[RE-wrenches] offgrid system question

Phil Undercuffler P.Undercuffler at conergy.us
Mon Aug 18 15:18:09 PDT 2008


My .02 would be a close examination of the batteries, and a realistic
realignment of their expectations of their capacity.  12 sun extender
sealed AGM batteries, 305 AH at 12 vdc, wired for 915 AH at 48 volt DC
-- sounds like those are the PVX-2580.  They're only rated 305AH at the
120 hour rate.  If you're hitting that bank with a fast discharge rate
(is 104 amps at 120v or 240?), you'll do better to consider the bank's
capacity at the 24 hour rate (258AH) or even 1 or 2 hour rate ( 165 and
209 AH respectively).  Realistically, those three strings of batteries
are really a 774, 627 or even a 495 AH bank, depending on how fast
you're discharging them.

 

Make sure the batteries have temperature compensation on all charging
sources, and that the batteries are not exposed to high temperatures.
All batteries are affected by temperature, but if VRLA batteries are
charged without temperature compensation when in a hot environment they
will lose electrolyte which cannot be replaced.  Additionally, ensure
all connections are good and tight, and that the bank's series and
parallel connections are sized adequately to handle the surge.  

 

Finally, check the LBCO settings on all the XW inverters.  I can't
remember the default setting, but my memory was that it is a little too
high - especially when the battery bank is small and surge loads are
high.  I worked on a troubleshoot the other week where the installer set
the LBCO only a bit below the AGS Start DCV 30 second voltage, on an
older battery bank of questionable capacity.  Unfortunately, the
batteries bottomed out before the generator could get started and the
system shut down a couple times.

 

 

 

Phil Undercuffler

Director, Battery-based and Off-grid

Conergy Sales & Systems, Americas

Our World Is Full of Energy

1730 Camino Carlos Rey Suite 103

Santa Fe, NM  87507

p.undercuffler at conergy.us <mailto:p.undercuffler at conergy.us> 

Direct | 505.216.3841

Toll Free | 888.396.6611 x4841

Fax | 505.473.3830

www.conergy.us <http://www.conergy.us/> 

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Max
Balchowsky
Sent: Monday, August 18, 2008 2:01 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] offgrid system question

 

 

Dear wrenches, going to look at a system installed by others and would
like some input from some of you with more off grid experience than I
have ( 4 systems over the years). the system was put on a new home - off
grid 20 sharp ND123UJF panels 4 modules in series - 5 parrallel strings,
2460 total array dc voltage. mppt 60-150 charge controller, 12 sun
extender sealed AGM batteries, 305 AH at 12 vdc, wired for 915 AH at 48
volt DC. The system is tripping off when the AC unit trys to start - AC
is comfortmaker 3.5 ton 13 seer. They say start up inrush is 104 amps
(sounds high to me) and they put a DST 10 soft start on the unit (I
think that's just a big capacitor). I haven't been on site yet but it
sounds to me that they just didn't design enough inverter capacity into
the system...... What are your thoughts?

 

Max Balchowsky

SEE Systems

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