battery watering systems [RE-wrenches]

[Darryl Thayer]

Thanks Robert for your experiences, I am adding them
to my battery information archive.

On my experience with the flooded cell fire the
batteries were new.  I do believe the fire was as I
described because the cells had just been topped off
that afternoon, and the fire started that night. The
charger might have been set to equalize, I do not
know.  Some of the cells in the string had become
electrically very discharged, some had a full charge. 
>From the damage the fire was started at two adjacent
batteries in a U shaped battery string.  Indeed I
believe the charge rate was perhaps over 100 amps, I
believe the adjacent batteries were fully charged,
there was at least 24 volts between adjacent battery
posts, and the cases were forced against each other.
(no gap between cases)  Due to parallel strings, the
parallel set of 850 amp hour batteries indeed would
have forced power back into the damaged set once the
short between cells occurred.  Also the failure would
have increased the charging  current.  

The other failure resulting in fire was with AGMs a
depleted electrolyte battery.  It was a case of four
paralleled strings, 48 volts each string, during a
charging cycle.  One of the battery strings became
warmer than the other string which resulted in a
decrease in voltage, the lower voltage string then
received more charge current than its paralleled set,
which caused it to heat more.  The owner noticed the
smell and stopped the charge current, however the
paralleled batteries dumped their energy into the
lower voltage string.  After some period of time the
batteries burst into flame. (note I found a web site
where telcom batteries fires occurred with AGM's)

Consequently I am very frightened of poor battery
installations.
Darryl

<robertwarren at mail.com> wrote:
> Brad,
>  You are absolutely right to say you can't be too
> careful around 
> batteries. I have been thinking more about how
> Charlie put together his 
> automatic battery watering system, 
snip
snip
> Daryl, I would say that it is more likely your
> battery fire was caused 
> by either a serious overcharge or more likely, an
> internal short, which 
> can happen when the batteries get old and the slag
> piles up at the 
> bottom like stagmites, and short out the plates. I
> have seen this happen 
> once in a battery room I had to clean up and
> re-build for the Navy, 
> about 8 years ago. Once the short happened, the
> others in the string 
> started feeding current into the short, boiling off
> the sulpheric acid. 
> Fortuneatly this triggered an alarm and the Haz-mat
> team came in and 
> dumped the couple 50 pound sacks of baking soda over
> the mess before it 
> got hot enough to start a fire. 
> 
> On the subject of battery fires and explosions, I
> had a Best UPS 
> customer at Boeing with a 7 or 8 year old gel
> battery that exploded. The 
> security guy heard it, and called me in to deal with
> it. While it made a 
> noise like a small gun going off, it was contained
> somewhat by the fact 
> that it was surrounded by other batteries on two
> sides and inside a 
> metal cabinet. but there was only a small smear of
> paste on the inside 
> of the cabinet and a pretty good split on one side.
> the inside of the 
> gel cell was pretty damn dry and it doesn't look
> like it could have 
> started a fire or damaged much of anything. so ever
> since that, I have 
> always considered sealed starved electrolyte
> batteries quite a bit safer 
> than wet cells. The real downside is that you don't
> get as many cycles 
> or years out of them. 
> 
> I hope this is helpful. 
> Robert Warren
> 

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