Multi RS Solar unwanted charging from the grid

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Mihai asked Mar 12, '24

Multi RS Solar unwanted charging from the grid

Hello,

I have a Multi RS Solar with two strings of solar panels and a 14KWh Lifepo4 battery.

I am using the ESS mode "Optimized without battery life" and a "Minimum discharge SOC" of 25%.

While the AC input (grid) is connected, I'm getting a constant charging of the battery from the grid with about 300-400W of power (~8A/52V).

I don't want to charge the battery from the grid, I just want it to remain at the 25% SOC threshold until PV energy is available to charge the battery .

Using the "Disconnect AC input on Voltage" option doesn't really help me because I could end up with unwanted charging/discharging cycles during night or cloudy days.

You may see in the above captures that there is a residual power going from the grid into the battery.

Did anyone noticed this behavior? I don't think this is normal, is there something I'm missing?

Thank you all,

Regards

ESS Multi RS

ac-input-relay-closed.png (12.5 KiB)

charging-from-ac-input-ac-input-relay-closed.png (12.7 KiB)

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Modifications Space

Node Red Space

Answer 1 · 2024-03-13T16:54:55Z

Mihai answered · Mar 13 at 04:54 PM

Just want to add some findings:

1. The current going into the battery is exactly 10% of the "Max charge current" setting (80A). When modifying this limit, it follows the new setting.

2. After the battery reached floating point (charged completely), it started to discharge like expected...

Could this behavior be triggered because of the "Repeated absorption" setting? It seems to be set up for 7 days interval.

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Answer 2 · 2024-03-13T18:26:51Z

Alex Pescaru answered · Mar 13 at 06:26 PM

That residual current is consistent with the "slow/force charge" that is performed if the SOC is below set Minimum SOC for more than 24 hours. But this, from what I know is true for "Optimized with batterylife". Maybe what I know is wrong...

The algorithm's correct functioning, from what I saw, depends greatly on the system knowing the exact battery's state and the exact system's state. So, let the system perform a full excursion from full charged to minimum SoC and don't perform any additional intermediary settings.

Also, even if you set "Optimized without batterylife" or even "Keep batteries charged", the system still computes in the background a lot of things as if you've had set "Optimized with batterylife". It doesn't use these computed things, but they are there for "just in case" you switch to "Optimized with batterylife". It's a good thing, because the system keeps track of the solar power available / bad / good weather continuously.

Do you have a Cerbo to read battery info and send it to Multi RS?

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Answer 3 · 2024-03-13T19:26:58Z

Mihai answered · Mar 13 at 07:26 PM

Hi @Alex Pescaru , thanks for taking time to answer.

At first, I also thought it's because of the "...with battery life" option I used few days before, and somehow it was still trying to reach that internally dynamic SOC threshold... But I wasn't expected to go all the way to full charge.

The battery SOC seems to be calculated pretty well by the Multi RS. I don't have a Cerbo (yet), just the JK BMS that is not directly compatible with Victron from what I understood.

I'm gonna keep an eye on the system for the next days and not change the "without battery life" setting. I really don't want the battery being charged from the grid since it defeats the purpose of using the solar energy at maximum.

I also changed the "Repeated absorption" setting to every 35 days instead of 7 days. Just in case...

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Alex Pescaru commented · Mar 13 at 08:14 PM

Hi @Mihai ,

If you don't have a Cerbo, maybe this could be a problem with the charging algorithm inside Multi RS.

I can confirm that when using Cerbo, the system behaves the way you wanted. It keeps the SoC at the Minimum SoC set in the configuration menu.

Also a nice thing about Cerbo is that you can modify a lot of scripts inside its Linux system and customize it to suit your needs. Not to mention the NodeRed...

Alex

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