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jonnyjnr avatar image
jonnyjnr asked

3 Phase system component help

Hi All,

I'm currently having a go at building my own off-grid 3 Phase system, I want to keep the option of grid use for random heavy 3 phase use (e.g. welder) but don't want to feedback to grid.

I'm not sure on the best configuration of panels, mppts (size), and if I need a BMS.

I’ve attached a schematic of what I think it should look but not sure if its correct.

Would love some expert help.

I currently have 3x Multiplus II 48v/5000/70
1x Cerbo GX and GX touch display
32x Trina 390w panels in an 4(strings) x 8 panels
7x Pylontech US3000c batteries in rack.

What size MPPT(s) do i need? Will 2x 250/100 be sufficient? or do i need bigger? BMS?
I do want the ability to add a further 5 batteries later. screen-shot-2022-06-14-at-84114-pm.png
Multiplus-IIMPPT Controllers3 phase
screen-shot-2022-06-14-at-84114-pm.png (510.3 KiB)
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2 Answers
nickdb avatar image
nickdb answered ·

A few things to consider, this forum is not meant for designing systems, this is best done with your seller/distie.

3-phase systems are complex and nuanced - "having a go" can lead to expensive mistakes and problems.

There are tons of docs on the subject which is the place to start, the community here can help but it isn't a short-cut or substitute for a professional installer.

Even the battery docs show you are way underspec for the size of the install - 10 modules are the recommended number for 15kVA of inverter.

If you want to save some money, pay someone to help - it is cheaper in the longer run.


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jonnyjnr avatar image
jonnyjnr answered ·

Thanks Nick,

Unfortunately the only local seller/installer is somewhat of a crook. He was marking up the components 100% of what i can buy online and then wanted $30k fee to install. in total he tried to charge me over $90k for it. I've contacted Victron Energy head office to ask for some guidance or another contact but after 1 call and 3 emails I've not yet got a response.

I was hopeful of some charitable assistance from the community or even willing to pay for some assistance with the design. I'm an aircraft engineer and understand the principles but green still and trying to work my way through to get the right result. Unfortunately it seems there is considerable arrogance in the space from those in the know.

All the best


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