Need a little help setting up first battery

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Bjorn Embrechts asked Feb 3, '21

Need a little help setting up first battery

Hi everyone,

I need some help planning some stuff...

I would like to set up (at leased) two 18S1P packs whit individual Bms's and parralel them to supply a 3f multiplus II 5000 System and monitor every cell.

I'm having trouble wrapping my head around this as this is my first large scale pack.

Do I need a BMS that talks victron, or can I just stand alone the packs and use the lynx shunt to measure the overal battery array... And tune the bulk, float, absorb settings.

I'm not sure what the pitfalls are, and hope you guys Can enlighten me sort of speek.

Projected materials:

- Daly Smart BMS (has CAN and UART, but don't think it speaks the same language)

- 36 x 280Ah lifepo4 cells devided in to two 18S packs

- Lynx shunt

- Lynx disributer

Lithium Battery BMS

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Answer 1 · 2021-02-05T09:57:03Z

Jesse answered · Feb 05, 2021 at 09:57 AM

I don't think the BMS needs to "talk victron". It simply balances the cells and disconnects the output when things are unsafe. Power off is a universal language!

Given it's an 18S2P system it would be worth considering for redundancy having two separate strings each with their own BMS, though I've also seen them simply wired together 2 parallel cells each in each link of the series.

Otherwise sounds like you're ready to go. I don't have any experience with the Lynx Shunt, looks like it's expecting a Venus device to talk to so you can control a relay using state of charge for instance? Not mandatory, properly configured the Multiplus shouldn't damage the battery but it could be hard to limit it to a 20% depth of discharge for instance.

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Bjorn Embrechts commented · Feb 05, 2021 at 10:44 AM

Hi Jesse, thanks for your insight on the matter.
I'm pretty new to this low voltage stuff but reading tons of forums you start reading about the dangers of using 2 different BMSs in parralel, forced charge from the other pack and stuff like that, and because the charge and discharge line is the same there is no real way of separating the 2 packs... because eventually they will always be discharging on the same potential wire to the inverters.

I would not mind trying it... doesn't make sens to buy 1 BMS anyway, might as well buy 2.
I read a post somewhere about the Daly BMSs (at leased some models) do talk to Victron via the USB-UART adapter, plugged in to a Pi with VenusOS or whatever its called.

For now I am tempted to go with the set and forget approuch to the battery, just wack an overkill BMS in there, with balancing, let it do its thing, and use a Shunt to keep track of the SOC ... somehow... it will probably take some tweaking to get it right by just trying it i guess, and i can experiment with the UART to USB thing to my Cerbo...
The Shunt connects to the Cerbo to so...
That's an other thing... how does Victron react to multiple batteries reporting SOC...

(Down the rabbit hole we go)

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Answer 2 · 2021-02-05T10:53:37Z

seb71 answered · Feb 05, 2021 at 10:53 AM

For a 48V (nominal) system, use 16 LiFePO4 cells in series, not 18.

Keep the other four cells as spares, if you already got them.

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seb71 commented · Feb 05, 2021 at 10:55 AM

Also, get a SmartShunt instead of a Lynx shunt. It's cheaper and does the same thing.

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seb71 commented · Feb 05, 2021 at 11:03 AM

You are also missing a GX device. So add a Cerbo GX to your list.

Charging only from the grid?

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Bjorn Embrechts seb71 commented · Feb 05, 2021 at 11:30 AM

Hi Seb, thanks for your reply,

I will use a Cerbo (all my victron stuff is on order)

I chose the Lynx Shunt because i also chose the Lynx distributor, given my OCD when it comes to clean wiring, this will help me sleep at night lol, it also holds the main battery fuse.

I opted for a 18S because of a tip someone gave me, it lets me get that extra voltage, lower current, less losses on DC side though probably negligible. but also extra capacity in the same "2 strings".
The Victron can take op to 66V but i don't plan on pushing it over 60 while charging.
The extra cell also allow me to lower the DOC and prolong the life of all the cells... at leased that's what i understand... it does limit my BMS choices significantly though...
I dont have the cells Yet, they take months to get here with chinees new-year and all.

I Ordered 150 x 280Ah LiFePo4 cells, 38 of those are reserved for my project, is any more people cancel there pre-order i do consider going 3 packs of 16S but i don't think i need that capacity (famous last words i know)

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seb71 Bjorn Embrechts commented · Feb 05, 2021 at 11:46 AM

60/18=3.333V maximum voltage cell.

This is somewhere in the middle of the charge curve for LiFePO4. You can't balance there.

Don't do this.

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Bjorn Embrechts seb71 commented · Feb 05, 2021 at 01:21 PM

Good point... Thanks!

18x3,65 is 65,7, close to the multiplus max but resting voltage should be lower right? or am i missing something?

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seb71 Bjorn Embrechts commented · Feb 05, 2021 at 01:44 PM

Don't get any cell above 3.6V either.

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Bjorn Embrechts seb71 commented · Feb 05, 2021 at 11:37 AM

Charging from Solar btw via AC

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seb71 Bjorn Embrechts commented · Feb 05, 2021 at 11:47 AM

Add at least a small PV array with a solar MPPT charger.

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Bjorn Embrechts seb71 commented · Feb 05, 2021 at 01:20 PM

I have a 9.3kW array on a 3Face inverter, i will be using the EM24 to balance my production with the charging.

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seb71 Bjorn Embrechts commented · Feb 05, 2021 at 01:44 PM

The purpose of that MPPT charger is as a fail safe in case grid is not available and the batteries got deeply discharged.

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