3 phase 10kw Multiplus II’s running a voltage sensitive data server and computers. Grid backup has variable voltage and frequency characteristics, so I want to run the server continually off the inverters and battery, but keep the batteries charged with the grid when it is available.
Is this possible without a separate charger under ESS. The ESS manual has this pretty poor explanation I think of what I am trying to do
Can someone explain this to me please
Not possible, all multiplus and quattro inverters need to close their relays to connect to the grid, connecting the AC input with the AC output.
When a multiplus or quattro is connected to the grid system frequency=grid frequency.
This also applies without ESS.
With the architecture of a MultiPlus-II, when there is an AC input connected, it directly switches through to the output (so in your case, the inverter runs parallel to the grid). So the AC Output voltage and frequency will follow the input until the grid input is disconnected for some reason.
So there’s this diagram in the MultiPlus-II manual:
And, relevant to your question, this diagram in the ESS guide - note the loads on the input side of the MultiPlus-II:
https://www.victronenergy.com/media/pg/Energy_Storage_System/en/ess-introduction—features.html
You can make the requirements for connecting (and disconnecting) the grid quite stringent, but unlike some UPS designs, the charger and inverter are both on the same AC bus. So if your grid is really flaky, and your power supply quality requirements are really stringent, this will be a factor.
You don’t say whether you are thinking about other sources of charging (eg: solar) but the ESS can do “UPS” with “keep batteries charged” mode, or scheduled charging etc…. keeping in mind that the power for the loads has to come from somewhere. So the discharging of the batteries, because the grid has been disconnected, needs to be balanced with a load that doesn’t outrun the grid input power required to run the load and charge the batteries.
Critical loads are connected to AC out. All system loads include loads measured on the grid meter. The ESS will charge the battery if the grid is negative and if it’s positive, export to offset the loads. This is what an ESS system looks like with excess grid-tied solar export and battery charging. The AC loads are the critical loads. If you have only critical loads selected, it will ignore the loads on the grid.
