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gnagflow avatar image
gnagflow asked

max SOC limit setting in ESS is very necessary

Hello,

there is a very very important feature missing in the victron ESS settings. You can set a MIN SOC, which is great in winter, to let the battery not stay a long time on a bad low voltage.
But there is no MAX SOC setting, which is more important. In sommer times, the battery is almost always full, this is the worst voltage setting and the battery wear of the battery is high. Nothing is worse than sommer with full battery and high temperatures. Every normal user would like to restrict the MAX SOC in summer, there is no such feature in ESS settings. I cannot explain my customers, why this does not exist in the great Victron world, where you can do almost everything, but not one of the most important settings.

Next: In times like today, where the average person gets more money for selling energy than it costs (buying contracts least a year for change, selling contracts are mostly the average price of the last three months) nobody wants to store the energy in the battery, customers need a setting to bypass the battery with a MAX SOC setting, e.g. 50%. Than the battery can do a kind of sleep, during months where energy sales prices are very high.

Next: I changed the control of my Victron system by external NodeRed programming to not regulate the grid connection to ZERO, for optimizing the own energy usage, but at that time i regulate the Multiplus System to get ZERO at the battery, this is the best way to bypass the battery to sell as much energy as possbile.

Those are two very simple features, that are very important for the VALUE of Victron ESS: 1. MAX SOC setting, 2. MIN Battery usage regluation.

I tried to set the grid setpoint to a high minus value, but this is not a usable solution.

Please check this CHANGE REQUEST, I cannot program for every customer an external control.

ESSSOCbatterylife
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baxter avatar image baxter commented ·
The Community here is still not understanding the physics behind so limiting the SoC was not supported, pls see my feature request and vote for it. Do not be afraid about warranty issue. Best operating window of LFP cells is up to 90%SoC.
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gnagflow avatar image gnagflow baxter commented ·
I support you! We need max. SOC feature. We need more people to support the change request!
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gnagflow avatar image gnagflow commented ·

@victron @mvader please check the change request, i am an installer for ESS systems and very frequently my customers asking, why they cant set an max. SOC in summer to prevent wear on the lithium battery - when it is almost all the day on 100% SOC during months.

It is evident, that full battery charge during a long time at high temperature like in summer is the worst for life time.

At the moment i change BMS settings for summer and for winter time at some customers making them happy, but makes me crazy, when you could implement a very simple feature of "MAX SOC" - what they would appreciate to have in their remore ESS settings.

thank you in advance for considering this request!




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gnagflow avatar image gnagflow commented ·

Typical summer SOC from an installation with about 14kwh capacity lithium storage,

its always full and never goes down to 50 percent SOC.

Could I decrease the max SOC easily, i would do it.


1661436474772.pngunfortunately i have a problem with the dvcc max voltage charging setting, it does not work, tried it today and tried it much earlier, for any reason it is not working satisfying see picture from today:

changed max. charge voltage and multiplus further charges, made a reboot of the venus gx and multiplus further charges still at 57,6V even if the max. charge V setting is at 56V. what could be the reason for that behaviour?

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4 Answers
nickdb avatar image
nickdb answered ·

Some of this has been discussed at length - why keeping a (lithium) battery at full charge isn't as big a problem as the internet tells people it is, and why keeping it undercharged is a bad idea.

None of the supported batteries want that behaviour and it will impact your warranty.

If you search on this forum you will already find a feature request topic where you can vote for this feature.

https://community.victronenergy.com/idea/149175/configurable-maximum-soc-in-dvccess-controled-syst.html

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gnagflow avatar image gnagflow commented ·
Unfortunately that is not true, keeping lithium batteries at full charge is the worst idea. So, we do it at all Victron systems the whole summer in ESS situations, the batterie is full in the morning until the night starts. There is nothing else that wears the battery more than full charge for a long time.
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Mike Dorsett avatar image Mike Dorsett gnagflow commented ·
One other point is that the time spent at max charge is usually fairly short - typically 5 hours or less per day. Over-discharging the cells leads to far more failures than overcharging. Restricting the Cell MAX VOLTAGE is the only accurate way to do this. I know I've been there. If your system is set up right, then SOC is recalibrated to 100% when the battery reaches a designated voltage. Some BMS systems train the SOC to react to the average cell voltage. In either case, SOC is a derived (calculated) parameter rather than a directly measured parameter and therefore a lot less accurate.
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gnagflow avatar image gnagflow Mike Dorsett commented ·
yes of course, the soc is calculated and most cheap bms calculate very wrong, but if the coloub counter works and a high voltage and low voltage calibration is done, and the approx. cell capacity is known, the SOC is quite easy and good...


SOC is just a more customer friendly value than the voltage, but for me it is only important that the customer can stop the full charges in summer, so he needs a min SOC in winter, to do not destroy the battery. A customer wants to care for his invest.

Maybe another solution would be that the "battery life" option should be enhanced to also care in summer and not only in winter times.

For me there was a problem with the DVCC max. charge voltage in combination with CANBUS battery, multiplus and MPPT's - I have to check it again!


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Mike Dorsett avatar image Mike Dorsett gnagflow commented ·
depending on your BMS, you should be able to trim the cell max voltage down by 50 to 100mV , this will achieve your Max SOC regulation. If you have your SOC rest threshold set to the lower value, this will also reset to 100%, BUT you can tell your customers that this is really 90% - its just scaled. Voltages depend on your chemistry, but LIFePO4 is normally max Cell of 3.65 +/- 50mV. Ive been working well with 3.55V max per cell.
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baxter avatar image baxter Mike Dorsett commented ·

The most common misconception about charging lithium batteries is believing that the State of Charge and by extension overcharging have anything to do with voltage. They don’t

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hjohnson avatar image hjohnson baxter commented ·
They do have something. Lithium still has a charge curve, it's just much much flatter than Lead Acid. There are two "knees" when the battery is near full, and when it is near empty. If you stay out of those knees, which you can do with voltage, then you've significantly reduced your wear on the batteries.
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baxter avatar image baxter hjohnson commented ·
As you say, the charge curve is very flat, so just lowering the voltage will not work. eg 53.4V can be 80 or 50% SoC.

Using the voltage will not work using Lifepo4, thats fine for Lead Acid or maybe Lipo.

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gnagflow avatar image gnagflow Mike Dorsett commented ·

Hi, unfortunately the dvcc setting of max. charge voltage never works for me at customer sites for stopping multiplus 2 to charge.

See enclosed the test from today. For me this setting always works only for the MPPT's and not for the multiplus charging.

Whats wrong?

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Paul B avatar image
Paul B answered ·

The just reduce the max charged voltage in the ESS or in the charger its self this is far better than SOC as it more accurate in most cases - I do not see the need for a max SOC when a MAX voltage is the same thing.

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baxter avatar image baxter commented ·

Because max voltage is not the same thing using Lifepo4. You can fully charge a LFP cell using 3,45V or 3,65V, just a matter of cut off current. You can even overcharge a LFP cell using lower voltages. That is a common missunderstanding when using Lifepo4

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nickdb avatar image nickdb ♦♦ commented ·
Exactly. SOC is a terribly inaccurate metric due to drift, drift which only increases the less frequently a battery is properly charged.

DVCC already lets you lower the charge voltage, though for DIY it may be better to limit via the BMS - at least you will have a better chance of avoiding imbalance.

Nonetheless, if you bought a decent battery pack, they will pretty much already have done this to keep cells in an optimal range for extended use, with temperature compensation, using specs beneath that of the cell manufacturers standard charge and discharge.

The risk of imbalance and subsequent wear to the battery is far greater than anything they are trying to solve here, but if they want to derate the cell's performance twice that is their choice. It is just unlikely this will ever be implemented into the product.

Battery tech and design in a samsung phone is not the same as a LiFe battery, but anyhoo.


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baxter avatar image baxter nickdb ♦♦ commented ·

Regular top balancing is the answer you are looking for, eg once a month, depends on your battery (can be automated based on weather forecast). A lot of larger DIY batteries are not getting a full charge during winter time and cycling below full SoC. They just need more top balancing cycles in spring to bring SoC aline. Lowering the charge voltage must not end and up in lowering the SoC, see my comment above.

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gnagflow avatar image gnagflow commented ·

Hi, yes i think its my mistake, i am good with the setting of the DVCC max. charge voltage, if it overwrites the canbus values (if they are higher) - i had the problem that those dvcc values didn work for the multiplus, just for the MPPT controllers - if it works also for the multiplus in combination with canbus battery???


even though i understand the need for max SOC for lifepo systems.


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Paul B avatar image Paul B gnagflow commented ·
It works fine on all our sites and most have a Multiplus plus a MPPT or two
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gnagflow avatar image gnagflow commented ·

unfortunately this function does not work for me when charging with multiplus in ESS system, i tried it several times at different sites. What could be wrong?

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tyr avatar image tyr gnagflow commented ·
Settings in the Multi via VEConfigure?
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djbower1 avatar image
djbower1 answered ·

Just use Node-red to disable the charger at a SOC of your choosing. Easy????

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andreym032 avatar image
andreym032 answered ·

Hello, I'm using Home Assistant and connected Victron by ModBus

Based on https://www.victronenergy.com/live/ess:ess_mode_2_and_3


I added 3 sensors :

modbus:
  name: hub1
  type: tcp
  host: 192.168.8.116
  port: 502
  sensors:
    - name: 'V1 : Battery State of Charge'
      unit_of_measurement: "%"
      device_address: 100 # Change it if you are using BMS 
      address: 266
      scale: 0.1
      precision: 0
      device_class: battery
    - name: 'V1 : ESS Mode Number'
      data_type: uint16
      device_address: 100
      address: 2902
    - name: "V1 : DVCC Max Charge Current"
      unit_of_measurement: A
      device_address: 100
      address: 2705
      device_class: power

* I found that modbus configuration applies only after full reboot home assistant.


After configuration you can manage DVCC Max Charge Current (for my installation 0 for idle, 100 maximum charge current) - I tested and it's work on ESS mode 1 & 2

service: modbus.write_register
data:
  hub: hub1
  address: 2705
  slave: 100
  value: 0

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Related Resources

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