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marv2097 avatar image
marv2097 asked

Random ESS Discharge Behaviour

Often I am seeing my grid usage is all over the place, ESS seems unable to keep it near zero. Its mostly high levels of export when none is expected. Grid setpoint is 0 but its often exporting more than 500w. This isn't just transient as the AC loads change but consistent over many minutes/hours.

It seems to happen when there is excess solar and either ESS is not able to bring the grid to 0 or the commanded value isn't implemented as charging power. Occasionally I see the system discharging higher values from the battery (2-3kw). Once solar is less than the AC loads it works as expected.

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As a test if I increase the grid setpoint to offset the discharge power value then this brings it in check so proves the battery is able to accept the excess power level.

All grid meters are ET112 with USB to RS485 cables connected directly to the Cerbo. The solar W readings match the PV inverter and the AC loads values look correct but has not been tested with a meter.

See below for more specifics but if I can add any info then let me know. Any help debugging this would be appreciated. Thanks!



Canbus BMS Params
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ESS Setup

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DVCC Setup

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1698328880540.png


System Overview:

Cerbo GX Running Large OS 3.11
2x Multiplus 48/5000 running in parallel single phase. v506 Firmware. (internal current sense).
2x Seplos Mason 48v 280Ah batteries connected via BMS-Can and using DVCC
AC Connected 5kwp solar on AC input.


ESS
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1698329123572.png (11.5 KiB)
1698328942663.png (17.4 KiB)
1698328913020.png (27.4 KiB)
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3 Answers
marv2097 avatar image
marv2097 answered ·

Im narrowing down on where this issue is. Its related to the fact I have two multi's in parallel. Both multi's seem to work together for most tasks but not when ESS is telling them to put power in the batteries.


I've done some basic testing with a current clamp on the DC cables of each multi:

Normal - 0w Setpoint. Solar Off. Approx 800w AC Loads. Both multi's share the inverting load.
- Cerbo: -17A
- Multi1: -8A
- Multi2: -8A

High AC Load - Turning on loads results in a 5.2kW AC Load. Both multi's share the load.
- Cerbo: -87A
- Multi1: -45A
- Multi2: -43A

2kW Solar Input - 0w setpoint. Approx 800w AC Loads. Charge is not Balanced.
- Cerbo: 10A
- Multi1: 10A
- Multi2: 1A

Grid Setpoint 2kW- Solar Off. Approx 800w AC Loads. Grid shows 1500w. Charge is not Balanced.
- Cerbo: 11A
- Multi1: 10.5A
- Multi2: 1.5A

Grid Setpoint -2kW - Solar Off. Approx 800w AC Load. Grid shows -1945w. Both inverters working.
- Cerbo: -55A
- Multi1: -28A
- Multi2: -27A

Sched Charge - Approx 800w AC Loads. Grid shows 7900w. Both multi's share the charging.
- Cerbo: -120A
- Multi1: -64.6A
- Multi2: -55.7A


Based on this i suspect the assistant in Multi 2 is not working as it should. To attempt to resolve this I have removed the assistant and re-added and will monitor during the day to see if this is improved.


Notes:

There is some variance because i had to move the clamp meter around. Also I notice that multi2 is generally doing a little less charging/inverting based on the DC current values. All multi's and batteries are connected via a Lynx power in bus bar and cable lengths are exactly the same. All cables as per manuals with multis having 70mm2

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nickdb avatar image
nickdb answered ·

This is most commonly seen in parallel systems.

Things you have to check, is the age difference - check the manufacture date in the serial numbers.

Always set the newest one to master.

AC cabling also plays a part, apart from being symmetrical, having connections that are too short and too thick a gauge can also be problematic, they need some resistance to balance.


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marv2097 avatar image marv2097 commented ·
Thanks @nickdb, When i upgraded from a single 5k I ordered 2 new ones to try and keep them as close as possible. Checking the serial's they seem close:


Master: HQ2313
Slave: HQ2314

I will try to re-configure them to swap them round and see if this makes any difference.

Good point on the AC side cabling, I will have a look at that thanks

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marv2097 answered ·

This has now been resolved see here for more details:

https://community.victronenergy.com/questions/240839/ess-power-not-balanced-in-parallell-multiplus-ii-s.html?childToView=259445#answer-259445

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