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heggink avatar image
heggink asked

Multiplus II Lifepo3 settings for REPT 280AH

I really need some help with the correct Inverter and ESS Settings for my new config.

I have the following:

  • 3x MP-II 5000 in a 3 phase config
  • 3 strings with 16 REPT 280AH LIFEPO3 each with a JK BMS, total 840AH. REPT specs seem extremely similar to CATL and EVE.
  • max discharge load 70 amps per inverter

The system has just been brought up since 24 hours. Initially, doing some testing with lower loads were all fine. As soon as I increase discharge load then then the voltage of the string drops quite a bit after the battery gets below 50% SOC causing battery low warnings. Voltage ultimately ends up being 45V where the BMSs (not connected to the ESS) and the smart shunt still think the SOC is 42%. So that is one challenge I have. I made some changes to the settings but I don't think I want to go too low (e.g. 42V cut off) under load. If anyone has any hints as to how to arrive at the best settings and why there seems to be a discrepancy between the SOC and voltage then please shout.

Secondly, I just tried the charge cycle which seems to work similarly: the moment the load increases, voltage goes up quite fast causing the MP-IIs to reduce power quite quickly. From 45V to 52V took 30 minutes where the SOC went from 42 to just over 47. Any advice on charge settings here would also be appreciated.

In summary, the batteries seem to vary quite substantially in voltage under high loads causing the system to struggle with load/unload parameters.

Thoughts? Many thanks in advance.

ESS
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2 Answers
seb71 avatar image
seb71 answered ·

LiFePO4 (not LiFePO3).


Did you fully charge all cells individually before making the battery strings?

What is your Absorption voltage?


How are the strings put in parallel? Using busbars, where each string has its own wires?

What is the cross section (gauge) of the battery wires and inverter wires? How long are the battery wires and inverter wires?


You should stop the discharge at 48V. Going lower than 3V cell voltage you risk damaging the cells, especially if the cells are not well matched or equally charged.


210A draw from a 840Ah LiFePO4 battery bank should not cause such a voltage drop.

Maybe test each battery string individually with loads up to 100A (on DC side) to see if all behave the same.

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heggink avatar image heggink commented ·
I did not fully charge so in the process of doing that now. I did check all the voltages of the batteries when I got them (all identical).


Changed the absorption to a better level indeed.

Strings are connected with busbars, each string indeed having its own connection using 35mm2 cable to support the 70 amps. Battery and inverter wires are between 40 and 70cm.

I made sure that I can switch off individual batteries so will follow your advice to test the strings individually if the problem persists. Many thanks for your advice.

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heggink answered ·

Answering the second question myself, I adapted the float and absoption settings on the charge tab which made it a lot better.

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