Batteries - Caution!
The
active materials within a battery are lead and sulfuric acid. Lead compounds
formed through the charging and discharging of the battery. The electrolyte
composition by weight is 33% sulfuric acid; the remaining two thirds by weight
are lead compounds. Sulfuric acid is most concentrated and at its heaviest
specific gravity (sg) when the battery is fully charged, with concentrations as
high as 40% sulfuric acid.
When a
battery is charged, additional energy is "stored" in chemical changes within the
electrolyte. As the battery is discharged, energy is "removed" through the
reversal of these chemical changes. Fully charged, the positive plate is lead
and the negative plate is coated with lead dioxide.
When
the battery is substantially discharged, both the positive and negative plate
coatings are converted to lead sulphate. At this point the sulfuric acid
concentration may be less than 10%.
Caution!
The
electrochemical energy of a fully charged battery is enough to vapourize over
half of the battery materials.
Anthology of a Shorted Battery
What if
a fully charged lead-acid battery cell is shorted? Hopefully the device
shorting the battery is protected by a breaker or fuse; otherwise it becomes hot
and melts or vapourizes the device, clearing the short. Within off-grid
installations, there is enough energy available to vapourize copper buss bars,
cables and other circuitry. Vapourizing copper has the same expansion rate as
dynamite.
What
happens if the short doesn’t clear itself? When a short is placed across a
string of batteries, the resulting fault current will begin discharging all of
the cells until one or several cells fail. Rarely do all cells fail at the same
rate. The cells that have not failed dissipate their energy into the failed
cells. Not only do the failed cells typically melt and give off vapours, but
these failed cells can become arc furnaces due to the energy contribution from
the rest of the battery string. Unless the battery fails in such a way as to
disconnect the circuit the amount of energy dissipated in the failed cell(s) is
usually enough to totally vapourize the whole battery.
If
melting battery cells find ground, the circuit continuity is continued through
the melted parts and the conductive object. This is typically called a battery
fire. Toxic clouds of sulphuric acid mist, vapours and metals are present
during this type of fire.
Always
Treat Batteries with Extreme Caution and Respect
Under
normal conditions with batteries your exposure includes hazardous substances and
hazardous materials. Hydrogen gas may be released and accumulate to explosive
levels.
Concentrated, sulfuric acid, lead and other materials may be easily transferred
from the battery posts to other areas including the hands, equipment and eyes of
a careless operator.
Make sure a tool cannot fall on top of your battery array
Always wear eye protection and wear protective gear.
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