Back up generator for deep well pump

I am having a well drilled to 400' and will get a 220v 1.5 hp motor for the pump. I would like to buy a back-up generator in case of extended power outages. Can anybody tell me what watt generator I would need? Thanks - Robert
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1 hp = 746 watts so you so need at least 1120 watts to run a 1.5 hp motor. The actual wattage depends on how much power the pump draws when it starts - starting draw can be 2 or 3 times running power, usually just 2 or 2.5 times. Also, a generator can usually supply more than the rated power for a short time, enough time to get pump to speed. A 3000 watt generator should be plenty and you could probably get away with 2500 watts.
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11/2 hp motor will drow 11.35 amps. x 220 = 2497 watts at start up perhaps x 2.5b42.5 watts

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8KW min.

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The smallest generator you can get, that produces 240 volt is probably going to be around 2500 watts, which would be fine

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Scratch the above, I mistook 1.5 for 1/2 HP. You'll be drawing around 12 amps @240, and factoring in starting current, you'll need around 6KW, which will have a higher peak

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Robert wrote:

A holding tank would be cheaper.
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Such interesting answers! You need to actually measure the current as the motor starts. Typically a 1.5hp motor will run on 8a, and start with 24a (6500w), but most motors aren't typical; you have to actually measure yours.
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Quoting Reinhard: "1 hp = 746 watts so you so need at least 1120 watts to run a 1.5 hp motor. The actual wattage depends on how much power the pump draws when it starts - starting draw can be 2 or 3 times running power, usually just 2 or 2.5
1120 divided by 220 is about 4 1/2, so I'm not sure how you get your eight amp number.
That's the best advice is to actually measure it. And then figure one and a half, to be sure. As the motor ages, the current draw may increase.
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Robert wrote:

Why stop with well? I have a 7,350 starting watts, 5,500 running watts generator that handles well, furnace, 2 freezers and refrigerator as well as a few lights and TV. With bottled water to drink and stored water to flush toilets, we've lasted up to 3 days without electricity, but we lost food in freezer then and another time house got down in the 40's even when I was burning 2 fireplaces. Stove, water heater and AC are out of the picture but we can live comfortably for days without them. Frank
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Thanks everybody for replying. I can see now that I need a significantly higher capacity generator than I bought today at 4000w peak. I had a 25% off coupon at Checkers that was due to expire so I thought a generator would be a good idea. Luckily, before I opened the box, there was a warning stating that it would not start an air compressor or circular saw. That's when I posted here.
I think I'll look into something like Frank has. Thanks again.
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Because it can be difficult to find gas during a power outage. How many gallons a day does that burn?
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That depends where you live. What you say is true for hurricane intensive regions but where I live it is localized with fallen trees. If I had natural gas service, I would have got a generator that works on gas or propane. My generator uses about 10 gallons of gasoline a day if run continuously but in real life where I turn it off at night when sleeping or when nobody is home, I use about 5 gallons/day. Refrigerators and freezers can usually get by without power for half a day. So with two 5 gallon cans of gas and a full tank in the generator, I'm good for 3 days. Not mentioned in thread is need to buy a decent generator. Honda's are best and quietest but cost twice as much. El cheapo's like Coleman may work but be difficult to get replacement parts. Then there is need to install a transfer box in house electrical system. Frank
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