1.5 HP well pump [RE-wrenches]

[Windy Dankoff]

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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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