The demand for power is rising continuously in automobiles. Starter motors, increasing number of electrical devices are demanding more input from the battery and alternator. Vehicle’s energy sources, battery and alternators face several challenges such as:
Battery principle:
A chemical reaction between the electrodes and electrolytes generate electricity. Battery is the storage unit for the electricity and supplies it to the vehicle loads based on the demand. The supply of electricity discharges the battery; therefore it requires an external source to recharge itself. Alternator recharges the battery by supplying current.
Starter motor has the highest current consumption of all the loads, even though for a small period of time. This is due to the fact that the suction, compression and exhaust strokes provide a lot of resistance to the crank movement. Therefore, higher power supply is required to overcome the resistance and crank the engine.
Battery supplies power only under these circumstances:
BATTERY OPERATION:
The battery must have enough energy to start the engine, especially at low temperatures. When the engine is started, the battery takes the role of electrical energy storage unit to store the current produced by the alternator. This energy is used to start the engine again next time after it has been switched off.
The battery also absorbs peak voltage to protect the sensitive loads from damage. Typically, a Lead-Acid battery is used in automobiles, which is enough to meet the energy demands. A 12V battery is used in light commercial vehicles (for e.g. Cars) and 24V battery is used in heavy duty vehicles (for e.g. Trucks).
Design:
It consists of two electrodes of different materials PbO2 (Lead peroxide) and Pb (Lead) dipped in an electrolyte solution of dilute H2SO4 (Sulfuric acid) of density 1.28 kg/l. Both the electrodes have different potentials when immersed in the electrolyte. The difference in potential between the electrodes is known as the cell voltage.
The PbO2 electrode is the positive electrode (cathode) and Pb is the negative electrode (anode). The entire setup where the two electrodes are immersed in an electrolyte is known as a cell. Two or more cells arranged in a series in known as a battery. A cell generates 2V. In a 12V battery, six cells are arranged in a series.
Battery Discharge (Generation of Current):
When load is applied, electrons flow from the negative electrode (Pb) to the positive electrode (PbO2). The flow of electrons is known as current and this current is passed to the load (for e.g. a lamp bulb placed in between the 2 electrodes starts glowing due to electron flow).
As a result of this electron flow, the bond between lead and oxygen atoms is broken. The lead at positive electrode becomes bivalent positive ions (Pb2+) and oxygen becomes bivalent negative ions (O2-). The electrolyte (H2SO4) separate into sulfate ions (SO42-) and hydrogen (H+). Meanwhile, the negative electrode Pb is converted into bivalent ions (Pb2+).
The lead (Pb2+) and sulfate ions (SO42-) combine at both positive and negative electrodes to form lead sulfate (PbSO4). The oxygen ions (O2-) combine with hydrogen ions (H+) to form H2O (water).
Battery Charging:
Battery charging process is the inverse of the discharging process. Current is supplied to the battery from an external source (alternator). The current flows in reverse direction, from positive electrode to the negative electrode. As the electron flows into the negative electrode, the lead sulfate (PbSO4) molecules are broken down. As a result, the bivalent lead (Pb2+) is converted to Pb. The sulfate ions (SO42-) are released into the electrolyte.
At the positive electrode, the lead sulfate (PbSO4) molecules are broken down and tetravalent lead (Pb3+) is formed. The sulfate ions (SO42-) are released into the electrolyte.
The water molecules (H2O) in the electrolyte are broken down into H+ and O2- ions. The hydrogen ions (H+) and sulfate ions (SO42-) combine to form dilute sulfuric acid (H2SO4) as the original electrolyte.
At the positive electrode, the bivalent negative oxygen ions (O2-) and tetravalent lead ions (Pb3+) combine to form lead peroxide (PbO2).
BATTERY CONSTRUCTION:
A 12 V battery consists of a series of 6 cell packs arranges in a case made of polypropylene material. Each cell pack is made of two lead plates immersed in dilute sulfuric acid. The positive and negative polarity plates are separated by a semi permeable membrane known as the separator. Even the cell terminals, connectors and plate straps are made of lead. Likewise, 5 more cell packs are arranged in a series and the top layer is sealed by a hot molding process.
Each cell pack has a vent plug which allows refilling the electrolyte when the density of electrolyte drops. It also allows the gases in the electrolyte chamber to escape.
Battery Case:
The battery case which is made of polypropylene is acid-resistant. It is provided with partitions to separate the cell packs. The case is provided with a sediment chamber below the lower edge of the cell packs. During electrochemical process, lead accumulates as sediment as a result of plate disintegration. The sediment should not be in contact with the plates in order to avoid short circuit. Therefore, the sediment is collected in the sediment chamber.
The cell packs are connected in series using cell connectors which provide a connection to the cell terminals via an opening through the cover. The positive plates are connected using plate connectors, and the same goes for negative plates. Both positive and negative plates are separated with the help of separators.
Cell Packs:
A battery’s ampere-hour (Ah) capacity can be increased by increasing the number of plates in a cell pack. More number of plates increases the overall surface area of the plates and thus Ah capacity increases. The number of negative plates is usually one more than positive plates.
The plate is nothing but grid plates made of lead with active materials pasted on them. The active material on the negative plates is made of pure lead in the form of spongy lead (Pb) and it is of metallic grey color. The active material on the positive plates is made of lead peroxide (PbO2) which is dark brown in color.
Separators:
Separators made of polyethylene are a vital part of the battery to avoid short circuiting. The positive and negative plates should never be in direct contact. Separators should be acid resistant and have a micro-porous structure to allow ion migration.
Cell Terminals:
The plate strap of the positive plates should be connected to form the positive terminal in the first cell. The plate strap of the negative terminals in the last cell pack should be connected to form the negative terminal of the battery. As a result, terminal voltage of 12 V is available between the two terminals.
BATTERY TYPES:
Based on the grid material used for the positive and negative plates in a cell pack, a battery can be divided into 3 types:
Maintenance requisite batteries (lead-antimony alloy):
These types of batteries require regular maintenance to make sure that the battery performs as intended. The grid material used as plates is made of lead-antimony alloy (PbSb). Addition of antimony to lead can make the manufacturers achieve thin grid plates. It provides the strength to withstand operations at extreme conditions.
There are various disadvantages of using antimony with lead as grid plates. They are:
Hybrid Batteries:
In hybrid type, there are two different materials used for the plates. Lead calcium (PbCa) alloy is used for negative plates and lead antimony (PbSb) alloys are used for positive plates. The positive plates are manufactured using casting process, whereas negative plates can be manufactured using simple drawing process.
Even though the maintenance required for hybrid type is less compared to the previous type, it still does not meet the extreme low water consumption demand because of the presence of antimony.
Maintenance Free Batteries:
- High power demand at extreme weather conditions (at cold temperatures, electrical devices demand higher power supply).
- To have higher load capacity at low speeds.
- Smooth operation at high loads.
- Undisturbed power supply at all conditions to safety systems (ABS, Traction control, etc.)
Battery principle:
A chemical reaction between the electrodes and electrolytes generate electricity. Battery is the storage unit for the electricity and supplies it to the vehicle loads based on the demand. The supply of electricity discharges the battery; therefore it requires an external source to recharge itself. Alternator recharges the battery by supplying current.
Starter motor has the highest current consumption of all the loads, even though for a small period of time. This is due to the fact that the suction, compression and exhaust strokes provide a lot of resistance to the crank movement. Therefore, higher power supply is required to overcome the resistance and crank the engine.
Battery supplies power only under these circumstances:
- When the engine is OFF: To crank the engine and also to supply power to other electrical loads such as lighting, music, etc.
- When the engine is ON: Once the engine is cranked, alternator not even meets the power demand of the loads, but also charges the battery. When the engine is running at idling speed or lower speed, the battery must be able to supply power to the electrical devices for a brief amount of time. Also when the power demand overcomes the alternator supply capacity, the battery assists in meeting the demand.
BATTERY OPERATION:
The battery must have enough energy to start the engine, especially at low temperatures. When the engine is started, the battery takes the role of electrical energy storage unit to store the current produced by the alternator. This energy is used to start the engine again next time after it has been switched off.
The battery also absorbs peak voltage to protect the sensitive loads from damage. Typically, a Lead-Acid battery is used in automobiles, which is enough to meet the energy demands. A 12V battery is used in light commercial vehicles (for e.g. Cars) and 24V battery is used in heavy duty vehicles (for e.g. Trucks).
Design:
It consists of two electrodes of different materials PbO2 (Lead peroxide) and Pb (Lead) dipped in an electrolyte solution of dilute H2SO4 (Sulfuric acid) of density 1.28 kg/l. Both the electrodes have different potentials when immersed in the electrolyte. The difference in potential between the electrodes is known as the cell voltage.
The PbO2 electrode is the positive electrode (cathode) and Pb is the negative electrode (anode). The entire setup where the two electrodes are immersed in an electrolyte is known as a cell. Two or more cells arranged in a series in known as a battery. A cell generates 2V. In a 12V battery, six cells are arranged in a series.
Battery Discharge (Generation of Current):
When load is applied, electrons flow from the negative electrode (Pb) to the positive electrode (PbO2). The flow of electrons is known as current and this current is passed to the load (for e.g. a lamp bulb placed in between the 2 electrodes starts glowing due to electron flow).
As a result of this electron flow, the bond between lead and oxygen atoms is broken. The lead at positive electrode becomes bivalent positive ions (Pb2+) and oxygen becomes bivalent negative ions (O2-). The electrolyte (H2SO4) separate into sulfate ions (SO42-) and hydrogen (H+). Meanwhile, the negative electrode Pb is converted into bivalent ions (Pb2+).
The lead (Pb2+) and sulfate ions (SO42-) combine at both positive and negative electrodes to form lead sulfate (PbSO4). The oxygen ions (O2-) combine with hydrogen ions (H+) to form H2O (water).
Battery Charging:
Battery charging process is the inverse of the discharging process. Current is supplied to the battery from an external source (alternator). The current flows in reverse direction, from positive electrode to the negative electrode. As the electron flows into the negative electrode, the lead sulfate (PbSO4) molecules are broken down. As a result, the bivalent lead (Pb2+) is converted to Pb. The sulfate ions (SO42-) are released into the electrolyte.
At the positive electrode, the lead sulfate (PbSO4) molecules are broken down and tetravalent lead (Pb3+) is formed. The sulfate ions (SO42-) are released into the electrolyte.
The water molecules (H2O) in the electrolyte are broken down into H+ and O2- ions. The hydrogen ions (H+) and sulfate ions (SO42-) combine to form dilute sulfuric acid (H2SO4) as the original electrolyte.
At the positive electrode, the bivalent negative oxygen ions (O2-) and tetravalent lead ions (Pb3+) combine to form lead peroxide (PbO2).
Negative plate reaction:
Pb (s) + HSO4- (aq.) ↔ PbSO4(s) + H+ (aq.) + 2e-
Positive plate reaction:
PbO2(s) + HSO4-(aq.) + 3H+(aq.) + 2e- ↔ PbSO4(s) + 2H2O (liq.)
Total reaction:
Pb (s) + PbO2(s) + 2 H2SO4 (aq.) ↔ 2 PbSO4(s) + 2H2O (liq.)
s- solid
aq. - aqueous
liq. - liquid
BATTERY CONSTRUCTION:
A 12 V battery consists of a series of 6 cell packs arranges in a case made of polypropylene material. Each cell pack is made of two lead plates immersed in dilute sulfuric acid. The positive and negative polarity plates are separated by a semi permeable membrane known as the separator. Even the cell terminals, connectors and plate straps are made of lead. Likewise, 5 more cell packs are arranged in a series and the top layer is sealed by a hot molding process.
Each cell pack has a vent plug which allows refilling the electrolyte when the density of electrolyte drops. It also allows the gases in the electrolyte chamber to escape.
Battery Case:
The battery case which is made of polypropylene is acid-resistant. It is provided with partitions to separate the cell packs. The case is provided with a sediment chamber below the lower edge of the cell packs. During electrochemical process, lead accumulates as sediment as a result of plate disintegration. The sediment should not be in contact with the plates in order to avoid short circuit. Therefore, the sediment is collected in the sediment chamber.
The cell packs are connected in series using cell connectors which provide a connection to the cell terminals via an opening through the cover. The positive plates are connected using plate connectors, and the same goes for negative plates. Both positive and negative plates are separated with the help of separators.
Cell Packs:
A battery’s ampere-hour (Ah) capacity can be increased by increasing the number of plates in a cell pack. More number of plates increases the overall surface area of the plates and thus Ah capacity increases. The number of negative plates is usually one more than positive plates.
The plate is nothing but grid plates made of lead with active materials pasted on them. The active material on the negative plates is made of pure lead in the form of spongy lead (Pb) and it is of metallic grey color. The active material on the positive plates is made of lead peroxide (PbO2) which is dark brown in color.
Separators:
Separators made of polyethylene are a vital part of the battery to avoid short circuiting. The positive and negative plates should never be in direct contact. Separators should be acid resistant and have a micro-porous structure to allow ion migration.
Cell Terminals:
The plate strap of the positive plates should be connected to form the positive terminal in the first cell. The plate strap of the negative terminals in the last cell pack should be connected to form the negative terminal of the battery. As a result, terminal voltage of 12 V is available between the two terminals.
BATTERY TYPES:
Based on the grid material used for the positive and negative plates in a cell pack, a battery can be divided into 3 types:
- Maintenance requisite batteries
- Hybrid batteries
- Maintenance free batteries
Maintenance requisite batteries (lead-antimony alloy):
These types of batteries require regular maintenance to make sure that the battery performs as intended. The grid material used as plates is made of lead-antimony alloy (PbSb). Addition of antimony to lead can make the manufacturers achieve thin grid plates. It provides the strength to withstand operations at extreme conditions.
There are various disadvantages of using antimony with lead as grid plates. They are:
- Due to corrosion at positive plates, the antimony molecules are separated from the grid plates and start travelling towards the negative plate via separator and electrolyte and starts poisoning it.
- As a result of the above point, the negative plates start self-discharging at a higher pace.
- Gassing occurs at lower voltage.
- As a result of the above factors, the battery starts getting overcharged leading to increased water consumption. This as whole results in increase in the amount of antimony released.
- The self discharge of the negative plates is one of the prime reasons why starter motors don’t receive adequate current to start the engine.
Hybrid Batteries:
In hybrid type, there are two different materials used for the plates. Lead calcium (PbCa) alloy is used for negative plates and lead antimony (PbSb) alloys are used for positive plates. The positive plates are manufactured using casting process, whereas negative plates can be manufactured using simple drawing process.
Even though the maintenance required for hybrid type is less compared to the previous type, it still does not meet the extreme low water consumption demand because of the presence of antimony.
Maintenance Free Batteries:
- Lead calcium alloy (PbCa): In this type, both the plates are made of the same grid material. Lead calcium alloy (PbCa) is used as a grid material for the plates. Use of PbCa avoids the poisoning of negative plates because PbCa does not react during electrochemical process. As a result, the self discharge of negative plates can be prevented. It also means that gassing will occur at appropriate temperature. Therefore, water consumption can be kept low and overcharging can be prevented.
- Lead calcium silver alloy (PbCaAg): In a bid to withstand adverse temperatures, the battery has had a recent development in the alloy used for the grid of positive plates. A small proportion of silver is added to the PbCa alloy and it has proven to be reliable even at higher temperatures.
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