Large load: 3-phase instantaneous water heater (3×20 A)
When the water heater starts, I sometimes get “Inverter overload on L1”, even though the grid is present and net current per phase stays below 25 A. However, the peak is 37A.
It seems this happens because sudden step loads pass through the inverter on AC-OUT, causing a brief inverter overload before grid current ramps up.
Question 1:
Is it considered best practice to connect large, non-essential step loads (water heater, sauna, EV charger) directly to AC-IN to avoid inverter overloads, accepting that they are not backed up during grid failure?
Question 2:
If such loads are connected to AC-IN, will the Victron ESS still offset their consumption using the battery (i.e. reduce net grid import / discharge the battery) when electricity prices are high and the battery SOC is sufficient, assuming feed-in/export is allowed?
Interested in how others design this in real ESS installations.
Hi i have a similar system and grid, large loads (ceramic cooking and oven 3x16a) are on ac in side, rest of the house is on ac out (incl. quooker, washing machine, dryer, AC, microwave, dishwasher, etc.) never had any problems
ess will compensate loads on ac in side but you will need a fast grid meter (em540 or v3mp) and i would recommend a energy meter on those loads
I have a em540 for grid, an et340 for ac in loads
However in a few weeks my heating wil be done by a heatpump and thats going te be supplied from ac out
(and for heatpump an et 340 and et 112 are going to be used, not necassary, but im going to use them on the gx for home assistant)
Hi Marc, thanks for your insights, your setup makes things clear for me..
With large loads on AC-IN, the measurement delay actually works in your favor. The step load goes directly to the grid, the MultiPlus is not in the current path and therefore does not have to absorb any peak. ESS can then calmly compensate (discharging the battery / reducing grid import) without any short inverter overload.
That delay only becomes an issue when the load is on AC-OUT. Your setup nicely demonstrates why AC-IN is the robust choice for large step loads in practice.
I don’t think the peak warnings are a problem at this stage. But I know what to do to get rid of them.
What battery do you have and what is its dcl?
Overloads when transitioning loads can also be an indication of an undersized battery which the inverter leans on despite it being grid attached and is the primary provider in an ESS.
