My inverter was installed for me to get everything tested before connecting the battery (the electrician changed my consumer unit at the same time). The inverter was happily running and I had done most of the configuration.
The electrician came back to disconnect the TNS Earth (as I had a TT Earth installed for island mode, and by chance grid TNS earth was poor) and change my main switch (in meter box to time delay RCD) - this work was all in the meter cabinet and 10m from any house wiring.
At some point in this process of disconnecting power (2 hours), my inverter is now tripping my 40A MCB that feeds the AC In. The battery is still not connected, and no load is currently connected to AC Out (however it was working ok with a load on AC Out previously). In Charger only mode, or normal mode, when the inverter turns on it causes a large spark in the 40A MCB and as a result it trips.
I have read on this forum that I need a battery connected, but I cannot understand why everything was working fine before? Nothing that changed would have an impact on the inverterā¦
I have also seen some people on the victron forums complain of this issue, but Im not clear what the solution is as there was no solution posted? (E.g. here - Multiplus 2 trips breaker - VictronEnergy with @mattfr)
Oh yes it has, you now have a new breaker, which may well be much more sensitive than the old breaker.
The Multiplus has a large bank of capacitors on the DC input. Without a battery installed, the first thing that happens when the Multiplus closes the input relay is a large inrush current charging these capacitors. Perhaps the old breaker allowed this inrush current through and the new one does not. Power it up with the battery first, ideally with a precharge circuit.
Its a 100mA Slow RCD on Grid input, and this has never triggered, the only thing that keeps tripping is the 40A MCB that feeds the AC In on the inverter (all RCBOs are downstream of inverter - but again even if I move the āessential loadsā to be grid provided the Multiplus still trips the MCB)
For the sake of providing some clarity to future users, when the battery is connected then everything works as predicted, with no blowing of my MCB.
I really think this should be mentioned more clearly in the manual as it really isnt mentioned, and to be honest it sounds like a fairly crucial requirement. Either way Iād love to know why the inverter behaviour changed, despite there being no attributable change in configuration/setup, but I guess it is unlikely Iāll get this.
Iāve also noticed this behaviour (itās always tripped the mcb with no battery connected for me). My issue with this behaviour is that when using lifepo4 batteries, should they go into low soc discharge protection then you are screwed, you canāt just connect to ac and have the Multiplus ii charge the batteries because it trips the MCB, even though the batteries are connected and need a charge to release them from protection mode. Its a pretty rubbish design flaw in my opinion!
The Multiplus should reconnect to the grid way before the batteries themselves disconnect.
And even if they donāt, Iāve ājumpstartedā systems with empty batteries by connecting the Multi to AC.
What you call ārubbish design flawā is actually a well documented user error being blame-shifted on the manufacturer.
If you have a grid, your system will connect to it in case the batteries run empty - unless you explicitly donāt allow it to, in which case the blame is on you and not on Victron.
If you donāt have a grid, itās clearly stated that you should install an MPPT to prevent a deadlock situation when batteries are empty.
The environment into which I have a Multiplus ii installed does not happen to have a permanent ac supply, itās a mobile installation and ac is available intermittently. I consider it a pretty rubbish design flaw for my specific application. I appreciate you may have a different view, to which youāre entitled.
I will admit that Iām in a grumpy mood at the moment and that this shows in my comments.
That doesnāt change the fact that if youāre running off-grid or with an unreliable grid, it still is well documented that you should install an MPPT, explicitly to avoid the deadlock situation where you canāt start the Multi from AC because the batteries are dead.
And Iāll state again that Iāve jumpstarted a Multiplus-II system with empty batteries (by connecting it to a generator).
Since this was a properly configured system, the Multi went into Low SoC Shutdown before the batteries themselves disconnected.
The Multi and GX were still powered by the batteries, only no AC Out was available.
As soon as AC was applied to the input, the Multi started recharging the batteries - all before the batteries themselves went into Low SoC shutdown.
So yes, I am being very grumpy in my reply, but it is clearly stated: if you manage to run your batteries down so far that you canāt reconnect to a grid connection, you will more than likely have put yourself in that position by ignoring design guides & requirements.