OutBack Questions re 3hp well pump [RE-wrenches]

[Allan Sindelar]

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Christopher,
A variation on Ray's question that is relevant for us right now, please:
We have a customer with an existing new PS/2-VFX3648 offgrid system who
wishes to run his 3hp Franklin motor well pump off of ONE inverter with an
X-240. His rationale is that this is temporary, the pump will be controlled
manually during construction, and there will be no other loads when the pump
is run. His budgetary motivation is to put off the cost of the second
inverter for a year or two until his home is built. He also will eventually
pump open discharge, but would pressurize now, adding additional load onto
the motor.

We have told him we don't think that it will work with a single inverter,
and nobody else has been able to provide a reliable (from experience)
prediction. If the inverter won't start it, we return to add a second
inverter. He accepts this, and we'll hook it up in a week or two.

Your comments are appreciated.
Allan at Positive Energy

----- Original Message ----- 
From: "Christopher Freitas --- OutBack Power" <cfreitas at outbackpower.com>
Ray and Wrenches -

Here are my comments with the questions included:

What is the maximum pump HP that can be run with a pair of Outback
VFX 3648s.
We have had a number of systems reported to us which are running 3 HP
pumps on two OutBack 24 or 48 vdc inverters without issues.  I would not
suggest going to a larger pump without adding more inverters. The X-240
autotransformer is highly recommended when pushing the inverters hard
like this. The real variable is what else might be running when the pump
starts.

The locked rotor amps is a worst case scenario - which is why we like to
reference it.  In the real world the pump requires less amps to start
(unless you have really high mineral content and the pump sits off for
long time periods). I typically see about 2/3rds of what the book says
with a meter set to the 1 millisecond peak max setting on my trusty
Fluke 87 meter with an AC clamp probe.

Even if the pump needs more than the OutBack inverter is able to provide
- we don't just shut off like some older inverter designs - we actually
provide the 70 amps maximum and allow the output voltage to droop a
little - often this is hard to measure in the field because it usually
only happens for part of a cycle or for a few cycles.  This typically
will not cause any issue with other loads operating at the same time
such as computers, TVs etc.

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