Hot batteries

littleharbor2

I have a friend who just found the middle pair of 6 volt deep cycle batteries in a 2s3p (12 volt bank) set of batteries very hot and excessively percolating. Other than both of them being internally shorted I don't know what would be the cause of this . All connections were tight. The batteries appear to be holding voltage. The charging cycle was most likely near or at absorb state with voltage measuring 14.4 volts. When disconnected the individual batteries measured 6.35 volts. This system has been cruising along fine with no problems as far as I know and nothing has been done to any settings.
 Any ideas or suggestions?  I have pulled the two hot batteries from the bank and hopefully she can limp along for now. 

Dave Angelini

How hot?  They probably would not be shorted (unless breaking down under charge) if you measure 6.3 vdc. 
Good news, if the 3 strings were not wired identically there could be nothing wrong as it can be normal for a string of batts to charge faster then the other strings. Not that this is good, just saying!  Need to know the temp of each string. If there is a sensor, can you move it?  Flooded battery right? Maintenance done?

littleharbor2

Hi Dave,
FLA batteries. Maintenance, I doubt it. Pretty sure all 6 batteries are the same age. The hot string is in the middle of the other two strings. Outer strings acting normally and not anywhere near as hot, just warm. As far as wiring , each series pair have one + - series cable and then parallel cabling across the positive and negative terminals. Looks like 2/0 size cables I don't see a BTS anywhere. The charging source is two Xantrex C-series PWM controllers. How hot, Pretty damn hot, like almost burn your hand on the side of the battery case. and bubbling like I've never seen. 

Dave Angelini

Ouch!  So it is good now with the bad string out. Hard to feel sorry for someone who did not do maintenance. Replacement time.
Good Luck! 

littleharbor2

Dave Angelini said:

Ouch!  So it is good now with the bad string out. Hard to feel sorry for someone who did not do maintenance. Replacement time.
Good Luck! 

Yes, apparently things are ok this morning save for a diminished capacity battery bank. Very few people down here maintain their batteries as they should. I've been away from FLA batteries so long now It seems strange that most people still use wet batteries. Then again many of these people are still using their old Trace/Xantrex controllers and inverters with 12 volt systems because this equipment just wont give up the magic smoke.

RCinFLA

"batteries very hot and excessively percolating."

This means there is overcharging happening.

Either the overall charging voltage is too high or there is shorted or high leakage current cells causing other cells to get overcharged.

littleharbor2

RCinFLA said:

"batteries very hot and excessively percolating."

This means there is overcharging happening.

Either the overall charging voltage is too high or there is shorted or high leakage current cells causing other cells to get overcharged.

Would have to be the latter as I personally set the voltage settings on her CC's and know this is fine. Temporarily swapping out the rest of the batteries for an AGM bank this morning. She is buying a 400 ah. set of drop in lithium batteries next week.

Thanks all for your help and suggestions.