question

Magnus Pernemark avatar image
Magnus Pernemark asked

MultiPlus-II 48/3000/35 disable discharge, starts charging at max

I have 3 MultiPlus-II 48/3000/35 in ESS grid-tie configuration with external control mode.
They are controlled with external bms and 2-wire bms configuration.

Relays switch AUX1 and AUX2 depending on allow charge/disable discharge. When relays are open charge/discharge is stopped.

This works great for "Allow charge". When AUX1 is tripped - it will stop all charging. (battery almost full)

But att the other end of battery state of charge. If Battery is almost empty AUX2 is tripped. Disable discharge (and of course charge is enabled). Grid set point is -20 at all times.
When AUX2 is tripped, the MultiPluses starts to charge att maximum capacity. They just don't stop discharge, they force them self into max charge.

If both AUX1 and 2 is tripped charge and discharge not allowed - it will stop charge and discharge.

1. AUX1 and AUX2 tripped = all activity stops

2. AUX1 is tripped= charge stops

3 AUX2 is tripped = discharge stops - BUT FULL charging starts

Is this a bug in the MultiPlus-II? Or have I missed some configuration setting?

Multiplus-IIESScharger
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marekp avatar image
marekp answered ·

Hi,

To me it is normal behavior.

If system "learns" that the battery is discharged (AUX2 tripped) it will charge the battery if it has energy to do so.

I would imagine it will do the same even without the Aux2 tripped and Aux1 not tripped.

Or, I do not understand what you mean by FULL CHARGING.

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Magnus Pernemark avatar image Magnus Pernemark commented ·

I have set grid point to -20, which means keep grid import/export to -20W
When AUX2 is tripped, it ignores the grid set point of -20 and starts to import 6000W.

So out of a ESS stand point, there is no excess energy available. Excess energy would mean the grid point is less than -20, and it is not.

When AUX1 is tripped (do not charge) it does just that. It stops charging, it will not start discharging 6000W

The current setup makes AUX2 useless as a "do not discharge", since it acts as "Do not discharge but start to charge at maximum inverter capacity regardless of grid set point"

In VRM status changed to "Sustain" when AUX2 was tripped, if that makes more sense

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marekp avatar image marekp Magnus Pernemark commented ·

Ok, now I think see your problem.

I have similar system and do not have this problem.

I have grid set point at -50W,

I have LFP battery with two signal BMS,

and I have ESS running.

My system discharges battery only down to 20% so the AUX2 (do not discharge) is newer tripped. In reality my BMS reports SOC at 25% when my ESS stops discharging at 20%.

I would think that what is happening in your system is normal reaction to the fully discharged battery. System should immediately start charging to take battery from this fully discharged state as it is not healthy for it.

You might have battery configuration problem, and the ESS system thinks battery is bigger than it really is. Assuming that in the ESS you stop discharging at 20% SOC.

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Magnus Pernemark avatar image Magnus Pernemark marekp commented ·
I was running ESS in mode 3 (external control). So, I send no signal to charge only - disable discharge. Then I would expect it to just disable discharge and do nothing.


Any other idea how to stop discharge, when running 2-wire bms with external bms with ESS in mode 3?

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