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wheeto avatar image
wheeto asked

Basic MultiPlusII question

Hello,


I've recently moved home and inherited a solar setup on the UK's Feed In Tariff, which I'm reluctant to interfere with for the time being.


My question is whether I can use a MultiPlusII as in the diagram below, to 1) charge a battery bank rather than feed in to the grid, 2) use battery charge overnight (less solar than demand) down to a pre-set battery charge (20%?) and 3) keep a small load (fridge) running in the event of grid loss?


I understand that in the event of grid loss, the inverter will anti-island shut down so the batteries won't be charged even on a sunny day.


My main point of confusion is that the MultiPlusII's AC connections are labelled as outputs (I understand the difference between O1 and O2) and input - so I'm not clear whether the MPII can actually output energy through the terminal labelled Input when the batteries are sufficiently charged, and demand exceeds supply.


basicbatterystore.png



I'm a programmer by trade who has previously worked on embedded systems, so I hope to expand and augment the setup I've drawn above (with demand shifting, and using PowerAssist with a generator for offline use), but I want to check I'm not completely barking up the wrong tree to start with, expecting power to be Output from the Input terminals!

Many thanks!

Multiplus-II
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3 Answers
wkirby avatar image
wkirby answered ·
Yes, in ESS mode it does output energy via AC-IN terminal.

The terminals are labeled in and out for standard operation when not in a grid interactive (ESS) mode.

Also, as my previous comment, the 5kVA MultiPlus II is certified for UK grid connection (G99).

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ludo avatar image
ludo answered ·

At the moment the mpii is not certified for uk,

And, a fridge is not a "small" load.


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wkirby avatar image wkirby ♦♦ commented ·

The MultiPlus II is certified for UK use.

Check out the certificates section, the units have passed the new certification ammendments.
https://www.victronenergy.com/upload/documents/Certificate-ESS-G98-1-all-MultiPlus-II-(GX).pdf
https://www.victronenergy.com/upload/documents/Certificate-ESS-G99-1-2021-Multiplus-II-48V-3K(GX)-48V-5K(GX)-24V-3K(GX).pdf

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wheeto avatar image wheeto wkirby ♦♦ commented ·
That's great! Was the first poster right about specific sizing guidelines for fridges on the MPII, or will I actually be OK as planed?
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wheeto avatar image wheeto commented ·

Thanks for your reply!


The fridge is plated at 400VA, which I consider as small for an inverter rated at 5000VA. Even allowing for inrush currents, would you disagree?


Do Victron share their roadmaps, re UK grid tie certification?


Also, aside from the certification matter at the moment and to just answer the question, can the MPII "output" power via its "input" terminals?

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ludo avatar image ludo wheeto commented ·
400va is not small for the inverter, but maybe for the battery
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Kevin Windrem avatar image
Kevin Windrem answered ·

If the grid is lost the AC input to the Multi disconnects so your PV array will also shut down. It would be possible to move your array to the output of the Multi assuming it's output power can be controlled via frequency shift. That way you benefit from solar to feed loads or charge your battery bank even with a grid failure.

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wheeto avatar image wheeto commented ·
Hello Kevin,


I had seen that as an option, but power failures here are rare, and then particularly power failures in bright summer sun such an "edge" case that I wasn't going to worry about firmware upgrades and compatibility (it's quite an old inverter).


I appreciate the comment though, thanks.

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sharpener avatar image sharpener wheeto commented ·

Take heart, I did this with 11 y.o. inverters (Steca) and it worked no problem, no updates required or anything.

It can help avoid the need for an external CT, if everything is on the AC-Out the one in the Multi is then sufficient.

But either way you will need an ET112 meter or similar between the FIT meter and the CU or the solar PV will not show up correctly on the displays.

Fridge should be fine, I have fridge and freezer on a 5k, you can see them cycling on and off below, some quite big spikes when the motors start, but no issues

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