I have two lead acid batteries each 100Ah connected to a BlueSolar MPPT 100/20 with a SmartShunt connected to 4x100W modules. With this I run a small compressor refrigerator via a Phoenix inverter 800VA.
In summer everything was still ok, now in autumn I have these problems.
Details in the graphs below.
Many thanks and best regards
Volker
Battery voltage is proportional to SOC. The lower SOC, the lover the battery voltage.
Battery voltage drops under load because battery has and internal resistance.
Internal resistance depends on the battery temperature.
The lower the temperature the higher the internal resistance.
Also Battery capacity depends on its temperature.
Capacity is lower at lower temperature, so in lower temperature battery will discharge faster under the same load.
OK, but 2V jumps with a SOC of ~95% is this a usal behavior ?
Interesting info about LA battery internal resistance.
Quick calculation of your battery internal resistance.
Current 5A
Voltage drop under load 0.2V
0.2/5=0.04 Ohm = 40 mOhms
Your battery according to the author from the above link is "Probably unusable".
From the link:
In a LA Battery, the lower the battery internal resistance the more the battery in good condition.
To be exact, for a 12V LA Battery,
If IR>30 milliohm, battery is in very bad condition. Probably unusable.
If IR is between 10 to 30 milliohm, still poor condition but may be usable or revivable.
If IR is between 5 to 10 milliohm, it is in good condition.
If IR is less than 5 milliohm, it is in very good condition.
But all this given criteria are just an estimate and does not guarantee the battery condition. As the condition depends upon some other factors too.
Hi @vmmarwitz
It's not normal, and I think your batteries may have failed. Even with that tiny load they don't seem to hold V very well.
The Smartshunt mightn't be set up optimally either. That doesn't seem like a really good solar day for you, but it still managed to sync..
Batteries rarely fail together at the same time. You could try separating them to see if the 'bad' one stands out.
