[RE-wrenches] Fwd: Refractometer reading has me stumped
Dan Fink
danbob88 at gmail.com
Mon Dec 21 10:21:43 PST 2015
Allan;
Wow, that's a nightmare. All I can suggest for now is to X out some obvious
things and CYA. Sounds like you are CY someone else's A now. I get these
sort of calls too. Usually it's a townie PV installer who knows nothing
about off grid and programmed some equipment wrong.
~ measurement error? did you calibrate the refractometer with distilled
water before your tests? Do you have a float hydrometer for backup?
~ did you check SG on *every* cell? one bad one can ruin the whole bunch.
~ Did you view the battery bank on a thermal imager whilst charging or
discharging?
~ Isolate and load test a battery. I have a nifty antique adjustable load
tester that does this, but any DC load will do it. I'd shoot for a C/5 -
C/10 rate. With SG that low, you should know in a couple hours if it has
any capacity left at all.
~ Can you put a non-system-integrated coulomb counter SOC meter into the
system? Remove it later, just use for diagnostics?
My gut feeling is that for some reason, maybe programming of that mishmash
of equipment, either the PV array or generator or both is not charging
correctly, and these batteries have been starving. Or that there's one
really bad cell that's milking them down. I think I'd hit my thermal imager
first thing on this one.
Good luck! Keep us posted! I love this list because i can learn from
everyone else.
Dan Fink
Adjunct Professor, Ecotech Institute
IREC Certified Instructor™ for:
~ PV Installation Professional
~ Small Wind Installer
Executive Director, Buckville Energy
NABCEP Accredited Continuing Education Providers™
970.672.4342
On Mon, Dec 21, 2015 at 10:16 AM, Allan Sindelar <allan at 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*
> allan at 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 <505%20780-2738> cell*
>
> _______________________________________________
> List sponsored by Redwood Alliance
>
> List Address: RE-wrenches at 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
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20151221/0782edf1/attachment-0002.html>
More information about the RE-wrenches
mailing list