three phase unbalanced for multiplus 2

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groningen asked Jun 5, '24

three phase unbalanced for multiplus 2

Dear All

I am thinking to install three MP2 (5K) on a three phase line coming from the grid.

They supply the house that is used for accommodation units so each unit has it's own 230V supply between (L1/N) / (L2/N) & (L3/N). [NO three phase equipment on site]

My Question:

Will the MP2 be OK with an unbalanced load i.e. lets say two units are occupied but the third unit stays empty of 2 nights - later on all three is occupied, then only one etc. (and all possible options).

(NO Generator, just RS 450/100 "on roof" with -+ 25 kWh battery)

(GRID will still be there for "support" if SOC is low or draw is higher then .... )

(Main objective is to lower Grid cost - but the grid is not always reliable so hence for the time being - No PV-AC (fronius). Maybe later)

Any advise will be appreciated.

Multiplus-II 3 phase

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Duivert NL answered · Jun 05 at 11:09 AM

hi, what you are planning to do is perfectly possible, normal house dont have balanced loads either

you might want to take a look at the ESS and 3 phase manuals for more info:

https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/index-en.html

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sharpener answered · Jun 05 at 11:16 AM

As you do not need to maintain a 3-phase synchronous supply if grid fails, in principle you do not need a multiphase setup at all.

So 3 separate installations would be easier and less likely to share problems/faults across all 3 accomodation units than if they are linked.

But you do not have a choice if you are going to have them all sharing a common battery, you will have to have a proper master-slave 3-phase setup. This should cope OK with unbalanced loads though.

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Answer 1 · 2024-06-06T07:47:42Z

groningen answered · Jun 06 at 07:47 AM

@sharpener (or ..)

From what I can see, three 10 kwh batteries will cost more then two 15 kwh batteries.

But as you pointed out, the complexity would be less and might be beneficial as it would not affect the other units if something goes wrong.

What is your take on

- Three phase install with two 15kw batteries

- Or three separate installations with a battery (i.e.3)

Just food for thought on my side.

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Duivert NL commented · Jun 06 at 08:50 AM

three phase is cheaper in setup, 3 multis, battery, cerbo, but in case of problems the whole system can be off

3 separate will be more expensive 3 multis GX or 3 normal with 3 cerbo, 3 batterys, but the others will still run if one has an issue

both will work just fine with unbalanced loads

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Answer 2 · 2024-06-06T10:51:08Z

groningen answered · Jun 06 at 10:51 AM

@Duivert NL

Ja, ik vergat dat er 3 cerbos nodig zijn.

So indeed, three phase setup.

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Answer 3 · 2024-06-06T14:57:38Z

sharpener answered · Jun 06 at 02:57 PM

Just as well I can read a bit of Nederlands!

As @Duivert NL says you can use 3 x Multi II 5k GX, it works out a bit cheaper and is neater to install (I have one). Personally I would go for this.

Not sharing the one battery is an advantage in your scenario since the occupants of one unit can run their battery flat without affecting the other two.

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