[RE-wrenches] Surrette Battery Question

Fri Aug 1 19:18:58 PDT 2008

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 <mailto: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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