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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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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