AC well pumps (Was outback fx2000 experience?) [RE-wrenches]

[Allan Sindelar]

Wes,
We helped Windy with some numbers for this document back during the Y2K
kafuffle. It may help you. I think it's on Dankoff's web site (and may have
been updated), but here it is as a text document from '99.

Inverter Sizing for Submersible Pump Applications

By Windy Dankoff

One of the most vital uses of a home power system is to power a water well
pump. A pump can be a real power hog! Conventional pumps require a high
surge of current in order to start. The entire circuit, from batteries to
invert to pump, must be sized to handle the starting surge at the same time
as other loads. Otherwise the inverter will shut down. Use the following
chart as a guide to inverter sizing.

Minimum continuous power rating of an inverter
to start an AC submersible well pump (with no additional loads)
Pump HP- Min. Size MSWInv - Min.Size SWInv - Max. Run.Power, Watts*
1/2                         2.0                         1.5
970
3/4                         2.4                         2.0
1325
1                            2.8                         2.5
1600
1.5                         4.5                         4.0
2150
2                            5.0                         4.5
2650
* Typical running power is 10-20% less, but add 10% for typical inverter
loss. For "modified sine wave" add
another 15%, due to loss of efficiency in the motor.

An inverter sized by these minimum guidelines will dip its voltage during
the starting surge. This is not harmful, but it will cause lights to dim.
Fluorescents may blink off, and computers are likely to crash. To eliminate
voltage dips, oversize the inverter by an additional 50% minimum plus the
watts capacity required to handle other household loads at the same time.
Minimum inverter sizing is based on field experience with Trace inverters,
allowing ~25% voltage drop during startup. To eliminate noticeable voltage
dip, add 50% to the minimum size. Other brands of inverters differ in their
surge capacity relative to continuous rating. Exact starting capacity is
difficult to predict and inverter manufacturers are hesitant to specify it.
Dankoff Solar welcomes your feedback and will publish more information as a
result.
If a "modified sine wave" inverter is to be used and pump's control box is
labeled "solid state", then the control box must be changed. Obtain a
relay-type control box or a relay conversion kit from any pump supplier.
Most well pumps require 230 VAC. Either two stacked inverters, or an
inverter with 230V output, or a transformer must be used. (The Trace T-240
transformer will handle 2 HP max.). If all of this is too expensive for your
situation, consider replacing it with a lower power pump, carefully selected
for the best efficiency (watts per gallon). You can also consider an
intermediary storage tank with a DC pressurizing pump. The use of a storage
tank will relieve your well pump from the need to start every time the
pressure runs low (many times per day). You can pump into the storage tank
just once or twice per week, and then use a DC pump to supply the water
pressure as needed (or use gravity flow, if feasible). You may also be able
to change to a lower power well pump, even a DC well pump, after this step
is taken because less pressure and less flow will be required from the well
pump.
Note: If the pump is a "two-wire" type (having no control box), oversize the
inverter by an additional 50%. A two-wire pump may not always work on a
modified sine inverter. For further information, contact Franklin Electric,
(800) 348-2420; www.franklinelect.com.

Copyright © 1999 by Dankoff

----- Original Message -----
From: "wes kennedy" <wes.kennedy at jademountain.com>
To: <RE-wrenches at topica.com>
Sent: Thursday, November 21, 2002 4:07 PM
Subject: outback fx2000 experience? [RE-wrenches]


Howdy Wrenches,

I've an off grid client with virtually no loads save a 240 vac 3/4 hp pump.
We are talking DC solar pumps, but out of curiosity what inverter will for
sure run that pump? DR2412 or 2424? DR3624?  I've heard stories of the
fx2000 being under rated and having healthy surge capacities, any one try to
run a 3/4 hp pump on it?  Oh, and assume a 120/240 tformer to get the
voltage....

Thanks for the collective wisdom..
Wes Kennedy
Jade Mountain

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