IEEE 1188a-2014 pdf download

IEEE 1188a-2014 pdf download.IEEE Recommended Practice for Maintenance, Testing, and Replacement of Valve-Regulated Lead-Acid (VRLA) Batteries for Stationary Applications.
Cell dry-out is the result of an abnormal increase in the rate of water loss from the cell, which leads to reduced contact between the plates as well as a reduced contact with the sides of the container. The following efects were originally thought to be independent of each other, are now understood to be related to negative self discharge andor dry out. Some of these are reversible and some are not.
一Higher acid specifie gravity (stronger acid) as water is lost. (The open circuit cell voltage increases as the acid speeifie gravity increases).
Higher float current occurs even when the float voltage is corret This is the most direct and practical indicator of negative self- discharge.
Negative strap corrosion (which is virtually never seen on vented (looded) bttres).
Increased rate of positive grid corrosion (This leads to shorter life if the cell does not dry out first).
-Excssive positive grid growth rates leads to possible short cireuits under the negative straps. This abnormally high positive grid growth can be visually observed when the covers are pushed out around the positive posts and the covers are distorted in those loeations as compared to the rest of the cell cover. Higher positive grid growth rates can also lead to other intemnal short circuits.
Measuring plate potentials in a vented (looded) cell is relatively casy, but it is much more complicated in a VRLA cell. This difficulty is why one of the simplest field measurement to determine the presence of negative self-discharge is the float current of the string. Open cireuit voltage of the cell is another method.
In a vented (looded) cell it is easy to check plate voltages separately by placing a reference electrode into the cell electrolyte and reading the“af-cell” voltage directly with a voltmeter. But a VRLA cell is sealed to prevent oxygen from entering. so if the vent is removed to insert a reference elecrode, the oxygen from the outside air will oxidize the negative plate, depressing its voltage and thereby disturbing the reading.
Isalling a reference ectrode into a VRLA cll in a lab is certainly possible, if done with great care, but extremely difcult to do so in the field with the battery in service. That is why the easiest and best field measurement to determine the presence of self- discharge in the field is to measure the float curent, since float current tends to increase with time and the dry-out in all cells that are prone to negative discharge.
However, this reading is not instantaneous, but rather a matter of multiple readings to record and establish trends.
Another factor that helped conceal the self- discharge phenomenon from the battery industry for so long is that plate voltage readings will generally be quite satifactory on all VRLA cells when they are new. This result is because new cells are generally shipped very wet with electrolyte so that they behave esentially like vented (loo) cells for the first period to time (perhaps a year or more). After this time frame the battery will continue to dry out, become true VRLA cells, and will begin to deteriorate. At this point the battery will either have a problem of negative self-discharge or not depending upon the purity of their naste.
With vented (flooded) cells, the negatives are submerged in acid so that the oxygen in the headspace of the cell can’t get to the negative plate to discharge it. In VRLA cells, on the other hand, oxygen is channeled directly 1o the negatives through voids in the AGM separator. (Indeed the principle of the VRLA cell depends upon this process). If the negative plate also has a propensity to self-discharge chemically simply due to its own impurity, the two efeets taken together, oxygen and impurity, can lead to negative plate self-discharging during float charge.
There are methods available to recover reversible PCL. These are catalysts, rehydration and high-rate charging. These are described below.