battery bank problem

[MALVANUA]

I am getting problems with my solar system. two SMA sunny boys each has 6x 200w panels running a sunny island 5048
two battery banks each is made up of 8 x 8L16 batteries 8x6v = 48 volts one cell in each bank has died no sp gravity reading my question is should I make one good bank and one bad bank I am on an island in the tropics will be next year before I can get a new set what would your thinking be? Does having a bad cell run the rest of the batteries down .I may be able to reconfigure the inverter to 46 volts.

[inetdog]

I am getting problems with my solar system. two SMA sunny boys each has 6x 200w panels running a sunny island 5048
two battery banks each is made up of 8 x 8L16 batteries 8x6v = 48 volts one cell in each bank has died no sp gravity reading my question is should I make one good bank and one bad bank I am on an island in the tropics will be next year before I can get a new set what would your thinking be? Does having a bad cell run the rest of the batteries down .I may be able to reconfigure the inverter to 46 volts.

Having one bad cell does not drive the rest of the batteries down, but if it has high resistance it may limit both the load and charging current or if it is shorted internally (most likely) it will cause your CC to overcharge the rest of the cells in the system.
If you can reconfigure the inverter you also need to reconfigure your CC to the proper voltage before you fry the rest of the cells in your battery with overcharging.

[Sunking]

two battery banks each is made up of 8 x 8L16 batteries 8x6v = 48 volts one cell in each bank has died no sp gravity reading my question is should I make one good bank and one bad bank

No just one good bank is likely all you can do. The answer lies in what your Charge Controller can do or NOT do.

Does having a bad cell run the rest of the batteries down .I may be able to reconfigure the inverter to 46 volts.

Yes a bad cell can bring down a whole string. 95% of all battery failures are from Sulfated battery plates. That means very high resistance that prevents the batteries from conducting current. One cell will prevent the whole string from charging. The symptoms are classic. You put the batteries on charge, and the charger indicates quickly the batteries are fully charged and shuts down or goes to Float. Either way the charger is fooled into thinking the batteries are fully charged up. Then when you put a load on the batteries, the voltage collapses immediately. Sound familiar?

If you remove a cell from each string, you might get away with it, or do a lot of harm to the remaining batteries. You have to do 2 things to work around

1. Check and see if you can lower the Invert Cut-Off voltage by 2 volts. That is not real critical if you cannot. Just means premature shut down. Ask your wife she knows all about it.

2. What is critical is lowering your Charge Controller Voltage. Not many are designed to be lowered. Example you would need to lower Absorb from 59.2 volts down to 56.7 volts, and float lowered from 52.8 to 50.6 volts. So the answer lies in what your CC can or cannot do. If you cannot lower the voltages low enough, you will have to use 1 string to prevent damaging them from over charge.

You mentioned L16 batteries are they Trojan?

[MALVANUA]

The make is not stamped on them anywhere just the model 8L16 they are six volt 3x2v ,one 2volt cell is bad in each bank. Would you recommend mixing the banks so to have one bank made up of the good batteries and the other have 2 faulty cells ie 44 v. or keep the banks balanced and reduce the charge controller I can move the settings down to 46 or 44v.
I have been given conflicting advice just trying to make the best move.

[Sunking]

Ok my bad, I assumed they were 2-volt cells. L16 is a BCI case size or jar they are in, not a voltage reference. L16's come in 2, 4, and 6 volt packages. With one bad cell in a 6 volt case means the whole 6-volt battery is a boat anchor, so there is no way to just use 7 cells or a 42 volt system as it is just way too low for 48 volt equipment and way too high for 36 volt equipment.

Pick your best 8 batteries, and make a string out of them. Save the other 8 for recycle when when you can afford replacements. Sorry, no real alternatives if you cannot afford to replace them. Using the 6 that are left out and still good could be used as a 36 volt system, but that requires buying all the equipment and you would have two systems. No sense in spending that cash for a short term solution.

Take your losses and chances. Use what you got and run with it.

Good Luck

SK