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khapele avatar image
khapele asked

Battery Voltage Drop Then Sudden Recovery

Hello all,


I have an issue with my battery behavior and was wondering if it is the battery, or something else.

When charging during the day, I have only one fan turned on which consumes about 50W. However, when there is no more sun and I leave the fan turned on, the battery seems to be draining for 2-3 hours (goes below 9V). Then, suddenly the battery voltage goes back to a healthy 12V.


If there is nothing turned on, there is no such issue.


Do you have any idea why this might be happening?


My setup is as follows:

Controller: Victron SmartSolar MPPT 100/30

Inverter: Victron Phoenix 800VA

Battery: Banner Energy Bull 130Ah

Attached you will find the stats I have for several days in a row.

img-8935.jpeg img-8934.jpeg

batterybattery system voltagevoltage drop
img-8935.jpeg (235.4 KiB)
img-8934.jpeg (291.9 KiB)
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1 Answer
pwfarnell avatar image
pwfarnell answered ·

Does the fan stop running when the voltage reaches 9, and does it stay off when the voltage recovers. The voltage pattern is exactly like a load is discharging the battery, the load stops taking power at low voltage and then when the load is removed the voltage recovers, the load that disconnects is probably the inverter. Do you have anything else connected. Is this a 12V DC fan or is it an ac fan powered by the inverter.The

This might be a problem that you do not have enough solar power to fully recharge the battery so it is never full at night and you are trying to use more energy each day than you are generating. A lead acid battery will fail early losing capacity through sulphation when treated like this. The battery really needs to get above 14.2V and the charge current fall to less than 2A to be full.

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