“My UPS is not giving sufficient back up”. This is the most common complaint raised by PC users. It is not the fault of the UPS, but is due to the poor maintenance of its battery. Sealed batteries are used in UPS, Emergency lamps etc do not require water and acid top up. There is no water loss in these batteries during the charge/discharge cycle and it can be positioned in any direction like vertical, horizontal etc. These sealed batteries are known as SMF (Sealed Maintenance Free) or VRLA (Valve Regulated Lead Acid) batteries and they work on the oxygen recombination principle. SMF battery is totally maintenance free and has longer cyclic life, thus compensating the initial higher cost. One of the important aspects of battery life in relation to the use of equipment is the cut off voltage set in the equipment. If properly maintained, the sealed battery can give sufficient back up time. Let us see the tips to increase the life of UPS and Inverter battery.
Based on the use, the SMF battery is classified into three types
1. 6 Volt 4.5 Ah type
These are used in Emergency light applications and telecom instruments. These are small sized with 4.5 Ampere hour current capability.
2. 12 Volt 7.2 Ah type
This type is used in offline UPS and can deliver much current.
3. Big type
Big type SMF battery is used in Online UPS.
New forms of SMF batteries are being designed to get better performance and cost effective. Some of the specially designed batteries include Deep discharge battery for longer cyclic life, high discharge battery, Front access battery to monitor the terminal voltage, Gel type battery for longer cyclic life and temperature tolerance etc.
Long Cyclic life
SMF battery is totally maintenance free and has longer cyclic life, thus compensating the initial higher cost. One of the important aspects of battery life in relation to the use of equipment is the cut off voltage set in the equipment. For example in inverter systems using high current batteries like 150Ah, a cut off voltage less than 10.5 volts can shorten the life of the battery. If the cut off voltage is set as 11.5 volts, it will increase the battery life since the battery is not entering into the deep discharge state.
In the SMF battery, the chemical recombination occurs in the Positive plate as per the following equation
H2O = ½ O2 + 2H+ + 2e-
In the negative plate, the reaction occurs as
2Pb + O2 = 2PbO
PbO + H2SO4 = PbSO4 + H2O
PbSO4+2e- + 2H+ =Pb + H2SO4
During the chemical reaction, the oxygen evolved from the positive plate recombines at the negative plate and the hydrogen formation is suppressed. As a result, there is no gas formation inside the battery, during its operation. This makes the battery clean and eco-friendly. Another important feature of the battery is that there is no free acid or electrolyte so that the battery can be placed in any position and there is no leakage. There is an Absorbed Glass Mat or AGM inside the battery that holds the acid. The acid is thus in an immobilized form as gel. In order to avoid excess pressure and battery explosion, vent valves are provided to release the pressure inside the battery.
How to optimize the SMF battery performance?
In order to increase the life of battery, it is necessary to monitor the battery performance constantly. Here are some tips to optimize the battery performance.
1. The SMF battery should be placed in well ventilated area to avoid high temperature environment. With each 10 degree rise in air temperature, the float life reduces to half. If the battery is installed in equipment, it is necessary to isolate it from heat generating components like transformer.
2. In order to prevent deep discharge, it is necessary to set the cut off voltage to 11.5 volts in 12 volt battery and 4.5 in 6 volt battery.
3. It is necessary to prevent no load battery drain. The additional components of the equipment such as sensors, displays and indicators consume power in the no load condition. So if the equipment is not provided with automatic charging, this power loss leads to deep discharge.
4. Boost cum float charging is suitable for SMF battery. If the power failure is frequent, the battery should be charged immediately to acquire full charge before the next power failure.
5. If there is any problem such as low backup time, battery heating, low terminal voltage even after continuous charging develops, the battery should be attended immediately.
6. If the equipment is not using for long time, it should be charged once in every week. If the battery is allowed to charge and discharge frequently, its life can be extended to 3-5 years.
7. Do not over charge the UPS battery. Do not leave it plugged always. Charging during the PC use is sufficient to keep the battery charge.
8. If there is no power failure, discharge the battery once in a week, by running the PC in UPS.
9. It is better to give an external boost charging to Inverter battery once in a month using a 15 volt 5 Amps charger after disconnecting the inverter from the battery.