1.5 HP well pump [RE-wrenches]

[Travis Creswell, Ozark Solar]

Windy,

Good job.  I was just testing to see if anybody caught my obviously
inaccurate statement.  You passed the test.  OK, maybe that's not totally
true.

Thanks for the lesson.  I admit I didn't believe you so I checked out my own
3 wire, 1 hp well pump.  You're right. I was...I can't quite say it ...
wrong... there I said it.  I found that my pump has the same surge with the
pressure tank at 40 PSI (cut in for my 40/60 system) as it does at 0 PSI.
If I may try to regain a little pride (I've got plenty to spare so I could
actually stand to loose some) I would like say that I made that observation
by watching the DC amps climbing as the pressure in the system approached
cut off.  At the time I assumed it was coming from a combination of
increasing system pressure and that some was the battery bank voltage
dropping under a heavy load (ohm's law).  Now it's apparent the ALL of the
increase in amps comes from battery bank voltage dipping.

On my system, the AC amperage drops ~1% from 0 psi to 65 psi.  So it might
be more accurate to say "the amps of a centrifugal pump drop significantly
only when it cavitates".

I have a fair amount of experience in centrifugal pumps, HVAC and
circulating so I should have realized this.

Thanks again for the lesson,

Travis Creswell
Ozark Energy Services



-----Original Message-----
From: Windy Dankoff, Dankoff Solar [mailto:windydankoff at mac.com] 
Sent: Tuesday, August 09, 2005 10:57 AM
To: RE-wrenches at topica.com
Subject: Re: 1.5 HP well pump [RE-wrenches]

and Travis,

I disagree about reducing pressure switch setting or even pumping to a 
storage tank at 0 pressurizing. 2 reasons:

1. The starting condition that the inverter system can't handle is the 
initial kick from 0 RPM, also known as "locked rotor" condition. That's 
the same (during the very first applied AC cycle) whether the motor is 
on the bench or on a pump or actually locked. The mechanical load on 
the motor only effects the duration of the starting surge, not that 
initial peak of current draw. In the worst of cases, once the motor 
starts to move, it's generally "home free" (disregarding energy use 
after that).

2. The load on any centrifugal pump (that includes all of today's AC 
submersibles) is INVERSELY related to the pressure load on the pump. 
When it is against more pressure, it actually draws LESS current. Did 
you ever clog a vacuum cleaner (a centrifugal air pump)? It SPEEDS UP!  
All centrif water pumps act this way. But as the current draw drops a 
bit with pressure increase, the flow rate drops quickly. So the 
efficiency certainly decreases as should be obvious.