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Old 02-01-2013, 03:46 PM   #1
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Using well pump with generator


A friend of mine recently installed an interlock kit to use with his backup generator during power outages. The generator is a Yamaha EF4600-something, on the label it says it is 4000 watts running and 4600 max, 120/240 volts. We hooked it up to see if it would work with his well pump, which he believes is 1 & 1/2 horsepower, and is on a 20 amp double pole breaker. When we first started it the "economy switch" was on, which keeps the engine speed low at no load. We turned on the well and it died instantly. We restarted the generator and shut off the economy switch, so it was running full speed. We then turned the well on and it seemed to run fine, although there was a noticeable change in the engine speed initially. The pump re-pressurized the water and then shut off like it should. Is there a chance we could damage the pump or the generator if it is used during power outages?

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Old 02-01-2013, 03:55 PM   #2
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Using well pump with generator


Nope, but he should have taken the time to figure out what he expected the generator to power before buying it.
4000 is not going to power much under load, why have one if it's not going to to what you need it to do?

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Old 02-01-2013, 04:12 PM   #3
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Using well pump with generator


I should have mentioned that it was bought used from a friend probably 10 years ago back when they lived in the city and only needed to run a fridge and some lights. I don't think Yamaha makes that generator anymore. The plan is to only have the well pump running when everything else is off to refill it once or twice a day.
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Old 02-01-2013, 04:50 PM   #4
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Using well pump with generator


It is perfectily normal for the genny to groun
a little during pump start up.
It will probably take just about all its got to get it started !
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Old 02-01-2013, 06:37 PM   #5
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Using well pump with generator


1.5 hp is about 1.1 KW. The problem is that the starting current of an electric motor can be as much as 10 times the running current. That's more than twice the capacity of your generator. You're lucky the pump started at all.
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Old 02-01-2013, 06:54 PM   #6
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Using well pump with generator


Yeah, what all the others said. I think mine is 7500 max, and when the well kicks on, the genny def loses a few paces. Once repressurized, it's fine.
I agree, 4000 is kind of low, but sounds like he might get by with it.
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Old 02-01-2013, 07:25 PM   #7
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Using well pump with generator


Maybe it's a lucky coincidence that it works.
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Old 02-01-2013, 08:41 PM   #8
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Using well pump with generator


I think the older style gennys seem to handle these things
much better then the newer one's can.
Cause it's only a very short term overload.
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Old 02-01-2013, 10:13 PM   #9
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Using well pump with generator


I had someone tell me that 5,000 watts would be the absolute minimum that would handle it due to startup....guess not?
Like I said, with the economy switch on it died instantly...
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Old 02-01-2013, 10:21 PM   #10
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Using well pump with generator


Yes ! but your genny has a surge rating of 4600w
which is close enough.
Provided the genny doesnt have to power anything else
you will borderline get away with it !
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Old 02-01-2013, 11:48 PM   #11
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Using well pump with generator


The issue with most of small generatours is the surge or starting wattage is not really huge so that one thing when you try to start up the motour do expect the speed of generatour to drop some which it is normal to do that.

As other mention the starting wattage vs running watts with most motours it will go anywhere from 3X to 8X of running watts and expect the voltage and HZ to dip some way until it get back up running speed.

The most noticeable units are typically 3600 ( 60 HZ verison ) two poles units but 1800 ( 60 HZ ) four pole is little less senstive due it will have more intera to act like flywheel to get thru the starting bump.

But just becarefull if you run with any electronic loads like computer and belive or not., Furance control board is pretty flicky with Hertz if get off wacker it will not able respond the control properly.

Merci,
Marc
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Old 02-02-2013, 03:59 PM   #12
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Using well pump with generator


Quote:
1.5 hp is about 1.1 KW.
Not when you are dealing with motors designed for heavy loads, such as well pumps.
I would expect something around 10 or 11 amps @ 240V.
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Old 02-03-2013, 07:28 AM   #13
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Using well pump with generator


Quote:
Originally Posted by Oso954 View Post
Not when you are dealing with motors designed for heavy loads, such as well pumps.
I would expect something around 10 or 11 amps @ 240V.
There is a strict mathematical relationship between KW and HP. 1 KW equals 1.34 HP no matter what sort of motor we're talking about.
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Old 02-03-2013, 12:46 PM   #14
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Using well pump with generator


I know you learned 746w=1 hp. It is an equivalence formula. But it doesn't tell you what the load or draw of a motor is, when it has a heavy load.

Your post implies that he will see a running load of 1,100 watts on his generator.

The real world running load on his generator is going to be twice that, and probably a bit more.
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Old 02-04-2013, 09:39 PM   #15
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Using well pump with generator


A 4000 watt generator can produce a LOT more than 4000 or even 4600 watts for the time it takes a typical well pump motor to start.

I would have no problem at all running a 1-1/2HP pump on a 4000 watt generator, provided there were minimal other loads on when the pump started. A couple of incandescent lights would be about it. No other motors and nothing electronic.

The reason the pump wouldn't start when the gen was idling is because the engine cannot speed up the generator and start the motor at the same time. The reason it did start the pump when it was running full speed is because the rotor in the pump motor needs less inertia to start than the rotor of the gen plus the engine can produce.

Starting motors with gens depends far less on the power output of the engine than it does the mass of the rotating parts.

Rob

P.S. The locked-rotor (starting surge) current on most capacitor-start motors is roughly 6 times the running current. Most well pumps have capacitor-start motors.


Last edited by micromind; 02-04-2013 at 09:42 PM.
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