Multiplus - Charge Current Adaption if a BMS switches off one of several batteries in a bank

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olaf-leonhard asked Apr 21, '22

Multiplus - Charge Current Adaption if a BMS switches off one of several batteries in a bank

Charging more than one Lithium battery with internal BMS in the battery bank and one BMS switches off ones battery, what is the setup to make a Multiplus adapt the charging current to the number of batteries being still charged?

Example:
You have two batteries, each one should be charged with 50A. So as long as both are charged, you can program a Multi to charge with 100A. But if for some reason one battery stops being charged, the other one is charged with the 2-fold current which one may like to avoid with with respect to lifetime. So the charged current of the Multil should adapt correspondingly from 100A to 50A from that point on.

Should it be done with smart shunt communication to a cerbo and some small skript adressing the Multi?

As many users do have more than one battery I could imagine that there is already an approved solution (besides using the victron smart batteries with external bms).

Thanks in advance

MultiPlus Quattro Inverter Charger

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Answer 1 · 2022-04-21T13:35:07Z

Trevor Bird answered · Apr 21, 2022 at 01:35 PM

Hello @Olaf Leonhard , if the battery has an internal BMS, how could any external equipment know the battery has open circuited based on internal BMS activity? The Smartshunt doesnt know the battery has removed itself from the circuit. It is not possible to trigger an event relating to charge current based on an internal BMS activity because the Internal BMS is "internal",

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Answer 2 · 2022-04-21T18:01:58Z

olaf-leonhard answered · Apr 21, 2022 at 06:01 PM

Of course one cannot use an internal BMS to trigger something outside, this why put it clear , in opposite to external BMS, so that one does not have this option.

But

as for example the

SmartShunt measures the charging current constantly itself

and so it has the information about it to drop to zero or in more general term if it drops underneath a given treshold, this being sufficient equivalent for the purpose,

and the

SmartShunt itself can communicate with the Cerbo anfd forward the information to it

in order to make it execute a programm,

a script on the Cerbo with the aim to reduce the charging current on the Multi

Something like

IF ( Current B1 smaller Treshold T1) do set Multiplus Charge Current M to 50 A

IF ( Current B2 smaller Treshold T1) do set Multiplus Charge Current M to 50 A

IF ( Current B1 and Current B2 bigger than Treshold T2) do set Multiplus Charge Current M to 100 A

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Answer 3 · 2022-04-22T00:59:05Z

Trevor Bird answered · Apr 22, 2022 at 12:59 AM

The Smartshunt measures current but if one string of a parallel battery bank removes itself the current will then be provided to the remaining batteries in the bank. In other words the Smartshunt will see no difference.

If the current does reduce because the internal resistance of the remaining batteries is higher than the internal resistance of the complete bank, you don’t need to reduce the charging current setting because it has already been reduced.

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Answer 4 · 2022-04-22T04:34:43Z

kevgermany answered · Apr 22, 2022 at 04:34 AM

Assuming these are wired in parallel.

Check the BMS specs, but if one battery is shuts off, the others will see overcharge and also stop charging.

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