What is VRLA Battery
VRLA Batteries
Batteries can store DC energy and these energies are used to operate our devices and systems that require electricity to operate.
Batteries are created by flowing an electric current between two different metals absorbed in a solution (electrolyte) and creating an electrical potential between the two plates. The potential value (or voltage) depends on the plate materials used and the electrolyte.
Battery capacity is defined in Ampere hours (Ah). The battery voltage increases with the number of cells, and the battery capacity increases with the plate surface.
Many types of batteries are used today. Batteries are divided into types according to the types of metals used such as lead acid, nickel cadmium, nickel iron.
The lead acid battery cell uses lead and lead-oxide plates absorbed in sulfuric acid electrolyte.
There are two types Lead Acid Battery. Valve Regulated Lead–Acid (VRLA) and Flooded Vented Lead–Acid batteries.
A valve regulated lead–acid (VRLA) battery is a type of lead–acid battery characterized by a limited amount of electrolyte absorbed in a plate separator or formed into a gel.
There are two primary types of VRLA batteries, absorbent glass mat (AGM) and gel cell. Gel cells add silica dust to the electrolyte, forming a thick putty like gel. AGM (absorbent glass mat) batteries feature fiberglass mesh between the battery plates which serves to contain the electrolyte and separate the plates.
Both types of VRLA batteries offer advantages and disadvantages compared to flooded vented lead–acid (VLA) batteries, as well as to each other.
VRLA Batteries can be mounted in any orientation, and do not require constant maintenance due to their construction.
While in VRLA battery, they preserve the generated gases internal to the battery till the time that pressure levels are in a safe limit. In general functioning scenarios, the gases might get combined inside the battery or in some cases using a catalyst substance or an electrolyte. Though the pressure value surpasses the safety levels, then safety valves are opened to allow additional gases to escape. And thus because the pressure is regulated to the permitted levels. Because of this, the batteries are named as “Valve Regulated”.
Therefore, it is very safe and has a much longer shelf life.
VRLA Batteries are used as backup energy sources in Uninterruptible Power Supplies in case of mains power failure or if Uninterruptible Power Supplies are out of operating tolerances. Batteries can be mounted in the cabinet of Uninterruptible Power Supplies, they can also be mounted in a separate cabinet or can be placed on racks.
Generally Nominal Voltage of VRLA battery used in Uninterruptible Power Supplies is 12 Volt formed by the serial connection of six cells.
Since the batteries are connected to the DC Bus line of the Uninterruptible Power Supply, they are connected in series until the Uninterruptible Power Supply DC Bus voltage is obtained.
The total voltage of the connected batteries is equal to the total voltage of each battery connected in series, and the number of batteries must be determined in accordance with the DC Bus voltage value of the UPS. With this connection type, the total battery capacity does not change, it remains equal to the Ah capacity of any worst battery.
The backup time of the Uninterruptible Power Supply in case of an outage is directly proportional to the battery capacity. If this period is desired to be extended, either the Battery Capacity must be increased or the Battery Group must be connected in parallel. Parallel connection is created by connecting two or more serial battery groups in parallel with each other. Each branch should have the same number and capacity of batteries. Batteries are connected in parallel for two reasons:
• Increasing the capacity (total capacity is equal to the sum of each battery arm capacity.)
• Increasing system reliability (Thanks to the batteries in the parallel arms, a single defective battery in a branch does not prevent the UPS from feeding from the battery.)
It is not common practice to normally use more than six parallel battery branches.
The batteries used in both series and parallel connected battery groups must be the same with each other.
In parallel connection, the battery charge capacity of the Uninterruptible Power Supply should also be taken into consideration. Using more batteries than the battery that the UPS can charge will cause the batteries to be charged in a longer time and with less capacity, thus reducing the safety of the system and shortening the battery life.
FACTORS AFFECTING THE OPERATING LIFE OF BATTERIES
• NEVER store VRLA batteries in a discharged or partially discharged state. (An open circuit voltage lower than its nominal value may indicate sulfation)
• Do not exceed the battery waiting time on the shelf. Please refer the manufacturer advise for recharging operation.
• Do not overcharge batteries. Excessive charging voltages cause excessive charging currents to flow from the battery, causing thermal power losses and gas release from the safety valve. This situation causes corrosion of the positive plate material in a short time and shorten the life of the battery rapidly.
• Batteries should be stored in suitable temperature and humidity conditions.(Recommended 20-25 °C).
• Battery life decreases to 25% at 40 °C temperature.
• High temperature shortens the service life of the battery and causes oxygen / hydrogen gas to form. The battery in this state cannot be restored.
• Batteries should never be subjected to deep discharge.
• 1.67 V / cell is the limit value for most VRLA batteries.
• It negatively affects the battery capacity and service life.
• It causes the plates to become sulphated and the internal resistance of the battery to increase.
• Depending on the depth of discharge, the battery can be restored by careful recharging.
• Batteries should be charged with a clean DC Voltage.
• Batteries are DC power storage elements and need to be charged with DC voltage. AC voltages on the DC charging voltage reduce the operating life of the batteries.
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