Multiplus-II 48/5000 inverter stops at ~ 3x3450 W and does not go above

DIY
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1

My test scenario/problem:
in cerbo-GX:
—Settings/System setup/ESS I switch the “grid setpoint” to -14000 which brings the inverters within a few seconds to ~ 3* 3450W output and stabilizes there with +/-50W.
—in my test i also switched on consumers with a total consumption of 12500W in the house - inverters also stopped at ~ 3* 3450W and the gap (~2000W) was filled with electricity from the grid.

Some details about my system:
-2* 48V 16kwh battery packs supporting 400A and configured for 300A max. discharge. (config in JK-BMS, serialbattery-driver, aggregateBatteries; aggregateBatteries provides 300A discharge current to the cerboGX in the parameters)
-1* Lynx shunt between both batteries and rest of the system
-3* muliplus-II 5000 in a 3-phase configuration
-DC wiring is 50mm² between busbar and MP and 95mm² between batteries and busbar, busbar is 1000A Victron distributors and power-ins.
-MPPTs are not really relevant, the problem persists also when PV provides (partially) the power to feed the inverters directly.
-AC cabling is 16mm² to each multiplus (=>4x16mm²) connected directly to connection house <=> grid.
-Fuses for the AC between MP-II and grid are 32A circuit breakers (per phase) and 50A (melting) fuses (per phase) for the whole house.
-MP-IIs are connected to AC-IN, AC-OUTs are currently not used.
-MP-IIs are controlled via Cerbo via the EM540, which is placed first, when cables come into the house from the grid (after the 50A fuses).
-Software/firmware: I am using latest/stable for all devices, so e.g. v3.60 on Cerbo.
-System is running for 3 months, Victron equipment bought new in 08/2024.

What I did:
-checked multiplus settings via VE Configure
-checked JK-BMS, serialbattery, aggregateBatteries for possible wrong limits
-checked CERBO-GX settings (v2):
— System Setup/ESS/Peak-shaving: “Multiphase regulation” => Total of all phases
— System Setup/ESS/Grid feed-in: “DC-coupled PV - feed in access” => on
— System Setup/ESS/Grid feed-in: “Limit system feed-in” => off
— System Setup/ESS/Peak-shaving: “Peak-shaving” => Always
— System Setup/ESS/Peak-shaving: “Limit system AC export current” => off
— System Setup/ESS/DVCC: “DVCC” => on
— System Setup/ESS/DVCC: “Limit charge current” => off
— System Setup/ESS/DVCC: “SCS- Shared current sense” => on
— System Setup/ESS/DVCC: “SCS- status” => Disabled (external control)
— System Setup/ESS/DVCC: “Controlling BMS” => AggregateBatteries
-checked VRM portal settings:
—Dynamic ESS is enabled, but not used due to being switched off in the main dashboard
—Still all settings should be fine.
------System: “Maximum export power” is set to 15kw
------battery: “Maximum discharge power” is set to 15kw
-checked temperature above the MP-II: It goes up to max 40° (According to Victron docu the expected limit is at 45° ~3700W, so no explanation for the limit of ~3450W)

My strong assumption is that the MP-II should be capable of producing at least 3x3700W, so >11000W even at the highest measured temperature.
Also a technical issue inside the MP-II I would consider very unlikely, because the output rises more or less linear with constant speed to the 3450W.

Any ideas or tips how I could resolve the issue?

2

When I loaded 5k Multis in warmer ambient temps, it ran to its 4000W for a few minutes then derated to 3500W.
I could reproduce this at temps below 25C as well.

Exporting is less efficient, that needs to be considered as well, there are a few variables.

3

@guru_00_00

I had a similar issue.
Issue was different voltage measurements between MP2 internal and BMS, due to voltage drop on battery cables.

I ensured diagonal battery wiring - plus on bat 1, minus on bat 2.
I added a voltage sense line from MP2 L1 to bat 1 plus and bat 2 minus.
Now I can utilize full potential.

4

Hi Björn, that is actually a very helpful tip!
Do You know, which value the MP takes for comparing battery vs. MP-measured voltage? (Cerbo DVCC battery monitor or ESS battery monitor)
Did You try to turn off the MP battery monitor in the VE.config settings?
When You say voltage measurement, do You refer to these optional voltage sense cables, that are described as optional additional equipment for the Multiplus? (The MP quick installation guide shows just 2 thin wires to connect to battery + and - with 0,75mm² according to handbook)

Thank You in advance for Your answers!

5

Hi @guru_00_00

I do not remember if v-sense cables were included. I had both measurements (mp2 and BMS) active and selection was automatic.

I took some thin cables, added m8 cable lugs one site and screed the other side to the green v-sense plug.

Pls refere to mane chapter 4.4 and Anex A

I hope this helps.