Inverter/Battery Question (Round 2) [RE-wrenches]

Thu Jan 19 15:46:28 PST 2006

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I'll answer several questions here, from different responses:

>From John Blittersdorf: <we had 4 VFX  3524s - powering
the stage with peak consumption of 15kw with the average about  12kw. We had
32
Trojan L16P's feeding the 4 inverters, each inverter having a  set of 4/0
cables, 4/0 parallel jumpers and 2/0 series  jumpers.  I think we were
drawing at
about C2 or worse and we  destroyed that battery bank.>

Thank you, John, but there are some big differences: Your surge was 25%
above base load; you had 8 parallel battery strings, while we have one; your
batteries were near the end of their life, while these are new.

>From Travis Creswell: <We reluctantly installed 1hp VFX3524 and two 12
volt/225 Ah gel batteries
for 1hp well pump.  It was the inverter I was worried about, not the
batteries.  It's a three wire pump which greatly reduces the starting
current.  Using my 337 it surges to 29-30 amps AC and runs at just under 10
amps which is lot different then the numbers you're getting.  Your customers
pump could be a two wire.  I've seen the DC amps anywhere from 75-85
depending on battery voltage.

My suggestion would be to change it out to a 3 wire pump 3/4 hp pump along
with a large pressure tank (at least 25 gallons of drawdown) to reduce the
pump cycling time.>

The pump is a 10 gpm Sta-Rite, 4" 3-wire. The pump is set near the bottom of
the 400' well (I believe; I have a call in to verify this) but the static is
given as 123', with estimated yield of 10 gpm from the well. The Sta-Rite
curves suggest that with 50 psi pressure head plus 150' static head, the
pump is in its sweet spot at 11.1 gpm. However, if the well dropped to near
the pump, it's off the scale, so drawdown and dynamic head are important
here. However, getting water out isn't the problem, as the pump starts and
runs fine off the generator.

The pressure tank is big - I think about 80 gallons, which gives a 27+
gallon drawdown.

>From Brian Teitlebaum: <You said that the pump is at a 400' depth, but what
is
the actual head?>

If the log is to be believed, (about 150' plus 50 psi =) ~265'.

I covered this in my original question. It was originally to be open
discharge into a cistern, so gpm didn't matter as much as a) efficiency in
gallons pumped per watt, and b) staying small enough to allow one inverter
to do the job. DC pumps weren't in the picture, as a conventional driller
had already been contracted for the well by the time we were contacted. For
the same reason, I didn't suggest SQ or SQF, as most drillers use what they
know and are reluctant to use an unproven product based on the advice of
some solar yahoo they've never met. We had never worked with this driller
before. As far as whether this remains a pressure system, at this point, the
goal is to come up with the lowest cost workable solution to the present
situation. Pressure switch is set 30-50.

OK, I question it too; I think I got that wrong, by a factor of two. We ran
the pump off the generator, and I measured running amps at about 9.8, which
at 240 VAC is 2350 watts; divided by estimated 44 VDC, that's 53 amps, or a
C/4 discharge rate on the batteries. I don't know when to use amps as rated,
amps as measured, or rated watts, so I used measured amps, maybe
erroneously.

I'm thinking the same. And how would you size either SQ or SQF? I called the
driller's office; they sometimes use Grundfos, so a changeout by them might
be the best solution.

>From Ray Walters: <I'm surprised the VFX3648 wouldn't run a 1 hp pump. I've
got a pair of VFXs running a 3 Hp pump. My understanding was that the
Outbacks would limit current at 50 amps, while letting the voltage dip to
allow starting large inductive loads. The battery voltage could be dipping
too low, what is their instantaneous voltage dipping to? You can hit a T105
pretty hard. We regularly discharge them at C/0.5 rate without problems....
(well better not have any questionable connections at 450 amps) The voltage
drops pretty radically under this load, (a 144 v nom. bank at full charge
will go under 100 v). What was the inverter's failure mode: over current or
low voltage?>

I didn't check, and I should have. Could've, too, as I put a Mate in the
system. I also didn't check DC or AC voltage drop during the attempts.

What do you generally use as a single-pump solution in a similar situation?

Thanks for all the good advice
allan @+E

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