<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Hi Allan,</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">Thanks for the complete data situation, amazing as always. </div><div id="AppleMailSignature">As usual lots of basic problems that are so avoidable. </div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">I remember someone, on this list mentioned that refractometers are damaged by getting too cold and that they won't read correctly</div><div id="AppleMailSignature">I can't find that info however. </div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">As the situation is unclear, I would check with a fluid hydrometer to double check your battery SG results. </div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">Jay</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature"><br><br><br><div><br></div></div><div><br>On Dec 21, 2015, at 9:16 AM, Allan Sindelar <<a href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a>> wrote:<br><br></div><blockquote type="cite"><div>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
Wrenches,<br>
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. <br>
<br>
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.<br>
<br>
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. <br>
<br>
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. <br>
<br>
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.<br>
<br>
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. <br>
<br>
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.<br>
<br>
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: <br>
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.<br>
2) battery capacity was set at default of 440AH, when it was
actually about 850AH,so the charge rate would have tapered
prematurely.<br>
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.<br>
<br>
<p class="MsoNormal"><span style="font-size:12.0pt">Setting name<span style="mso-tab-count:5">
</span>Previous setting<span style="mso-tab-count:1">
</span>New setting<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Inverter LBCO
(V)<span style="mso-tab-count:5">
</span>40.0<span style="mso-tab-count:3"> (!) </span>45.2<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">LBCO delay
(seconds)<span style="mso-tab-count:4">
</span>10<span style="mso-tab-count:2"> </span><span style="mso-tab-count: 1"> </span>600<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">HBCO (V)<span style="mso-tab-count:6">
</span>70.0<span style="mso-tab-count:3"> </span>64.4<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Battery capacity
(AH)<span style="mso-tab-count:5">
</span>440 D<span style="mso-tab-count:3"> </span>800<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Max charge rate
(%)<span style="mso-tab-count:5">
</span>100 D<span style="mso-tab-count:3"> </span>72<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">AC2 input Vmin
(V)<span style="mso-tab-count:1"> </span><span style="mso-tab-count:4">
</span>80<span style="mso-tab-count:3">
</span>105<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">AC input
priority<span style="mso-tab-count:5">
</span>AC1<span style="mso-tab-count:3"> </span>AC2<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Charge control
and inverter EQ (V)<span style="mso-tab-count:3">
</span>64.0 D<span style="mso-tab-count:3">
</span>62.2<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">CC and inverter
bulk & absorption voltage (V)<span style="mso-tab-count:1">
</span>57.6 D<span style="mso-tab-count:3">
</span>58.8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">CC and inverter
float (V)<span style="mso-tab-count:4">
</span>54.0 D<span style="mso-tab-count:3">
</span>53.6<o:p></o:p></span></p>
<br>
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?<br>
Thank you, as always,<br>
Allan<br>
-- <br>
<b>Allan Sindelar</b><br>
<span style="font-size:10.0pt"><a class="moz-txt-link-abbreviated" href="mailto:allan@sindelarsolar.com">allan@sindelarsolar.com</a></span><br>
<span style="font-size:10.0pt">NABCEP Certified PV Installation
Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder (Retired), <span style="mso-bidi-font-weight:bold">Positive
Energy, Inc.</span><br>
<b>505 780-2738 cell</b></span>
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