Mixing two banks of batteries of close capacity but different vendors

[theologu]

Hello guys!

I am using my 16S2P bank made of 32x CATLs of 302Ah with a Seplos BMS for a few months now, and so far so good. I am prospecting however to build a second bank of 16S2P, but I would kinda go with EVEs 304Ah this time. It looks like it is easier to get grade A cells from EVE than CATL these days... Mine were bought from Docan, I don't say that they are bad, but some were slightly bloated... Now, in day to day usage, being compressed, actively balanced, they act quite well in terms of capacity and balance.

So - my question for you, based on your experience, should it be OK to mix 1 bank of CATLs and 1 bank of EVEs of almost the same capacity? My invertor is an Deye 12K 3P, so charge and discharge is on low rates even on my current setup. Adding a second bank would make charge and discharge at half for each bank - so stress will be at minimum. But, being different vendors, the batteries would have a slightly different charge/discharge curves - I don't know how much would this impact me.

Thanks!

 

[Steve_S]

No problem at all.
Best thing to do, is to make sure you have the same Make/Model/Version of the BMS to assure compatibility.
Simply put, LFP is LFP and get's along with its family regardless of relationship (manufacturer).

Actually, you can even run different capacity battery packs in parallel with little issues (not at all like old FLA & other chemistries). Even the Aging is NOT AN ISSUE, so if 1 year down the road you want to add another pack, No Problem !

Case in point, I run 2x174AH, 3x280AH and 1x105AH packs in parallel for 33kWh and no problem. The packs were assembled & put online over teh course of 3 years.

IMPORTANT TIP !
If you are building batteries with cells in Parallel within the pack, you are far better off getting Grade-A Cells with Factory Test Reports that show the Full Test Cycle. That way you can be fairly certain that all the cells will have an identical IR throughout the working voltage range. Be Aware that MANY Vendors do their own testing which is not proper... Many only provide the Voltage & IR Values at the storage voltage they have them at, that is pretty useless to be honest due to many variables.

You "may" have gotten lucky with the last batch of cells but just be aware of the consequences of choices.

Hope it helps, Good Luck

PS: Clarification
Battery Pack = A Set of cells with a BMS that makes one complete battery assembly (pack).
Battery Bank = a Set of Complete Battery Packs assembled into either/or parallel or series & parallel set to make a large bank.
A Bank can be anything from 2 Complete Packs up to ?

IE: Car Battery has 4 cells @ 3.0V each to make the 12V Battery. It is a Battery and not a Bank, cells are cells.

 

[RCinFLA]

Overpotential voltage versus cell current may be different between unmatched cells. Even same make and model cells. Overpotential is cell terminal voltage slump with load after the 1-3 minute decay, compared to rested unloaded open circuit cell terminal voltage. It is a function of cell current (discharge or charge currents). It gets worse at colder temperatures, particularly below 10 deg C.

Overpotential voltage is primarily the overhead power used within cell to drive lithium-ion migration to meet demanded cell current. It gets worse as cells age. On new cells, variations in overpotential is caused primarily by manufacturing tolerances on graphite and LFP electrode thicknesses.

It can cause significant difference in total load current sharing between parallel batteries.

At moderate load current, check current sharing between parallel connected batteries. More than 25% difference is not good. It causes faster wear on one battery driving further mismatching between batteries.

This current sharing imbalance also applies to charging current.

 

[TimE]

No problem at all.
Best thing to do, is to make sure you have the same Make/Model/Version of the BMS to assure compatibility.
Simply put, LFP is LFP and get's along with its family regardless of relationship (manufacturer).

Actually, you can even run different capacity battery packs in parallel with little issues (not at all like old FLA & other chemistries). Even the Aging is NOT AN ISSUE, so if 1 year down the road you want to add another pack, No Problem !

Case in point, I run 2x174AH, 3x280AH and 1x105AH packs in parallel for 33kWh and no problem. The packs were assembled & put online over teh course of 3 years.

IMPORTANT TIP !
If you are building batteries with cells in Parallel within the pack, you are far better off getting Grade-A Cells with Factory Test Reports that show the Full Test Cycle. That way you can be fairly certain that all the cells will have an identical IR throughout the working voltage range. Be Aware that MANY Vendors do their own testing which is not proper... Many only provide the Voltage & IR Values at the storage voltage they have them at, that is pretty useless to be honest due to many variables.

You "may" have gotten lucky with the last batch of cells but just be aware of the consequences of choices.

Hope it helps, Good Luck

PS: Clarification
Battery Pack = A Set of cells with a BMS that makes one complete battery assembly (pack).
Battery Bank = a Set of Complete Battery Packs assembled into either/or parallel or series & parallel set to make a large bank.
A Bank can be anything from 2 Complete Packs up to ?

IE: Car Battery has 4 cells @ 3.0V each to make the 12V Battery. It is a Battery and not a Bank, cells are cells.

How do you run a 105Ah pack with larger packs? What happens when the 105Ah pack is at 10% when the larger packs are still well charged?

 

[Steve_S]

How do you run a 105Ah pack with larger packs? What happens when the 105Ah pack is at 10% when the larger packs are still well charged?

The way I am setup, I have never gone below 20% total capacity. All of the batteries are quite happy while in the working range BUT as they get below 3.000Vpc you can see a transfer (slightly) from the big to small packs. It is not as significant as I observed but my LVD is 2.800Vpc.

The one thing that is odd at first blush which you get used to, is that the LFP Batteries charge & discharge PROPORTINATELY relative to their capacity. For example a 65A draw: my 280's could be outputting 14A ea the 174's output 8.7A and the 105AH outputs 5.5A or so. When I first saw that I wondered but through all the testing even the most abusive Thrash Tests, it remained consistent... I did Thrash Tests starting with the Chargery BMS' then a couple of JBD's and again when I switched everything over to JKBMS.

I should also mention, that as the batteries do that proportional discharge, it is similar when charging, the larger capacity packs take proportionately more amperage while charging. Also they do float up & down a bit as they do their work and is normal & expected.

The KICKER and that depends on your gear. I use Midnite SCC's and Samlex Inverter/Charger. These use EndAmps/Tailcurrent to switch from Bulk/Absorb (CC/CV) Constant Current/Voltage to Float which is Variable Current, Constant Voltage. Each pack has it's own EndAmps so I compromised and use an EndAmps value of 8.0A. The result is that by the time EndAmps is reached, the 105, 174's have been full for about an hour and NOT taking any charge while the 280's then finally top off and the packs go into sleep and self-balance between themselves as float services system demands and provides that balancing trickle for the packs.

 

[TimE]

The way I am setup, I have never gone below 20% total capacity. All of the batteries are quite happy while in the working range BUT as they get below 3.000Vpc you can see a transfer (slightly) from the big to small packs. It is not as significant as I observed but my LVD is 2.800Vpc.

The one thing that is odd at first blush which you get used to, is that the LFP Batteries charge & discharge PROPORTINATELY relative to their capacity. For example a 65A draw: my 280's could be outputting 14A ea the 174's output 8.7A and the 105AH outputs 5.5A or so. When I first saw that I wondered but through all the testing even the most abusive Thrash Tests, it remained consistent... I did Thrash Tests starting with the Chargery BMS' then a couple of JBD's and again when I switched everything over to JKBMS.

I should also mention, that as the batteries do that proportional discharge, it is similar when charging, the larger capacity packs take proportionately more amperage while charging. Also they do float up & down a bit as they do their work and is normal & expected.

The KICKER and that depends on your gear. I use Midnite SCC's and Samlex Inverter/Charger. These use EndAmps/Tailcurrent to switch from Bulk/Absorb (CC/CV) Constant Current/Voltage to Float which is Variable Current, Constant Voltage. Each pack has it's own EndAmps so I compromised and use an EndAmps value of 8.0A. The result is that by the time EndAmps is reached, the 105, 174's have been full for about an hour and NOT taking any charge while the 280's then finally top off and the packs go into sleep and self-balance between themselves as float services system demands and provides that balancing trickle for the packs.

Interesting. I am on a boat. We have a 280Ah 24v battery with JK BMS. I was think of building a second, smaller battery with another JK BMS and running them in parallel. We charge via 920w of solar and a pair of Victron MPPTs. It sounds like I could add a 100Ah battery in parallel with little concern

 

[luminaire801]

No problem at all.
Best thing to do, is to make sure you have the same Make/Model/Version of the BMS to assure compatibility.
Simply put, LFP is LFP and get's along with its family regardless of relationship (manufacturer).

Actually, you can even run different capacity battery packs in parallel with little issues (not at all like old FLA & other chemistries). Even the Aging is NOT AN ISSUE, so if 1 year down the road you want to add another pack, No Problem !

Case in point, I run 2x174AH, 3x280AH and 1x105AH packs in parallel for 33kWh and no problem. The packs were assembled & put online over teh course of 3 years.

IMPORTANT TIP !
If you are building batteries with cells in Parallel within the pack, you are far better off getting Grade-A Cells with Factory Test Reports that show the Full Test Cycle. That way you can be fairly certain that all the cells will have an identical IR throughout the working voltage range. Be Aware that MANY Vendors do their own testing which is not proper... Many only provide the Voltage & IR Values at the storage voltage they have them at, that is pretty useless to be honest due to many variables.

You "may" have gotten lucky with the last batch of cells but just be aware of the consequences of choices.

Hope it helps, Good Luck

PS: Clarification
Battery Pack = A Set of cells with a BMS that makes one complete battery assembly (pack).
Battery Bank = a Set of Complete Battery Packs assembled into either/or parallel or series & parallel set to make a large bank.
A Bank can be anything from 2 Complete Packs up to ?

IE: Car Battery has 4 cells @ 3.0V each to make the 12V Battery. It is a Battery and not a Bank, cells are cells.

Hi Steve,

I have a 2-month-old hybrid system comprised of a Deye Hybrid 8kW inverter, 8550kW panels, and a battery bank made of 2x100 Ah 51.2V battery packs wired in parallel via a battery combiner box (wall-mounted). I only discharge the batteries down to 20% SOC.

I want to add more batteries to my system however, my local supplier in the Philippines no longer sells the same brand/pack.
So I am left with no other option but to either try and find the supplier out of China (a long shot) OR to build my own.

I am leaning toward buying a plug-and-play pack since I have zero experience in building one myself, but I have not found any and thus I have begun my research.

So the battery pack (power wall as they are called here), is made with 16s 100Ah Gotion cells. As for the BMS, I have no clue as there is no branding.

Given the inverter I'm using, can I still combine different brands and capacities of battery packs?
Is there an easy way of determining the make/model/version of the BMS?

 

[luminaire801]

Here's a screenshot of the Li-BMS screen. It says PYLON in the top right. I did a search for "PYLON BMS" and it showed results of a pylontech battery packs. They definitely do not look anything like the ones I have (pics below). Maybe someone here can recognize them?




Here are my 2 x 100Ah 51.2V packs