pracman avatar image
pracman asked

Changing and Discharge from solar PV and Batteries in ESS- ZCells batteries

Love to be able to have ESS able to prioritizes discharge from one battery over another at a high rate - Use it at maximum power drain possible until zero SOC as quickly as possible.

I have 2 Zcells and 2 Multi-plus Inverters solar PV and Grid. My primary goal is for solar and batteries as a UPS for my on grid business. That's why I have 2 Victron Inverters now.

Currently discharge happens often to both batteries. Zcells need a full discharge to 0% SOC every 3 days. While Zcell has a device Extractor which saves a little power to the battery not in maintenance It slows the discharge process. A slow discharge rate means a battery is in maintenance cycle for a lot longer than desirable for a U.P.S.. Usual setting in ESS restrict the rapid discharge of the single battery in maintenance cycle

I want also to avoid discharging any PV until battery(ies) not in maintenance are fully charged.


  1. Discharge single battery in maintenance cycle to 0% SOC as quickly as possible for self counsumption or to the Grid
  2. Ensure other battery is not discharging and is 100% SOC while other battery is in maintenance
  3. Ensure Solar PV charges battery to 100% before discharging PV to grid (noting goal 1 as a priority)

Zcell are working on BMS side for me 'UPS mode 'and other Zcell users. Note RFX staff and executive are very helpful and approachable.

Happy to pay for this. If you can and have a freelancer or similar or quote directly for scripting as suggested to " Changing solar priority in ESS" by "Potgieter"

by Guy Stewart in this thread

Thanks. Not comfortable scripting this myself

ESSsolarRedFlow ZCell Flow Battery
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Simon Hackett avatar image Simon Hackett commented ·

That's actually quite straightforward to achieve with existing BMS settings and tools.

1) Enable the "Battery Optimiser' in the BMS - turn it on and set it to discharge one battery at a time (standard function of that optimiser)

2) If you want to actively accelerate the resulting discharge rate you can either put the ESS system back into its normal operating mode with ZCells [ Optimized (without battery life) ] and let the battery discharge into the local load (preferable) or (if necessary) you can set a negative grid setpoint to ensure that the system actively discharges the battery into the grid.

Step (2) can be achieved with the built-in "Digital I/O' rules engine in the BMS, which can send MODBUS-TCP commands to the CCGX at the appropriate points (i.e. when the battery starts its pre-maintenance cycle discharge).

We can help you with the specifics of this directly (via - as there are a number of other questions to ask about your setup before working out which of the approaches noted under item 2 above is best for your situation (i.e. switching the ESS operating mode vs merely changing the grid setpoint - but both can be changed with MODBUS-TCP commands, and those can be triggered at the perfect spots by the BMS's built in rules engine - that's the point).

i.e. no actual programming needed - just a little bit of careful configuration work in the BMS. I can help you with that directly (via

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pracman avatar image pracman Simon Hackett commented ·

Thank you.

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1 Answer
pracman avatar image
pracman answered ·

Having error appear on the system "VE.Bus Error: VE.Bus Error 11: Relay test fault"

I assume fault is hardware or software on one of my two Multi plus in master slave configuration.


1. Used power switch on Victrons.

a. Master Position 1 and Slave unit Off- shuts both down as expected 10:30

b. Master Position 1 and Slave unit Position 1- Grid relay fault as expected 10:31

c. Master Position 1 and Slave unit Position 2 10:35

i. Master “Mains” solid green light and “Bulk” solid amber light.

ii. Slave “Mains” flashing green “Inverter on” flashing green

1. 11:02 no change- One battery in maintenance discharging and one charging

2. 11:45 no change

a. Master Position 2 and Slave unit Position 1 at 11:50

i. Master “Mains” solid green light and “Bulk” solid amber light.

ii. Slave “Mains” flashing green “Inverter on” flashing green


Noted -Batteries behaved well in all positions except where the error "VE.Bus Error: VE.Bus Error 11: Relay test fault" caused victrons to disconnect from the Grid of course.

Questions to the Brains Trust. As error ""VE.Bus Error: VE.Bus Error 11: Relay test fault" seems eliminated by this test can I assume a hardware or a software error on the slave or master Multi plus?

FYI I am adding additional capacitors to both my Multi plus 2 48-500-70-50 and also a Automatic Transfer switch to my on grid set up with is principally a UPS. Also arranging a electrician to double check all wiring to eliminate this as a issue. This is as an addition insurance for my UPS which was helpfully suggested by my battery provider. Have a great weekend all

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