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

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.

parallel
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Alexander Ushakov avatar image

Here is the scheme


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