Electrical Systems - House --- Section 8
The Executive 2005
367
Hydrometers are available in different types, such as cylinder graduation
(shown here) or floating ball types. Hydrometers can be purchased from
most auto parts stores. The hydrometer tests the battery electrolyte solu-
tion, 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 temper-
ature 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.Another test that can be per-
formed 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 battery(s) 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.
W
ARNING:
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.
Hydrometer (Cylinder Type)
testing a LLA type battery.
030816b
Temperature Correction Chart.
030815
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