hours. For temperatures 40°F (4°C) to 54°F (12°C) use
four times the number of hours.
10.3 Equalizing Individual Cells
When only a few cells in a battery require equalizing, and
system voltage limitations do not permit raising the battery
voltage up to a recommended equalizing voltage, a sepa-
rate voltage regulated charger may be used on the affected
cells.
The charger must have complete AC line isolation and
should be paralleled across the below normal cell. Select
the equalizing voltage values listed in Tables D for the
type cell involved. The hours of equalizing may have to
be increased from listed values before stabilization of cell
voltage and specific gravity is achieved, especially where
below normal condition has existed for a prolonged period.
10.4 Equalizing Charge—Electrolyte
Levels
A battery which has electrolyte levels at the high level line
while on a float and then placed on equalizing charge will
result in a rise in electrolyte above the high level line. This is
a normal condition. DO NOT remove any electrolyte as the
levels will return to their former condition when the battery
is returned to normal float. Removal of the electrolyte with
subsequent restoration to proper electrolyte levels by water
addition could result in variations or sub-normal specific
gravity values.
SECTION 11
11.0 Specific Gravity
In a lead-acid cell, the electrolyte is a dilute solution of water
and sulfuric acid. Specific gravity is a measure of the weight
of acid in the electrolyte as compared to an equal volume of
water. Therefore, electrolyte with a specific gravity of 1.215
means it is 1.215 times heavier than an equal volume of
water which has a specific gravity of 1.000.
11.1 Hydrometer Readings
Specific gravity is used in determining a cell’s state of
charge. It decreases as the cell discharges and increases
as the cell is charged; reaching its original value when the
cell is fully charged. Specific gravity is expressed to the third
decimal place (1.215) and is measured by a hydrometer
float enclosed in a glass barrel/rubber bulb syringe. Draw
sufficient electrolyte into the barrels holding the syringe ver-
tical and with no hand pressure on bulb; so that float is freely
floating without touching sides or top of syringe.
The gravity is read on the hydrometer scale at the flat sur-
face of the electrolyte. (See Figure 5).
Clean the hydrometer glass barrel and float with soap and
water as required for ease of reading and float accuracy.
When recharging a lead-calcium cell, the specific gravity
reading lags behind the ampere hour input due mainly to the
very low end of charge currents. Mixing of the electrolyte is
slow due to the small amount of gas generated; so the gravi-
ty readings do not reflect the actual state of charge. A similar
condition exists after water additions. Therefore, meaningful
gravity readings can only be obtained at the top of the cell
after an equalizing charge or after six weeks on float.
For this reason, most GNB lead-calcium cells have electro-
lyte withdrawal tubes to permit sampling of the electrolyte
at a point one third down from the top of the plates. A long
rubber tip on the hydrometer is inserted into the tube to
provide an average value of cell specific gravity and a more
accurate indication on the state of the charge.
9
CAUTION!
WHEN INDIVIDUAL CHARGER IS REMOVED
FROM CELL WHICH HAS BEEN EQUALIZED,
A DROP IN VOLTAGE BELOW THE
AVERAGE STRING VOLTAGE MAY OCCUR.
THIS IS NORMAL, DUE TO THE EXCESS
INTERNAL CELL GASES PRESENT. AS
THESE EXCESS GASES DISLODGE FROM
INTERNAL CELL COMPONENTS, THE CELL
VOLTAGE WILL RISE GRADUALLY, WHICH
MAY TAKE FROM TWO TO FOUR WEEKS.
Figure 5
