Anyone combined different LiFePO4-sets in a system?

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spithost asked Jun 15, '24

Anyone combined different LiFePO4-sets in a system?

I've got a system with a perfectly working BYD B-BOX 10.0 set of 10kWh (4 modules in a case).
I'd like to expand the system-capacity to 15kWh or even 20kWh but these typical modules are not produced by BYD anymore :-(
I know that BYD produces some units on demand every now and then, but then the modules are quite expensive and I don't know of anyone having the same "expansion-problem" willing to part with their 10kWh set ;-).
If someone does know of such a system, I'm interested in acquiring 5 or 10kWh (depending on the price ofcourse ;-)).

So I'm looking for an alternative solution that maybe one of you have explored and tried and maybe even have in use...
Is there someone out there, that has "mixed" different brands of LiFePO4-sets in parallel, (with their own BMS'es) in one system?
In a way that both sets are seen by a Cerbo and the charging somewhat controlled by it?
As the charging-voltage of LiFePO4-sets is often "comparable", it could be possible to read out the two different BMS'es in the Cerbo and take action to the charging MPPT's if needed and maybe not keep both sets at 100%, but maybe one at 100% and the other at 95% or so.

BMS BYD lifepo

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Answer 1 · 2024-06-15T15:00:40Z

Duivert NL answered · Jun 15 at 03:00 PM

You can only do that with same type battery and same type bms, cerbo can not control 2 different bms, you could use 1 bms and 1 shunt but, if batterys are different charging will not work very well

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Answer 2 · 2024-06-15T17:47:47Z

Alexandra answered · Jun 15 at 05:47 PM

@Spithost

Yes we have. A BYD and other brand.

They have the same charge voltages. The BYDs control the system in DVCC since they are the ones that have the warranty. It just needed extra storage not charge and discharge ability. We can see the second batteries in the device list and on the vrm though.

They charge at different rates and discharge at different rates (amps) but interestingly they sort themselves out in the end. Probably also best to mention they are different capacity cells too, so the difference is really the resistance in them.

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Answer 3 · 2024-06-16T10:25:24Z

Björn Kellermann answered · Jun 16 at 10:25 AM

@Spithost

you can combine different types of battery and BMS if they match voltage (number of cells and chemistry, e.g. 16s LFP) and aggregate BMS data using battery safety controller or Peter board.

https://github.com/shining-man/bsc_fw

BR, Björn

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spithost commented · Jun 16 at 04:00 PM

What's a battery safety controller or Peter board? Is that sort of a BMS that controls all other BMS'es? ;-)

I "scanned" the information behind the url, you gave, VERY quickly, so if you have some more basic information of the principle, it would be very much appreciated ;-)

If it delivers a safe solution to combine two set's of LiFePO4 with different (supported) BMS'es to safely control the charging in combination with the Cerbo/Multi, I guess it could be a perfect combination with what @Alexandra mentioned about that solution.

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Björn Kellermann spithost commented · Jun 17 at 09:16 PM

Hi @Spithost

both are special hardware devices with a firmware which aggreate data from several BMS.
Batter Safety Controller was ment as secound sevaety net for a battery but turned out as being capable to combine different BMS and improve their behavior. E.g. a PACE BMS is not able to cahnge Charge Voltage based on SOC. Wiht BSC you can change it based on SOC.The BSC support CAN, serial and BlueTooth connectoin also intetrating externaly activae blancer like the Neey.

Most imporant and ko cretiera is the nominaly voltage and chemistry of your battery. Pylontech use 15 cells LFP resulting in a lower voltage, whereas other likek Gobel Power use 16 cells LFP. The cell cehmestry like LFP determs the genreal cell volatege as well as the spread between empty and full and the curve. LFTP has very low change between 10 adn 90 % SOC.

You can only combine battery packs of same chemistry and amount of cells.

I have not found spesc for BYD B-Box but your provides sprec leads to the conclusion they are 16s and not 15s like Pylontech. An alternative is Gobel Power GP-SR1-PC200.

Than you net a BMS aggregator like BSC, Peter Baord or in software serial battery on Cerbo.

the current does not care about the BMS, but you likek to have currect values in Cerbo.

Check out Andy's Offgrid Garage on YT.

Hope this helps a little.

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Answer 4 · 2024-06-16T15:36:22Z

spithost answered · Jun 16 at 03:36 PM

I had in mind to combine the BYD-set and Pylontech (5000US), because they are also supported by Victron and a lot cheaper then BYD's, but they have different absorption and float values:

Voltages	BYD	Pylontech
Absorption	55.2	52
Absorption (offgrid)	56.5
Float	55	51

Apparently the Pylontech's are significantly lower in voltages :-(
So I guess that's out of the question then.

@Alexandra what second type batteries do you use? Are they self made or also "off the shelf"-type batteries and/or BMS? And if so.... are they still available (as in.... do you have a url ;-))
I also just need them for extra (solar) storage and not extra charge and discharge-capacity.
I use the BYD's in combination with a MultiPlus II 5kVA and that MultiPlus II can carry our loads more then adequately.
I guess you have the end-points of the batteries both connected to the same DC-rails without any extra "stuff" between them and those rails connected to the Multi?
This way the batteries will sort of "equalize" between them "automagically" because of the same voltages I guess ;-)

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Alexandra ♦ commented · Jun 16 at 03:40 PM

@Spithost

They are modified ones (Chinese battery -with an awful bms - because cheap cells and then the bms changed) so we can program to the same voltages.

Yes we use a bus bar and then a slightly longer absorption time.

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