Explain Installation & Maintenance of VRLA Battery.
Installation & Maintenance of VRLA Battery:
General
All POWER STACK batteries are rated to an end cell voltage of 1.75 VPC at all rates of discharge.
Floating Charge Method
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.
Voltmeter Calibration
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.
Recharge
All batteries should be recharged as soon as possible following a discharge with constant voltage chargers.
Determining State-of-Charge
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
General
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.
Equalizing Frequency
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.
Equalizing Charge Method
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.
Table-C
| Temp | Cell volts | Time |
| <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.
The following surveillance data must be read and permanently recorded for review by supervisory personnel so that any necessary remedial action is taken.
- Upon completion of the freshening charge and with the battery on float charge at the proper voltage for one week, read and record the following :
- Individual cell voltage
- Battery terminal voltage
- Ambient temperature
- Every 3 months, a complete set of readings as specified in paragraph A above must be recorded.
- Whenever the battery is given an equalizing charge, an additional set of readings should be taken and recorded as specified in paragraph A above.
The suggested frequency of record taking is the absolute minimum to protect warranty. For system protection and to suit local conditions or requirements, more frequent readings may be desirable.
Section 9 – Temporary Non-use
As installed battery that is expected to stand idle for over 6 months should be treated as follows.
Give the battery an equalizing charge as per section 6. Following the equalizing charge, open connections at the battery terminals to remove charge and load from the battery.
Every six months, temporarily connect battery to charger and give it an equalizing charge.
To return the battery to normal service, re-connect the battery to the charger and load, give an equalizing charge and return the battery to float operation.
Section 10 – Unit Cleaning
Periodically clean cell covers with a dry 55 mm paintbrush to remove accumulated dust. If any cell parts appear to be damp with electrolyte or show signs of corrosion, contact your local representative of the manufacturer.
| CAUTION
Do not clean plastic parts with solvents, detergents, oils, mineral spirits or spray-type cleaners as these may cause crazing or cracking of the plastic materials. |
Section 11 – Checking Connections
Battery terminals and inter-cell connections should be corrosion free and tight for trouble free operation. Periodically these connections should be inspected.
If corrosion is present, disconnect the connector from the terminal.
Gently clean the affected area using a brush or scouring pad. Apply a thin coating of petroleum jelly to the cleaned contact surfaces, reinstall connectors and retorque connections.
ALL TERMINALS AND INTERCELL CONNECTIONS SHOULD BE RETORQUED ATLEAST ONCE EVERY YEAR.
Section 12 – Determination of State of Charge of VRLA Batteries
Sealed Maintenance Free Valve Regulated Lead Acid Batteries represent the state of the art in Lead Acid technology.
The maintenance-free feature of these batteries often raises a practical problem in the field. How can the battery bank be monitored ? In conventional flooded batteries, the specific gravity of the electrolyte gives a fairly good indication of the state of charge of the battery. However, in a VRLA battery, it is not possible to measure the specific gravity of the electrolyte since it is completely absorbed in the spun glass microporous separator.
The terminal voltage of the battery is directly related to the concentration of the electrolyte. Therefore, if one were to measure the open circuit voltage of the battery, the state of charge can be determined. The Open Circuit Voltage (OCV) readings should be taken 24 hrs. after charging is discontinued. The OCV value is co-related to the state of charge of VRLA batteries as per the table enclosed.
Sometimes, it may not possible to disconnect the batteries from service for 24 hrs. and then check the OCVs. Then the pattern of charging current delivered by a temperature compensated voltage – regulated charger after a discharge provides the alternate method for determining the full state of charge. The temperature compensation factor is –3 mV per cell oC rise from ambient temperature of 27oC.
Under normal conditions the batteries are floated at around 2.25 volts per cell, i.e. in a DOT System 24 cells are floated at 53.5 volts. During charging as the cells approach full charge, the battery voltage rises to approach the charger output voltage, i.e. 53.5 volts and the charging current decreases to the float current value of around 50 mA/100 AH for VRLA batteries. So, when the charging current has stabilised at the float current for three consecutive hours or the voltage across the battery bank terminals is constant for six consecutive hours, then the battery bank can be considered as having reached full state of charge.
If the charging voltage has been set at a value higher (but equal to or less than 2.30 VPC) than normal float voltage (so as to reduce charging time), it is normal practice to reduce the charging voltage to the float value of 2.25V after 12 hrs. Then the float current will soon stabilize and the above methods can be adopted for determining the state of charge.
CAUTION: It was noticed in some of the exchanges during the normal course of day to day working, the exchange failing due to low voltage condition even though the batteries appear to be in healthy condition while they are on float as indicated by the daily readings recorded. To avoid this it is recommended that the batteries be discharged periodically, say once in a month by switching off the FR and the exchange load may be allowed to be taken by the battery for half an hour. The individual cell readings are to be taken and no cell voltage should fall below 2.10 V. Some cells which are faulty, may show negative values with reference to the other cells. If the voltage of any individual cell differs from others in this manner it is recommended that the cell be replaced.
Table
| % State of Charge | Open Circuit Voltage |
| 100 | 2.15 |
| 90 | 2.13 |
| 80 | 2.11 |
| 70 | 2.09 |
| 60 | 2.07 |
| 50 | 2.05 |
| 40 | 2.03 |
| 30 | 2.01 |
| 20 | 1.97 |
| 0 | 1.95 |
Float charging is at 2.23 VPC and the recommended boost charge voltage is 2.30 VPC.
If the charger does not have a float cum boost mode, it is important to switch over
to float after boost not later than 24 hours under steady current conditions.
Safety precautions
In normal use, VRLA batteries will not release hydrogen and oxygen gasses, will not release acid mist and will not leak acid. Thus they are more safer than conventional lead acid batteries. However, under abnormal conditions, or as a result of damage, misuse or abuse, these potentially hazardous conditions can occur. Hence the instructions given by the supplier is to be strictly followed.
Stacking limitation
The recommended limits on stacked battery configurations are as follows . See the diagram also .
| Module arrangements |
Max Modules |
| Horizontal single stack | 8 High |
| Horizontal multiple stack | 8 High |
Module assembly
This design is arranged to provide the shortest connections between modules using rigid lead coated copper strip connectors to maximise system performance
Modules are identified with a label located at the end of the module.
Each module is provided with a protective cover to prevent accidental contact with module live electrical connections.
Acceptance test for VLRA batteries
Charge the battery bank at 55.2v for 20 hours irrespective of the state of charge of the battery. Keep the battery under open circuit for not less than 12 hours and not more than 24 hours . Then discharge the battery at a constant current of I = 0.1 x C10 Amps. Stop discharge when the voltage of the battery falls to 42.0 V irrespective of individual cell reading .
Time in hours elapsing between the beginning and end of discharge shall be taken as period of discharge
The average ambient temperature during discharge shall be the average of the ambient temperatures noted at hourly intervals during discharge.
Correction for variation of capacity with temperature to 27o C shall be made in accordance with the formula given below
Capacity at 27o C=Ct + {Ct x R (27 – t )}/100
where Ct = Obtained capacity at t o C; R = variation factor from the table shown below
t = average room temperature.
| Discharge Rate | Variation factor in capacity per degree C; R percent |
| C10 | 0.43 |
| C5 | 0.58 |
| C3 | 0.68 |
The actual capacity corrected to 27o C shall not be less than 90 % of the rated capacity
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