1.5 HP well pump [RE-wrenches]

Wed Aug 10 17:11:24 PDT 2005

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Windy,

Thanks for the expertly detailed explanation on sub-pump motor technology.

But you might owe me dinner! I have customers that run Grundfos SQ AC pumps
on DR's with no problem. I'm sure that the efficiency is way lower then it
would be with sine-wave power, but it still works fine. Most households
don't use enough water for the efficiency to be a big issue.

However, I don't know anyone who has tried the SQE on mod-square (let's
start calling it what it is!). My guess is that it wouldn't work very well
at variable speeds, but I don't know for sure. If someone out there has
tried the SQE, let us know.

Cheers,

Brian Teitelbaum
AEE Solar

-----Original Message-----
From: Windy Dankoff [mailto:windydankoff at mac.com]
Sent: Wednesday, August 10, 2005 4:23 PM
To: RE-wrenches at topica.com
Subject: RE: 1.5 HP well pump [RE-wrenches]

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Dave, Todd, Travis, Matt,

Honk if you're a solar bozo.

Thank you. Now, allow me to straighten out some possible
misunderstandings.

Grundfos SQ, SQE, SQ Flex, and Lorentz Solar Submersibles have 3-phase
AC motors, not DC motors. They include variable frequency inverters as
part of the system. Variable frequency produces variable speed control
of the motor. The motor contains water, so leakage is never a factor --
just like conventional AC pumps. No brushes. Very reliable.

Grundfos SQ and SQE are AC products, but internally, AC is rectified to
DC, then inverted, in order to vary the frequency (and to produce
higher RPM than normal for an AC induction motor).

Grundfos SQ Flex and Lorentz pumps are designed to run on variable DC.
They both include a solar matching system, a specialized inverter, and
3-phase motor. A fundamental difference is that SQF has the electronics
built into the motor housing, and Lorentz has it in a separate
enclosure above-ground. Other than that, they are substantially similar
in overall concept.

To call these DC pumps is not strictly true. TRUE DC pumps have a DC
motor that uses brushes. It is correct to call the newer technology
"electronically commutated DC motors" but don't place them in the same
experiential basket as older-technology brush-type subs (mechanically
commutated).

Matt -- you suggest considering a constant-pressure SQ system without a
pressure tank. That was discussed recently and agreed to be very
inefficient because the pump spends lots of time running at reduced
speed (and low efficiency) in order to maintain pressure at times of
low usage (or even minute plumbing leakage).

Travis -- you are correct that a non-sinewave inverter will require
more power to run a sub pump (or any electro-magnetic device for that
matter). It turns out to be in the range of 15-25% more! The motor runs
hotter, wasting watts.

Matt suggests having the customer simply replace the pump with a 3/4 HP
one. Since we have not heard about the total dynamic head required
(depth to water etc.), we can't assume the exact HP, but if a smaller
pump will do the job, that might be a relative cheap way out IF the
folks don't need lots of water -- especially since they already own the
inverter capacity. As Dave says, if the customer has modest water
consumption, the energy waste becomes relatively small. Warning! It
must be a "3-wire" pump (with above-ground starting control box) or it
will not start gracefully on the mod-sine. (Aside, I would bet my
dinner that an SQ pump would not like mod-sine.)

I've always been a realist (well, sometimes), so I honor informed
decisions made by experienced wrenches. After all the shake-down that's
occurred in the pumping world in the last 10 years, I believe all the
major pump products on the RE market are now viable.

End of honk.
Windy

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