank again.
    And the Harbor Freight 4000/3200 watt model is on sale for $289.99.
    Just want to make sure it will do the job for the pump.
    ( I already have an efficient Honda EU2000i to power other small 120 volt items.)

    Arky
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,383
    Location:
    Lubbock, Texas
    I have a Honda 3500 that I use to test wells with a 1.5 HP pump. It will start the three wire, with control box pump easily. I don’t think it would start a 1 HP in 2 wire.

    There is a company that makes controls that will start and stop a generator using the pressure switch on the pressure tank. Pretty cool. I will post the link tomorrow when I get to my office.

    Also, if you use the longest length of the smallest wire recommended for the motor horsepower, it makes a soft start and is much easier on the generator.
  5. VAWellDriller

    VAWellDriller New Member

    Messages:
    170
    Location:
    Richmond, VA
    You mentioned you already have a honda EU 2000...I know for a fact that you can run a Grundfos 1/2 hp 115 volt 3" SQ pump on the 2000 eu with no problems whatsoever. You can also run that same grunfos on a 1000 running / 2000 surge inverter with no problems at all. If you spend a little more on getting that pump, you won't have to buy what is sure to be a very poorly made Harbor Freight generator.
  6. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas
    You make a very interesting point.

    For some reason, I was thinking that I had to buy the wire locally (don't know why I didn't check online, brain lapse I guess) and the
    largest available submersible pump wire locally is 12 ga.

    And according to the Goulds specs for their 1/2 hp, 115 v, 2 wire pump, the FLA is 7.9 amps and the maximum wire run should not exceed 178'
    which is just under my run of 180'. That is the reason that I thought that I needed to go with 240 volts.

    But if I go with 10 ga. wire, it would be a different story.

    Now, If I'm figuring this right, the total dynamic head that the pump would see for my desired 30 to 50 psi pressure
    would be 173 feet (100' to pump + 4' uphill + 69'(30psi) to 219 feet (100' to pump + 4' uphill + 115'(50psi).

    So, in order to keep this total dynamic head (173' to 219') within the performance curve of either a Goulds or Grundfos 1/2 hp, 115v, 2 wire pump:

    The Goulds pump would be the 7gpm, mod#7GS05421C with a FLA rating of 7.9 amps and a locked rotor rating of 28 amps.

    And the Grundfos pump would be the 5gpm, mod#5SQ05-180-115v with a FLA rating of 7.7 amps
    and a overload (locked rotor ?) rating of 11 amps.

    Now, as I mentioned, my wire run is 180'.
    For the Goulds pump, their max recom. run for 12 ga. is 178', and for 10 ga. is 284'.
    For the Grundfos pump, their max recom. run for 12 ga. is 220' and for 10 ga is 360'.

    These figures seem a little odd, however,
    since Grundfos is allowing for a longer wire run even though their pump FLA is practically the same as the Goulds.

    Also, I'm confused by what Grundfos is calling the overload amps; surely this is not the locked rotor or start current,
    or is it, since one of the features of the Grundos pump is stated as:

    "Excellent starting capabilities
    The integrated electronic unit of the motor features soft starting. Soft start reduces the starting current and thus gives the pump a smooth and steady acceleration.
    The soft starter minimizes the risk of wear on the pump and prevents overloading of the mains during start-up.
    The excellent starting capabilities are a result of the high locked-rotor torque of the permanent magnet motor together with the few pump stages. The high starting reliability also applies in case of low voltage supply."

    At any rate, my main question is: is this model Grundfos the same one that you are referring to that you said that your Honda EU2000i
    can start without any problems ?

    And is their overload rating of 11 amps really the start current ?
    If so, I can see how the Honda will start it with no problems.

    I can't see the Honda, however, starting the Goulds pump with its 28 amp start current
    (that's 3220 watts, Honda is only rated for 2000 watts surge)

    One more question: Even though it appears that I might be able to use the 115v Grundfos pump successfully
    and start it with the Honda, is there any major downside (besides not being able to use the Honda)
    in my particular situation, for using a 115v pump rather than a 230v pump ?

    Thanks,
    Arky
  7. craigpump

    craigpump Member

    Messages:
    856
    Location:
    ct
    You're thinking this thing to death.

    Use a 230 volt pump, Goulds or Grundfos with #12 wire and be done with it. We install 2 and 3 wire pumps, they both seem to have the same reliability. Given the thunderstorms in Ar, I would probably go with a 3 wire and keep an extra control box handy.

    And forget about a Harbour Freight generator, it will let you down when you need it the most.
  8. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    Craig, it's in a home that is "off-grid" so I can see why he's interested in these numbers.
  9. craigpump

    craigpump Member

    Messages:
    856
    Location:
    ct
    He said the generators main purpose is to power the pump during power outages.

    He isn't going to save any money by using a 115v unit, in fact it may cost him more when you consider that #12 is good for about 160' before he would have to up his wire size to #10. In addition, the 230v unit will draw less current which in theory should run cooler and provide a longer life, plus he can run #12 up to 650,' or for more savings he could use #14 and run it 400'.

    I'd go with a 230volt unit
  10. valveman

    valveman Moderator Staff Member

    Messages:
    4,383
    Location:
    Lubbock, Texas
  11. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    Oops, got the OP confused with another poster from Ark. that was off-grid. My mistake.

    I would probably go with the 230V 3 wire pump and spend a little extra coin and get the Honda 3500 generator. That harbor freight unit isn't worth buying.

  12. DonL

    DonL Jack of all trades

    Messages:
    3,815
    Location:
    Houston, TX
    You do not really need to spend a lot on a generator.

    Any 8 HP with a briggs will work good.

    That one at HF looks like 6.5 HP and you would be happier with a 8 horse.


    Good Luck
  13. guy48065

    guy48065 New Member

    Messages:
    111
    Location:
    SE and north MI
    Not always. I bought a Champion 3500/4000W genny, chosen because it far exceeded the ratings for my submersible. I connected to my panel with everything shut off and when I threw the breaker for the well the generator stalled like I had shoved a crowbar in it. My guess is the rotating mass of these cheap & light Chinese generators is insufficient to push through the startup current of a submerged pump.

    It's probably best to do the math and make the best selection rather than buy on price or convenience.
  14. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    What is your submersible? Brand/Horsepower?
  15. DonL

    DonL Jack of all trades

    Messages:
    3,815
    Location:
    Houston, TX


    The Champion 3500/4000W is a 6.5 HP gen.

    The 8 HP Briggs with the cast iron flywheel will keep you operating at 60HZ.

    A lot of the newer BS has a aluminum flywheel and depend on the flywheel affect to happen in the generator, When you really need the weight on both ends of the Crankshaft.


    Inverter Generators can work good IF you have batteries connected.


    Have Fun.
  16. VAWellDriller

    VAWellDriller New Member

    Messages:
    170
    Location:
    Richmond, VA
    I just mentioned the 115 Grundfos because he ALREADY has probably the coolest and nicest generator anyone can buy, the Honda 2000EU. Then he would save lots of money since he wouldn't have to buy another generator.

    DONL -- Inverter generators don't need any batteries connected, not sure what you meant by that, but they are freestanding....they're just great all around. I have a pair of the 2000 eu's and a Honda 7000IS for the house....I have lots of other generators, couple Northern Tool, couple B&S, couple Generac...and I would take the Honda Inverters over all of them.
  17. Arky217

    Arky217 New Member

    Messages:
    43
    Location:
    Arkansas
    Yes, I would much, much rather spend even $300 on a better pump if I can run it with my Honda EU2000i, 120 volt generator
    than to spend the $300 on a cheap junkie 240 volt generator.

    There must be something about the Grundfos pump motors that allow them to start on a much lower surge current than conventional motors.
    Their 2 wire, 5gpm, 115v model#5SQ05-180-115v shows to have a FLA rating of 7.7 amps and an overload rating of 11 amps.

    In their technical data, it says under starting current, "The motor starting current is equal to the highest value stated on the motor nameplate".

    If that value is synonomous with what they're calling the overload rating, then I can understand how a Honda EU2000i could
    easily start it.

    Under features, it does say: Soft-Start: Both the SQ and SQE motors have a soft start because of
    the integrated electronics. Soft start reduces the starting current and gives the pump a smooth and steady acceleration.

    Perhaps the 'overload current' IS the actual start surge current; maybe it has something to do with them having permanent-magnet motors.

    Arky
  18. VAWellDriller

    VAWellDriller New Member

    Messages:
    170
    Location:
    Richmond, VA
    The grundfos 3" motors are very, very high RPM motors...which makes me think they must have relatively low torque. They also have a very slow start, probably a full second or more to full speed....if you start one out of the water, it sounds like a dremel.
  19. Texas Wellman

    Texas Wellman In the Trades

    Messages:
    522
    Location:
    SE Texas-Coastal
    VA, the high RPM is because of the fact that it is a 3" pump and it needs that much speed to make the necessary pressure and flow (smaller impellers vs. a 4" pump).

    They have low starting current because they do take a few seconds to wind up-they don't surge on start-up.

    Also, I would mention that if your well makes any sand or grit this pump would not be a good choice due to the high rpm's. Overall I have never heard anyone say they didn't last a long time except for if the well makes sand, and then all pumps have a shortened life.
  20. DonL

    DonL Jack of all trades

    Messages:
    3,815
    Location:
    Houston, TX

    My comment was more about going off Grid. Normally that is what generators can help you do.

    If you are charging and running batteries you can run the Inverter , without the generator running.

    Then you can just run the gen, when the batteries need charged, or charge them with Solar or Wind.

    It makes the electrical switch over easy, and safe. But it has its losses.


    Have Fun, Be careful Playing with Electricity.
    Last edited: Oct 22, 2013
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