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cajanus avatar image
cajanus asked

Bulk never ends, sits at 85%, keeps charging from grid overnight

Hi,
What is supposed to trigger the end of Bulk charging?
- Voltage reaching Absorption voltage?
- Low charging current?
- SoC?
- Some combination of the above?

I have a single-phase MultiPlus Compact 24/2000/50 which is AC-coupled to a 2kW Fronius MPPT. Batteries are 300Ah NiFe (nickel-iron).
The MultiPlus is the only device connected to the batteries. There are no other chargers or loads or BMSes.

Six months ago, the MP used to finish Bulk charging and occasionally go into Absorption as scheduled. All good.

But now it stays in Bulk forever (32V, 6A, SoC=85%), continuing charging all night from the grid.
Absorption voltage = 32V
Float voltage = 28.5V
SOC when bulk is finished = 85%
Assistant = Self-Consumption Hub-2 V3 (0182)

Could this be a bug introduced when I last upgraded all Victron software?

If I reload the Assistant, on the first day, it "Disconnects From The Grid At Night" at sundown and starts inverting as expected. From day two onwards it just stays in Bulk, charging overnight.

Thanks,
Mark



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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

Try looking at the multi's battery settings - in particular, "stop after excessive bulk".

Bulk normally terminates on reaching both the absorption voltage and the charge current dropping to a low level - normally about 2 -5 % of Ah capacity set.

Also - test the charge current into the battery as the charge ends - if the current is not dropping, then there may be a battery issue with one cell not reaching full voltage.

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cajanus avatar image cajanus commented ·

Thanks Mike.
How many times have I seen "stop after excessive bulk" and not read it? I have now set it. So far no change in charging behaviour, but it has been cloudy for the past few days.
I wonder what it considers to be "excessive"?


Bulk normally terminates on reaching both the absorption voltage and the charge current dropping to a low level - normally about 2 -5 % of Ah capacity set.

2% of 300Ah = 6A. While sitting on 85%, it sometimes drops to 5A but continues charging.


Also - test the charge current into the battery as the charge ends - if the current is not dropping, then there may be a battery issue with one cell not reaching full voltage.

All 20 cells sitting on 1.59V. I don't think sitting on 6A is a battery fault, just NiFe chemistry. Probably just wasting power making hydrogen.


Sunnier today: it has been sitting on 85%, charging 5A or 6A @ 32V for 3 hours. Why does the MultiPlus stop counting SoC? SoC should be 90% by now.



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