strix avatar image
strix asked

Check: the difference between AC-out-2 and AC-in

Hi, I am just starting out with Victron, and want to ensure that I have understood the Multiplus II's AC logic correctly (specifically, in ESS mode).

It's clear enough from documentation that AC-out-1 is protected by the battery and always live (provided no fault condition), and AC-out-2 is only energised when power is present on AC-in. I also gather from Appendix B of the manual that the transfer relay is normally closed when AC-in is live and that, to the MP2, there is no difference between loads on AC-out-1 and AC-out-2.

Appendix B also shows that current is measured at two points: directly at the inverter output, and at AC-in. Between them, so far as I can work out, they allow the MP2 to detect and prevent overload conditions on the inverter, to implement PowerControl, and anyway to limit current drawn on AC-in by the charger according to something less than the breaker supplying AC-in. PowerAssist is implemented by means of an ET112.

That all seems fairly straight forward. (Have I missed anything?)

Does it matter if there are loads, possibly quite large loads (oven, 3kW kettle, 2kW AC etc) between the ET112 and AC-in, or do they have to be connected to AC-out-2? In an ESS situation, do I ever need to use AC-out-2 for any purpose?

It seems not, so far as I understand it. Their current draw will still be seen via the ET112 and, because AC-in, AC-out-1 and AC-out-2 are all directly coupled via relays, even loads upstream of the inverter will benefit from PowerAssist (so long as grid power is present, of course). This is also why PV inverters can be installed in parallel with any of the AC ports on the MP2: everything is galvanically connected when grid power is present.

The one difference I can see is that PowerControl likely won't work if I do not have my non-essential loads wired into AC-out-2, because it probably does not look at the ET112 for the current draw of upstream loads. But I also don't see how that matters in a situation where it is impossible, or else very unlikely that even with the MP2's charger drawing as much current as it can, that total load could exceed cutout/service fuse rating (or that of respective RCBOs').

In which case, when I install this thing, I have a bit more freedom as to where to install the MP2. I need only divide my consumer unit into two, install two runs of 10mm² (good enough for 50A) from the consumer unit to AC-in and back from AC-out-1 to the consumer unit to power protected half.

Have I understood all this correctly? Thanks.

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Alexandra avatar image
Alexandra answered ·


I use ESS without any metering.

Power control works. Power control is the inverter's ability to not draw too much from grid for higher loads or for loads and charging from grid - so will stop charging the battery if your loads use the whole input current limit and solar is not aiding it.

Solar provides power for both AC outputs.

And the AC2 can be programmed to switch off any non essential loads under a certain battery percentage, but its default state is off when there is no grid. And back on a above it so it uses mainly solar and we do cycle the batteries a bit every day. It can also be programmed to stay on if grid remains available but i dont want that.

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strix avatar image strix commented ·

Right, I read in the ESS Manual that the external meter is optional (although I think my supplier has configured my unit to expect one). Also that yes, you can reserve a proportion of battery for loss of grid conditions.

(I don't yet have solar, but that will come when I can afford it.)

But power control is the wrong end of the question I asked, namely whether the MP2 requires all other loads to be downstream of either of AC-out-1 or AC-out-2, or whether it is quite happy for some loads to be drawing power from between the ET112 meter and the MP2 itself, provided I don't care that the charger won't adapt to other loads (since it doesn't matter if it doesn't).

I think it should be fine because the three AC terminals are galvanically coupled when the transfer relay is closed, but I wanted to check that I have understood this correctly before I proceed.

Thanks for the reply!

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