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Lead-Acid Battery Construction
Lead-Acid Battery Construction Cont’d
Chemistry of lead acid battery
Pbo2 + Pb + 2H2SO4 PbSO4
+ PbSO4 +2H2O+e
Why does a battery die?Antimony
Acid
Temperature
Components of lead acid batteryPositive plate: Lead peroxide on lead
antimony/calcium grid.
Negative plate: Spongy lead paste on lead antimony/calcium grid.
Separator: PVC, fiber glass layered PVC material.
Electrolyte: Very weak sulphuric acid
Types of lead acid batteriesCranking Batteries: C20 rated
Stand-by Batteries: C10 rated
Traction Batteries: C5 rated
VRLA/SMF Batteries: C10/C20 rated
Solar/Wind/Renewable Energy Support Batteries: C10/C20 rated
Cranking Batteries Batteries with pasted positive and pasted negative
plates at C20/C10 rating.
For cranking 2 wheeler, 4 wheeler engines, aircraft, diesel engines and DG sets.
Capable of delivering very high one shot current equivalent to 5 times the rated capacity.
Stand-by Batteries With tubular positive and pasted negative plates,
generally rated for C10 rate of discharge.
Designed to deliver steady current for a definite duration with a defined end voltage.
Generally used as emergency support batteries in power generating stations, electrical sub stations and for all stand-by power requirements.
Traction Batteries Compact cell assembly with tubular positive and
pasted negative plates, rated at C5 rate of discharge.
Used in all electric vehicles, electric material handling equipments and for all traction applications.
Valve Regulated Lead Acid(VRLA) / SMF Batteries Batteries with pasted positive and pasted negative
plates with an absorbent type separator and a starved electrolyte design, rated C10/C20.
Designed to support stand-by applications such as UPS systems and also to meet brown-out requirements.
Solar/Wind/Renewable Energy Support Batteries Tubular positive with pasted negative, rated C10/C20
rate of discharge.
Designed with minimum self loss and best chargeacceptance qualities.
The battery grid is made of lead-calcium alloy tominimize heat generation, thus preventing water loss.
Improper initial charging.
Continuous usage of the system without focus on local generation.
Long duration of low charge level in the battery.
Why does a battery die in a solar installation?
Abuse in the form of external loads on the battery.
Having no alternative charging facility available at site.
Lack of preventive maintenance.
Types of Charging systemsTrickle charging
Float charging
Boost charging
Equalizing charging
Trickle ChargingGiven to cells when there is no permanent load on the battery bank.
Float ChargingSelected when there is a
permanent DC load. This charger continuously compensates the self loss of the cells and also takes care of the permanent DC load.
Boost ChargingBoost charger will have the facility of boost charging and trickle charging and also comes with float mode and boost mode depending up on the load pattern in the station.
Equalizing ChargingEqualizing charger is used once in a year
while correcting the imbalance in the specific gravity readings in a battery bank.
Generally the capacity of a boost charger will be to charge the batteries at max 5% rate of the capacity of the battery bank.
Voltage Setting for the Charger Trickle Charging:
2.16 to 2.25 volts per cell depending up on the type of battery selected. This charger cannot manage permanent DC load
Float Charging:
2.16 to 2.25 volts per cell depending up on the type of battery selected which accommodates a flow of 10% of the capacity of the battery plus the total DC permanent load in the station.
Boost Charging:
Boost charging mode will be capable of building the cell voltage from 2 volts per cell to a maximum of 2.75 volts with a maximum current of 15% of the capacity of the battery. This mode recharges a fully discharged battery.
Why and what is specific gravity imbalance?All cells record uniform specific gravity
reading above 1200 at room temperature.
All cells record low gravity less than 1200.
Some cells are ok but some cells low gravity.
All/some cells record high specific gravity beyond 1200 going up to even 1300.
High temperature effect on batteries
Battery is hot to touch.
Heavy acid smell in battery room.
High gravity in cell.
Battery looks bulged.
Drinks more distilled water.
Low float voltage effect on cellsBattery remains cool – no gassing, no
bubble.
Battery looses specific gravity gradually – 1200 – 1190 – 1150 – 1130 – nil.
When loaded voltage dips below 2 volts per cell and refuses to take the load.
“Sulphation” sets in.
Health check of a battery Check float voltage in the charger.
Check specific gravity of the battery – all the cells.
Check physical appearance of the battery – ok –swollen – hot – top dirty – white formation on terminals – smell of acid in the room.
Subject the battery bank for boost charging and record the time taken to attain maximum voltage on charge.
Discharge the battery at the rate of discharge recommended based on the type of battery.
The right battery room Battery room should have proper ventilation in the
form of air inlet and outlet system.
Should have a running water system.
Should have acid proof tiles on the floor and up to 6 feet in the wall.
The lighting and fan fixtures should not be vertically above the battery bank, that is the roof and should be on the side walls.
All metal portions like door knobs and windows should be painted with acid proof paints.
Cell configuration for 110 volts system If 55 cells are selected to provide 110 volts DC system –
2.25 volts X 55 cells = 123.75 volts.
This is more than the maximum DC tolerance on the load side. The maximum DC voltage required is 110 +/-10% = 121 volts.
Hence, the number of cells commissioned for 110 volts DC system is 110 volts / 2.25 volts = 53.77 cells. Therefore maximum cells can be 53 cells.
Cell configuration for 220 volts system If 110 cells are selected to provide 220 volts DC system
–
2.25 volts X 110 cells = 247.50 volts.
This is more than the maximum DC tolerance on the load side. The maximum DC voltage required is 220 +/- 10% = 242 volts.
Hence, the number of cells commissioned for 110 volts DC system is 220 volts / 2.25 volts = 107.55 cells. Therefore maximum cells can be 107 cells.
What happens if floated at 2 volts per cell?No current will flow into the cells.
Battery slowly discharges and sulphation starts.
Will refuse to take load when needed.
If floated for long at 2 volts per cell, the battery bank dies.
What happens if floated at higher voltage beyond 2.25 volts per cell?Cells get overcharged.
Temperature shoots up.
Heavy gassing and water evaporation and records high specific gravity.
The battery bulges.
Battery room smells of acid.
Battery bank dies prematurely.
Hydrometer – Why is it needed?
What happens when the battery is under fed?
Discharged Battery:PbSo4(positive)+PbSo4(negative)+h2O+0e
Fully Charged Battery:
Pbo2+Pb+H2So4 PbSo4+PbSo4+H20+e
Battery Terminals
• Positive Terminal diameter is bigger.• Negative Terminal diameter is smaller.
Battery Terminal Cables• Copper multi strand cable to be properly soldered to the terminal.
• Any loose strands leads to loss of energy and heat generation at the terminal.
• Further leads to corrosion and sulphation.
What is Sulphation?
White formation on the terminals.
Green formation on the terminals.
Electrolyte turning milky white.
Positive and negative plates having white spots/flakes.
Causes for Sulphation
A discharged battery kept unfed for long
Dead short in some of the cells.
Topping up with tap water, borewellwater, mineral water.
Foreign material falling into the cell like nuts or bolts.
Remedies for Sulphation
Immediate recharging removes sulphation from the cells.
Removal of the foreign body from the cell and feeding energy till it is fully recovered.
Removal of the impure electrolyte from the cell and topping it up with distilled water and recharging the cell.
Storage of Battery A dry and uncharged battery is electrically
inactive and can be stored for a long period.
Addition of electrolyte begins the life of the battery.
A wet battery should be kept fully charged and should be on trickle charge mode always.
A discharged battery should not be kept without feeding. This will terminate the life of the battery.
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