I have 20kw of battery 48v, 6000w of solar 5000va Solar Fronius Primo inverter (only solar charger) and a 5000va Multiplus 2. - Offgrid
Normally it works fine the Multiplus throttles the output of the Fronius as the battery fills. The issue is when the battery is full (56.8v for my system,) and the base load is about 1000w, the PV has been throttled to keep the output matching the load. But if I turn the kettle on 2100w, all is good for the duration of the kettle heating, the Multi releases the brakes on the Fronius and it comes up to supply the kettle and home around 3100w. The kettle then goes instant off when its done, the Multi now has to deal with the excess 2100w and it pushes a little into the battery before ramping the Hz to pull back the Fronius output. In this moment in time one or two of the RCD's trip on the output side of the multi(physically 20m away by 10mm sq cable), generally the kitchen RCD, which also does the garage and office, so we loose internet / aka view into the system.
I don't see that its a Factor 1 rule (I may have it wrong) as the two inverters are the same size at 5000Va, and at the point in time when the kettle goes off the load on the Fronius is generally running around the 3000w to 3500w load mark(slightly throttled already), and the multi is rated to 4000w continuous at this time of year of 20 to 25 degree temps. We also have an electric on bench oven and an air fryer all around similar watts, all three have the same issue so I don't think its a kettle issue.
It doesn't seem to happen if the battery is in a lower state of charge 90% or less. The batteries are set to stop taking charge at 58v on the BMS so there is a little head room. I have tried lowering the max charge voltage to 55 in the Multi and it doesn't seem to make any difference.
