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BATTERY repair
Sulfated Battery :
In addition to the required routine maintenance, storage batteries may, at some time during their service life, require more extensive or unusual care. Such care should be given as soon as it has been determined that a problem exists or that trouble may be developing. As a result, this section deals with the means of identifying existing or impending problems and offers possible solutions.
If the suggested operational remedies are ineffective, it may be assumed that there is an internal problem and it will be necessary to disassemble the cell or cells to inspect the elements and sediment well. If the cause of the problem can only be corrected by com- pletely rebuilding cells or the battery, this should be reported to the designated person in authority.
Restoring a Sulfated Battery
Undercharging a battery, even to a small degree, if continued, leads to excessive “sulfation.” The same is true of batteries which have been left standing in an uncharged state for an extended period. High temperatures rapidly accelerate sulfation when batteries are left standing in a partially charged condition. The cells of a sulfated battery will give low specific gravity and voltage readings. The battery will not become fully charged after a single normal charging when sulfation has taken place over a prolonged period.
If the sulfation has not progressed too far, it may be possible to restore the battery to a serviceable condition by using the following special procedures:
(1) Thoroughly clean the battery
(2) Bring the electrolyte level up to a point which is just visible over the separator protector by adding approved water.
(3) Put the battery on charge at the prescribed finishing rate until the rated ampere-hour capacity has been returned to the battery.
Record the voltage and specific gravity readings. Correct the specific gravity readings for temperature. If the temperature at any time during these procedures exceeds 110 degrees F., stop the charge and allow the battery to cool to 90 degrees F. or below before continuing. Charge the battery until the specific gravity shows no change during a 3 hour period while taking hourly readings. With automatic charging equipment, the battery may have to be placed on equalizing charge two or three times. If a battery is badly sulfated, the specific gravity may rise only 30 to 40 points (.030 to .040) during the first charge.
(4) Place the battery into service and discharge it to a fully discharged condition.
(5) Charge the battery again until the specific gravity shows no change during a 3 hour period.
(6) Repeat the cycling process until the specific gravity rises to within 30 points of a normal fully charged battery, then place the battery back in routine service. Even though specific gravities may be lower than normal they should not vary much from cell to cell. If they do, problems other than sulfation may be present. If the spread between the highest and the lowest gravity reading is 50 points or more, refer to the Troubleshooting Chart, Table 3-1, for help in identifying the problem. If the battery still has not responded to treatment, it should be replaced.
Cell Discharge :
Correcting Excessive Self-Discharge
While a storage battery is in a charged state, a local electrochemical reaction takes place within the cells which causes very gradual discharging. This is known as self- discharge. A small amount is quite normal in motive power batteries where grids are made from antimonial lead. The rate of self-discharge is temperature related, however, and increases significantly as temperatures rise. Table 3-2 shows the relationship between temperature and loss of specific gravity. The normal rate at 77 degrees F. to 80 degrees F. causes a loss in specific gravity of about one point (.001) per day. This becomes of concern only when a wet battery is to be stored for weeks at a time. It can be ignored as a factor in normal battery operation.
It is possible, however, particularly during the latter stages of a battery's life, for the rate of discharge to become much greater and even limit the battery's duty cycle. Excessive selfdischarge may be caused by defective separators or plates which have become shorted at the edges. Edge shorting is usually caused by loss of positive active material which can fill the sediment well or build up on the top or sides of the plates and eventually bridge the space between the positives and negatives. If a shorted condition seems likely, the element should be pulled for examination and the defective separator replaced, shorts cleared or cells replaced. Usually, if the sediment well is full, salvage is impractical.
Test Discharge
A capacity test is sometimes desirable to determine a battery's actual discharge capability as compared to its 6 hour rated capacity. This can be a significant diagnostic tool when equipment does not operate as expected and it can help determine when the battery should be replaced. When a battery consistently delivers less than 80% of its rated ampere-hour capacity, either some cells are sub-standard or it has reached the end of its useful life and should be replaced.
A test discharge is performed by discharging a fully charged battery at a fixed rate under carefully controlled test conditions.
DID YOU KNOW THAT ...
The individual cells, which con tain the energy generating components of the battery, may be arranged slightly differently for various types of batteries. The typical cell arrangement for 12 volt batteries (6 cells) is a single row of 6 cells; for 24 volts (12 cells) it is either two rows of 6 cells each or three rows of 4 cells each; for 32 volts (16 cells) it is four rows of 4 cells each; and for 36 volts (18 cells) it is three rows of 6 cells each.