# How much generator to run a 1.5HP well pump?

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#### Chris142

I'm trying to be somewhat prepared for an emergency. Especially since I'm only 15 miles from the SanAndreas fault. I have a 300ft well. The pump is 1.5hp and is at the bottom of the well. The pump is 220v. Assuming that a large quake or other disaster does not sand my well will a 4k generator start and run the well pump? The Generator does have a 220v outlet.

#### 901Memphis

Wouldn't it be important to know the amperage draw of the pump to make this decision?

#### Chris142

Probly. How do I figure out how many amps a 220V 1.5hp pump pulls ?Especially when starting.

#### Jim_Truett

Originally Posted By: 901Memphis
Wouldn't it be important to know the amperage draw of the pump to make this decision?
1 HP roughly equals 746 watts. Approximately 1200 watts running give or take, with roughly 300% of running wattage for startup. I say a 4kw peak generator would be borderline, but might work in our California climate.

#### MolaKule

Staff member
Assume you will need 2.25 Horsepower of electrical power due to starting surge and resistance loss in the power line. 2.25HP = 1679 Watts. So a generator of 2,000 Watts or 2kW should be sufficient. A 4kW genset would provide some extra capacity for sure! Just make sure it has a 240V capability and outlet. BTW, I would use 10 guage wire rated for sump pump use.

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#### scurvy

Originally Posted By: 901Memphis
Wouldn't it be important to know the amperage draw of the pump to make this decision?
Fortunately we already know that. 1 HP ~= 750 watts. So a 1.5 HP pump will consume roughly 1125 watts. So a 4 kW generator should run and start the pump just fine, considering it puts out 3.5x what the pump should pull.

#### Chris142

Great! Thanks guys.

#### MolaKule

Staff member
Originally Posted By: 901Memphis
Wouldn't it be important to know the amperage draw of the pump to make this decision?
Since 1.5 HP = approx. 1200 Watts. P = 1200 Watts, and P = I*V, Then I = P/V = 1200/220V = 5.5 Amps.

#### Chris142

i plan on running it with a 3200/4000w generator and it has a 30a breaker on the 220 plug.

#### JHZR2

Staff member
Originally Posted By: MolaKule
Assume you will need 2.25 Horsepower of electrical power due to starting surge and resistance loss in the power line. 2.25HP = 1679 Watts. So a generator of 2,000 Watts or 2kW should be sufficient. A 4kW genset would provide some extra capacity for sure! Just make sure it has a 240V capability and outlet. BTW, I would use 10 guage wire rated for sump pump use.
I agree that 2kw is about right. Much of the starting power requirements are overblown with the intent to sell bigger generators. We have done all varieties of transient and pulsed loads against standard commercial generators as well as higher end mil spec generators. Reality is that some voltage fluctuation aside, and/or a temporary bimodal frequency behavior, even the HD cheapies can do the job. If you continuously do this to them, they will walk across a floor... But a well pump should only run so often, so the start transient is not that often.

#### edhackett

Y'all are forgetting the efficiency of the motor. A direct conversion from watts to HP isn't going to work as the motor is not 100% efficient. A quick look shows 11.5 amps for a 1.5 hp Dayton submersible. Chris is going to need a bigger generator. Somewhere between 23-35 amps are going to be needed for start amperage. Ed

#### eljefino

Your 4 hp will do fine, assuming it's a 3600 RPM one. The flywheel effect of it running will keep it running long enough to start the well pump. You can also put your finger on the governor/ carb to rev it up just before plugging in your cord.

#### totegoat

I assume you are going to try it. Let us know if the 4kw pumps water.

#### Rand

probably abit small isnt 1.5hp huge for a pump? or maybe I'm just not used to wells that deep. At least its 230v so it wont be one of those 115volt legs putting out only half the generator power issues. Probably need at least a 6kw generator for good starts. 7-8k would be better. the running draw will be around 10amps, but you would need upto 5x that for fast startup.. in short I think 4k generator is just too small it would grunt. the voltage drops to about 100v and pops a breaker.

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#### cronk

I have a 3/4 hp in my 150 foot well. Last power outage I tried it with my 3500/4000 surge 6.5 hp generator. It started it and ran it, but it really loaded it up starting. I think I'd want something bigger for a 1.5 hp pump, probably like 7-8000.

#### DSparks

Startup amperage is the deal breaker on generators...bigger is always better...get biggest one you can afford....lotsa neat info on this site..buncha smart guys..lol.. www.microcogen.info

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