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  1. #1
    Platinum Member TheGoose's Avatar
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    Default Using a generator to power a water well pump

    I have read a lot of threads on here asking about using a generator to power a water well pump so I wanted to pass some info along.

    My intent here is only to clear up some confusion about using water wells and generators, which many of us have to do while living in the country. First, a little about myself. I used to be in the business, so I know a little about water well issues etc. While I am no longer in the business, I haven't totally forgotten everything I knew LOL.

    I noticed that most posters are listing their well depths, water level, pump types, draw-down, etc. etc. While this information is important to the overall design of the well, the only thing that has any real effect on selecting a generator is the Horsepower of the motor on the pump.

    What you need to be looking for is the HP of the pump, usually found either by looking on the side of the motor of a jet-pump or looking on the control box of a submersible pump. Most jet pumps will either run on 115v or 230v by switching the wires in the motor. Submersible pumps are almost always 230v and cannot be switched (to my knowledge). The HP of the motor will determine how many amps the motor will pull, and this will give you how many watts. 230V setups are better because they will pull half the amps of 115v (but use the same watts).

    Of course, requirements vary region to region as water tables, well depths, well yield and water requirements change from house to house. But what I have found that most people can be well served with a 1-HP setup. Some slightly more, some slightly less. Obviously, a 1.5 HP motor needs double the watts as a 3/4 HP etc, but 1-HP is a good start with a single residential dwelling with a decent water level. The water level in a well is somewhat independent of the total depth of the well.

    For instance, my home has a well that is 535 feet deep. The water at the bottom of the well is under pressure which pushes the water to within 60' of the surface. So I am drawing water from 60', not 535 feet. I will set my pump at 140' to ensure that it stays completely submerged with no chance for the draw-down to let the pump run dry. Some areas closer to Houston have water levels approaching 200' feet deep, so obviously they need larger HP etc to get the same amount of water to the surface. Desert and mountainous areas may also have deep water levels and HP will go up. Lower well yield means deeper pump settings etc.
    YMMV.

    Regardless of the well depth etc. the HP of the motor determines the size of the generator. When starting, the motor surges the amps by at least double, and your generator needs to be able to handle this surge.

    The brand of the generator makes a very big difference when using a generator to power a well pump. The internally regulated generators have an extra winding in the generator stator. The extra winding senses the output current to automatically adjust the output voltage. Thus you can use a smaller internally-regulated generator to start a well pump than a larger externally regulated generator. I have seen this with my own eyes. A good Honda EG-3500 watt generator will start a 1-HP jet pump while a 5KW Lowe's special often cannot do the same thing.

    The wiring also makes a difference. The smaller or longer the wire, the more voltage is lost due to resistance, and the more amps the motor has to draw to make up for the difference. Remember, Watts = Volts x Amps. If the volts go down, the Amps go up to compensate.

    When using a generator I always try to wire the pump up separately with a short-run of wire, usually 10 gauge for 1.5 or less pumps. Always try to run the pump on 230v if it is equipped to do so. I only run the well pump by itself so I am not using any of the generators extra capacity on other items. I normally will pressure up the tank to it's normal operating pressure or maybe slightly above by increasing the pressure switch setting. By doing this I can put 40-60 gallons in a standard 80-gallon tank at ~60 psig. I can then disconnect my well from my generator and use water sparingly. As the water level goes down the pressure gets lower and lower until I finally have to run the well again. Using this method you can easily use 20-30 gallons of water from the tank before having to kick the well back on. If I'm using a lot of water I will disconnect the generator from everything else if possible and only run the well.

    Most submersible motors use Franklin electric motors and they have published a guide for using generators that can be found here:

    Service: Franklin AIM: Page 5 - Americas Water Systems - Franklin Electric

    If you notice they list a 1-HP pump as needing a 4KW externally regulated generator to run. I tend to favor on going with a good quality 5.5KW generator set which gives you a little reserve for using other applications.

    I hope this was helpful, I will try to answer any questions you throw my way.

  2. #2
    Platinum Member
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    BX22

    Default Re: Using a generator to power a water well pump

    I agree with all that you said. Today, however, the generator is the biggest factor. Since the motor, or any induction motor, will require a much higher inrush current when starting, it is the capacity of the generator to be able to handle the inrush that counts. If the generator does not have enough capacity to get the pump motor spinning fast enough, during the inrush period, the motor will never get to speed. Continuing to run the pump when it has not achieved running speed will result in an overload and possibly damage to the motor.

    Many imported generators today scrimp on "iron" and "copper". Going cheap on copper will increase internal resistance and not enough iron reduces the magnetic flux capacity. Both are critical to surge capacity. Better generators will be heavier partly due to this reason. "Surge Ratings" on generators is not a well defined parameter, and you should not rely too much on it. So go for one with a high enough rating, not a surge rating.

    paul

  3. #3
    Elite Member CurlyDave's Avatar
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    Default Re: Using a generator to power a water well pump

    I will set my pump at 140' to ensure that it stays completely submerged with no chance for the draw-down to let the pump run dry.

    My well is 710 feet and I have the pump at 670, even though my water level is closer to 60', just like yours. The reason is that water levels fluctuate over time and this way I can withstand a large drop and still be OK. Also, the amount of water stored in the well bore is significant.

    It requires very little extra energy to pump, only the friction losses in the extra pipe, the hydrostatic head only depends on the actual water level and is the same no matter what the pump depth.
    40 Acres on a hill - fantastic view. JD 110 TLB, 4-n-1, 12" bucket, 18" bucket, Addington thumb, rock bucket (doubles as root grapple)

    Not only do we not understand the universe, if someone explained it to us, we would not know what he was talking about.

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  4. #4
    Elite Member timswi's Avatar
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    Default Re: Using a generator to power a water well pump

    My house is all electic with a well..I've run a fair amount of the non220 circuts along with the well with a 7000 run/8750 surge generator..No issues with that at all. Just have to be reasonable on what you are expecting to power..Some lights, a tv and the well.
    BX23TLB & RTV1100 with 72" Power Angle Plow

  5. #5
    Elite Member whistlepig's Avatar
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    Default Re: Using a generator to power a water well pump

    My house is all electric also. I can run the 230V well pump, two refrigerators, pellet stove, TV, and some lights with a 5000/6500 watt surge Honda generator easily. The Honda was well worth the extra money for me.

  6. #6
    Platinum Member TheGoose's Avatar
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    Default Re: Using a generator to power a water well pump

    You have a low yield well...that is why the pump is set so deep. My well here easily could produce 60 gpm if I put a bigger pump in (4" well).

    Yes, the static water level is the pumping depth, not the level of the pump. The pump HP is still the only important factor.


    Quote Originally Posted by CurlyDave View Post
    I will set my pump at 140' to ensure that it stays completely submerged with no chance for the draw-down to let the pump run dry.

    My well is 710 feet and I have the pump at 670, even though my water level is closer to 60', just like yours. The reason is that water levels fluctuate over time and this way I can withstand a large drop and still be OK. Also, the amount of water stored in the well bore is significant.

    It requires very little extra energy to pump, only the friction losses in the extra pipe, the hydrostatic head only depends on the actual water level and is the same no matter what the pump depth.

  7. #7
    Elite Member timswi's Avatar
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    Default Re: Using a generator to power a water well pump

    Quote Originally Posted by whistlepig View Post
    My house is all electric also. I can run the 230V well pump, two refrigerators, pellet stove, TV, and some lights with a 5000/6500 watt surge Honda generator easily. The Honda was well worth the extra money for me.
    I actually have one of those knock-off Powerland things...It works very well given the cost...Got a killer deal on it when another state outlawed them for environmental reasons... Electric start, very quiet and pretty powerful. I'll run it until it gives up then get a Generac or Honda.
    BX23TLB & RTV1100 with 72" Power Angle Plow

  8. #8
    Gold Member
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    Default Re: Using a generator to power a water well pump

    We have all electric and no generator yet. Is there someone who can explain how to wire the pump so that it can be run from a generator. Can you splice in a plug at the control box, does there need to be a transfer switch wired to it? I'm just trying to get basic information on how I would "plug" in my well pump to a generator. Thanks.

  9. #9
    Platinum Member TheGoose's Avatar
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    Default Re: Using a generator to power a water well pump

    Assuming you have at least a little electrical knowledge I will try to give you the simplest scenario. If you have never had any electrical experience or have very little electric ability I would stop right now and discontinue reading. You could fry your pump, cause a fire, or even injure or kill yourself or somebody.

    Another word of caution: If you do this wrong or your generator is under-sized or malfunctioning you can damage your motor/wiring. For example, if the motor is wired for 115V and you connect it to 230V and run it for more than a few seconds it will damage the motor. If you have insufficient voltage to the motor the amps will go up and that too will damage the motor. I can't stress enough that you are taking property and potentially lives in your hands and that if you do not know what you are doing it is just best left alone or for more experienced folks.

    MOST water well setups whether they are a submersible or jet pump have a pressure switch somewhere on the system. If you have a variable speed pump I would not attempt this as they have different connections. Variable speed means constant pressure (but not cycle stop valve). The pressure switch is normally the Square D variety. There should be 4 screws inside the pressure switch with wires attached regardless if it's a 230V or 115V setup. Each pair of screws makes a connection through contacts. You need to figure out which ones go to your pump and which ones go to the supply voltage. It should be easy to tell which wires go to the motor and which wires to go the voltage supply.

    FIRST (VERY VERY IMPORTANT) kill the power to the pump by throwing the breaker. If you do not know which breaker goes to your pump I cannot help you. It is usually a double 20 or 30 amp breaker. AFTER you've tested the pressure switch to ensure that the power has been killed (with a voltage meter) disconnect the wires coming from the power supply. Secure these wires and tape or otherwise seal off the bare wire so they cannot touch anything or anybody. These wires will be hot if the breaker gets thrown so it is important they do not pose a hazard to anybody.

    Assuming you only plan to use the generator to power the well obtain a length of either #10 or #12 wire with ground. 1-HP and below are good with #12, 1.5HP should be #10. I like to keep about 20 feet of 10AWG with a generator plug at one end just for this purpose. If you have more than 1.5HP you should check to see what size cable/generator you will need.

    Connect the wire to the supply voltage side of the pressure switch. It does not matter which wire goes where as long as you are wiring up 230V motor to 230V supply. Make sure to connect the ground to the grounding screw. Close the pressure switch and make sure all wires/etc are tight and secure. Again, injury or damage can occur if a loose wire contacts metal or ground.

    Start the generator. Let it run for a few minutes to warm up etc. Plug in the generator plug and listen for the generator loading up or the well motor starting. Sometimes there will be a breaker on the generator that is faster than your ability to push/pull a plug. If so equipped, leave the breaker off until you are ready to run the pump. When ready, throw the generator breaker on. If the well motor appears to be lugging or running slowly or buzzing/humming immediately disconnect the plug from the generator. You have either connected something wrong or your generator is not big enough to run the pump. Unfortunately if you have a submersible you probably won't be able to hear the motor/pump running enough to tell if it's responding properly. The best way to tell is to connect an amp-meter up to the motor to see if it is pulling the proper amps. Too high or too low and there is a problem.




    Quote Originally Posted by anojones View Post
    We have all electric and no generator yet. Is there someone who can explain how to wire the pump so that it can be run from a generator. Can you splice in a plug at the control box, does there need to be a transfer switch wired to it? I'm just trying to get basic information on how I would "plug" in my well pump to a generator. Thanks.

  10. #10
    Elite Member timswi's Avatar
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    Default Re: Using a generator to power a water well pump

    Everything Goose said is correct. Gotta be real careful if you're hardwiring the pressure switch. I try to avoid doing that wherever possible, although I know many people who do it all of the time.

    One thing you might want to look into is a meter mounted transfer switch. Many utilities offer them for a few hundred dollars. The only thing they do is make certain that you're not back feeding the overheads (very bad). You just plug your generator into the transfer switch. You still MUST self regulate your in house power usage...Shut off all 220's except for the well. Also limit all power hogs (microwaves,sweepers, shop tools etc.). Just leave a minimal amount of breakers powered on. Do all of this before you plug in the generator.

    Of course, this assumes that your genset has enough watts /amps to do all of this. Personally, I think that anything less than 5000 watts is taking chances on being underpowered.

    Just my opinion.
    BX23TLB & RTV1100 with 72" Power Angle Plow

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