Hi there tech people,
I have a 520 watt solar string, connected in series, so 24 VDC nominal, connected to a Victron MPPT 100/50, monitored with a Victron MPPT Control and a Victron BMV700, charging two parallel 12VDC Victron 200 AH VRLA lead acid batteries (which are quite old).
I am observing a few phenomena, leading me to a few questions:
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OBSERVATION 1: When the battery bank is - for example - at 96% SOC before the sun rises. Early in the morning, after the sun comes up, the BMV suddenly indicates a SOC of 100%, although the MPPT light indicates it is charging in bulk mode and there is hundreds of watts flowing into the battery. Obviously the battery is not at a SOC of 100% at this time.
QUESTION 1: Is it because the solar array is "pushing" voltage into the battery, that the BMV thinks that it is suddenly at 100% SOC shortly after the sun has begun shining on the panels in the early morning?
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OBSERVATION 2: When the battery is almost full and the MPPT is in float mode and there is absolutely zero consumption from inverter (switched off) or any other consumers, I see that the system is still charging with 1-10 watts for a long time.
QUESTION 2: Does this come from the internal resistance of the lead acid battery chemistry, resulting in slower and longer charge stages when compared to a LiFePo4 battery?
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Any ideas?
