question

carsten2 avatar image
carsten2 asked

ESS with BMS battery, conditions for absorption, bulk, float

What are the conditions for the Multiplus II to change the bulk, absorption, float LED in a system with ESS, DVCC and a BMS battery?

What settings from the ESS assistent are still active and not disabled by DVCC or BMS?

What causes the Multiplus to switch of the charger when the battery is full?

In my system the bulk LED is almost always on. I observed short cycling around bullk and absorption, when the BMS reduces voltage to stop charging (CCL=0 doesn't work reliably). In rare cases I obsorved that all charging LED were off, but I am not able to figure out the conditions.


battery charging
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

1 Answer
Alexandra avatar image
Alexandra answered ·

@carsten2

Bulk absorption and float are shown in the charger curve in the manual.

It switches from bulk to absorption once the battery is drawing under a certain number of amps trying to reach abtarget voltage. Stays in absorption for however long it is programmed to (at the target voltage) then drops to float. This usually has a few amps in and out evry now and then, depends on the battery.

In an ESS system, the MPPTs will stay in bulk so dont reflect the battery state.

The system since it is under BMS control will either says external control or be in whatever the battery dictates.

In DVCC the only thing that is ignored is CCL when you are feeding back to grid, otherwise everything else is adhered to.

It sounds like your battery is trying to balance. Dont forget also that there is some power assist as well with ESS so a bit of in and out is also to be expected.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

carsten2 avatar image carsten2 commented ·
This is not what I observe.I am talking only about the Multiplus not additional solar chargers which I do not have.


1) Even though CCL is very low or even 0, and the charging current is almost zero, the Multiplus does NOT change to absorbtion. It only change to absorbtion when the charging voltage is decreased by the BMS under the current battery voltage.


2) Even though I have to no MPPTs but I think the MPPT will only be at full power if "feed exessive DC solar power to grid" is active. Otherwise they would overload the battery.


3) Also CCL is not ignored otherwise it would overload the battery. Unfortunately is not perfectly adhered to in the special case CCL=0, because even then then Multiplus is charging by about 1 amp unless the charge voltage is reduced by the BMS. In my opinion this is a bug in the Multiplus because it can drive the battery into emergency shutdown because of overvoltage in a single cell if the battery is almost full. If the battery dictates CCL=0 i.e. it cannot accept more charging and the Multiplus is still charging there is a high propability of the BMS to cut the charging forcefully. Unfortunatel this usually restarts the whole Multiplus inverter to even power the the critical loads are lost for some seconds.


4) It seems the BMS controls the Multiplus only by the parameters charge voltage, charge current limit and discharge current limit. There seems to be no other parametes with which a BMS to force the Multiplus into other charging states.


5) Powerassist from the battery should not occur if there is plentry of excess AC solar power which is even exported to the grid. In case of excess solar power the Multiplus should never discharge the battery.


0 Likes 0 ·