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.
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.
