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khachatur avatar image
khachatur asked

Off-grid system design with a custom battery

Hi Community,

I am designing a three phase 400VAC off-grid system with custom designed battery pack, PV and Wind.

Could you please help me with the questions I have?

Below are the details of the system.

Battery pack:
custom made Li-ion NCA, 75kWh, 10x 12s53p modules, 43.2V nominal voltage, LiBalance n-BMS

PV setup:
20.8kWp, 64 Heckert SolarNemo 2.0 60M 325Wp panels, 40.94Voc per panel, 16 strings with 4 panels in series, 4 Victron Smart Solar MPPT 250/85 - MC4 VE.Can

Wind setup:
BWind 6kW wind turbine, Kostal Piko 4.2 & Kostal Piko 2.5 single phase inverters

Loads:
single phase loads distributed between three phases, max 15kWp load

Questions:
Will the already installed MPPT chargers be able to properly charge the battery pack (voltage and power)?
Will the Victron GX be able to communicate with the LiBalance n-BMS?
Is there communication needed between the BMS and Victron GX?
What Victron inverters should be used for creating the three phase system?

Thank you in advance.

ESSoffgridsystem design
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2 Answers
shaneyake avatar image
shaneyake answered ·

You really don't want to run 12S NCA batteries.
12 x 3V = 36V All the Victron inverters can't run below 38V and really would prefer 40V.
So the lowest you will be able to go is 3.16V per cell which is probably okay but 13 or 14S would be much better if you can do it. The inverters and MPPT can go to 60V/66V so 14S is totally fine.

I personally would use 2x RS 450/200 MPPTs so you can run 8 strings of 8 panels, each with there own tracker. String would be at 328V and less than 10A which makes cabling easy. It would also give you the full 20kw.

4x 250/85 MPPT should be fine, I would use the victron calculator to just confirm everything is safe.
Voltage and current on the output side is fine but will be limited to 14.6kw at 12S and 17kw at 14S.

I don't know the LiBalance n-BMS, can you setup custom CAN messages with battery parameters? If so then it will work with the GX if not then no. I prefer https://www.orionbms.com/ BMS and they work very well with the GX. I would look into them.

The short answer is No, you don't need communication with BMS and GX but it is very helpful to have communication, especially with custom battery as you can monitor cell voltages and temperature on VRM. It also limits bus voltage if a cell needs extra time to balance.

If you have no grid then 3x Multiplus-II 5kva if you have grid and generator Quattro-II 5kva.
If you need more power then 4x Multiplus-II 5kva, 2x inverter on one phase and more some more load to that phase.

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khachatur avatar image khachatur commented ·

Hi @shaneyake ,


Thanks for your response and for the advice.

I would definitely prefer to use 13s or 14s configuration. However, the battery pack has been already assembled.

Regarding the choice of the solar charge controllers, the project client already has 4x 250/85 installed from a previous project. The output charging power of the charge controllers will be 4x85x4.1x12 = 16.7 kW. Taking into account the weather here, the PV output will rarely reach 20 kW. If the client is okay with getting new charge controllers I will go for changing it and using the full PV power.

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nickdb avatar image nickdb ♦♦ khachatur commented ·
Make sure the client understands that unsupported batteries means no support for the system from victron/supplier. So if it doesn't work as planned, you are on your own.

The reality is that most problem systems originate from non-standard components where people have bitten off more than they can chew.

It helps to have really good product knowledge. Not knowing the Victron ecosystem well, and getting creative with the battery/bms is rarely a recipe for success.


2 Likes 2 ·
khachatur avatar image khachatur nickdb ♦♦ commented ·
Thanks @nickdb,

I am new at Victron Ecosystem and I am currently waiting for the local distributor to get back to me to have a call to discuss the best solution for the client's system.

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nickdb avatar image nickdb ♦♦ khachatur commented ·
Great, nothing avoids problems like proper planning and understanding potential challenges. Good luck!
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khachatur avatar image khachatur commented ·

Hi @shaneyake,


Do you know if there is a list of CAN messages needed for the correct communication between the BMS and Victron system?


Thanks.

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klim8skeptic avatar image
klim8skeptic answered ·

@Khachatur Have a look at the Tesla battery threads.

That will give you an idea as to what problems and solutions people have with 12 series batteries.

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