"Limit inverter power" in ESS – protecting GEL batteries

Q&A and troubleshooting DESS
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1

Hi everyone,

I’m about to switch from an off-grid system to a Victron-based setup. My current inverter allows me to protect my GEL batteries by limiting high discharge rates, which has worked well so far. In a couple of weeks I’ll be installing the Victron system, and I want to be sure I can achieve the same kind of battery protection.

Here is the hardware I will be using:

  • MultiPlus-II 48V 5 kVA
  • Cerbo GX
  • Two SmartSolar MPPT charge controllers
  • SmartShunt
  • GEL batteries, still in good condition (and I don’t want to replace them yet)

I’m planning to use ESS mode, and my goal is to configure the system as follows:

  • Limit the discharge from the GEL batteries to a maximum of 1000 W, in order to preserve their lifespan.
  • Allow full use of solar energy from the MPPTs to power loads.
  • If solar production is insufficient, the system should draw the difference from the grid (AC-in), not from the batteries beyond the defined limit.

I’ve read about the “Limit inverter power” setting, but I have some doubts before using it:

  • According to the documentation, it does not take into account the power coming from the MPPTs.
  • It only applies when AC-in is present.

I’m also aware of the “Limit discharge current” option, but it seems this only works with lithium batteries with BMS, and is not available for GEL batteries.

So my question is:
Is there a way to configure Victron to protect GEL batteries from discharging above 1000 W, while still allowing solar to power loads and using AC-in as a backup if needed?
Or perhaps some combination of settings (via ESS or GX) that can enforce this logic?

Thanks in advance for any technical guidance or shared experience.

2

Normally the batteries installed would be able to support the full discharge current of the inverter.
However, there are a couple of solutions to your problem:

  1. Set up the inverter such that it switches back to AC in, whenever the load power exceeds 1000W. This will not take into account any dc feed in from the MPPT’s.
  2. Set up a control system in node red on the cerbo which monitors the battery current, OR deducts the MPPT power from the inverter power, and sets the power from grid accordingly. This is a much more complicated set up.
    Neither solution would be able to limit the battery current in the event of a mains failure, where the batteries would need to support the full load.