CH17 batteries theory, diagnosis, and service STUDENT VERSIO

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Chapter 17

Batteries:

Theory, Diagnosis, and Service

Basic Battery Theory

• Restores chemical nature of cells

• A chemical reaction causes current flow

within the cells

• Each battery has own charging requirement

• Follow charging procedures to prevent

battery damage

Cell Arrangements

• Voltage depends on cell materials and chemicals used

• Most produce between 1.2 – 4.0 volts

• To produce higher voltage, cells are connected together

Series Connections

Battery Hardware

• Battery Cables

– Must be able to carry current to meet demands – 12-volt cables 4 or 6 gauge

– Connections can be top or side post

– Must be clean and tight

– HV cables on hybrid vehicles are orange

Battery Hardware (cont’d)

Recycling Batteries

• Do not discard batteries with trash

• 98% of lead-acid batteries are recycled

• Additional information:

– Interstate Batteries

– BCI

– EPA

Battery Ratings

• Voltage rating may be expressed as open

circuit voltage – the voltage measured when there is no load on the battery

• Operating voltage is measured with the

battery under a load

Battery Ratings (cont’d)

• Cold Cranking Amps (CCA) Rating

– The load in amperes that a battery can deliver for 30 seconds at 0°F (-17.7°C) without the

voltage dropping below 7.2 volts.

• Cranking Amps (CA) Rating

– Current a battery can deliver for 30 seconds at 32°F (0°C) without the voltage dropping below 7.2 volts.

Safety Issues

• HV circuits identifiable by size and color

• Cables may be enclosed in orange shielding

Lead-Acid Battery Construction

Basic Construction (cont’d)

• Grids are lead alloy

frames that support

the active material

of each plate

Basic Construction (cont’d)

Basic Construction (cont’d)

• Electrolyte is a solution of sulfuric acid and water

• The sulfate reacts with the lead and lead

peroxide to release energy

• Also acts as the carrier for electrons as they move

• Desired solution is 65% water and 35% acid

Casing Design

• Two terminals

• Specified by the Battery Council International (BCI)

Discharging and Charging

Charging

Maintenance-Free and Low-Maintenance Batteries

• Low-maintenance battery is a heavy-duty normal lead-acid battery

• Have vents which allow water to be added

• Maintenance free batteries do not have

external caps

• Water is not added

Factors That Affect Battery Life

• Improper Electrolyte Levels

– Only water should be lost due to hot weather and gassing

• Temperature

– A battery is at about 40% at 0°F (-17.7°C)

– Batteries can freeze if charge is too low

– If too hot, the electrolyte can evaporate

Factors That Affect Battery Life

– Causes a loss of water in cells

– Produces excessive heat

Factors That Affect Battery Life

Servicing and Testing Batteries

• Always wear safety glasses or goggles

when working with batteries

• Hydrogen gas emitted during charging

– Any spark or flame can ignite the gas

• Sulfuric acid causes severe skin burns

– If acid contacts skin or eyes, flush area with water for several minutes

– Do not rub eyes or skin – call a doctor

Battery Safety

• Observe polarity when making connections

to the battery

• Always disconnect the negative cable first

• Always connect the negative cable last

• Follow manufacturer’s recommendations when charging

• Do not wear jewelry when servicing a

battery

Battery Inspection Tips

• Check the case for damage, dirt, and corrosion

• Check the electrolyte level, color, and odor

• Check the case for cracks and loose terminal posts

• Check the condition of the cables

• Check the battery hold-down fixture

• Check the heat shield for proper installation

Cleaning Battery Terminals

Built-In Hydrometers

Open Circuit Voltage Test

• Can be substituted for specific gravity test

• Battery temperature should be between 60º and 100ºF (15.5ºC and 37.7ºC)

• Allow voltage to stabilize at least 10 minutes

• May need to disconnect negative cable

• Apply a heavy load for 15 seconds to a just recharged battery

Battery Load Test

• Determines performance under load

• Carbon pile tester applies load

• Maximum current draw, within acceptable voltage, is compared to battery rating

• Can be performed in or out of vehicle

• Battery should be close to 80ºF (26.7ºC)

Battery Capacitance Test

• Also called a conductance test

• Describes the batteries ability to conduct current

• Tests battery plate surfaces, cell defects, shorts, aging, and open circuits

Battery Drains

• Parasitic loads drain current with key off

• Some parasitic load is normal

• Excessive amounts discharge the battery

• Refer to the manufacturer’s specifications for allowable amount

• 30mA is normal for most vehicles

Battery Cables

• Poor connections cause voltage drops

• Voltage drop across connections

• Heavy corrosion is obvious but can also form a nearly invisible barrier

• Damaged, bent or out-of-shape terminals will cause excessive resistance

Battery Chargers (cont’d)

• Always charge in a well ventilated area

• Charger should be off when connecting and disconnecting battery leads

• Never attempt to charge a frozen battery

• Disconnect battery cables when charging in the vehicle

– Meets or exceeds power requirements

– Fits hold-down fixtures

Isolating High-Voltage Systems

• Ensure HV system is shut down and

isolated before working on HV component

• Use insulated tools

• Never leave tools near battery pack

• Do not wear anything metallic

Isolating High-Voltage Systems

(cont)’d

• Do not touch HV cables or parts without the correct protective gear

• Wear HV gloves when de-powering and

powering the HV system

• Follow each manufacturer’s procedures for de-powering HV systems