Upgrade to 2x3 MultiPlus II 48V 3kVA 230V parallel - not running stable

Q&A and troubleshooting
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1

Dear community,

during the past years I designed and set up several Victron installations. Now I’m running into some problems for the first time after upgrading an existing installation.

After one year of operating a 6,8 kWp east-west roof array connected to a MPPT RS 450/100 with a 3-phase MultiPlus II 48V 3k 230V ESS and a DIY 15 kWh LFP Battery the decision was made to basically double up the system due to the planned installation of a heat pump and potentially an EVCS in the near future.

Unfortunately after installing the additional hardware and commissioning the system I ran into stability issues and the 6 MPs are not able to keep the Grid Setpoint stable at 0W.

The Master units are all Serial Numbers HQ2226 and have been the existing 3-phase setup. The Parallel Units are S/N HQ2143, HQ2152 and HQ2230 and have been running as a 3-phase ESS without any issues for 2 years in my house, before they were decommissioned due to an upgrade to 5k MPs. In the webinar on 3-phase and Parallel installations it is stated the age difference is supposed to be maximum one year - which is the case here. All 6 units were updated to FW v555.

The AC IN wiring is carried out in 3x1,5mm2 and matched to the exact same length of about 400 cm to a sub-distribution panel where all the devices are fused, combined and then run as 5x4mm2 to the main distribution board. AC OUT 1&2 are not connected at the moment.

The DC cabling (35mm2) is also length-matched for both the units on each phase.

I would maybe have the chance to swap the Parallel Units (HQ2143/2152/2230) to 3 ‘identical’ units of a 2238 manufacturing date, which is much closer to 2226 date of the Masters. But before doing so I would like to exclude any other potential problems within my setup.

Has anyone successfully setup a 2x3 phase parallel system and can provide a heads-up? Anything I’ve overlooked?

Below you find an image of the MP side of the installation, the MPPTs und batteries are on the backside of the same wall. 3 of the MPs are shut down because I have un-paralled the system again in order to get the ESS operational again.

Thanks in advance and best regards, Jochen

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2

I recently upgraded my system from 2x3 to 3x3 Multiplus and both configurations work fine.
What model of grid counter do you use ? I dont see one in your AC distributor.

3

Thanks for the reply and the link, will have a closer look shortly. What is the difference in age between your units?

The distribution box on my picture is just a sub-panel near the PV installation. In the main panel there is a EM24 connected via RS485 to USB interface to the cerbo.

BRGS Jochen

4

3x1,5mm2 is really small, could that be the isseu?

I would use at least 4mm2, mine are on 6mm2 however

But it all depends on local regulations

5

Best is to put them under load and use a clamp meter to check if they are all at least behaving the same for AC IN/OUT.
I have a node red flow that does this digitally as well.

6

Thanks for your reply!

In the document Parallel, split- and three-phase VE.Bus systems [Victron Energy] there is the following statement:

Warning against over-dimensioning the AC wiring

Note: Do not over-dimension the AC cabling. Using extra thick cabling has negative side effects.

Therefore I chose the minimum acceptable cable dimension according to German VDE regulation. One MP2 3k can provide 3kVA continuous which equals about 14A. 3x1,5mm2 is good up 17,5A acc. VDE if installed in conduit or trunking - so that’s what I went for.

In the sub-distribution panel the 6 3x1,5mm2 wiring from the 6 MP IIs is joined and runs in a 5x4mm2 to the main distribution panel.

What wire dimensions are other operators of 3k parallel installations using?

7

Thank you, I will do that and report back.

However during first power up with only about 1500W of load on the ESS and with a half-full battery and plenty of pv power the system was unable to keep the grid consumption at or around 0W as set in the ESS menu, instead about 5kW were immediately drawn from the grid as soon as the MPs went online.

Therefore I suspect some issue concerning power measuring / regulation.

8

Your peak power is much higher than 3kva, 5500W 23A

so i would suggest to use that for sizing of your cables

Regulations in NL are different from DE, to install 1,5mm2 with 23A would not be ok here :blush:

4mm2 would be the minimum here

9

So you say you have 3k parallel system running with 4mm2 cabling and no problems? I would happily go up one or two steps here but the above mentioned warning from the OEM kept me hesitating.

If you have done so I will give it a try once the system is running…

10

No i dont, my whole house is on 3phase single 3kva multiplus 2, hence the 6mm2

Just pointing out that i think that even with DE regulations your 1,5mm2 is too thin

Oversize is not ok, but undersize also :blush:

11

@ all:

In order to solve the problem I played a bit with the AI and although not extremely specific at one point I was asked if I had connected the Neutrals on the AC OUT side.

At the moment actually there isn’t any kind onf wiring on the AC OUT side - it is yet completely unconnected. Backup power will be the next step once feed in works. Therefore I didn’t yet wire up AC OUT.

Could this be the reason for my problems?

12

System should work without ac out loads,

but no wires at all wont work in parallel i think, they need to be connected to eacyt other on ac in and out, not only neutral, phases too

13

I will test it with AC OUT completely connected on Monday and report back…

14

The last 3 of my MP2-5k are 2 years younger than the other 6. They are all updated to same FW version.

AC connection is 3x4mmq to distributor 1,5m, then 30m using 5x16mmq to grid. Maximum grid feed in is limited to 30kVA as I dont have CTs for the grid counter.