MYTH: When you overcharge Gel Batteries they
explode or leak electrolyte excessively.
You could get Mythbusters to "Confirm" or "Bust"
this myth or take my experience and decide for yourself.
SITUATION - 3000VA UPS containing 16 batteries
rated at 12V 7Ah sealed Gel Battery
TRIGGER - to cause Battery Charger to fail to a
full charge with no regulation was the failure of a 11kV
lightning arrestor which caused the fuse on one phase of a two
phase supply to a pole mounted transformer to blow. A second
effect of the arrestor failure was that it provided a path to
earth which allowed the transformer to give an output of
approximately one third normal supply volts.
CONSEQUENCE - At first there was no indication that
there was a problem with the UPS except it was noted that it
seemed to be operating at a higher temperature than normal and
the fan was coping with this situation. The temperature at the
top of the box was only a few degrees above normal but checking
the temperature at the bottom revealed that the batteries were
too hot to handle.
After a few days it was noted that there seemed to
be an unusual smell that was difficult to trace as it filled the
room when it had been closed for a while.
Next, it was noted that when it switched over to
UPS battery backup that run time was considerably shortened and
eventually the UPS went to Fault condition.
INSPECTION - A voltage check of the batteries
revealed that the normal 200V battery bank was about 50V and
that all batteries would have to be replaced. Normally it is an
easy process to remove batteries but I soon found out that the
heat had affected the batteries that they had fused to become
one big block and that the cases had bulges that conformed to
fill the spaces surrounding them.
REMOVAL - To remove the batteries it was first
necessary to separate them from the adjacent cell by use of a
hammer and screwdriver to release the bonds and the try to
remove then one at a time. As the cells were now larger than the
access space it meant that the only way to do this was by brute
force. This was achieved with a hammer and a block of wood. My
concern was that I might spill electrolyte and make cleanup
difficult but I had no need to worry as every cell had totally
dried out with the excessive charging.
