Transcript 02 Secondary Cells

NE 139
6029G
Revision
Primary Cells
Two dissimilar metals in an electrolyte
Acid
 Electrolyte can be

Alkali (Base)
Salt
Also known as a voltaic cell
 Only able to be used once Can’t be recharged

Revision
Primary Cells
 Cell Voltage: Dependant on electrode type
 Cell Current: Dependant surface area of electrode
 Suffers from: “Local Action”
“Polarisation”
Secondary Cells
Plates generally are of the same material
 Electrolyte is: • Acid

• Alkali (Base)

Chemical reaction is reversible
Plante Cell
Developed by Raymond Gaston Plante
1834 - 1889
Lead (Pb)
Lead (Pb)
Sulphuric Acid (H2SO4)
Charged
Anode
Pb + HSO4+ + H2O
Lead
Cathode
Sulphuric Water
Acid
PbO2 + 3H3O+ + HSO4- + 2eLead Peroxide
Acid
Discharged
PbSO4 + H3O+ + 2eLead Sulphate
PbSO4 + 5H2O
No Acid
Cell Voltage = 2V
Charged
∙
Anode or Negative plate Lead
∙
Cathode or Positive plate Lead peroxide (Brown)
∙
Acid as electrolyte
Discharged
∙
Both Negative & Positive plates Lead Sulphate
∙
Water as electrolyte


Lead is soft, plates distorted easily
Amps/m2 small, surface area needed to be
increased (post card size only produces 1 Amp)

Plates change size as they take on sulphate

Cannot remain uncharged as Sulphate crystals grow
(can’t be converted back)
Developed by Camille Alphonse Faure (1840 - 1898)
1880
Red lead
coated lead plates with a paste of lead oxides,
sulphuric acid and water, which was then cured.
The curing process caused the paste to change to a
mixture of lead sulphates Pb3O4
1881
Plates were perforated to provide a key for paste and
to increase surface area
Cast perforated lead plate
Separator
Pasted lead plate
Additives alloyed with lead to increase
strength may include:
•
•
•
•
Antimony
Tin
Calcium
Selenium
Plates are made thin and stacked to increase
current output
Number of plates indicate cells output
Standard Automotive Batteries
Designed to provide high currents for short
periods of time :- CC (Cranking Current)
Discharge
Typical = 5-10% of capacity
Maximum = 20% of capacity
Standard Automotive Batteries
Deep Cycle battery
Designed to provide Low currents for long periods of time
Discharge
Maximum = 80% of capacity
Plates are thicker & may be solid construction
Standard Automotive Batteries
Deep Cycle battery
Hybrid, or Marine battery
Designed to start motors and provide some low
currents for periods of time
Discharge
Maximum = 50% of capacity
Plates standard construction but are thicker
Standard Automotive Batteries
Deep Cycle battery
Hybrid, or Marine battery
Maintenance Free or VRLA battery
Valve Regulated Lead Acid
•
Absorbent glass mat (AGM)
•
Gel Cell
Chemical reaction causes release of: • Hydrogen
• Oxygen

Replacement of Antimony •

Increasing the capacity of the negative plate
•
•
Calcium
Selenium
Tin
Negative plate gives off Hydrogen when fully charged
If area of –ve plate is larger than +ve plate it will never
reach full charge.
electrolyte is absorbed into a mat of fine glass fibres
• Flat
• Cylindrical/Spiral
• wound
like wetplates
cell lead
are acid
thin battery in a
rectangular case
• lead in their plates are purer as they no
longer need to support their own weight
• internal resistance is lower than
traditional cells due to close plate
proximity and the pure lead plates have
lower resistivity
• Sulfuric acid is mixed with a silica fume, which makes
the resulting mass gel-like and immobile
• Do not need to be kept upright (though they cannot be
charged inverted).
• Virtually eliminate the electrolyte evaporation, spillage
(and subsequent corrosion issues) common to the
wet-cell battery
• Often referred to as sealed lead-acid (SLA) batteries
• Antimony in the lead plates is replaced by calcium
• often referred to as a lead-calcium battery
Positive / Cathode: Nickel oxide-hydroxide
Negative / Anode:
Electrolyte:
Cell Voltage:
Iron
Potassium hydroxide
1.2 Volts
Invented by: Waldemar Jungner 1899
Also invented the Nickel-Cadmium battery
Developed by: Thomas Edison 1901



1903 to 1972 by the Edison Battery Storage
Company
1972 the battery company was sold to the Exide
Battery Corporation which discontinued making the
battery in 1975
Only manufactured in china as of 2008
Advantages
•
•
•
•
•
•
•
•
•
Very long life ≈ 20Years
Tolerant of abuse
Plates do not corrode like Lead Acid
Can be left discharged
Does not contain dangerous chemicals
Disadvantages
• Low energy to weight ratio
• Slow to take/ deliver charge
• More expensive than lead acid
Overcharge
over-discharge
short-circuiting
thermal shock
1.-1 hr discharge rate
2.-2 hr discharge rate
3.-3 hr discharge rate
4.-4 hr discharge rate
5.-8 hr discharge rate
6.-10 hr discharge rate
7.-20 hr discharge rate
8. Normal charge
9. Rapid charge
Memory effect
Problem where the Ni-Cd battery would remember
the amount of discharge for previous discharges
and limit the recharge life of the battery
Crystal growth can occur when a modern Ni-Cd
battery is recharged before it is fully discharged.
The crystal growth can eventually prevent the
battery from discharging beyond that point
and/or cause rapid self-discharge of the battery
 Series
 Parallel
 Series/Parallel
Higher voltage than a single cell
can supply
Higher current than a single
cell can supply
Higher voltage & current than a
single cell can supply
2 Volt
0.5 A
Total Voltage = 4
62
Total Current = 0.5 A
2 Volt
0.5 A
Total Voltage = 2
Total Current = 0.5
1.5
1.0
Dependant upon:





Materials used in the cell
Surface area of the electrodes
Distance between the electrodes
Operating temperature of the cell
Cells state of charge
Look at this next lesson
Causes a:
 Limit in the maximum current that can be
supplied by the cell
 Terminal voltage drops as current increases
Maximum Current
0.2 2/0.2 =10 Amps
Ri
2V
2.0
2/2 =1 Amp
20
2/20 =0.1 Amp
Terminal Voltage
Load Current = 0.1 Amp
Ri
0.2
2-(0.2 x 0.1) =1.98 Volts
2.0
2-(2 x 0.1) = 1.8 Volts
20
2-(20 x 0.1) = 0 Volts
2V
Parallel connected Cells
Ri
Number of cells
Ri = 0.1
0.033
0.05
Ri = 0.033
Ri = 0.1
V=2V
V=2V
Series/Parallel connected Cells
Ri x Number of series cells in branch
Number of Branches
Ri = 0.3
V=6V
Ri = 0.3 0.15
2
Ri = 0.15
V=6V
 CCA Cold Cranking Amps
 CA
measurement of the number of amps a
battery can
deliver at -17° C for 30 seconds
Cranking
Amps
and not drop below 7.2 volts
measured at 0° C. This rating is also called
Marine Cranking Amps.
Hot Cranking Amps is seldom used any
longer but is measured at 26.7°C
 CCA Cold Cranking Amps
 CA
Cranking Amps
 RC
Reserve Capacity
the number of minutes a fully charged battery
Hour
 AH atAmp
26.7°
C will discharge 25 amps until the
battery drops below 10.5 volts.
If a battery is rated at 100 amp hours it should
deliver 5 amps for 20 hours
Standard lengths of time are 10 or 20 Hours
10 hours for standard batteries
20 hours for deep cycle batteries
100Ah battery should supply: 1 Amp for 100 Hours
2 Amps for 50 Hours
5 Amps for 20 Hours
Not possible as battery may 10 Amps for 10 Hours
not be able to deliver this
100 Amps for 1 Hour
current
Decreasing the discharge period decreases the
AH output of the battery
Battery
Charging
Cell Charging
 Appling a voltage that is larger than the cells
terminal voltage
 Current then flows in the opposite direction
 Chemical change takes place
 Energy is stored as a chemical change
Dependant upon:





Materials used in the cell
Surface area of the electrodes
Distance between the electrodes
Operating temperature of the cell
Cells state of charge
Increases as cell discharges
Decreases as cell charges
 CCA Cold Cranking Amps
 CA
Cranking Amps
 RC
Reserve Capacity
 AH
Amp Hour
 Measurement of open circuit terminal voltage
 Measuring the acid concentration
 Placing the battery under a controlled load
 Coulomb counting
 Electrochemical Impedance Spectroscopy
Factors to consider:
 Cell Type
 Cell temperature
 Cell age
 Time since last charge
Electrolyte
Temperature
(Celsius)
100%
SoC
75%
SoC
50%
SoC
25%
SoC
0%
SoC
48.9°
12.663
12.463
12.253
12.073
11.903
43.3°
12.661
12.462
12.251
12.071
11.901
37.8°
12.658
12.458
12.248
12.068
11.898
32.2°
12.655
12.455
12.245
12.065
11.895
26.7°
12.650
12.450
12.240
12.060
11.890
21.1°
12.643
12.443
12.233
12.053
11.883
15.6°
12.634
12.434
12.224
12.044
11.874
10.0°
12.622
12.422
12.212
12.032
11.862
4.4°
12.606
12.406
12.196
12.016
11.846
-1.1°
12.588
12.388
12.178
11.998
11.828
-6.7°
12.566
12.366
12.156
11.976
11.806
-12.2°
12.542
12.342
12.132
11.952
11.782
-17.8°
12.516
12.316
12.106
11.926
11.756
Lead Acid
Electrolyte
Temperature
(Celsius)
100%
SoC
75%
SoC
65%
SoC
50%
SoC
25%
SoC
0%
SoC
48.9°
12.793
12.563
12.463
12.313
12.013
11.773
43.3°
12.791
12.561
12.461
12.311
12.011
11.771
37.8°
12.788
12.558
12.458
12.308
12.008
11.768
32.2°
12.785
12.555
12.455
12.305
12.005
11.765
26.7°
12.780
12.550
12.450
12.300
12.000
11.760
21.1°
12.773
12.543
12.443
12.293
11.993
11.753
15.6°
12.764
12.534
12.434
12.284
11.984
11.744
12.752
12.522
12.422
12.272
11.972
11.732
12.736
12.506
12.406
12.256
11.956
11.716
12.718
12.488
12.388
12.238
11.938
11.698
-6.7°
12.696
12.466
12.366
12.216
11.916
11.676
-12.2°
12.672
12.442
12.342
12.192
11.892
11.652
-17.8°
12.646
12.416
12.316
12.166
11.866
11.626
10.0°
4.4°
-1.1°
Lead Acid (Ca)
Acid Concentration Measurement
Specific Gravity
ratio of the density of a given solid or liquid
substance to the density of water at a specific
temperature and pressure.
Generally at 4°C and 1 atmosphere
Battery Standard = 30° C
Can’t be measured on Alkaline cells
Electrolyte
Temperature
(Celsius)
100%
SoC
75%
SoC
50%
SoC
25%
SoC
0%
SoC
48.9°
1.249
1.209
1.174
1.139
1.104
43.3°
1.253
1.213
1.178
1.143
1.108
37.8°
1.257
1.217
1.182
1.147
1.112
32.2°
1.261
1.221
1.186
1.151
1.116
26.7°
1.265
1.225
1.190
1.155
1.120
21.1°
1.269
1.229
1.194
1.159
1.124
15.6°
1.273
1.233
1.198
1.163
1.128
10.0°
1.277
1.237
1.202
1.167
1.132
4.4°
1.281
1.241
1.206
1.171
1.136
-1.1°
1.285
1.245
1.210
1.175
1.140
-6.7°
1.289
1.249
1.214
1.179
1.144
-12.2°
1.293
1.253
1.218
1.183
1.148
-17.8°
1.297
1.257
1.222
1.187
1.152




3 x of batteries AH rating is placed across
terminals OR ½ x CCA of Battery
After 15 - 20 seconds terminal voltage is
measured
The higher the voltage the better the battery
Voltage should not be less than 9.6V 1.6 V



Coulomb = Current and Time
Computerised
Current is measured going into and out of the
battery
Electrochemical Impedance
Spectroscopy
 Injects Multiple frequencies ranging from 202,000 Hertz.
 The signals are regulated to very low voltages
 The results are computer analysed to determine
batteries capacity
Cell Charging
 Appling a voltage that is larger than the cells
terminal voltage
 Current then flows in the opposite direction
 Chemical change takes place
between
 Compromise
Energy is stored
as a chemical change
Plate (Grid) Corrosion or Sulfation
High Voltage
Low Voltage
2.45 V
2.30 V
Type dependant on how the battery is used
Permanently Connected
Isolated to be charged
Float
Output Voltage lower than normal charges to
reduce danger of over charging
Output Current supplied at very low levels, but
above leakage currents
Lead Acid
Lead Acid (Ca)
Lead Acid
(AGM)
Lead Acid
(Gel)