the nameplate, and should not require adjusting during
of readings may be obtained by different men taking
the life of the battery, unless electrolyte is actually lost
hydrometer readings of the same electrolyte.
or spilled. Replacement of spillage should only be
b. Draw off enough electrolyte to fill the barrel of
made in regular battery shops.
the syringe to a level which will permit the hydrometer to
float freely without touching the barrel at either top or
124. Hydrometer Readings-Effect of Temperature
bottom. Allow the rubber bulb to expand completely and
and Level
hold syringe by the neck of the bulb.
a. Hydrometer or specific gravity readings of the
c. Shake the syringe gently to be sure hydrometer
electrolyte are affected by temperature.
Correct
is floating freely.
hydrometer readings if the temperature of the electrolyte
d. Hold the syringe at eye level.
is very much above or below 77F.
e. The point at which the electrolyte level appears
b. For each 3 degrees above 77F. add one point
to interseat the stem of the hydrometer, will indicate the
(.001) to the hydrometer reading, or for every 15 F.,
specific gravity readings to be recorded.
add 5 points.
f. Empty the hydrometer syringe completely,
c. For each 3 degrees below 77 F. subtract one
making certain that the electrolyte is returned to the
point from the hydrometer reading or for every 15 F.,
same cell from which it was taken.
subtract 5 points.
g. A clean accurate hydrometer syringe must be
d. Hydrometer on specific gravity readings are also
used. It must be disassembled and washed thoroughly
affected by the electrolyte height. The full charge
at least once a month. Avoid any dripping of electrolyte
specific gravity is based on the electrolyte level being at
from the hydrometer syringe.
the high limit of one-eighth inch below the bottom of the
h. To insure accuracy when water is added, take
filling tube in the cover. If the electrolyte level is at the
hydrometer readings before adding water. Water is
splash cover, the specific gravity readings are increased
lighter than electrolyte and will float on top of the
from 15 to 45 points, depending on the type of battery
electrolyte when added. A day or two will be required
involved.
for the water and electrolyte to mix thoroughly, after
which hydrometer readings may be assumed to be
125. Specific Gravity Reduction with Age
accurate again.
a. A too frequent mistake is made in assuming that
i. The fully charged specific gravity varies in
every battery, when charged, will reach the maximum
different types of batteries and is shown on the battery
specific gravity specified by the manufacturer.
nameplate.
b. A gradual reduction of fully charged specific
j. The discharged specific gravity (not shown on
gravity may be expected as the battery ages. This
the battery nameplate) also varies with the battery type,
reduction should not exceed 15 to 20 points during the
but is usually around 130 to 140 points lower than the
life of the battery, and should be taken into account
fully charged specific gravity.
when a battery is recharged.
k. The specific gravity or hydrometer reading of
c. Any greater reduction in fully charged specific
the electrolyte lowers on discharge and rises again on
gravity may indicate a loss of electrolyte. This may be
charge. Consequently, if we know the specific gravity
the result of watering too high, which could cause the
temperature and height of electrolyte above the splash
cells to overflow while on charge. Any electrolyte lost is
cover, we can estimate the approximate state of charge,
replaced with water, and will result in a loss in fully
provided that no electrolyte has been lost or added to
charged specific gravity.
the cells.
d. If no electrolyte is lost from a battery it should
l. A specific gravity reading 100 points below the
go through its entire life without the necessity of a
full charge value is a warning not only that the battery
gravity adjustment.
needs charging immediately, but that the charging
equipment probably has failed in some way and should
126. Low Individual Cell Readings
be checked.
a. Low individual cell readings (voltage or gravity)
m. The fully charged specific gravity of electrolyte
may be the first indication of trouble.
in new batteries is adjusted within the limits shown on
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