question

save1power avatar image
save1power asked

Multiplus 2 with ESS Assistant shows strange Float charge behaviour...

I use the following setup: ESS System with a Multiplus II 48V, CerboGX and a Lithium NMC battery that is protected by a built in BMS. The Multiplus does not communicate with the battery. Charging and discharging is controled by voltage.


I am currently testing the following settings:


TAB: General

System frequency 50Hz

Shore current 13.0 A

Overruled by remote unchecked

Dynamic current limiter unchecked

External current sensor connected (see manual) unchecked

State of charge when Bulk finished 100.0 %

Battery capacity 50 Ah

Charge efficiency 0.95

TAB: Grid

Country / grid code standard Germany: VDE-AR-N 4105:2018-11, internal NS protection

LOM detection AC input 1 Type B (grid code compliant)

rise-in-voltage protection U> 253.0 V

start network service HF treshold 50.20 Hz

P(f>) droop 5.00 %

Use Aux1 as disable FeedIn signal checked

Maximum AC current for charge or feed in 100.0 %

Reactive power regulation Use a fixed Cos Phi

Filter time for reactive power 3.3 s

Cos phi at point 1 1.00

TAB: Inverter

PowerAssist unchecked

Inverter output voltage 230 V

Inverter DC shut-down voltage 39.20 V

Inverter DC restart voltage 45.60 V

Low DC alarm level 45.60 V

Do not restart after short-circuit (VDE 2510-2 safety) unchecked

enable AES unchecked

TAB: Charger

Enable charger checked

Weak AC input unchecked

Stop after excessive bulk unchecked

Lithium batteries checked

Configured for VE.Bus BMS unchecked

Charge curve Fixed

Absorption voltage 53.00 V

Float voltage 52.98 V

Charge current 35 A

Repeated absorption time 0.25 Hr

Repeated absorption interval 45.00 Days

Absorption time 1 Hr

TAB: Virtual switch

TAB: Usage

Virtual switch usage Do not use VS

TAB: Assistants

TAB: Assistant Configuration

ESS (Energy Storage System) (size:962)

*) System uses LiFePo4 with other type BMS

(This can be either a BMS connected via CAN bus or a BMS system in which the

batteries are protected from high/low cell voltages by external equipment.)

*) The battery capacity of the system is 50 Ah.

*) Sustain voltage 44.80 V.

*) Cut off voltage for a discharge current of:

0.005 C= 47.80 V

0.25 C= 47.20 V

0.7 C= 46.60 V

2 C= 46.10 V

*) Inverting is allowed again when voltage rises 1.20 V above cut-off(0).

*) Relevant VEConfigure settings:

- Battery capacity 50 Ah.

- PowerAssist unchecked

- Lithium batteries checked

- Dynamic current limiter unchecked

- Storage mode unchecked



Total size of all assistants including the required

(hidden) system assistants is: 1021





It works pretty well...


Now my question:

When there is enough solar to power home consumption the rest is used to recharge the battery. In bulk charge it all works fine, as soon as the absorption phase ends, the inverter discharges a little bit to reach the float voltage of 52.98 V. But then the inverter stays on (green light is on) all the time.... even though there is enough solar power to power the house and therefore the inverter not needed.


How do I have to change the settings in order to prevent this behaviour?

Or is there a way to completely disable float charge, as it is not useful for my type of Lithium-Ion battery?


Thanks in advance for your feedback and help!


Multiplus-IIbattery chargingESSLithium Batteryfloat
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2 Answers
Alexandra avatar image
Alexandra answered ·

@save1Power

With ESS assistant programed, in the solar should not be idle, and the mppt should stay in bulk. The state is not triggered by the battery.

What is your grid set point (on the GX device)? Is it lower than your loads?

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Thanks for your reply!

I don't have any MPPT's as the solar is AC-coupled. The MultiPlus II stays in bulk until the batttery reaches absorption voltage. Or do I get something wrong...?


The grid set point is set at zero. What do you mean by "is it lower than your loads"??

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Alexandra avatar image
Alexandra answered ·

The inverter light is supposed to stay on if the inverter is ready to invert in case of grid failure.

When connected to grid you will see grid on, inverter flashing/on and whatever light corresponding to the battery state. (Bulk absorption and float)

If you set a higher grid set point it will pull from the grid rather than use the solar to power loads.

You can disable float by setting the same voltage as bulk/absorption. It is up to you how you want to run your battery, hnless the manufacturer has stated otherwise. You may still see the float light appear on the multiplus, but the voltage you want your battery at will remain correct.

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