Hi Allan, Thanks for the complete data situation, amazing as always. As usual lots of basic problems that are so avoidable.
I remember someone, on this list mentioned that refractometers are damaged by getting too cold and that they won't read correctly I can't find that info however. As the situation is unclear, I would check with a fluid hydrometer to double check your battery SG results. Jay > On Dec 21, 2015, at 9:16 AM, Allan Sindelar <al...@sindelarsolar.com> wrote: > > Wrenches, > For years I have carried and used a refractometer to accurately measure SG of > FLA batteries. I currently have a decent one, a nearly new Bosch Robinair > 75240 that has always performed as intended. > > A couple of days ago I was hired by another local company to investigate and > troubleshoot an off grid system that they had recently installed that was not > keeping up with the customer's needs and had crashed. I'll give more details > below, but the short question is that on a very cold day, I began measuring > the SG of the batteries and got readings of between 1.00 and 1.10 on all of > the cells I tested, with no obvious cause. I have never seen this and am > stumped as to the cause. I tested SG on about six cells in various locations > and got readings nearly identical, and all off the scale on the low side. > Note that I used the supplied pipette to sample electrolyte well below the > surface of the full cells, and they were lightly gassing at the time, so I > don't think that this is simply highly stratified electrolyte. > > The system: 12 x 327 Sunpower modules (3.9 kW) on fixed rack; Schneider > XW6048 with Power Distribution Panel, XW600-80 charge controller, System > Control Panel, unused AGS and Schneider's new Conext Battery Monitor. > Batteries are two strings of 8 Surrette S550s, for about 32 kw-hours of C/20 > storage to 80% DOD. The system has been in operation for only about 3 months. > The installation quality is mediocre at best, was located in an unheated > TuffShed and is powering a doublewide mobile home. The inverter, controller > and SCP were connected by the Xanbus system, but the Conext battery monitor > was not. > > The backup generator was a very basic manual-start 6kW Briggs & Stratton that > had not been able to charge through the inverter as the inverter hadn't been > properly programmed and would overload it. The site is at about 8,000' > elevation, so we estimated about 4kW maximum output at 240V AC. > > I hadn't seen pictures or been given an accurate component list before > arriving on site, so was not fully prepared for what I found. The day was > sunny and especially cold - best guess a high in the mid-20s (F). After four > hours on site my fingers were too stiff to write normally. The battery SOC > monitor indicated 100%, and the SCP bar graph also estimated the batteries to > be nearly full. Battery voltage under charge on each 6V battery ranged from a > low of 7.38V to a high of 7.50V, with a charge rate low enough to suggest > absorption. The batteries had not been equalized since new, but new was > claimed to be three months ago, and this appeared accurate. > > The system owners are new to off grid, and while living frugally, claimed > that the system worked well during sunny periods but had crashed on about the > second day of cloudy weather. They had been using the forced air furnace, and > when I arrived had a heat lamp (not labeled as to watts, but I assume 250W > 130V) inside the leaky battery box, shining on some of the batteries. > > As an aside, the 600V Schneider controller has no built-in display/interface, > so there was no easy way to determine the charge mode or anything else except > through the System Control Panel. That seems pretty bogus to me. I had not > seen one of these previously, nor had I seen Schneider's shunt-based SOC > meter. When I have installed XWs and SW Conexts I have always used Midnite > E-Panels, which have conventional 500A shunts, and TriMetrics to offer > accurate SOC for the customer. > > The system settings all appeared to be set to default, other than "flooded" > for battery type. Here are the changes I made in the setup. A couple of > things I noticed: > 1) with a default LBCO of 40.0V, on at least two occasions the batteries > had been completely drained, and had been recharged only by the (substantial) > array; but as the array is in theory (3.9kW/58V = 65A in good sun, or a c/12 > charge rate, this suggests that even empty batteries will be recharged to > full in 2-3 days. > 2) battery capacity was set at default of 440AH, when it was actually > about 850AH,so the charge rate would have tapered prematurely. > 3) The bulk voltage was the default for 'flooded' - I don't know the > default, as it isn't given in the XW manual and I changed it to 'custom'. I > assume about 58.4V. > > Setting name Previous > setting New setting > > Inverter LBCO (V) 40.0 > (!) 45.2 > > LBCO delay (seconds) 10 > 600 > > HBCO (V) > 70.0 64.4 > > Battery capacity (AH) 440 D > 800 > > Max charge rate (%) 100 D > 72 > > AC2 input Vmin (V) 80 > 105 > > AC input priority AC1 > AC2 > > Charge control and inverter EQ (V) 64.0 D > 62.2 > > CC and inverter bulk & absorption voltage (V) 57.6 D > 58.8 > > CC and inverter float (V) 54.0 D > 53.6 > > > Given all of this, I can't explain the extremely low SG readings. I tested > about six or eight of the 48 cells, and all showed the same range. I admit > that I trust my refractometer, but given the other readings, could I actually > have completely dead cells, only three months old, showing close to 60V with > little current flowing in while I measured them? WTF is going on here? > Thank you, as always, > Allan > -- > Allan Sindelar > al...@sindelarsolar.com > NABCEP Certified PV Installation Professional > NABCEP Certified Technical Sales Professional > New Mexico EE98J Journeyman Electrician > Founder (Retired), Positive Energy, Inc. > 505 780-2738 cell > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org >
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