I actually operate a zero-export system with 2 MultiPlus IIs.
When the battery is empty, shouldn’t the MP-II switch off?
I have just discovered that apparently last night, from about 4:00 a.m. to 5:00 a.m., both of my MultiPluses started charging the battery from 10% to 30%!!! WHY???
Here is the charging display for my battery while it was still discharging:
First, switch the ESS mode to “Without Battery Life” and observe the system again to see whether it discharges down to the configured 10% SOC. The other possibility is a system-adjusted “Battery Life” setting, which could well be causing your minimum SOC to be overridden in the background. That would be the 15% …
But does this mean that the battery will no longer be charged from the grid?
The main question was why the battery is being charged from the grid in the first place… but I’d also be interested to know why the battery was discharged down to 10%!
I’d also take a look at the sustain voltage in the ESS Assistant. If it’s set too high, the battery may be recharged as well.
Furthermore, there are batteries that only allow discharge down to 15% and then trigger an alarm. In that case, the BMS would need to be set to 7% (anything below 10% will do) for this to work with your limits. However, you haven’t written anything about the battery/BMS.
The relevant data is also sent by the battery to the Victron system.
In VRM, there should be a “BMS charge/discharge limits” graph.
Even if the charging current in the MultiPlus is set to 0 A, the battery may, under certain circumstances, be charged using energy from the grid to protect it.
From the charger—that’s what’s shown in your picture.
You’ve already been advised twice to reduce the sustain voltage. In the previous picture, I can see 50.00 V. Try setting it to, say, 48.00 V; then your system shouldn’t charge from the grid tonight (or at least it should start much later and charge less). Of course, this also depends on your consumption during the night.
Reducing the sustain voltage is treating the symptoms, not the cause.
Charging from the grid takes place when the battery has been discharged too deeply.
Either below the cut-off value (which should only happen in the event of a grid failure), or when the battery sends a DCL of 0 A.
Depending on how the BMS is configured, discharging to 10% can quite easily trigger one of the two conditions.
That is why it is generally recommended to discharge only down to 20%.
If you increase it from 10% to 15%, you’ll use more electricity from the grid because your minimum SoC is higher, meaning you draw less energy from the battery. However, your battery probably won’t be charged up to the sustain voltage.
Yes, exactly. Your values aren’t wrong for a 16S battery. If you look at your graph above and see how quickly your battery voltage drops from around 3:40 onwards at the same current, I’d say a minimum SoC of 10% is too low.
Okay, I’ve now set the value to 15%. (I can’t access the page via the web at the moment. I did this on my smartphone.)
Just to make sure I understand…
The sustain voltage is the voltage at which the MP-II starts charging the battery so that it doesn’t become/remain too deeply discharged?
By setting the minimum value to 15%, should the discharge cut-off voltage tend to be slightly higher, thereby resulting in less grid power being used to charge the battery?
The only question I still have is where to set the charging power and the charge cut-off (in %).
Because you can clearly see that the battery is ALWAYS charged up to 30%, including last night
Basically, the Sustain voltage is the voltage that “just about keeps the system alive”. If a system cannot be charged for an extended period … snow, etc. … and the voltage slowly drops below the Sustain range … the Multi simply charges the battery back up a little … this should actually happen even when the “Charger” setting is set to “0” … I THINK Matthias mentioned that once, but no guarantees
Why your SOC is now determined to reach 30% … ??? … I would have expected the 15% to be the limit, rather than the voltage of just under 50V
You can of course set the charging power under “Charger” … or (indirectly) as an input current limit … but then it applies to the entire AC input
The sustain voltage is the voltage at which the MP-II starts charging the battery so that it doesn’t become/remain too deeply discharged? NO, THIS IS THE VOLTAGE UP TO WHICH THE BATTERY IS CHARGED AT LEAST ONCE AGAIN AFTER IT HAS DROPPED BELOW A CERTAIN DISCHARGE LIMIT
Setting the minimum value to 15% should tend to make the discharge cut-off voltage somewhat higher YES, and therefore result in less grid power being used to charge the battery? YES AND NO, LESS CHARGING OF THE BATTERY, BUT YOU WILL NATURALLY ALSO DRAW POWER FROM THE GRID FOR YOUR LOADS WHEN THE BATTERY IS NO LONGER SUPPLYING ANYTHING
That just leaves me wondering where you can set the charging power and the charge cut-off (in %). IN THE MULTIPLUS AND CERBO SETTINGS
Because you can clearly see that the battery is ALWAYS charged to 30%, including last night
THE 30% COULD COINCIDENTALLY BE THE LEVEL OF YOUR SUSTAIN VOLTAGE. YOU HAVEN’T CHANGED IT, HAVE YOU?
ACTUALLY, EVERYTHING IS DESCRIBED QUITE WELL IN THE OPERATING MANUALS
ARE YOUR TWO MULTIPLUSES EACH CONNECTED TO ONE PHASE AND PROGRAMMED THAT WAY AS WELL?
… I would have expected the 15% to be the limit, rather than the voltage of just under 50V