11kw Generac Struggles with 1/2 hp Submersible

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  #1  
Old 12-28-15, 10:54 AM
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11kw Generac Struggles with 1/2 hp Submersible

Recently I installed a 11,000 watt generac backup generator with a Whole House Automatic Transfer Switch.
It works fine until I try to start a 1/2 hp submersible pump.

With no loads, other than the pump on the generator, the generator almost drops out when the pump starts then settles down.

Here are the facts
11,000 watts or 48 amps available from the generator.
LPG fuel, 1000 gal. tank, with dedicated Hi Press line and 750k BTU regulator.

Pump is a F&W 1/2 hp pump, 2-wire (capacitor on the pump)
100 ft down a 5" casing, with static water at about 15 ft below grade.

The pump data sheet states 32 Locked Rotor Amps (LRA) for starting the pump.
The generator produces 48 amps.
Again, I only have the 20A breaker closed when I try to run the pump, everything else is open.
Also nothing else is competing for the LP Gas.

Lastly, I have tried the same experiment, except starting a 3 ton HVAC unit instead, and no problems. I did notice the load come on but the generator just grunted a bit and continued on. Same when I started up a 4500w water heater.

It seems the generator is working fine except when it comes to the pump.
Oh and BTW after all this I swapped out the pump thinking it was failing due to 30 years of service, and still the same problem.

Any ideas out there?

Thanks In Advance
 
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  #2  
Old 12-28-15, 11:17 AM
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Is it a 120 volt pump or 240?

What gauge is the wire to the pump?

Have you tried connecting your "extra" pump directly to the generator just as a test, without all the intervening wire and switchgear?

FWIW, my 7500 watt Generac starts my 1 HP well pump pretty easily; although it is a 240 volt pump.
 
  #3  
Old 12-28-15, 12:28 PM
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It's possible that the load from the pump is too small for the generator to operate efficiently. Most generators, especially larger stationary ones like this need a decent baseline loading to run efficiently and effectively.
 
  #4  
Old 12-28-15, 02:18 PM
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I suspect the large load exceeds the genny's ability to instantaneously regulate the voltage.
Not that uncommon an occurrence. I believe the Starting Current of some motors can be higher than their Locked Rotot Current.

An electrician should be along before long to confirm or deny my suspicions and explain far better than I could ever hope to.
 
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Old 12-28-15, 02:22 PM
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It's important to know if that is a 120v or 240v pump.
 
  #6  
Old 12-29-15, 05:37 AM
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230v

Yes it is a 230V single phase pump
Wire gage is at least 12 gage, and perhaps 10 gage stranded.
I installed all new wire when I replaced the pump.
Although the wire from the well head to the house was not replaced seeing it is buried 5ft below grade.

In regards to amp pull, there is an instantaneous draw of about 22 Amps that I have measured with my FLuke, and then settles down to 6A for the remaining pump cycle. All of which matches what the pump manufacturers cut sheets state.

Generator Loading has been tested with just the pump, and or, pump and water heater, pump and 3 Ton HVAC, pump and some basic lighting, etc...
Always the same result.
Again, when I have tried just the HVAC the generator works fine.
The AC compressor has a LRA of 77A and a RLA of 14A
My Pump, LRA of 32A, and RLA 6A
LRA = Locked Rotor Amp
RLA = Running Load Amp


So the comments about the generator not having a base load, or the generator not being big enough I believe are not an issue.

Lastly, I had not thought of using the old pump as a genie pig, but that still may not be a fair assessment, seeing that it is a 3/4 HP, vs the 1/2 hp that I now have, and that I really don't feel like pulling a 100 ft of cable, wire, and the pump out when there is 2 feet of snow on the ground and its currently about 15 deg. F.
I suppose I could whip up something to do a test, but would still be tough without water.

Next.
 
  #7  
Old 12-29-15, 06:31 AM
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Man, no way that generator should have a problem with that pump, but I guess you know that

Does the gen have automatic idle control and can you turn it off? (Where gen idles down when there is no load).
 
  #8  
Old 12-29-15, 06:48 AM
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Where did you take that 22 amp measurement,right at the panel?
 
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Old 12-29-15, 07:45 AM
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Yes, I measured appox. 22 amps at the panel
 
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Old 12-29-15, 07:50 AM
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No the generator does not have a low idle. Most all whole house back-up generators run at I believe 3600 RPM at all times, at least for the 8,11, and 16kw units. The larger 20-22kw units will run at 2400 rpm only during their weekly exercise run.
I have read where the next generation of generators from generac may have the low idle ability similar to how some of the Honda's run.
 
  #11  
Old 12-29-15, 01:45 PM
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Low idle would only be useful for exercising. You wouldn't want a whole house generator running at low speed and then hunting with an applied load....especially an electronic load.

My portable Hondas all have auto idle. Unless I'm using just power tools on them.... they always stay in normal idle.
 
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Old 12-29-15, 06:24 PM
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Most all whole house back-up generators run at I believe 3600 RPM at all times, at least for the 8,11, and 16kw units.
Generac also makes some 1800 RPM models that are much quieter and needed in some municipalities that have a sound ordinance.
 
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Old 12-30-15, 04:10 AM
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You might want to check the pump start capacitor in the control box.
Could just swap it out or often you can sometimes see corrosion or electrolyte on the top and around the burst disk.
 
  #14  
Old 12-30-15, 06:19 AM
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It is a 2-wire pump, meaning the start capacitor is built into the pump - 100ft down.
 
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