Two Multiplus in Three-Phase Grid with two batterie banks

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daniel-schenke asked Jan 30, '21

Two Multiplus in Three-Phase Grid with two batterie banks

Hi everyone,

Is it possible two use two Multiplus in a three phase system with a seperate battery bank for each Multiplus.

Each battery bank has its own BMS. And should be charged/discharged by its Multiplus individually.

I already have one Multiplus running in a solar setup with ESS and three phase energy meter on the grid. The Multiplus is connected to the Venus GX. It's connected to the first phase on the grid side.

Now I want to add another Multiplus with its own battery bank to have more capacity and redundancy. This shall be connected to the second grid phase.

Can I setup both Multis individually? Will the ESS take into account the two Multis for calculation of phase compensations?

Multiplus-II ESS Venus GX - VGX solar multiple inverters

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Paul B answered · Jan 30, 2021 at 10:35 AM

******* NO this is NOT recommended. *****

A 3 phase system must have 3 multiplus units and these have to be configure to ONE battery bank and setup as a 3 phase set being L1 L2 and L3 (L1 being master)

you then have to add 3 more at a time to increase capacity if needed. but always to the same battery bank. you can also increase the battery bank size at any time.

its done this way so that the ESS etc can be controlled fully especially if you have grid tie connected.

Now if you did do this, you can damage your down stream equipment and or the multis. as a example.

if you setup 2 multis with separate batteries only, on two phases which MAYBE possible. and these would then operate as single phase units, but would not be able to see each other and then when the mains did go down there 120 deg phase sync would drift out as well as there is no link to control this.

and another reason say the grid fails then down stream one 3 phase motor will suddenly only get two phases and thus burn out.

also you cant share the Venus unit each multi would need its own

there are also lots of other reasons for NOT doing it as well DONT DO IT

It is not recommended in any way shape or form

NOW if you dont have any 3 phase equipment AT ALL , then you could look to convert to single phase. then you could MAYBE parallel all the multis if they were all the same size etc

but one battery bank would be needed

and you could use the same venus

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marekp answered · Jan 30, 2021 at 01:25 PM

If you do not have any 3-Phase equipment, it is possible to have even 3 separate Multiplus units, each with is own battery.

BUT, it will not be 3-phase system.

You will have 3 separate 1-phase systems.

Also I do not thing one GX will be able to control such configuration.

You would need separate GX and 1-phase Power Meter for each MP channel.

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Modifications Space

Node Red Space

Answer 1 · 2021-01-30T12:38:15Z

daniel-schenke answered · Jan 30, 2021 at 12:38 PM

Hi Paul,

thank you for your quick response. Even though I would have liked to read something different.

I have found this thread in the forum which implies that it is possible to use two Multiplus in a similar setup (just without the solar on the DC side, but Solar on the grid side (3-Phase inverter):

https://community.victronenergy.com/questions/35012/2-x-multiplus-split-phase-setup-with-ess.html

Also in the "VE.Bus Quick Configure" Tool there is the option to setup a split phase system.

So, if I combine the two battery banks to one battery pack, have one Multi connected to L1 and one Multi to L2. This wouldn't work?

Let's say I have 7kW from my solar plant on the grid side. Each Multi should take 3kW to save this energy to the battery bank. This is not possible with one Venus GX and ESS?

If the grid power goes down, which is very very unusual in my region, it would be ok if the Multis shut down too.

Also there is nothing connected to the AC-OUT. I am just using the AC-IN on my firts Multiplus-II 3kW.

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daniel-schenke commented · Jan 30, 2021 at 01:00 PM

Quick schematic

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img-20210130-135830.jpg (2.2 MiB)

Answer 2 · 2021-01-30T14:32:44Z

daniel-schenke answered · Jan 30, 2021 at 02:32 PM

But I could setup two Multiplus in parallel on one phase, charging/discharging one battery bank with ESS?

Making sure that cable lengths on AC and DC are the same and selecting cable/fuses according to maximum power etc.

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marekp commented · Jan 30, 2021 at 02:37 PM

If you have the need for that much power on one phase you can connect them in parallel.

They would have to be identical in design and firmware.

Both Multis would have to be connected to the same battery.

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daniel-schenke marekp commented · Jan 30, 2021 at 04:13 PM

I guess the whole system then would be more vulnerable to faults. Also I barely need the extra power that comes with the second Multi. So I'll probably just go for extending the battery capacity by combining the two battery banks and keep the single MultiPlus. It's probably not worth the effort to setup two Multis in parallel.

And if I decide that I need more power in the future I may just change my MultiPlus to the 5kVA version.

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