[RE-wrenches] Surrette Battery Question

[David Palumbo]

Surrette Battery QuestionAllan,

These are (2) cell 4 volt batteries (4,416wh each battery (4v x 1104)),
correct? How many does your client have? I'll guess (6) of them, if that's
the case they have  26.5kWh of rated storage.
The pv array total is approx 2kW (about 60A rated current at max power).  So
depending on how the math is done the charge rate is C/13 (26.5kWh/2kW), or
C/18 (1104ah/60). I'm thinking that this is a good charge rate for New
Mexico. If the array and MX60 are working properly, and the client's are not
using more watt hours than the system is designed for, the batteries should
be getting adequate charging. As you know these Surrette's need to charge to
relatively higher voltages than other makes of lead acids. 29.6VDC sounds
good to me. Surrette may want that bulk raised a bit with older age cells if
performance is dipping?

A couple of additional thoughts. 1) TriMetric voltage readings can vary from
MX60 voltage readings which may account for that 31.1 to 31.4v difference.
2) Remind your client's that equalization questions are best answered by the
use of a hydrometer (or refractometer) to test the SG of every cell. If they
are relatively equal (within .015 basis points lowest cell to highest cell )
than your batteries are equalized and it really does not matter that the
voltage did not go up to some arbitrary number. It is more important that
lead acid cells are regularly fully charged at a high enough voltage to
significantly gas each cell for a long enough period of time. This is where
absorption time is so important. Equalize charges (controlled over voltage
charge) on a regular basis (every month or two) need to be done more on
systems that do not regularly reach their fully charged state as often as
they should. I coach my client's (and program their TriMetric's) to see to
it that their battery banks receive a full charge at least every 10 days.

Best,

Dave Palumbo
Independent Power LLC
Hyde Park, VT
  -----Original Message-----
  From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org]On Behalf Of Allan
Sindelar
  Sent: Friday, August 01, 2008 10:19 PM
  To: RE Wrenches
  Subject: [RE-wrenches] Surrette Battery Question


  Wrenches,
  In late 2003 we installed a 24V set of Rolls-Surrette 4-KS-21PS 6V 1104
A/hr batteries in the off-grid system of a long-time client. The client's
system had a democracy array of around 800 watts of tracked PV. In early
2005 we added 1,280 watts of additional PV, and the client hasn't run the
generator since; the system rarely drops below 80% and fills to 100% most
days in sunny New Mexico. Batteries are located in a basement, so
temperatures stay relatively constant, although it will vary slightly
seasonally. MX60 controller is temperature compensated, with 29.6 VDC bulk
and 31.4 VDC EQ set points.

  The problem is that the client reports being unable to achieve previous EQ
voltages, and this inability appears to be a new development. The system is
otherwise performing well. As the client is sharp and pays close attention
to the system's operation, I'm not ready to blame user ignorance (with one
possible exception; read on). This may be an issue of seasonally warm
temperatures, but I'm not sure this would explain the full 0.4 VDC reduction
in voltage. I told him that I would post his problem to this list, and also
request advice from Surrette Battery.

  Here is the client's description of the symptoms:
  I'm concerned that I am unable to equalize batteries at this time.  Up
  until June of this year the Tri-Metric readings during equalizing
indicated
  holding voltage at 31.1, with maximum amps gain of around 52.   Three
weeks
  ago, when set on equalize, the maximum voltage reading was 30.7, with
  maximum amps of 46; this was reached around noon, and by around 1:30 pm
  voltage/amps began its typical afternoon drop-off.  I attempted equalizing
  on two other occasions since then--the last time this past Saturday, with
  clear skies up until mid-afternoon--but having the same results.  So, the
  question is: are my batteries beginning their decline? We've had this set
  for 4 1/2 years, so it would seem a bit too early for this, given that
these
  batteries are expected to last 7-10 years.

  Second issue, possibly related:

  On another matter, I have been using deionized water for the batteries for
  as long as we've been using photovoltaics (since 1991), as it is my
  understanding that deioinized water is virtually the same as distilled
  water--I just checked Wikipedia on this (using "deionized and distilled
  water" as the search phrase), and this appears to be the case.

  I don't know the answer to this question, as we have always recommended
distilled water only in batteries, and have never faced this question.

  Any help would be appreciated.

  Allan Sindelar
  allan_(at)_positiveenergysolar.com
  NABCEP certified solar PV installer
  Positive Energy, Inc.
  3225A Richards Lane
  Santa Fe NM 87507
  505 424-1112



  Allan Sindelar
  allan_(at)_positiveenergysolar.com
  NABCEP certified solar PV installer
  Positive Energy, Inc.
  3225A Richards Lane
  Santa Fe NM 87507
  505 424-1112
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