I've got a weird problem here.
I've got a Multiplus 24|800|16, a Phoenix Inverter 24|1600 and a SmartSolar MPPT 100|50, all connected to the same battery. I've had the Multiplus in use as a glorified UPS, i.e. a plug on end and a power cord on the other to feed the TV and a few lights. It was not wall mounted at the time and the chassis was not earthed. This worked fine. Now I'm mounting it to the wall, fitting breakers etc. and adding a Phoenix inverter for extra inverter oomph and a SmartSolar to recharge the battery from a PV panel array.
The Multiplus is set to start recharging the battery from the mains when the clamping voltage drops to below a certain threshold (which is reached when there's no sun for several days). The MPPT is currently only connected to the battery and not to the PV panels, since the installation of the latter isn't quite complete yet.
Everything is connected to a common earth point. All units (Phoenix, Multiplus and SmartSolar) have their chassis earth connections wired to it, as well as the earth leads on the 230V outputs of the Phoenix and the Multiplus. This common earth point is connected to the house earth. There is no connection between neutral and earth on the 230V connections of the Phoenix and the Muliplus (since this should only be done at the mains entry point of the house, which it is). The settings for the Multiplus' earth relay are left at default (i.e. the relay connects the neutral of the AC output to the chassis while inverting but not while on mains).
Neither the Multiplus nor the Phoenix feeds back into the DB board; everything connected to the outputs is separate. Only the earth wires on the output sides are connected to the house earth (because otherwise I'd have a floating earth which offers no protection against electric shock in case of electrical faults).
The problem: the Multiplus begins to charge the battery, and after a while the earth leakage switch (a.k.a. RCD a.k.a. GFI a.k.a. GFCI, et cetera ad nauseam) on the house's main DB board trips. Sometimes it trips after a minute, sometimes after five or even ten minutes. Once it has tripped and I leave the Multiplus on, it trips again within a few seconds after resetting it. If I disconnect the Mulitplus from the mains before resetting the earth leakage switch it once again takes a while (1-5 minutes so far) before it trips again. When the Multiplus is in inverter mode everything is fine.
I have experimentally disconnected the common earth point to which all the Victron boxes are connected from the house earth, but this makes no difference.
I disconnected the load (three fridges) from the Phoenix (the Multiplus is still unloaded because I'm still busy with the installation) and that makes no difference, even unloaded it trips the earth leakage after a few minutes.
The earth leakage on the DB board is fine; it hasn't tripped for months.
What has me stumped is the variable time it takes for the Multiplus to trip the earth leakage. If there was a genuine earth fault or a wiring error, this would happen right away.
What could possibly be going on here???
// FvW
