question

OxyFly avatar image
OxyFly asked

OffGrid - Battery bank upgrade

Hello everyone.

I'm looking for adding more battery capacity on my off-grid system

Right now, i have the following system working 24/7.

  • MultiPlus-II 48/5000/70-48 – v475
  • BlueSolar Charger MPPT 150/60 rev2 – v3.13
  • Cerbo GX - v3.10~7
  • 2 x Pylontech US2000 Plus 48V (2,4 kw/h)
  • 2S+2S+2S
    1. 2x Q.Cells Q.PEAK DUO XL-G9.3-455
      • Vmp – 44.61V ,Imp – 10.20A, Voc – 53.22V, Isc – 10.67A
    2. 2x Q.Cells Q.PEAK DUO XL-G9.3-455
      • Vmp – 44.61V ,Imp – 10.20A, Voc – 53.22V, Isc – 10.67A
    3. 2 x DMEGC 455w Half Cell Mono
      • Vmp – 41.04V ,Imp – 11.10A, Voc – 50.42V, Isc – 11.51A

This system is working without a glitch 24/7 for the pass year and i added the last 2 DMEGC panels to max out the MPPT a couple of months ago and now i reach 2400/2500w.

On the battery side during the night the SOC% stays above 85% but now i want to plug some sensors a small fridge and a couple of lights and i don’t want my SOC% to drop below the 60%.

So my idea is to add more capacity to the battery bank now im not sure if i sould buy Pylontech US5000C (4,8 kw/h) or 2 x US2000C (2,4 kw/h)

From what i read they are all compatible and i just need to make sure to put the newest as Master and that i have to charge all of them at the same % before connect them together.

Price wise its cheaper to buy 1 US5000C, but the difference is not a deal breaker.

My major concern is that Victron recommends 4 modules for the 48/5000 Multiplus but when i bought the Kit i didn’t knew that...

So what do you guys think is better for the overall quality and durability of the system?

Cheers for all the opinions.

Pylontechoffgridbattery capacity
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4 Answers
dayandnight avatar image
dayandnight answered ·

Hello @OxyFly ,

I recommend to go for same type of batteries. I have a Pylontech Stack with 2 x 7 pieces US2000 (mixture of type B and type C) and one Pylontech HUB. All batteries behave very well and they are fully balanced to each other. I think, but this is only based on a feeling, neither knowledge nor practice that to mix batteries with different capacities and different maximum current isn't a good idea. Mainly I would see problems to manage a perfect DC wiring when mixing different types of Pylontech batteries.

Servus - DayAndNight - Ewald

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mvas avatar image
mvas answered ·

You wrote ...

On the battery side during the night the SOC% stays above 85% but now i want to plug some sensors a small fridge and a couple of lights and i do not want my SOC% to drop below the 60%.

So then if you connect the new loads and SOC stays above 60% then you need to change nothing?

My major concern is that Victron recommends 4 modules for the 48/5000 Multiplus but when i bought the Kit i didn’t knew that...

What is " ... 4 modules ... " ? 

and that i have to charge all of them at the same % before connect them together.

Technically, you charge all the batteries to the same measured voltage ( not necessarily the same % SOC ) before connecting parallel.

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dayandnight avatar image dayandnight commented ·

Hello @mvas

What is " ... 4 modules ... " ?

This is based on the Victron/Pylontech documentation.

Servus - DayAndNight - Ewald

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Mike Dorsett avatar image Mike Dorsett commented ·
4 modules of the US200 battery, ths is so the battery can supply the max peak current for the inverter, without exceeding the battery module max current. This is important if you are adding a fridge to the system, as the compressor starting current tends to be high.

I would stick with the same module type, rather than adding a 5000c


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OxyFly avatar image
OxyFly answered ·

Thank's for the reply's.


@mvas right now during the night im using 12 % to 15% because i turn off all the apliances and sensores. I did some tests and if i leave everything plug on, my SOC% will drop below 60% thats why i want to get more battery's.


@DayAndNight from what i reading,i totaly agree with you. Adding 2 more modules of US2000C its the easy/safest way to go.

But is it the best option in for long term solution, future upgrades?

You wrote that you have a "Pylontech HUB" do i need one?


Cheers


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Alexandra avatar image Alexandra ♦ commented ·

@OxyFly

Do you have US2000 or 2000c?

2000 can be used uo to 8 modules in a stack, 2000c is 16 units.

And they can be mixed with other modules.

FYI the 5kVa MP2 needs a bank that can supply 120A nominal. You are fairly short of that (min sizing has nothing to do with load size or night energy needs).

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OxyFly avatar image OxyFly Alexandra ♦ commented ·
Hi, @Alexandra .


Can you explain a litle more on the MP2 needs.

Keep in mind im just a guy that bought a pre-build kit and is learning is way arround :)

:)

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Alexandra avatar image Alexandra ♦ OxyFly commented ·

@OxyFly

The US2000 pylontec can supply a nominal current of 25A. You have 2, that is 50A. The MP2 5kva needs (5000÷48v) 105 Amps min nominal. So 4 absolute minimum US2000 pylons. (I would prefer 5). I use the word nominal as they can peak higher for a few seconds. I have seen firsthand the damage this does to pylons when it is repeated though so not a recommended way to size the bank.


This is sized for the safety (not loads) of the inverter as well as a number of things.

The inverter needs the amps from the battery so it can shut down safely without damage. You should never have a situation where the battery switches off first. The battery needs to be able to supply the amps without being damaged within its normal rating.

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OxyFly avatar image OxyFly Alexandra ♦ commented ·

Undersood, thanks for taking the time to explain. :)


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dayandnight avatar image dayandnight commented ·
Hello @OxyFly ,

when I started with US2000B it was only possible to address in one stack eight pieces. With US2000C it should be possible to address sixteen pieces in one stack.

When you have more than one stack of batteries, than you need a Pylontech HUB!

Servus - DayAndNight


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kevgermany avatar image
kevgermany answered ·

I'm quite surprised by some of the advice here. Pylontech say the mix is OK. Yet there are many unjustified recommendations to not mix.

Are there valid reasons?

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dayandnight avatar image dayandnight commented ·

Hello @kevgermany ,

I see the biggest challenge in the wiring. For my stack with 7 US2000 batteries I proceed as follows. The batteries are connected to each other with the short Pylontech cables. The bus bar is connected at the top and bottom with one cable each from the battery stack to the bus bar. As an example, if 140A of current is requested from the batteries, the current is distributed at 70A each over each individual bus bar cable. The internal wiring is evenly loaded and each Pylontech battery supplies an equal share of the current requirement with 20A. In my opinion, this ensures that the energy capacity is always proportionately available both when charging and discharging. Each battery provides an equal share of the total SOC of the battery stack.
I simply cannot imagine how I could achieve this "equal" state both in terms of the current load on the cabling and in terms of the proportion of the available capacity with battery modules of different sizes within a stack.

As I explained, I've been driving it very well for years, even with two stacks of batteries, and I've had no problems. I wouldn't go for changing a winning team!

Servus - DayAndNight

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Related Resources

Victron Offgrid page

Victron Pylontech battery compatibility guide

Additional resources still need to be added for this topic