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Discussion Starter #1
I'm new out here and pretty darned clueless about electricity. I'm trying to figure out how powerful a generator I need to run my well pump. And I'll begin with an apology: I know that this question is asked on the internet every five minutes; I've read endless posts and blogs and websites about it. I've talked with two electricians and a generator dealer. And yet--I can't find the answer.

First, this is the pump in my basement that moves the water from the external well water line to the holding tank and into the house. It's not a submersible well pump.

Here is the information on the pump itself: Volts 115/230; HP 3/4; Amps 4/5.7; RPM 3450; Max Load Amps 14.8/7.4. There are a few more letters and numbers if I'm missing anything important.

I understand the difference between starting and running power. The generator will be run through a transfer switch, so I can manually dedicate the generator to the water pump as needed. The generator is solely for emergency backup to my house during outages; I'm comfortable getting a smaller generator and switching between the freezer, furnace, and some lights. It's the water pump that has me stumped.

I would be eternally grateful for any help!
 

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It is my understanding you should size the generator to the LRA (Locking Running Amps), which is the initial current inflow rush to the motor from a stationary position. If not indicated on the plate, the LRA is generally estimated at 4-5 time the full running amps (FRA).
 

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Based on my above response, you would need a generator with a surge capability of close to 40 amps @ 240VAC or 9600 watts to power the pump. A 10kw run rated unit gives you the excess capacity for other appliances mentioned
 

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Discussion Starter #4
THANK YOU! That's not a small generator, unfortunately, but at least I'm saved the expense of buying a big-ish one (7kw) and being left high and dry.
 

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THANK YOU! That's not a small generator, unfortunately, but at least I'm saved the expense of buying a big-ish one (7kw) and being left high and dry.
you might want to look in to a transfer pump that runs direct on gasoline for back up.
so what is the rise on the water?
or how far up hill does it need to transfer?
i use the little pacer brand pumps.
click here for the link to tsc pacer pump
they are 2 inch. and will produce 50 psi..
so if you decide to use something like it
make sure you have a good pressure regulator on the system for house use.

so is the electric pump you have now running on 120 vac or the 240 vac?
you could test it with meters to see what the start current is.
and if it is not too large of current you could use an easy start on it to help with the in rush
click here for the page with the easy start link

so do you have a large bladder tank in the house??
those help!
they keep the pressure steady as well as raise the on off cycle time.
they also make 12 volt pumps for in house booster for pressure that they use on campers.
just a thought... you could use that in the basement by the water tank..
 

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Based on my above response, you would need a generator with a surge capability of close to 40 amps @ 240VAC or 9600 watts to power the pump. A 10kw run rated unit gives you the excess capacity for other appliances mentioned
My multiplier of 4-5x was a rule of thumb. The motor plate should provide a letter indicating motor type. You can then use this information to cross index the correct multiplier on the published tables to arrive at the LRA Based on the stated RLAs.
 

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Discussion Starter #8
I'm listening and grateful for the thoughts. Thank you, iowagold, for your ideas about the pump. It's actually a dug well that is uphill from the house. Never a problem in forty years!

One reason I find it confusing is that, according to many websites, a 3/4 hp pump shouldn't be that hard to run. On the other hand, those amps might suggest the need for considerably more power. (On the third hand, I don't know what I'm talking about.) In other words, I'm VERY grateful for the responses but it really does seem to be difficult to come up with a simple answer, which surprises me since there has to be an answer

Jackruf, I appreciate your detective work. Here is a more complete rundown of the information on the pump:

It's a Goulds Jet Pump, undoubtedly for a "shallow well," model JL07N. It's over twenty years old and was rebuilt once (not by me). A sticker says "Motor connected 230 volts." It says PH1 Code L HZ60 SF1.5 INSULClassB TypeC. And, to repeat, the above, Volts 115/230; HP 3/4; Amps 4/5.7; RPM 3450; Max Load Amps 14.8/7.4.

I do have one more question. If I try a generator that is too small, am I risking the pump or the generator? Let's assume it's a decent generator with appropriate fuses and shut-offs.

The company is still going and I could give them a call, too. To repeat, there has to be an answer to have many watts I need to get this thing running!
 

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I would call the company and ask the LRA for that specific model. Using the tables and assuming it is an "L" Design, the multiplier would be 9.0 - 9.9. The formula for LRA = (Code Letter Value x HP x 1000)/RatedVoltage. I know you indicated you are fine with managing loads between the various appliances to keep the generator size down, but I will tell you, that gets old really quick, especially if you are looking at an extended outage. Best of luck with it.
 

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I have a goulds J10S shallow well jet pump - 1 hp and had no problem running it on an very old wheelhouse 5500 watt generator which was also running 2 large portable AC's, many lights, large TV and 4 large computers.
 

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Good grief! 746 watts per Horsepower and this is a 3/4 HP pump. Add to that an external pump does not start with a LRA as it builds pressure moments after it starts. I am sure the pump has a tendency to draw a small amount of overcurrent, but a 5KW would handle that pump all day long.
 

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Get an electrician to check the starting and running amps on the pump or buy you a cheap clamp on ampmeter and do it yourself. Then you'll know exactly what the pump pulls on startup as well as when it's running.
 

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Discussion Starter #13
THANK YOU. All of you. I feel much more educated and maybe a little schooled (in a good way!). BobS, I'm especially encouraged that you have a relatively similar pump and can run it with that generator. Tboney, I hear you; I might indeed try to get an electrician to do that. I might even try it myself ... if I can figure out how to use an amp meter. (Look for another post out here asking for instructions!)
 

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I won't bother with the amp meter for the pump. You would need one with an inrush feature to capture the max. power required to start the motor. A normal amp meter couldn't register the startup power (too short of a duration). A good 5.5 / 6 kw (not the surge number) would handle it with ease. I can also add that the 5,500 watt mentioned above handled 2 full refrig/freezers and a separate freezer. I would use a good Honda generator (expensive but a great investment) or a northern tool with a Honda gx engine and a mecca or stamford generator end. They deliver very good quality power and can last a decade if properly maintained.
 

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i guess with the experience with jet style pumps is the inrush has horrible numbers...
i agree a good site survey is needed on the real power demands.

most folks have gone the route of the pump in the well...
and for most areas where they water is not too hard it works good.

so how deep is the well and how far up is the rise to point of use??
 
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