23
Rev.12/31/97
Normal lead sulfate formed on discharge is in a form that a charge will
easily reconvert. When a battery is "over sulfated," plates are less porous
than normal and absorb a charge with difficulty. With this condition, an
ordinary charge will not reconvert all the sulfate to sulfuric acid and specific
gravity remains below normal. Active material of "over sulfated" negative
plates is light in color and either hard and dense or granular and gritty and
easily disintegrated. The negative plates require the prolonged charge
necessary to restore an "over sulfated" battery. An individual cell may
become "over sulfated" by external grounding, by an internal short, or by
drying out because of failure to add water. Over sulfation may also be caused
by prolonged low float charging.
easily reconvert. When a battery is "over sulfated," plates are less porous
than normal and absorb a charge with difficulty. With this condition, an
ordinary charge will not reconvert all the sulfate to sulfuric acid and specific
gravity remains below normal. Active material of "over sulfated" negative
plates is light in color and either hard and dense or granular and gritty and
easily disintegrated. The negative plates require the prolonged charge
necessary to restore an "over sulfated" battery. An individual cell may
become "over sulfated" by external grounding, by an internal short, or by
drying out because of failure to add water. Over sulfation may also be caused
by prolonged low float charging.
2.24 ELIMINATION OF OVER SULFATION
2.24 ELIMINATION OF OVER SULFATION
A battery or cell that is "over sulfated" should be charged fully in the regular
way until specific gravity stops rising. Then one of the weakest cells should
way until specific gravity stops rising. Then one of the weakest cells should
be discharged through a load resistor at the normal 8-hour discharge rate to
a final voltage of 1.75 volts. The battery is not over sulfated if the
representative cell gives normal capacity, that is, about 100 percent rated
capacity for a fairly new battery or down to 80 percent of initial rated
representative cell gives normal capacity, that is, about 100 percent rated
capacity for a fairly new battery or down to 80 percent of initial rated
capacity for a battery nearing the end of its expected life.
If the above capacity is not obtained, possible over sulfation should be
treated as follows:
treated as follows:
1. In cases where one or more individual cells have become "over sulfated"
and the rest of the battery is in good condition, these cells should be
treated separately after removing them from the circuit.
treated separately after removing them from the circuit.
2. Recharge the removed cells at half the 8-hour discharge rate. Record
hydrometer readings and temperature at regular intervals (3 to 5 hours)
during the charge to determine if rising specific gravity has peaked.
Maintain constant electrolyte level by adding water after each reading.
Do not add water before taking readings.
during the charge to determine if rising specific gravity has peaked.
Maintain constant electrolyte level by adding water after each reading.
Do not add water before taking readings.
3. Continue the charge, recording the readings until no further specific
gravity rise has occurred in any cell for 10 hours. If the temperature
reaches 100 °F, reduce the current or temporarily interrupt the charge so
as not to exceed this temperature. When the specific gravity has reached
maximum, terminate the charge and record the hydrometer reading of
each cell.
reaches 100 °F, reduce the current or temporarily interrupt the charge so
as not to exceed this temperature. When the specific gravity has reached
maximum, terminate the charge and record the hydrometer reading of
each cell.
4. The cells must be replaced if they again fail the capacity check in 2.24.