Here are outcomes of the measurement:
Inverter before fridge turning on: 13.25 V
Inverter during fridge turning on: dropped to 9.8 or so for a brief moment, then climbed back to 13.25 (Inverter went on error)
Battery before fridge turning on: 13.2 V
Battery during fridge turning on: 12.4 or so for a brief moment, then climbed back to 13.2 V
So, there is a bad connection on 12V DC line between the battery and the inverter.
I would suggest you reading Wiring Unlimited.
Thanks Eric. As the fridge worked perfectly beforehand, with the very same wiring, I would assume the length and the size of the wires is not the root cause.
I will check again if there are any loose connections… And based on the wiring diagram that I will receive, we will see if there are any devices in between the battery and the inverter…
You need to determine why you have a 2.6V drop between the battery and the inverter during turn on. Loose connection, poor breaker or switch contact. What length of wire and gauge of wire is used.
Start a load on the inverter that it can sustain, say 400 to 500W. Then with your multimeter check from battery + to inverter + and then from battery - to inverter -. These should be close to 0V, but one may be high. Then check from battery + to each connection on the + wiring looking for a large change in voltage. Then do t he same from battery - to the negative wiring connections. The above procedure will highlight where the highest voltage drop is.
You could reduce the low voltage setting on the inverter but that just hides the issue rather than solving it.
Thanks! I agree, let’s find the root cause! I will do the measurements and let you know the outcome.
elektra-schemav1.1_RAFfi.pdf (194,7 kB)
Hi Guys, I have received the wiring diagram, please see attached in pdf. Let me know if you see anything suspicious 
But in the meantime, the fridge started to work again, as before. So I guess there is a loose connection somewhere between the inverter and the battery…
Standard type set up, nothing that should cause your problems as long as your domestic battery is getting fully charged.
Small note: There is no RCD.
There is only a two-pole fuse at the input.
But that’s not the problem.
Have you measured the voltages where it breaks down?
Thanks Dirk! No, I haven’t made the measurements, but currently the fridge is working fine from the battery. Also, my access to the camper is limited as unfortunately I had to put it to a storage (in the Netherlands you cannot park your camper on the street for more than 3 days 
).
I have attached a screenshot of the voltage when I turned on the fridge last time (and was working fine).
I am not an expert but the lack of RCD seems like something I should solve do I need to install an RCD between the shore power input and the two-pole fuse? What kind/size of RCD will be needed? Thanks
I would place the RCD at the output of the transfer switch, so that the RCD protects all AC loads, unless they are powered from land line or from the DC/AC inverter. Normal 30mA RCD from the hardware store.
Thanks Dirk! We are not using the white internal socket at all, that’s why I thought the RCD should be after the shore power connection (marked with red)?
Another question please: the storage owner requested to turn off completely the electrical system of the camper (with the yellow main switch for the leisure system + the ignition battery). Would this cause any issues for the household battery, or any of the devices (inverter, solar charger, etc.)? I am still planning to use the car like every 2 months also during winter time.
Thanks!
Hi Guys, can you please give me feedback, especially about switching off the entire system for a longer stalling period? Thx
