Explain Installation & Maintenance of VRLA Battery.
All POWER STACK batteries are rated to an end cell voltage of 1.75 VPC at all rates of discharge.
In this type of operation, the battery is connected in parallel with a constant voltage charger and the critical load circuits. The charger should be capable of maintaining the required constant voltage at battery terminals and also supply normal connected load where applicable. This sustains the battery in a fully charged condition and also makes it available to resume the emergency power requirements in the event of an AC power interruption or charger failure.
Float and Boost Voltages
Given below are the float and boost voltage recommended for the POWER STACK battery system. The average “Volts per cell” (VPC) value of the series string should be set to the recommended voltage under Float and Boost conditions.
- RECOMMENDED FLOAT VOLTAGE 2.25 VPC AT 27oC
- RECOMMENDED BOOST VOLTAGE 2.30 VPC AT 27oC
Modern constant voltage output charging equipment is recommended for the floating charger method of operation of batteries. This type of charger, properly adjusted to the recommended float voltage and following recommended surveillance procedures, will assist in obtaining consistent serviceability and optimum life. The charging current for the battery should be limited to 20% of its nominal AH capacity.
After the battery has been given its freshening charge , the charger should be adjusted to provide the recommended float voltage at the battery terminals.
Do not use float voltage lower or higher than those recommended. This will result in reduced capacity and/or reduced battery life.
Check and record battery terminal voltage monthly. See Section 8, RECORDS Item B. If normal battery float voltage is above or below the recommended value adjust charger to provide proper voltage as measured at the battery terminals.
Panel and portable voltmeters used to indicate battery voltage should be accurate at the operating voltage value. The same holds true for portable meters used to read individual cell voltages. These meters should be checked against a standard every six months and calibrated when necessary.
All batteries should be recharged as soon as possible following a discharge with constant voltage chargers.
The approximate state of charge of the battery, to some extent can be determined by the amount of charging current going to the battery. While charging the current shown by the charger ammeter will start to decrease and will finally stabilize when the battery becomes fully charged, if the normal connected load is constant (no emergency load connected). The state when the current level remains constant, after it has started decreasing, for three consecutive hours would indicate full state of charge condition and the battery will be ready for normal use.
If the normal connected load is variable (e.g. Telecom application) the state when the voltage across the battery terminals is stable for six consecutive hours would indicate full state of charge condition and the battery is ready for normal use.
Temperature of the Cell
The temperature of the POWER STACK cells cannot be measured during operation. However, cell temperatures are normally within +5oC of the ambient temperature. All performance characteristics are measured at ambient temperature and corrected to 27oC.
Section 6 – Equalizing Charge
Under normal operating conditions an equalizing charge is not required. An equalizing charge is a special charge given to a battery when non-uniformity in voltage has developed between cells. It is given to restore all cells to a fully charged condition. Use a charging voltage higher than the normal float voltage and for a specified number of hours, as determined by the voltage used.
Non-uniformity of cells may result from low float voltage due to improper adjustment of the charger or a panel voltmeter which reads an incorrect (higher) output voltage. Also, variations in cell temperatures greater than 3oC in the string at a given time due to environmental conditions or module arrangement, can cause low cells.
An equalizing charge should be given when the following conditions exist.
- The float voltage of the pilot cell (as per section 7) is at least 0.05V below the average float voltage per cell in the bank.
- A recharge of battery is required in a minimum time period following an emergency discharge.
- Accurate periodic records (see section 8) of individual cell voltages show an increase in spread since the previous readings.
Constant Voltage charging is the method for giving an equalizing charge. Determine the maximum voltage that may be applied to the system. This voltage, divided by the number of cells connected in series, will establish the maximum volts per cell that may be used to perform the equalizing charge in the shortest period of time. Refer to Table-C for voltage and recommended time periods.
|<15° C||2.30||30 hrs|
|15-32° C||2.30||20 hrs|
|>32° C||2.30||12 hrs|
Raise the voltage to the maximum value permitted by the system equipment or recommended equalizing charge voltage whichever is lower. When charging current has tapered and stabilized (no further reduction for three hours). Continue charging for the hours shown in Table C until the lowest cell voltage ceases to rise. Monitoring of cell voltages should be started during the final 10% of the applicable time period to determine lowest cell voltage in the battery system.
Section 7 – Pilot Cell
A pilot cell is selected in the series string to reflect the general condition of all cells in the battery. The cell selected should be the lowest cell voltage in the series string following the initial charge. Reading and recording pilot cell voltage monthly serves as an indicator of battery condition between scheduled overall individual cell readings.
Section 8 – Records
A complete recorded history of the battery operation is most desirable and helpful in obtaining satisfactory performance. Good records will also show when corrective action may be required to eliminate possible charging, maintenance or environmental problems.