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spithost avatar image
spithost asked

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.

BMSBYDlifepo
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Duivert NL avatar image
Duivert NL answered ·

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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Alexandra avatar image
Alexandra answered ·

@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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Björn Kellermann avatar image
Björn Kellermann answered ·

@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 avatar image spithost commented ·
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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spithost avatar image
spithost answered ·

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 avatar image Alexandra ♦ commented ·

@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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Related Resources

Victron BYD battery compatibility guide

Additional resources still need to be added for this topic

Victron VE.Bus BMS product page

Victron 3rd party BMS compatibility page