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2008 knight
elecTrical sysTem - house — 8
Checking the Electrolyte Solution
The most efficient way of testing the batteries
is to check the electrolyte solution. The only
way to test a battery’s electrolyte solution is
with a hydrometer. Many styles are available,
from types with cylinder graduation (shown
here) to types with floating balls. Hydrometers
can be purchased from most auto parts stores.
The hydrometer tests the battery’s electrolyte
solution which is measured in specific gravity.
Distilled water has a specific assigned gravity
of 1,000. The hydrometer is calibrated to this
mark. Pure sulfuric acid has a specific gravity
reading of 1,840. The acid is 1.84 times heavier
than water. The electrolyte solution is about
64% water to 36% acid (fully charged battery).
Hydrometers with cylinder graduation are
graphed and the exact state of specific gravity
can be determined.
Temperature and recent battery activity
(charging or discharging) affect the hydrometer
readings. It is best to check the battery when
it has been “at rest” for at least three hours,
although readings taken at other times will give
a “ballpark” figure. When using the hydrometer,
draw the electrolyte solution up into the tube.
Allow the hydrometer to attain the same
temperature as the electrolyte solution. Note the
reading for that cell. Complete the same test for
the rest of the cells on that battery bank.
The hydrometer is calibrated at 80° F.
Temperature affects the hydrometer readings.
The higher the electrolyte temperature, the
higher the specific gravity reading. The lower
the temperature, the lower the specific gravity
reading. Add or subtract four points for each 10°
variance from the 80° F chart. Readings between
cells should not vary more than 50 points.
If one cell in a particular
battery bank being tested is at
a 50% state of charge while
the others are indicating a
full charge, charge only that
battery to see if the low cell
will come up. At the same
time, do not over charge the
“healthy” cells.
If the low cell does not
come up after charging, this
battery can damage the rest of
the battery bank and should
be replaced. An accurate
digital Volt meter
+
- .5% will
also give an indicator of the
battery’s state of charge.
Placing a load on the
Battery:
Another test that can be
performed is to place a specific load on the
battery for a predetermined length of time equal
to that particular battery’s rating. This machine
is usually an adjustable carbon pile that can vary
the load being applied to the batteries while
monitoring voltage to see if they will perform to
their specific rated capacities.
NOTE
See the chart for temperature
compensation. Liquid levels should be
even between the cells of the battery
being tested as it will affect the accuracy
of the test.
WARNING
Sulfuric acid in the batteries can cause
severe injury or death. Sulfuric acid
can cause permanent damage to eyes,
burn skin and eat holes in clothing.
Always wear splash-proof safety goggles
when working around the battery. If
the battery electrolyte is splashed in
the eyes, or on skin, immediately flush
the affected area for 15 minutes with
large quantities of clean water. In case
of eye contact, seek immediate medical
aid. Never add acid to a battery once
the battery has been placed in service.
Doing so may result in hazardous
splattering of electrolyte.
Battery Charge Time & Consumption Rate
Calculating Run Times:
Calculating run time figures when operating
120 Volt AC electrical items with an inverter
can be exponential due to battery characteristics.
Flow characteristics of electrons vary
with different battery types and chemical
compositions. Deep cycle batteries are generally
designed to slowly release a majority of their
charge capacity. Deep cycle batteries are
rated in amp hours (Ahrs) with the discharge
occurring over an extended period of time
before the battery is charged. Engine starting
batteries are designed to quickly release large
amounts of current for short durations, without
depleting battery reserves. Commercial type
batteries bridge the gap of deep cycle and engine
batteries. Commercial batteries release medium
amounts of current over a longer period of time
but they are not designed to cycle their charge
capacity.
Temperature
Correction Chart
030815
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