ELECTRICAL SYSTEMS - HOUSE — 8
186
2008 IMPERIAL
The hydrometer tests the battery’s electrolyte
solution which is measured in speci
fi
c gravity.
Distilled water has a speci
fi
c assigned gravity
of 1,000. The hydrometer is calibrated to this
mark. Pure sulfuric acid has a speci
fi
c 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 speci
fi
c 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
fi
gure. 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 speci
fi
c gravity reading. The lower
the temperature, the lower the speci
fi
c 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 speci
fi
c 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 speci
fi
c 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
fi
gures 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.
Temperature Correction
Chart
030815
