Diminishing trend in daily maximum battery SOC

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portsample asked Apr 14, '24

Diminishing trend in daily maximum battery SOC

About 10 days ago I set up two VEConfigure assistants that would close ACOUT-2 at 95% SOC allowing current to pass, and another assistant that would open the ACOUT-2 at 90% and stop the flow of current. ACOUT-2 is connected to a 500watt load. ACOUT-1 has no loads. Battery is a single generic lithium 48v 100A unit, (mfg by Chin). Combined panel output is 1200w, 16.6A, at 72v. Note: ESS state was 'Optimized with BatteryLife'.
Below is SOC as reported by Lynx shunt over the past 10 days. Note diminishing maximum SOC level.
As expected in the first couple of days, the VEConfigure assistants would open and close the circuits at around 90.0 - 90.5, and 95.0 - 95.5. As time went on, close began to be actuated at lower and lower levels as shown in the graph, with yesterday's switch closings occurring around 93% SOC. Levels of switch opening also may have increased somewhat. Questions: Where does the Multiplus II assistant derive it's SOC assessment? The Cerbo SOC assessment is set to pull from the Lynx shunt. Am I dealing with a difference in SOC assessments, or is this a reflection in an actual change in battery capacity? Suggestions for resolving this and keeping my VEConfigure assistants would be highly appreciated. Thanks in advance.

Multiplus-II SOC Assistants lynx shunt

sundayscreen.png (55.5 KiB)

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snoobler answered · 6 days ago

1) I thought you already established it was triggering on the basis of the "Hidden SoC" value. Suggest you either disable the inverter battery monitor or set it to 80% instead of 95% when bulk finished.

2) without periodic sync, shunts lose accuracy. If your efficiency is anything less than 100%, you will get drift.

3) not yet

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portsample commented · 6 days ago

Per answer 1) above, I did uncheck the inverter battery monitor checkbox in VEConfig. and changed the Cerbo setting for battery monitor from "Automatic" to "Lynx Shunt 1000A VE.Can on VE.Can". I am surprised as well that the assistants still appear to be relying on inverter SOC for their triggering.

Thanks for your thoughts and suggestions.

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snoobler portsample commented · 6 days ago

Did you try to change inverter battery monitor to 80% when bulk finished rather than 95%?

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portsample snoobler commented · yesterday

Okay...made the following changes 5 days ago:

- Lynx --> Settings --> Battery Bank --> Charged voltage = 57.0v to 55.0v...manual says 0.2 to 0.3v below float.

- Lynx --> Settings --> Battery Bank --> Peukert exponent = 1.25 to 1.05

- Lynx --> Settings --> Battery Bank --> Synchronized SOC to 100%

VEConfigure assistants are opening ACOUT-2 at 90.0% SOC consistently, however they are closing the switches generally around 95.0 to 95.3 percent.

Have not noticed any trend in the latter as of yet.

Accepting Snoobler's answer now. Thanks.

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Answer 1 · 2024-04-15T04:13:01Z

snoobler answered · Apr 15 at 04:13 AM

check Settings > System Setup > System status

Create a custom widget charging all three SoC:

VE.Bus SoC

VE.Bus Hidden SoC

Lynx SoC

That will show you what is happening.

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portsample commented · Apr 18 at 03:50 AM

Huh. Most curious. Here are VE.bus and Lynx SOCs plotted against each other per Snoobler's suggestion.

VEConfig assistants were set to close switches and allow current flow at 95% SOC, and open switches breaking current flow at 90%. This generally worked for the first week, then switches started closing at <95% SOC, and opening at >90%. Much higher incidence of see-sawing during those later days in spite of good sun. Removed all loads on 4/14, only batteries are connected until I get this sorted out.

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mixedsocs.png (167.6 KiB)

Answer 2 · 2024-04-18T07:50:00Z

JohnC answered · Apr 18 at 07:50 AM

@Glenn Hollowell

Those plots suggest the Assistants are using the VE.Bus SOC to switch. What they're supposed to use I've never seen documented. And there's nowhere to select the source. But Victron recommend to not have both sources enabled together anyway as it causes confusion. Seems they're right.

I'd disable the VE.bus SOC, the Lynx SOC will then be used. But may need tuning to be accurate. One thing you may need to allow for with your Assistants, is the need for the batteries to reach full charge so they can sync to 100% occasionally. This is determined by reaching Absorb V and a Tail current (which should be minimal).

I'm curious about the slight rise in both SOCs overnight. That may indicate the need for a Zero Current Calibration if there's no charge actually happening. Or ESS is feeding some current while solar is down.

SOC drift can happen. The heavy handed correction is to sync, but it could also need Peukert and Charge Efficiency tweaks to fine tune it, then you can stretch out the need for frequent syncs.

What you're doing there with ESS I have no idea.

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Answer 3 · 2024-04-18T12:13:11Z

Fideri answered · Apr 18 at 12:13 PM

@Glenn Hollowell

I haven't studied your documents very closely. Another option, if you haven't done it already, is to synchronize the battery SOC, as reported by your set battery monitor, with the VE SOC. There is a setting to do so under the "General" tab of VEConfigure.

F.

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Answer 4 · 2024-04-18T14:30:05Z

snoobler answered · Apr 18 at 02:30 PM

This has to do with the setup of the inverter battery monitor. It sets a given SoC when bulk is finished. I recommend you disable inverter battery monitor, enable DVCC SVS and SCS and ensure the Shunt is the active battery monitor.

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portsample commented · Apr 23 at 03:25 AM

Following steps were taken,

-VEConfigure, General tab, uncheck battery monitor.

-Cerbo, change "Automatic" to "Lynx Shunt 1000A VE.Can on VE.Can".

-Victron Connect, changed MPPT 250/60 solar controller from absorption = 57.4v and float = 57.2v to, 56.8 and 55.2 volts.

Notes: DVCC and SCS are enabled, SCS "status" is disabled.

In VEConfigure, General tab- state of charge when bulk finished = 95%, Capacity = 100A, Charge efficiency = 0.95

In VEConfigure, Charger tab- Repeated absorption time = 1.0hrs, Repeated absorption interval = 7.00 days, Absorption time = 1 hour

ESS is set to "Optimized with Batterylife".

MPPT settings are default.

The VEConfigure assistants are still opening the ACOUT-2 switches at below 95%. See table below. In addition, after several cycles today, it appears that this threshold is diminishing by approximately 0.6% per cycle (yellow high lights).

Questions...

1) Why is assistant closing switch at <95% SOC when 95% is the specified level in the assistant?

2) Align percent w/battery capacity per Midori's comment? But if I do this, won't I still keep losing the 0.6% each cycle as in above table and previous figure? Seems like a frameshift issue that needs resolving...

3) Do I want to enable tail current in MPPT settings? ...other advanced settings?

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soc-table.png (121.1 KiB)

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