Alexander Ushakov avatar image

2 Multis in Parallel

My system:

2 x MultiPlus 48/5000/70-100

8 x Delta Gel Batteries GX12-200 (12V, 200 Ah)

48 x 150W Solar panels

2 x BlueSolar MPPT 150/70-Tr/MC4

Color Control GX

My problem: 2 parallel units from time to time a few times a day switch to inverting without any reasons all of a sudden and sometimes are overloaded, when the real load is 2kW only – that’s what I call “moments of instability”.

I have unstable weak AC input (house is in village with rather weak transformer, which cannot quickly sustain stable voltage when someone switches on high load more than 2kW).

When I had only one Multiplus and updated it with the latest firmware 3 years ago, it started working excellently without overloading itself and without switching to inverting every time I switched high load. It worked perfectly until I had to upgrade the system and installed the 2nd Multiplus in parallel last year. Even now when I experiment and use only one Multiplus after programming it to standalone mode, it works perfectly. But when I use 2 units in parallel – my system keeps on switching to inverting – not all the time, but from time to time. And in these moments of instability I sometimes see that power, taken from my batteries, reaches 6kW – that’s what at least shortly indicated on CCGX and in reality it can be much more. This is crucial for my batteries and 2 out of 8 are dead by now. Yesterday I checked voltage on each battery under 1kW load: 2 indicated 10 V, others – 12.1V. So, I am prone to think that instable parallel work of Multiplus units caused death of batteries, since they are not intended to work in mode of sudden short and relatively high load, which all of a sudden occurs during these moments of instability.

I carefully read everything written here:

My system is up to date, all AC wires between Multiplus units and joint point are equal in size (2.5 mm^2) and length (750 mm) – yesterday I replaced 6 mm^2 wires with 2.5 mm^2 , trying to avoid over-dimensioning , but it did not have any result.

Dear Victron team – please admit that parallel systems were not supposed to work with weak AC input and I should replace my 2 Multis with one Quattro for 10 or 15kVA. I do not know what else I could do - everytime I wait for the new firmware with hope that it will solve my issue with parallel units as it did 3 years ago for stand alone unit, but all the last firmware files, including 2624473.vff, make no difference.

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3 Answers
Alexander Ushakov avatar image
Alexander Ushakov answered ·

Here is the scheme

1586683035711.png (6.3 MiB)
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tnt369 avatar image
tnt369 answered ·

Seems that i have the same problem. How did you solve the problem?

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No how. I had to replace all my batteries to new ones: 24 pieces of 2 volt SONNENSCHEIN A602 SOLAR 8 OPZV 1130 Ah. And I replaced 2 MultiPlus 48/5000/70-100 with one Quattro 15kW. That's it. It started working better.

I forgot t omention one very important thing - even when I replaced 2 Miltis with 1 Quattro it did not help. But hte problem was solved right after I disable LOM detection. Try this and it wil really help you diminish your problem.
tnt369 avatar image tnt369 Alexander Ushakov ·
Thank you very much. I am still working on this problem an did several things (quattros in serial, only 1 ac in ...). Nothing solves the problem.

Disabling the LOM will be my next try. But for this i need the Grid-Password. I am waiting for my supplier who will give me. But he is slow... Waiting now for more than a week for his response...

Did you install a external "Anti islanding protection" system instead of the internal LOM function?

Greetings from Spain


No, I did not.

[Moderator edit: the grid code is not supposed to be public]

tnt369 avatar image tnt369 Alexander Ushakov ·
Thanks a lot! Now you have a friend here in Spain! If you are ever here in Alicante let´s go for a beer or so!

Buddy, I am from Russia. I wish I could go to Austria or at least Andorra this year for skiing, but Europe is closed for us since our vacine is not approved there. So, if you are ever in RF, you're welcome to test our winter frost:

tnt369 avatar image tnt369 Alexander Ushakov ·
Thanks again for your help! Switched of the LOM detection and my system works stable now for three days. Problem solved!

Be careful - now life of outside electricians is partly in your hands. When they switch off power supply in order to do maintenance with equipment, your invertor may accidently deliver lethal electro power to outside grid. I would recommend to switch off grid feed-in in ESS and/or make an inscription near the main switch of your house/block to let them know that wires may still be powered.

tnt369 avatar image tnt369 Alexander Ushakov ·

I will install a "anti islanding box" with a ZIEHL UFR1001E unit. The system then complies with the local regulations and is safe.

If you install it, the problem will return. Please don't forget to tell me the results of this experiment.
Sander van Noort avatar image
Sander van Noort answered ·

Hello Alexander,

if you ask me the 400Ah Batterybank was way too small for 2 Multiplus 5000VA.
Always have a look at the battery specs how much Amp you are allowed to charge / discharge.
I have a 48v/400Ah/c5 Lead Acid OPz and am allowed only 75A cont. discharge,
so around 3600 Watt on the DC side! (ca. 3200 Watt on the AC side)
The same with charging, if the batteries are too small the Bulk phase is too short with too much
Amps beeing charged.
I have 2 Multiplus I 48/3000/50, and did not run into any troubles, but only use upto 5000W
at day, at night only 3000W.

Don't save on the Batterybank, or you will buy twice, and the second one has more Ah.


Sander van Noort

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