Over all Battery Bank Voltage Dropped

midijeep

I have a SMA Sunny Island with NiFe batteries @ 1.2v per battery .   With the sunny island setup I had to use 38 batteries instead of 40.   I have been running the batteries for about 3 years.  At float the voltage per battery  was 1.48v  (and steady ~56.2 v for the entire battery bank at float) until 3 Days ago.  Now, the battery bank voltage dropped and  is steady at 55.07v  (about 1 volt difference for the battery bank).  I tested each battery with a multi-meter and each battery was 1.45v.  so I didn't measure any batteries that where different from each other.

I am not sure if the sunny island decided to measure the voltage differently (it uses its own method of measuring voltage).

Should I worry about this steady 1 volt drop in the battery bank? Is there any other test I can do to determine if there is a problem with one of the batteries?

mike95490

i'd recheck all the connections, and then load the battery /inverter with at least a 500w load.  While loaded check the cell terminals of the far end of the cell you are checking, not on the terminal bolt, but the terminal bolt of the neighboring cell. you are looking for a poor connection which will have a higher voltage across it, than a good connection would.

midijeep

Thanks Mike .  I will give it a try later today.

midijeep

mike95490 said:

i'd recheck all the connections, and then load the battery /inverter with at least a 500w load.  While loaded check the cell terminals of the far end of the cell you are checking, not on the terminal bolt, but the terminal bolt of the neighboring cell. you are looking for a poor connection which will have a higher voltage across it, than a good connection would.

Check the connections and put a load on the bank.  Everything seems to check out.

I think the problem is with the SMA sunny Island.  It doesn't like the NiFe battery composition.  I have to use their NiCd preset on battery type because they do not have a choice for the NiFe composition.

I think what happened is the boost charge charged the bank to about 80% and the SI used that calculation.  What I did was a manual Boost charge and charged to 100%.  Now the battery bank voltage at float is now at 56.6v, which is what I have been seeing since the beginning of connecting the NiFe battery bank.  Thank for your help.

mike95490

NiCad and NiFe setting are, for nearly all purposes, the same.  Not sure what you are thinking is different between them

midijeep

SMA uses a self-learning current-voltage algorithm model  that adapts to the actual battery conditions within the battery type. It is more complex than using only one model e.g. a voltage model or current model or balancing the current model.