By Lt NS Wickramasinghe BSc(E & E Eng)Hons

By NS Wickramasinghe BSc(E & E Eng)HonsBattery

What is a Batterycollection of one or more electrochemical cells in which stored chemical energy is converted into electrical energy

Classification of BatteriesBatteriesOtherSecondaryPrimaryPhysicalEnergyChemical

Carbon-Zinc dry cellLithiumMercury OxideSilver OxideFuel CellSolar cellThermalNuclear EnergyLead Acid (Flooded/Sealed)Nickel CadmiumLithium Secondary

Lead acid batteries architecturesDeep-cycleDesigned for maximum energy storage capacity and high cycle count (long life), and are rated in Amp/Hours. This is achieved by installing thick lead plates with limited surface area.

Typical applications are boats, Uninterruptible Power Supplies(UPS)

Engine StartingStarter batteries are made for maximum power output, usually rated in CCA (Cold-Cranking amps). The battery manufacturer obtains this by adding multiple lead plates to obtain larger surface area for maximum conductivity.

Typical applications are vehicles &motorcycles

Lead-Acid BatteryConstructionLead-acid batteries are commonly made of five basiccomponents

A resilient plasticcontainer

Positive and negative internal plates made oflead

Plate separators made of porous syntheticmaterial

Electrolyte - 35% sulfuric acid and 65% water

Battery Terminals

Types of Lead-AcidBatteriesLead-Acid Batteries come in several differentconfigurations

Flooded Lead-acid Available in Deep cycle or Engine starting as sealed or open variety

Sealed Lead-acid - The liquid electrolyte is gelled into moistened lead plate-separators, which allow the case to be sealed. Safety valves allow venting during charge, discharge and atmospheric pressure changes.

Absorbed Glass Mat Batteries (AGM) - sealed lead-acid that uses absorbed glass mats between the plates. It is sealed, maintenance-free and the plates are rigidly mounted to withstand extensive shock and vibration

Capacity of a BatteryThe definition of Capacity is usually given in Amp-hours (Ah) or Cold cranking amps (CCA), cranking amps (CA), and Reserve Capacity (RC)

(Ah) is specifies the amount of current (measured in Amperes) it can provide over a 20 Hours period

(CCA) is a measurement of the number of amps a battery can deliver at 0 F for 30 seconds and not drop below 7.2 volts

(CA) is measured at 32 degrees F. This rating is also called marine cranking amps (MCA)

(RC) is a very important rating. This is the number of minutes a fully charged battery at 80 F will discharge 25 amps until the battery drops below 10.5 volts

Inside of a Lead Acid Battery

Creating Voltage

Charging a Lead-AcidBatteryParameters forRecharging

Charging Current - All batteries have a maximum current at which they can be safely charged

Charging Voltage - Applying a voltage across its positive & negative terminals that is higher than the voltage it already has across them

Charging Time - The charge time of a sealed lead-acid battery is 12-16 hours (up to 36 hours for larger capacity batteries)

Charging Current: All batteries have a maximum current at which they can be safely charged. High charging current means less time is necessary to complete the recharging process, however, a maximum value can also shorten battery life. Cases of extreme over-current could result in a hazardous condition due to battery overheating and thermalrunaway. Charging Voltage: A lead-acid battery is charged by applying a voltage across its positive & negative terminals that is higher than the voltage it already has across them. The greater the difference between the applied voltage and the battery voltage, the greater the charging current that will flow and the quicker the battery will becharged. Charging Time: The charge time of a sealed lead-acid battery is 12-16 hours (up to 36 hours for larger capacity batteries). With higher charge currents and multi-stage charge methods, the charge time can be reduced to 10 hours or less. It takes 3 to 5 times as long to recharge a lead-acid battery to the same level as it does to dischargeit.

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Electrochemistry principle of Lead Acid batteryDischarge Chemistry

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(l)

overall reaction:Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4-(aq) 2PbSO4(s) + 2H2O(l)

Electrochemistry principle of Lead Acid batteryCharging Chemistry

Negative plate reaction: PbSO4(s) + H+(aq) + 2e- Pb(s) + HSO4-(aq)

Positive plate reaction: PbSO4(s) + 2H2O(l) PbO2(s) + HSO4-(aq) + 3H+(aq) + 2e-

Overall reaction:2PbSO4(s) + 2H2O(l) Pb(s) + PbO2(s) + 2H+(aq) + 2HSO4-(aq)

Battery TestingThe most accurate method is measurement of specific gravity and battery voltageLoad testing is yet another way of testing a battery

Load testing is yet another way of testing a battery. Load test removes amps from a battery much like starting an engine would. A load tester can be purchased at most auto parts stores. Some battery companies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating. For instance, a 500CCA battery would load test at 250 amps for 15 seconds. A load test can only be performed if the battery is near or at full charge.13

Battery health

Typical BatteryProblems

Low chargeLow CapacityMismatched Batteries

Typical BatteryProblemsConversionEfficiency

This denotes how well it converts an electrical charge into chemical energy and back again. The higher this factor, the less energy is convertedinto heat and the faster a battery can be charged without overheating. The lower the internal resistance of a battery, the better its conversionefficiency.

Sulfation

Sulfation of lead-acid batteries starts when the electrolytes specific gravity falls below 1.225. It results in a salt-like substance forming on the battery plate surface and it can harden on the battery plates if left long enough, reducing and eventually blocking chemical reaction between the lead plate and the electrolyte. Equalization is the solution for this problem.

Sulfation

Sulfation of lead-acid batteries starts when the electrolytes specific gravity falls below 1.225, or when voltage measures less than 12.4V. Sulfation results in a salt-like substance forming on the battery plate surface and it can harden on the battery plates if left long enough, reducing and eventually blocking chemical reaction between the lead plate and the electrolyte. It disables the ability of the battery to generate its rated voltage and amperage. Sulfation is the main reason a significant percentage of lead-acid batteries dont reach their intended lifespan.

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Typical BatteryProblemsGassingBatteries start to gas when you attempt to charge them faster than they can absorb the energy. The excess energy is turned into heat, which then causes the electrolyte to boil and evaporate. is the suitable method for reduce this is good ventilated area.

Self-DischargeThe self-discharge rate is a measure of how much batteries discharge on their own. The self-discharge rate is governed by the construction of the battery and the properties of the components used inside the cell (alloy of the lead, sulfuric concentrations of the electrolyte,etc.).

GassingBatteries start to gas when you attempt to charge them faster than they can absorb the energy. The excess energy is turned into heat, which then causes the electrolyte to boil and evaporate. The evaporated electrolyte can be replenished in batteries with removable caps such as most flooded deep-cycle batteries, however, many car batteries are sealed and thus need to be replaced when their electrolyte evaporates overtime.

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Temperature Effects for BatteryOperation

The optimum operating temperature for the lead-acid battery is 25C (77F).

As a guideline, every 8C (15F) rise in temperature will cut the battery life in half.

A VRLA, which would last for 10 years at 25C (77F), will only be good for 5 years if operated at 33C (95F).

Theoretically the same battery would last a little more than one year at a desert temperature of 42C(107F)

Battery sizes

Electrochemistry principle of Ni-Cd batterypositive reactsNi(OH)2 - e + OH- -> NiOOH + H2O

Negative reactionCd(OH)2 + 2e -> Cd + 2OH-

whole reaction2Ni(OH)2 + Cd(OH)2-> 2NiOOH+ Cd+ 2H2O

When dischargedNiOOH + H2O + e Cd + 2OH- + 2e -> Ni(OH)2 + OH- Cd(OH)2

Main applications are two-way radios, biomedical equipment and power tools

Ni(OH)2 consistence reduced with NiOOH consistence increasing during chargingthe positive electrical potential gradually raised, while with Cd increasingCd(OH)2 is decreased, and the negative electrical potential gradually reduced

NiCd Batteries are Unique

NiCad batteries are different from typical alkaline batteries or lead-acid batteries in several key ways. One of the main key differences is in cell voltage. A typical alkaline or lead-acid battery has a cell voltage of approximately 1.5 V, which then steadily drops off as it is depleted. NiCad batteries are unique in that they will maintain a steady voltage of 1.2v per cell up until it is almost completely depleted. This causes the NiCad batteries to have the ability to deliver full power output up until the end of its discharge cycle. So, while they have a lower voltage per cell, they have a more powerful delivery throughout the entirety of the application. Some manufacturers make up the voltage difference by adding an extra cell to the battery pack. This allows for the voltage to be the same as the traditional type batteries, while still retaining the constant voltage that is so unique of NiCads. Another reason the NiCad batteries can deliver such high power output, is they have very low internal resistance. Because their internal resistance is so low, they are capable of discharging a lot of power very quickly, as well as accepting a lot of power very quickly. Having such a low internal resistance keeps the internal temperature low as well, allowing for quick charge and discharge times. This feature, combined with the constant voltage of the cells, allows them to put out a high amount of amperage, at a consistently higher voltage than comparable alkaline batteries.

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Electrochemistry principle of Li-ion batteryPositive reactionLiCoO2 -> Li1-xCoO2 + xLi+ + xe- Negative reactionC + xLi+ + xe- -> Clix whole reactionLiCoO2 + C -> Li1-xCoO2 + CLix Applications include notebook computers portable power tools, medical devices and cellphones.

Maintenance of BatteriesEnsure proper maintenance of engine starting batteries due to the extreme importance of getting a ship under way in any circumstances

Attention should be paid to the electrolyte level and specific gravity for vented batteries

A boost charge shall be given if the specific gravity of the battery cells meet the conditions stipulated by manufacturer

Ensure that the battery is not being overcharged

Keep engine starting batteries clean, dry and free of seawater

Period of inactivity for the ship of a week or more, give the battery a normal charge

Maintenance of Batteries Inspected for height of electrolyte once each week

The electrolyte level shall never be allowed to fall below the top of the separators

Add pure distilled water at any time to replace that which has evaporated

Add water just before the battery is placed on charge, as the water remains on top of the electrolyte until mixed with it by charging

After adding water, replace and tighten the vent plugs

Remove all water or electrolyte spilled during watering and make sure that the tops and sides of the cells are clean and dry

Maintenance of Batteries Ensure that distilled water that is to be used for watering batteries and mixing electrolyte does not contain impurities

Use only premixed electrolyte when replacing spilled electrolyte

Fully charged specific gravity between the limits of 1.220 and 1.210 specific gravity at 27 C (80 F)

The specific gravity of a cell that has fallen below 1.210 shall not be increased by the addition of acid untill it has been definitely ascertained by test that the low-gravity condition is not due to sulfation

The addition of acid to increase the specific gravity of a sulfated cell will aggravate the existing condition

Maintenance of Batteries The specific gravity of cells which exceed 1.220 shall be cut by the removal of an appropriate amount of electrolyte and the addition of distilled water

Sulfuric acid of a specific gravity greater than 1.350 shall not be added to a battery

Precautions for Mixing Electrolyte Personnel handling or mixing electrolyte shall wear proper protective items

If concentrated acid or electrolyte come in contact with the skin, immediately wash the affected with freshwater

As soon as possible get the medical assistance

During electrolyte mixing the acid must be poured into the water and not the water poured into the acid

The acid must be added slowly and cautiously to the water to prevent excessive heating and splashing

The solution should be continually stirred by a glass rod while the acid is being poured into the water to prevent the heavier acid from flowing to the bottom of the vessel

Personnel handling or mixing electrolyte shall wear proper protective items rubber aprons, rubber boots and rubber gloves, so that the acid does not come into contact with clothing or skin and The face must be guarded by a full face shield

If concentrated acid or electrolyte come in contact with the skin, immediately wash the affected area freely with a large quantity of freshwater for about 15 minutes

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Instructions for Mixing Electrolyte To prepare electrolyte, lead or rubber vessels and stirring rods are necessary

Only pure distilled water shall be used

Every effort must be made to keep impurities from the electrolyte while mixing, since they shorten battery life

Extreme care must be taken to ensure that acid container (carboys) are absolutely airtight

The addition of even a small quantity of water to a carboy of strong sulfuric acid may cause an explosion due to the sudden evolution of heat

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