Frequently Asked Questions
A battery can be anydevice that stores energy for later use. The word battery is limited to anelectrochemical device that converts chemical energy into electricity, by useof a galvanic cell. A galvanic cell is a simple device consisting of twoelectrodes – positive & negative and an electrolyte solution. Batteriesconsist of one or more galvanic cells with a potential difference between theelectrodes.
a. There are different types of batteriesdepending on the application.
b. Used for UPS,Telecom, Automotive and industrial applications
c. Used inlaptops, phones etc.
Lead-acid is the oldest rechargeable battery in existence. Invented bythe French physician Gaston Planté in 1859, lead-acid was the firstrechargeable battery for commercial use. LeadAcid batteries use chemical reaction between lead dioxide positive electrode,pure lead negative electrode and dilute sulphuric acid to store and regenerateelectrical energy as per requirement.
Lead Acid Batteries can be classified by application or byconstruction or by design.
· Used in automobiles forstarting the engine, ignition, and lighting
· Used for UPS, Inverter,Telecom, Solar
· Used forForklifts, Golf Carts, Railway coaches
· Traditionalbattery design where the battery container has liquid electrolyte and typicallythe containers are large and bulky.These batteries require periodic maintenanceby topping up distilled water as gases are vented during the operation of thebattery.
· Thebattery container is sealed and there’s no free electrolyte that will spill.This type of battery does not require any topping up of distilled water.
· Thepositive and negative plate inside the battery is of a flat construction. Theplate is made by pasting a mixture of lead oxide on to a grid made from leadalloy. This is then cured and the paste hardens into a cement like mass.Here the positive plate is made of a setof parallel tubes filled with lead oxide. The negative plate remains as a flatplate.
Mostpeople tend to associate a lead acid battery with an automotive battery andhence end up using automotive batteries for UPS & inverters leading toproblems. The two applications are vastly different from each other.
Thesebatteries are used for starting an engine which requires a very high currentfor a few seconds. Once the engine starts a small current is used for ignitionand lighting and the battery is already charging in parallel. Hence theautomotive batteries are designed with thin flat plates that are designed toprovide high current discharge for a very low duration. The plate thickness istypically below 2 mm. However the containers are very robust since they aremounted in moving vehicles and should withstand jolts and severe vibrations.
Thesebatteries are designed for variable and extendable loads and are hence morecomplex in design than automotive batteries. The different types of IndustrialBatteries are
· Theseare typically used for inverters.
· Theseare used for inverters, UPS and Solar applicationsThese are sealed maintenance freebatteries used for UPS, Telecom & Solar applications. ‘VRLA’ stands for‘Valve regulated lead acid’. In sealed batteries, due to chemical reactionsinside the battery gases are formed. Sometimes due to over charging, more gasesare formed that needs to be released from the battery container. This is doneby using valves that release under a certain pressure. Otherwise the batterieswill explode.
· LowerInitial Cost
· Easierto manufacture
· Shortlife span
Flatplate batteries are cheaper & easier to manufacture but offer lower cycliclife. Cyclic life is the number of times the battery can be charged anddischarged over its life span. A flat plate battery will typically offerbetween 200 – 400 cycles (depending on design, make etc) at 80% Depth ofdischarge. Depth of discharge is the extent to which the battery is dischargedbefore being charged. 80% DOD means it’s discharged to 80% of it’s capacitybefore being charged again.
· Longlife span – 3 times of a flat plate battery.
· Lowercost of ownership.
· Requiresless frequency of topping up than flat plate batteries. Battery can be revivedeven if plates sulphate due to improper maintenance.
· Initialhigher cost.
· Difficultmanufacturing process.
· Givesslightly lower backup time than flat plate battery of the same AH rating.Tubular batteries use a special technology wherethe active material is encapsulated in tubes that prevent ‘shedding’. This prolongsthe life of battery while undergoing long charges and discharges. Typicallytubular batteries give more than 1000 cycles of life at 80% DOD which is 3-5times that of a flat plate.
· Canbe used in extreme conditions like high temperature, since electrolyte loss dueto high temperatures can be compensated by frequent topping up of distilledwater.
· LowerCost per AH compared to SMF batteries.
· Regulartopping up and maintenance required, otherwise battery will die.
· Gasesgenerate unpleasant odour, hence cannot be used in regular office environment.
· Needsto be stored / used in vertical position.
· Needsfar more space than SMF batteries.
· Notopping up required.
· Environmentfriendly and can be used in office environment.
· Canbe stored / used in any position.
· Requiresvery less space.
· Cannotbe used in extreme conditions, since water loss cannot be compensated bytopping up. Life of SMF battery comes down by half for every 10 degree rise intemperature. Typical life is 250-300 cycles at 100% DOD at 25 degree Celcius.Can be used only with UPS or any device withclean DC charging. Use with inverters that has a high ripple content in thecharger will lead to shortened life of the plates.
AH is a measure of how much current a battery can dischargeover a certain period. It’s the ratio between current (A) and time – hour (H).For example a 100AH battery means the battery can discharge a current of 5 ampsover a period of 20 hours. It can also mean the battery can discharge a currentof 10 Amps over 10 hours. However the capacity of a battery that discharges 5amps over 20 hours is less than that of a battery that discharges 10 amps over10 hours, even though both are arithmetically 100AH. This is because higher thecurrent discharge, the more the energy loss and hence lower the time it candischarge.
That’s why it’s important to understand the standard ofdischarge to ensure accurate understanding of the rating. The industry standardis ’20 hours’. Therefore the rating of any battery means the quantum of currentthe battery can discharge over a period of 20 hours. A few examples are givenbelow for understanding.
It’s ameasure of the discharge time over which the battery is rated. C20 is a 20 hourdischarge, C10 is a 10 hour discharge, C5 is a 1 hour discharge and so on. Forexample a 7 AH battery should be able to discharge 0.35 amps over 20 hours. Butthe same battery will probably deliver only 9 hours of discharge if dischargedat 0.7 amps i.e double the current. This ratio delivers only 6.3 AH (0.7 amps *9 hours)
While purchasing a battery it’s important to check thedischarge ratios over different time periods to understand the efficiency ofthe battery. Any good manufacturer will always provide this data in the batteryspecifications.It’s important to note that in real life, mostbatteries used for UPS & Telecom backup applications are discharged over aperiod ranging from a few minutes to maybe 4 hours. So the real AH delivered isalways less than half to 3/4th’s of the rated capacity at 20 hours. This is oneof the reasons why the battery over sizing has to be considered whilecalculating backup times for a UPS.
Wh is a measure of power that a battery can discharge inWatts over a certain period . It’s the ratio between W(Watts) and Time(Hours).Relicell Ultra Gel Batteries are rated in Watt-hour since it gives the consumera precise idea of the load that can be supported for a specific period. Allratings are based on a repitive load of 400 Watts connected to an 800 VA homeinverter and the backup time obtained
For Example a 1000 Wh battery will deliver 2.5Hours of backup on a 400 Watts Load( 400 W * 2.5 h =1000 Wh)
Float life refers to the period the battery will last when it’s under‘float use’ i.e the battery voltage is maintained at approximately 13.5V duringusage. For a layman’s understanding, this is the condition the battery is inwhen connected to a UPS and there is no powercut or there’s generator backupi.e battery is never discharged.Battery float life for a VRLA battery variesfrom 3 years to as high as 25 years depending on the design. Lower the designlife, lower the cost of the battery and the quality.
isthe most destructive element in battery service. During overcharging, excessivecurrent causes the oxides on the plates of the battery to ‘shed’ andprecipitate to the bottom of the cell and also heat the battery, thus removingwater from the electrolyte. Once removed, this material (which representscapacity) is no longer active in the battery. In addition, the loss of waterfrom the electrolyte may expose portions of the plates and cause the exposedareas to oxidise and become inactive, thus reducing additional capacity. Sealedbatteries are not immune from the same internal results when overcharged. Infact, sealed batteries are particularly sensitive to overcharging. Oncemoisture is removed from the battery, it cannot be replaced. Portions of the batterydamaged due to overcharging are irretrievable. However, if detected early,corrective adjustments to the charging device will save the undamaged portionof the battery. Initial signs of overcharging are excessive usage of water inthe battery, continuously warm batteries, or higher than normal batteryvoltages while under the influence of the charger.
over a period of time also damages batteries.Insufficient charging leads to a problem called sulphation of the plates. Thisis a typical problem for long back duration UPS’s where the charger currentcapacity is less than 10% of the battery current rating. For example, whileusing a 100AH battery, the charger capacity should be ideally 10 amps.
Batteries go into a state of discharge when it reaches avoltage of 1.75 volts per cell or 10.5 volts in case of a 12 volt battery.Discharging the battery beyond this point may result in the battery reaching apoint of no return. The lowest a 12V battery should be discharged to is 9.6Vi.e 1.6V per cell. Continuous cycling to low voltage levels reduces the cyclelife of the battery.
Most devices have a ‘low battery cut off’voltage setting beyond which the battery is cut of from the circuit and stopsdischarging. If this is not present in a device using a battery, most certainlythe life of the battery will be drastically reduced.
The health of an SMF battery can be determined by checkingthe OCV (Open circuit voltage) of the battery. A healthy battery will have anOCV above 12.8V. Any voltage below this means the battery is not sufficientlycharged and needs a charge. The typical OCV readings should be as follows
· Justafter unpacking at site: Minimum 12.80 V
· Justafter connecting on float: Minimum 13.30 V
· After2 days of float charging: Minimum 12.95 V
The health of a flooded battery canbe determined by checking the OCV and also by checking the specific gravity ofthe electrolyte. Specific gravity is a unit of measurement for determining thesulphuric acid content of the electrolyte. The recommended fully chargedspecific gravity of flooded batteries is 1.255 to 1.265 taken at 80°F. Morethan .025 spread in readings between fully charged cells indicates that thebattery may need an equalization charge. If this condition persists, the cellis failing and the battery should be replaced. Since water has a value of1.000, with electrolytes having a specific gravity of 1.260, it means that itis 1.260 times heavier than pure water even while pure concentrated sulphuricacid has a specific gravity of 1.835.
The following table illustratestypical specific gravity values for a cell in various stages of charge:
· 100%Charged…….1.255 – 1.260 Sp. Gr.
· 75%Charged…….1.220 – 1.225 Sp. Gr.
· 50%Charged…….1.185 – 1.190 Sp. Gr.
· 25%Charged…….1.150 – 1.155 Sp. Gr.0% Charged…….1.115 – 1.120 Sp. Gr.
Batterycondition at time of installation:
· BatteryOCV should be minimum 12.8V. If less than 12.8V, then the battery should begiven a float charge till it reaches the desired voltage of 12.95 to 13V. Incase the battery cannot take charge, the battery has to be replaced.
· Ifconnecting in a string, then the OCV of all the batteries in the string shouldbe in the range of 300 millivolts of each other. For example if there are 16batteries being connected, then the OCV ideally should be between 12.8 to13.1V. Any higher or lower readings should be noted and the batteries given an‘equalisation charge’. This is done by float charging the battery for a minimumperiod of 12 hours (13.5 – 13.8V) and then doing a C10 discharge for about 6 to8 hours. Regular voltage readings of all batteries should be noted every 30minutes. The cycle of charge and discharge is done till all batteries reach thedesired voltage range within 300 mv. In case there’s a battery not within therange even after equalization, replace the battery.
· Physicallyexamine the battery for any sign of electrolyte leakage or visible damages tothe battery container.
· Checkthe condition of the positive and negative terminal connectors – they shouldnot be corroded.
Site condition at time of installation:
· Thesite should be well ventilated and airy to ensure proper dissipation ofhydrogen gas that is emitted by batteries. Hydrogen is highly inflammable andtherefore dangerous when accumulated in closed spaces.
· Properearth fault and insulation of the battery racks / stand to prevent currentleakage to the ground.
UPS condition at time of installation:
· Ensurecharging current is proper.
· Checkfloat and boost voltages of the UPS. Should be 13.5 – 13.8V for float chargeand 14.5 in boost charge mode with automatic return to float mode.
· Batterytype, capacity, make and age should be similar in the string.
· Thecorrect length and cross section of interconnecting cable to be used.
· Torqueused will be same for type of bolt used. Torque recommendations are typicallygiven in the battery specification sheets. It’s recommended that the techniciandoing installation use a torque wrench for tightening the bolts.
· Morethan 3 strings of batteries should not be paralleled. Here, it’s recommendedthat each string has a separate charger to ensure proper charging.