[RE-wrenches] State of Charge Meter for Sol-Ark
Dave Angelini Offgrid Solar
offgridsolar at sti.net
Fri Feb 9 16:08:36 PST 2024
I like Kent's answer ! Adding on I am not sure about this combo (not
the Solark) as I do not use it. Still not sure if it is closed loop? I
know when Schneider adds another closed loop LFP battery to it's
supported list, it really is the battery manufacturers responsibility to
make sure the RS485 canbus/modbus network is accurate or using the right
data.
You can load test also to see where the bottom is and if it is accurate?
Use an external Bat mon and shunt.
Usually these quality batteries have a 10 year warranty, user
replaceable BMS and Cal/test procedure for replacement of the BMS. There
is also a State of Life % as well as a USB output of battery internal
cells program. At least Discover does this. Nice 75 year old company
that makes Locomotive batteries ! Cheers time! Friday!
Dave Angelini Offgrid Solar
"we go where powerlines don't"
[1]https://offgridsolar1.com/ [2] [1]
e-mail offgridsolar at sti.net
text 209 813 0060
On 2024-02-09 3:18 pm, Kent via RE-wrenches wrote:
> William,
>
> I think that the SOC determined by lithium BMSs come with similar
> accuracy issues that occur with the Trimetric, FNDC, Magnum BMK,... -
> small measurement errors integrated over a long time become big errors.
> That's why Fortress (and every SOC meter) is saying that the battery
> needs to reach 54.4 volts once a week for recalibration. At least with
> lithium batteries the SOC meter doesn't need to account for the return
> current dropping down as is required with lead-acid batteries. The
> internal BMSs probably do a better job of estimating the SOC than these
> external devices, but I do not expect them to be perfect. Same goes
> with everyone's electric car, while we put a lot of faith in the
> displayed SOC it probably isn't much better than ±5% and if it were off
> by 10% you probably wouldn't know.
>
> In regards to your graph showing a big voltage difference between two
> 55% SOC occurrences over a 12 hour time frame. I question your
> assumption that the voltage should be the same. The data show
> different voltages for the same SOC, it seems unlikely that the BMS
> measurement drifted by enough to make that happen, so I think the data
> shown may both be correct within reason. The voltage of lithium cells
> is highly load dependent (probably somewhat temperature dependent too)
> so perhaps the Fortress battery is actually close to right at both
> times.
>
> Since using the SI SOC meter for starting the generator is problematic,
> an external device for starting based on voltage is a good idea. If
> you want a ready to go product to do that, I think the Morningstar
> relay driver will work well. A little difficult to program or reprogram
> but very reliable. One issue you will observe is that the generator
> won't start at a consistent SOC as indicated by the battery or the SI.
> Kent Osterberg
> Blue Mountain Solar
>
> On 2/9/2024 11:27 AM, William Miller via RE-wrenches wrote:
>
> Dave:
>
> I have to disagree with you here. To my knowledge every SOC system
> relies on coulomb counting and applying an efficiency value. That
> efficiency value is dependent on changing variables such as
> temperature, age of the batteries, charge rate, discharge rate-- to
> name a few. Every SOC system I have studied requires periodic
> recalibration. Maybe Discover is different but here is my experience
> with Fortress.
>
> Below is a chart of SOC versus Battery Voltage for a 4 Sunny Island
> system in a closed loop installation with 5 Fortress E-vaults:
>
> Inside the ellipse note that at 6:00AM the SOC is 55% and the battery
> voltage is about 50.8. At 4:00PM pm the same day SOC is again at 55%
> but the battery voltage is about 50.0 VDC. This is a drift in
> calibration of 0.8 VDC in 10 hours. In the context of LiFePo4 systems
> 0.8 VDC is a lot. Because this is closed loop, the drift was created
> in the BMS units, not the Sunny Island.
>
> Drake, to your question: The consequences depend on how much the
> system relies on SOC for operational mode decisions. I work almost
> exclusively with Outback and SMA SI and primarily in the off-grid
> segment. Since the SI is SOC-centric, the consequences experienced
> during the period charted above was that the system failed to start the
> generator and the system shut down.
>
> I am new to the use of Lithium batteries and don't work a lot with SI
> so it took me two trips to figure out what was happening. The
> diagnosis was complicated by a failed SD card and a catastrophic
> generator failure (shorted windings). It took a few days to get a
> replacement generator and the interim the Fortress BMSs failed to
> recalibrate and this caused the incorrect correlation between VDC and
> SOC.
>
> In conversation with Fortress tech support I was advised to make sure
> the battery voltage gets to 54.4 at least once per week. This is the
> voltage at which the E-vaults recalibrate SOC. During the winter this
> is sometimes difficult to do. I can't rely on the SI generator to
> auto-start and achieve 54.4 because it triggers on SOC values and if
> those values are wrong then the generator may shutoff prematurely,
> failing to reach 54.4. In this case the generator failed to start at
> all as a direct result of inaccurate SOC and the system crashed,
> causing an inconvenience to the client and to me.
>
> There are some settings on the SI that may force a full charge but I
> haven't drilled down yet to see if this can be configured to ensure
> that 54.4 once per week. If anyone has experience with this and can
> chime in it may save me some time. I suspect all settings rely on SOC
> so there will be no built in solution.
>
> If the inverter here was an Outback and I was not relying on an FNDC to
> control generator start (which I never do), this problem would not
> happen. The Outback would react to battery voltage only, as monitored
> over three different time periods. This is a superior method for sure.
>
> Battery inverters are very smart these days, but sometimes not quite
> smart enough...
>
> Drake, thanks for asking.
>
> William
>
> PS: Brainstorming a solutions here:
>
> A: I am sure I could program an Arduino or Raspberry Pi to take over
> generator auto-start duties. I don't prefer homemade solutions because
> of the time required to develop and test and I am not good at building
> interfaces.
>
> B: Maybe I could install a Mate3s and one FM60 charge controller. The
> charge controller would not connect to PV because this is an AC coupled
> system, but if were connected to the batteries it could monitor battery
> voltage and the internal aux relay could control the generator.
>
> Ideas, anyone?
>
> WM
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com [3]
>
> CA Lic. 773985
>
> From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
> Behalf Of Dave Angelini Offgrid Solar via RE-wrenches
> Sent: Friday, February 9, 2024 9:29 AM
> To: RE-wrenches
> Cc: Dave Angelini Offgrid Solar
> Subject: Re: [RE-wrenches] State of Charge Meter for Sol-Ark
>
> Hi Drake,
>
> I do not think there is a lack of accuracy in a good closed loop LFP
> battery system. The steep curve of Lithium is just not accurate for
> voltage and the Soc measurement from a quality BMS is super accurate.
>
> All I use is the Discover AES and unlike others here, I do not have any
> issues over 4 years and 45 mostly Offgrid homes.
>
> The closed loop UL 9540 systems save alot of fuel in generator use, are
> simple, and have happy clients for me.
>
> Dave Angelini Offgrid Solar
>
> "we go where powerlines don't"
>
> [1]https://offgridsolar1.com/ [2] [1]
>
> e-mail offgridsolar at sti.net
>
> text 209 813 0060
>
> On 2024-02-09 8:05 am, Drake Chamberlin via RE-wrenches wrote:
>
> How does the lack of accuracy in SOC detection affect the usefulness of
> closed loop systems?
>
> _Drake Chamberlin_
>
> _Athens Electric LLC_
>
> _Ohio Electrical Contractor's License 44810_
>
> _NABCEP Certified PV Installation Professional_
>
> On 2024-02-05 11:36, William Miller via RE-wrenches wrote:
>
> Jason:
>
> I am careful about getting my clients too dependent on SOC readings.
> SOC is a calculated value based on changing variables and is
> notoriously inaccurate.
>
> Below is a screenshot of the Optics reporting for a client. The graph
> line that begins as the lower of the two is the SOC, the other is
> voltage. The SOC is out of calibration until about noon when it jumps
> from about 20% to about 80%. This does not mean the SOC changed by
> that amount, it means that it was just very wrong. Who knows when it
> is correct?
>
> In spite of repeated entreaties this client still reads the SOC and
> becomes concerned when it gets low-- even if the voltage level
> indicates the batteries are well charged. I have to deal with his
> misplaced anxiety.
>
> Error! Filename not specified.Error! Filename not specified.Error!
> Filename not specified.
>
> This problem appears to occur across all battery/inverter technology.
> For example, SMA touts their "coulomb counting" as more accurate than
> others but I have witnessed otherwise. You'd think that BMS units
> built by lithium manufacturers for their own products would be
> consistently accurate but even those BMS units need to recalibrate
> frequently, this according to the battery manufacturer's engineers.
>
> It would be nice to offer clients a simple, accurate method of
> ascertaining battery charge levels. SOC is not that method. I train
> my clients to watch voltage levels and to understand these values are
> elastic. If you can see trends in the battery voltage, so much the
> better. This is why I like the Outback Optics interface. This is also
> why a good AGS system examines battery voltage over time.
>
> I no longer install Outback FNDC units. Without them there is no SOC
> reading. I don't install Sunny Island systems--they are SOC centered
> and suffer for it.
>
> William
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com [3]
>
> CA Lic. 773985
>
> From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
> Behalf Of Jason Szumlanski via RE-wrenches
> Sent: Sunday, February 4, 2024 7:30 AM
> To: RE-wrenches
> Cc: Jason Szumlanski
> Subject: [RE-wrenches] State of Charge Meter for Sol-Ark
>
> Are there any off the shelf solutions to view battery SOC via a wired
> meter mounted remotely on a property? I have a client with a simple
> voltage based meter for lead acid batteries that they are accustomed to
> using as a quick and approximate gauge of SOC. They want something
> similar for their new Sol-Ark with EG4 LL batteries.
>
> They will have smartphone app visibility, but they want something they
> can see inside the house without picking up a phone or going out to the
> inverter. Ideally the SOC will come from the inverter or the battery
> itself, not an external source (to avoid discrepancies).
>
> Jason Szumlanski
>
> Florida Solar Design Group
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[1] http://members.sti.net/offgridsolar/
[2] https://offgridsolar1.com/
[3] http://www.millersolar.com/
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