3x Multiplus 5k - ignores External control and discharges full power

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thoro asked Jun 30, '24

3x Multiplus 5k - ignores External control and discharges full power

Hello,

I have a system consisting of 3 Multiplus, with 120kWh Batteries (JKBMS), it is controlled externally via Modbus.

Charging stops at 56.9V (16s), the external control will still push the Charge command (never goes to 0), but the Multiplus will start to discharge with 12kW after around 50min with 0 Load. This is very consistent and happens each time the battery is charged to 100%. It takes around 20 minutes to stop again, until then no external control is possible.

What settings might cause this? I assume it's some security feature related to voltage? Might it be caused by some force-discharge communicated by JKBMS?

Thanks for any tips

Multiplus-II external control

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Answer 1 · 2024-07-01T07:05:25Z

danielj answered · Jul 01 at 07:05 AM

Allot of the following depends on how the BMS is communicating to the system and how it was set up but it is likely to be related to the CVL(charge voltage limit) of the battery. Bellow is an example of a freedom won Battery(orion BMS)
you will see as the battery gets fully charged the BMS pushes the CVL down to assist with balancing an prevent overcharging. Why this can cause your discharge event is due to the following.

The battery voltage can frequently be above the BMS CVL due to overshoot or the batteries balancing algorithm lowering the CVL after the battery reached a higher voltage. The only way for the system to reach this lower voltage set by the CVL is for it to discharge the battery until it reaches the CVL.

This could be the reason that the battery is discharging when it is full. There are additional factors that can also cause this when looking at BMS managed batteries but the above is one of the more likely reasons.

1719817049555.png (31.1 KiB)

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