lead acid batteries l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Lead Acid Batteries PowerPoint Presentation
Download Presentation
Lead Acid Batteries

Loading in 2 Seconds...

play fullscreen
1 / 35

Lead Acid Batteries - PowerPoint PPT Presentation


  • 132 Views
  • Uploaded on

Lead Acid Batteries . “The motor that could, the battery that couldn’t”. Review of Previous Concepts. A battery is a box that segregates charges Electrons are stripped from the anode This leaves holes in the valence orbits of the atoms of the anode Electrons are forced on to the cathode

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Lead Acid Batteries' - race


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
lead acid batteries

Lead Acid Batteries

“The motor that could, the battery that couldn’t”

review of previous concepts
Review of Previous Concepts
  • A battery is a box that segregates charges
    • Electrons are stripped from the anode
      • This leaves holes in the valence orbits of the atoms of the anode
    • Electrons are forced on to the cathode
      • This places extra electrons in the valence orbits of the atoms of the cathode
review continued
Review Continued
  • When an anode and cathode are coupled, you have a capacitor
    • Constructed as anode-insulator-cathode
  • If current is allowed to flow from the cathode to the anode, the capacitor will discharge
    • This tends to happen very quickly, so capacitors are not practical for the storage of large amounts of energy
review continued4
Review Continued
  • For a battery to be functional, we must have a way to keep stripping electrons from the anode and adding them to the cathode
    • This is possible through a chemical reaction
  • A battery is nothing but a mechanical assembly designed to extract energy from a chemical reaction
    • What is this similar to?
    • What can we say about the efficiency of lead acid batteries?
potential difference video
Potential Difference Video
  • Watch the video on potential difference
    • What is potential difference?
mechanism of chemical reaction
Mechanism of Chemical Reaction
  • Anatomy
    • Anode
      • Made of lead dioxide PbO2
    • Cathode
      • Made of pure lead Pb
    • Electrolyte
      • Water H2O
      • Sulfuric Acid H2SO4
      • “Poor, poor Willy, he is no more. What he thought was H2O was really H2SO4”
mechanism of chemical reaction continued
Mechanism of Chemical Reaction Continued
  • Physiology
    • H2SO4 breaks apart into two ions when dissolved in H2O
      • H2 forms a positive ion
        • Shortage of electrons in orbits
      • SO4 forms a negative ion
        • Excess of electrons in orbits
    • Ions are not happy
      • Their valence shells aren’t full, or are over full, so they’re unstable
      • Ions will seek out atoms to bond with to fill their shells
mechanism of chemical reaction continued8
Mechanism of Chemical Reaction Continued
  • Physiology of Cathode
    • SO4 negative ions bond with the lead of the cathode
      • This bond forms lead sulfate PbSO4
      • This lead sulfate molecule has an extra electron
      • Because of the extra electrons, the cathode is negative
mechanism of chemical reaction continued9
Mechanism of Chemical Reaction Continued
  • Physiology of Anode
    • SO4 negative ions wants to bond with PbO2
      • The O2 must be dumped for the Pb and the SO4 to bond
      • O2 dissolves in the electrolyte
        • When the O2 leaves, it takes several electrons with it
    • SO4 bonds with Pb creating PbSO4
      • Because the O2 took several electrons, the net result is a shortage of electrons in the anode
      • A shortage of electrons makes the anode positive
mechanism of chemical reaction continued10
Mechanism of Chemical Reaction Continued
  • Physiology of Electrolyte
    • The electrolyte started as H2SO4
      • It gave up the SO4 molecules to the anode and cathode
      • This leaves H2 atoms in the electrolyte
    • The anode started out a PbO2
      • It gave up O2 to the electrolyte
    • The electrolyte now contains three things:
      • H2O
      • H2
      • O2
further reactions in the electrolyte
Further Reactions in the Electrolyte
  • It is our hope that the dissolved H2 and O2 combine into H2O
  • As the battery discharges, the electrolyte goes from mostly H2SO4 to H2O
discharged battery
Discharged Battery
  • Discharged batteries freeze more easily
  • The density of the electrolyte changes
    • We can use a hydrometer to measure the amount of H2SO4 in the electrolyte
    • This is a predictor of state of charge
problems in the electrolyte
Problems in the Electrolyte
  • Sometimes, not all of the H2 and O2 combine into water
    • This results in H2 off gassing
  • H2 is a highly flammable gas, that will ignite with a small spark
    • For this reasons, sparks should be avoided around batteries
  • Question: How do we avoid sparks when jump starting vehicles?
chemical reactions
Chemical Reactions
  • We know that batteries work by chemical reactions
    • Electrons are stripped from the anode
      • Leaves holes in valence shells
      • This lack of electrons makes the anode positive
    • Electrons are placed on the cathode
      • Places extra electrons in the valence orbits of the cathode
      • These extra electrons make the cathode negative
  • How can we predict if two chemicals will react?
    • If we know the pattern, we can figure out other systems
driving force video
Driving Force Video
  • Watch the video on the driving force behind reactions.
    • When will two chemicals react?
    • What are some examples?
    • When will they not?
mechanism of chemical reaction recharging
Mechanism of Chemical Reaction-Recharging
  • Charging a battery simply reverses the discharge process
    • This is possible because energy is added by the charger
    • The current sent through the plates break chemical bonds
      • PbSO4 breaks down into Pb and SO4
      • SO4 is released into the electrolyte
      • Plates return to Pb
mechanism of chemical reaction recharging17
Mechanism of Chemical Reaction-Recharging
  • At the same time, H2O is split into H2 and O2
    • H2 combines with SO4 to form sulfuric acid
    • O2 combines with the Pb in the anode to form lead oxide PbO2
  • The reaction has now been fully reversed, and the battery is recharged
testing state of charge
Testing State of Charge
  • Because some of the H2O in the electrolyte has been converted to H2SO4, the density of the electrolyte increases.
    • This will show up on a hydrometer test
the entire cycle
The Entire Cycle

Discharging

Recharging

characteristics of the reaction
Characteristics of the Reaction
  • There are three basic ways to measure the characteristics of the reaction taking place
    • Potential difference developed
    • The rate at which the reaction happens
    • The overall energy released by the reaction
measuring potential difference
Measuring Potential Difference
  • Potential Difference is the amount of “push” that makes the electrons want to flow through the wire
  • “Push” as you will recall is voltage
    • Voltage can be measured with a voltmeter
measuring potential difference continued
Measuring Potential Difference-Continued
  • The potential difference depends on the chemicals reacting
    • The best possible combination is Lithium and Flourine
      • This would produce a potential difference of 5.9 volts
      • These material are unrealistic
    • Common batteries use lead and sulfuric acid
      • These reactants produce 2.1 volts potential difference
getting 12 volts
Getting 12 volts
  • Each cell of a battery produces 2.1 volts
  • Cells are stacked up in series to add voltages
  • 6 cells are stacked to make 12.6 volts in a healthy battery
  • Batteries showing less than 12.6 volts should be charged before further testing
critical question
Critical Question
  • If the chemical reaction produces 12.6 volts, how is it possible to get 9.6 volts under load?
characteristics of the reaction rate
Characteristics of the Reaction - Rate
  • Voltage is not a good predictor of the health of a battery
    • Would a 9 volt battery crank your engine?
      • Why not?
  • What is really important is the power available
  • One definition of power is the rate at which energy is being converted.
characteristics of the reaction rate26
Characteristics of the Reaction - Rate
  • When we measure the power output of the battery, we are measuring the rate at which the chemical reaction is happening.
  • The rate of the chemical reaction determines the electrical power available from the battery.
  • There are a number of factors that affect the rate of a chemical reaction.
chemical kinetics video
Chemical Kinetics Video
  • Watch the video on chemical kinetics.
    • What factors affect the rate of the chemical reaction?
    • How are these factors optimized in lead-acid batteries?
energy content testing
Energy Content Testing
  • Batteries are rated for energy content in Amp-Hours
  • Testing energy content involves measuring current vs. time and voltage vs. time.
  • Current and voltage are then multiplied to find power.
  • Most tests are conducted at a constant current.
energy content testing current
Energy Content Testing- Current
  • Amperage is held constant
energy content testing voltage
Energy Content Testing- Voltage
  • Voltage is allowed to vary throughout the test
  • Test stops when voltage drops to 10.5 volts
energy content testing power
Energy Content Testing- Power
  • Power = Volts X Amps
energy content testing energy
Energy Content Testing- Energy
  • Energy is defined as the potential to do work
  • Energy = Power X Time
  • How is this reflected in the graph?
finding area under the curve
Finding Area Under the Curve
  • How might you find the area under the curve?
  • See if you can figure it out on the worksheet!
energy density
Energy Density
  • Now that you know the energy in the battery, we can calculate energy density.
  • We know that the battery contains about 1.2 kilowatt-hours of energy
  • To make our comparison, it is necessary to convert that number to kilojoules
    • To get kilojoules from kilowatts, multiply by 3600
    • 1.2 kilowatt-hours X 3600 kilowatt-hours per kilojoule = 4,320 joules
energy density continued
Energy Density-Continued
  • To find the energy density, divide the energy content by the mass
    • Our battery has a mass of about 15 Kg
    • 4,320 kilojoules / 15 kilograms = 288 Kilojoules per kilogram
  • Gasoline has an energy density of 46 megajoules per kilogram
  • What can we say about the viability of the lead acid battery in weight sensitive applications?