Dear Enthusiasts, I set up a new System with NG-Battery (12V, 300Ah), NG-BMS, Multiplus 12/3000/120 and Cerbo. My initial charging (bulk) brought the voltage up to 13.7V. For 2 days now, the system is in “absorption” mode, but the charging de facto stopped and the voltage thus did not go up. It is at 13.7V for 2 days. Is that normal? I would have thought it would go to 14.0 or 14.2V, because the battery manual shows these values as recommendations. Any comment is appreciated.
screenshot (no AC or DC users connected):
absorption-mode.pdf (120,7 KB)
It is not in absorption, the battery is full and it is in float. The Inverter is in external control by the BMS. If you dig into the BMS or battery pages on the Cerbo you will see a page with CCL, (charge current limit) and CVL (charge voltage limit), these are the current and voltage the battery and BMS is requesting, you should find the battery requesting 13.5V but because it is full it is above this. You need to read and understand the battery and BMS manuals. Your system appears to be working properly, it is your understanding that may be off.
thanks for your answer. My current understanding is: my BMS takes control over the MP and uses its own set-values for the charging process. My BMS however, has a set value of 14.0V for considering a battery fully charged. I attach a screenshot of where this value is shown (although it is shown in German “Spannung geladen” == voltage fully charged). Despite this set-value the charging stops early, at 13.7 instead of 14.0V.
Where is my understanding falling short then? Any clarification appreciated.
That value is not a charge control voltage, it is used to reset the SOC to 100% when the battery is charging. It is an information only value.
The charge controls are shown in Section 4.3 of the BMS manual, the only items you can change are
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Absorption time: is set to 2 hours by default. This can be adjusted if necessary.
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Repeated absorption interval: the number of days at which a new full charging cycle is started if the battery SoC does not fall below the SoC threshold. The default is every 30 days and can be adjusted if required.
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SoC threshold: is set by default to 70%. This is the threshold at which the Lynx Smart BMS NG starts a new full charging cycle. This can be adjusted if required.A new charge cycle means that the CVL (charge voltage limit) is increased from 13.5V to 14.0V (28.0V, 56.0V).In addition to the SoC threshold, a new charging cycle is started after a firmware update, when the battery voltages are below 12V/24V/48V (3V per cell) or when a low cell voltage is detected.
So the battery voltage will remain at 13.5V until it falls below 70% when it will increase to 14.0V for 2 hours, or if it does not get fully charged in 30 days. Ideally the charged voltage on the monitor should be 13.9V so it is just below 14.0V.
You need to find this page on the Cerbo so you can find what the BMS is currently requesting. Then you will see what voltage it currently needs.
