48V Battery bank not entering float/rest voltage

Question

question

hybridizd asked Sep 4, '23

48V Battery bank not entering float/rest voltage

Hello

My 48V battery bank doesn't seem to be go into a float/rest voltage after reaching 56V as configured by the MPPT controller.

The bank will continue to sit at 56.0V all day. Little worried as bank does not get to rest after full charge.

My system configuration-

Victron Cerbo GX
Victron MPPT 250/85 VE/MC4
Victron Mulitplus-II 48/5000

2 x 48V 100AH Lithium batteries (Total ~20KWH)

DVCC Enabled
Shared Voltage Sense - Enabled
Shared Current Sense - Enabled

The Charge Voltage Limit (CVL) setting that is hard coded for the batteries - visible from BMS Cerbo/Touch screen is 56.0V

Picture of Victron MPPT Configuration

Any advice/suggestions appreciated

MPPT SmartSolar Lithium Battery float

19

2 |3000

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

seb71 commented · Sep 04, 2023 at 06:04 PM

Are you using ESS?

!6-cell battery, going by the voltages.

0 ·

hybridizd seb71 commented · Sep 04, 2023 at 06:08 PM

ESS is disabled

Yes I believe they are 16 Cell batteries

0 ·

seb71 hybridizd commented · Sep 04, 2023 at 06:24 PM

ESS is disabled

You mean not used, right?

-----------------

What is the state of the MPPT when the battery voltage reaches and then holds 56V?

0 ·

hybridizd seb71 commented · Sep 04, 2023 at 06:30 PM

yes ESS is not being used. The assistant is not installed.

The state of MPPT is Absorption, sits there all day at ~56.0V

Does not go into float @ 54V

0 ·

seb71 hybridizd commented · Sep 04, 2023 at 06:46 PM

What BMS is that?

Can it be used with DVCC enabled?

For troubleshooting, you could disconnect the MPPT from Cerbo, so that it charges by its own algorithm. See if in this case it changes states (and voltages) as expected.

0 ·

hybridizd seb71 commented · Sep 04, 2023 at 06:58 PM

JBD BMS

I was told by battery supplier to enable DVCC

Will try disable DVCC and use your suggestion

Do you think maxing at 56V 3-4 hours a day is doing damage to the battery bank?

0 ·

snoobler hybridizd commented · Sep 05, 2023 at 12:35 AM

Have you loaded the custom JBD driver and enabled CAN communication with the GX, or is it operating independently?

FWIW, 2X 48V 100Ah batteries are not 20kWh. They are 10.2kWh.

2 ·

hybridizd snoobler commented · Sep 05, 2023 at 06:59 PM

I'm running a custom CAT5 cable from RS232 port on battery BMS to the CAN on Cerbo-GX

Will look at installing the JBD driver into the Cerbo GX as suggested.

The RS485 ports are used on the batteries between Master & slave.

Would I be able to use the existing serial/comms link for communication once driver installed?

Thanks

0 ·

seb71 hybridizd commented · Sep 04, 2023 at 07:13 PM

JBD BMS

Does not appear in Victron's compatibility list, but it might still be OK with DVCC enabled. Or not.

Anyway, check its settings, too.

Do you think maxing at 56V 3-4 hours a day is doing damage to the battery bank?

Depends.

Do you see a large drop in charging current after 1-2 hours at 56V?

All cells have the same voltage (3.5V)? Or do you have big differences in cell voltages when the battery is at 56V?

0 ·

hybridizd seb71 commented · Sep 05, 2023 at 07:01 PM

yes I am seeing the current drop back from the MPPT after it reaches 56v. PV current from MPPT shows about 1-2A~ current when batteries at 56v.

0 ·

snoobler hybridizd commented · Sep 05, 2023 at 07:09 PM

If you use BMS comms, all chargers will behave according to the BMS parameters. Absorption and float are ignored. MPPT will indicate "external control." I was trying to eliminate it as a possibility.

Have you set a current limit in DVCC? if so, that overrides MPPT settings if lower than MPPT.

If you've set it to 56V in DVCC, and the MPPT is absorption at 56.8V, it will never get to 56.8V, and the MPPT will stay in absorption (might fall back to re-bulk level as well) until there is no longer enough solar.

Are you also seeing decent correlation between BMS reported voltage, MPPT reported voltage and any other source? Confirmed with a separate meter?

0 ·

hybridizd snoobler commented · Sep 05, 2023 at 07:29 PM

The MPPT Absorption setting has been set at 56V for a long time. Only recently changed to 55.80 to see if any difference. Back at 56.0V now.

Have not set the current limit in DVCC,

Cerbo is receiving the Charge Voltage Limit (CVL) at 56.0V and Charge Current Limit (CCL) of 100A from the BMS. These settings cannot be changed on the Cerbo. Hard set

The multiplus, MPPT, JBD BMS and SmartShunt are all reading the same voltage when steady at 56.0v

0 ·

snoobler hybridizd commented · Sep 05, 2023 at 07:51 PM

Now I'm confused. So the BMS is in control? Does the MPPT indicate "External control" in the app?

If that's the case, you're seeing normal behavior. The BMS does not know anything about absorption or float. it will seek the charge voltage and hold it. The MPPT settings are ALWAYS overridden by the BMS. You can think of this as a two stage charger... 1) CC to target voltage, 2) hold at voltage.

For LFP batteries, best to set to 55.2V (3.45V/cell). You'll get to 98%+ SoC without placing undue charging stress on the cells.

Ensure BMS is set to balance only at 3.40V or above, 20mV cell deviation and "balance only while charging" is DISabled.

0 ·

hybridizd snoobler commented · Sep 05, 2023 at 08:00 PM

Yes MPPT has External Control from the BMS, please see the above picture for my settings of the MPPT. The only difference is now the absorption setting on MPPT is 56.0V

Makes sense what you are saying.

So set 55.2V on the MPPT or will I need to set the CVL via the battery BMS?

Appreciate your time and help. Thanks

0 ·

Show more comments

question