Electric%20Vehicle%20Batteries

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Electric Vehicle Batteries North Bay Chapter of
the Electric Auto Association www.nbeaa.org Updat
ed 8/14/09 Posted at http//www.nbeaa.org/present
ations/batteries.pdf
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NBEAA 2009 Technical Series 1. EV
Drive Systems TODAY gtgt 2. EV Batteries 3.
EV Charging Systems 4. EV Donor Vehicles
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Agenda What is a Battery? Battery
History EV Battery Requirements Types of EV
Batteries EV Battery Temperature Control EV
Battery Charging EV Battery Management EV Battery
Comparison EV Record Holders Future EV
Batteries EV Drive System Testimonials, Show and
Tells and Test Drives
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What is a Battery?
During Charge
voltage and energy increases
heat
electrolyte
anode
cathode -
chemical reaction
heat
current
charger
energy
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What is a Battery?
During Discharge
voltage and energy decreases
heat
electrolyte
anode
cathode -
chemical reaction
heat
current
load
work
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Battery History Rechargeable batteries
highlighted in bold.
First battery, Voltaic Pile, Zn-Cu with NaCl electrolyte, non-rechargeable, but short shelf life 1800 Volta
First battery with long shelf life, Daniel Cell, Zn-Cu with H2SO4 and CuSO4 electrolytes, non-rechargeable 1836 England John Fedine
First electric carriage, 4 MPH with non-rechargeable batteries 1839 Scotland Robert Anderson
First rechargeable battery, lead acid, Pb-PbO2 with H2SO4 electrolyte 1859 France Gaston Plante
First mass produced non-spillable battery, dry cell, ZnC-Mn02 with ammonium disulphate electrolyte, non-rechargeable 1896 Carl Gassner
Ni-Cd battery with potassium hydroxide electrolyte invented 1910 Sweden Walmer Junger
First mass produced electric vehicle, with Edison nickel iron NiOOH-Fe rechargeable battery with potassium hydroxide electrolyte 1914 US Thomas Edison and Henry Ford
Modern low cost Eveready (now Energizer) Alkaline non-rechargeable battery invented, Zn-MnO2 with alkaline electrolyte 1955 US Lewis Curry
NiH2 long life rechargeable batteries put in satellites 1970s US
NiMH batteries invented 1989 US
Li Ion batteries sold 1991 US
LiFePO4 invented 1997 US
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EV Battery Requirements Safe High Power High
Capacity Small and Light Large Format Long
Life Low Overall Cost
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EV Battery Requirements Safe Examples of EV
battery safety issues Overcharging explosive
hydrogen outgassing thermal runaway resulting
in melting, explosion or inextinguishable
fire Short Circuit external or
internal under normal circumstances or caused
by a crash immediate or latent Damage liquid
electrolyte acid leakage
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EV Battery Requirements High Power Power
Watts Volts x Amps Typically rated in terms of
C the current ratio between max current and
current to drain battery in 1 hour example 3C
for a 100 Ah cell is 300A Battery voltage
changes with current level and direction, and
state of charge 1 Horsepower 746
Watts Charger efficiency 90 Battery charge
and discharge efficiency 95 Drive system
efficiency 85 AC, 75 DC
heat
heat
heat
heat
motor controller
batteries
motor
shaft
charger
100 in
60 - 68 out
32 - 40 lost to heat
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EV Battery Requirements High Power Example Accel
erating or driving up a steep hill Motor Shaft
Power 50 HP or 37,000 W Battery Power
50,000 W DC, 44,000 W AC Battery
Current 400A for 144V nominal pack with DC
drive 170A for 288V nominal pack with AC
drive Driving steady state on flat
ground Motor Shaft Power 20 HP or 15,000
W Battery Power 20,000 W DC, 18,000
AC Battery Current 150A for 144V nominal pack
with DC drive 70A for 288V nominal pack with
AC drive Charging Depends on battery type,
charger power and AC outlet rating Example for
3,300 W, 160V, 20A DC for 3,800 W, 240V, 16A AC
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EV Battery Requirements High Capacity Higher
capacity higher driving range between
charges Energy Watts x Hours Volts x
Amp-Hours Watt-hours can be somewhat reduced with
higher discharge current due to internal
resistance heating loss Amp-Hours can be
significantly reduced with higher discharge
current seen in EVs due to Peukert
Effect Amp-Hours can be significantly reduced in
cold weather without heaters and
insulation Example 48 3.2V 100 Amp-Hour cells
with negligible Peukert Effect and 95
efficiencies Pack capacity 48 3.2 Volts
100 Amp-Hours .95 efficiency 14,592 Wh 340
WattHours per mile vehicle consumption
rate Vehicle range 14,592 Wh / 340 Wh/mi 42
miles
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EV Battery Requirements Small and Light Cars
only have so much safe payload for handling and
reliability Cars only have so much space to put
batteries, and they cant go anywhere for safety
reasons Specific Power power to weight ratio
Watts / Kilogram Specific Energy energy
capacity to weight ratio Watt-Hours /
Kilogram Power Density power to volume ratio
Watts / liter Energy Density energy to capacity
to volume ratio Watt-Hours /liter 1 liter 1
million cubic millimeters Example 1 module
with 3,840 W peak power, 1,208 Wh actual energy,
15.8 kg, 260 x 173 x 225 mm 10.1
liters Specific Power 3,840 W / 15.8 kg 243
W/kg Specific Energy 1,208 Wh / 15.8 kg
76 Wh/kg Power Density 3,840 W / 10.1 l 380
W/l Energy Density 1,208 Wh / 10.1 l 119
Wh/l
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EV Battery Requirements Large Format Minimize
the need for too many interconnects example 100
Ah Long Life Minimize the need for battery
replacement effort and cost Example 2000 cycles
at 100 Depth-of-Discharge to reach 80 capacity
charging at C/2 5 years to 80 capacity on 13.8V
float at 73C Low Overall Cost Minimize the
purchase and replacement cost of the
batteries Example 10K pack replacement cost
every 5 years driven 40 miles per day down to 80
DOD 1825 days, 73,000 miles, 14 cents per mile

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Higher Temperature Reduces Shelf Life 13 degrees
reduces the life of lead acid batteries by half.
Source Life Expectancy and Temperature,
http//www.cdtechno.com/custserv/pdf/7329.pdf.
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EV Battery Comparison
Type Power Energy Stability Max temp Life Toxicity Cost
LiFePO4 -
LiCO2 - - - -
NiZn -
NiCd - -
PbA AGM - - -
PbA gel - - -
PbA flooded - - - -
Available large format only considered NiMH,
small format lithium and large format nano
lithium not included.
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Lead Acid Battery Peukert Effect Reduces Range
at EV Discharge Rates
A 75 Amp Hour battery that provides 75 amp
hours at the 20 hour C/20 rate or 3.75 amps only
provides 42 amp-hours at 75 amps, a typical
average EV discharge rate, or 57 of the
nameplate rating. Nickel and lithium batteries
have far less Peukert effect.
Data Source MPS 12-75 Valve Regulated Lead Acid
Battery Datasheet, http//www.cdstandbypower.com/p
roduct/battery/vrla/pdf/mps1275.pdf. Note do
not use Dynasty MPS batteries in EVs they are
not designed for frequent deep cycling required
in EVs
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Lead Acid AGM Batteries are Better for High
Current Discharge Rates Gels have higher internal
resistance.
Higher discharge rates are typical in heavier
vehicles driven harder in higher gears with
smaller packs and less efficient, higher current,
lower voltage DC drive systems.
Source Dynasty VRLA Batteries and Their
Application, http//www.cdtechno.com/custserv/pdf/
7327.pdf.
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Lead Acid Batteries Need Heaters in Cold
Climates They lose 60 of their capacity at 0
degrees Fahrenheit.
Source Capacity Testing of Dynasty VRLA
Batteries, http//www.cdtechno.com/custserv/pdf/71
35.pdf.
Source Impedance and Conductance Testing,
http//www.cdtechno.com/custserv/pdf/7271.pdf.
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Gels Have a Longer Cycle Life AGMs only last half
as long, but as previously mentioned can
withstand higher discharge rates.
Source Dynasty VRLA Batteries and Their
Application, http//www.cdtechno.com/custserv/pdf/
7327.pdf.
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Flooded Lead Acid Battery Acid Containment is
Required for Safety In addition to securing all
batteries so they do not move during a collision
or rollover, flooded lead acid batteries need
their acid contained so it does not burn any
passengers.
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Flooded Lead Acid Battery Ventilation is Required
for Safety When a cell becomes full, it gives
off explosive hydrogen gas. Thus vehicles and
their garages need fail safe active ventilation
systems, especially during regular higher
equalization charge cycles that proceed watering.
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High Power, High Capacity Deep Cycle Large Format
Batteries Used in EVs LiFePO4 Hi
Power Thunder Sky LMP Valence Technologies
U-Charge XP, Epoch PbA AGM BB Battery
EVP Concorde Lifeline East Penn Deka
Intimidator EnerSys Hawker Genesis,
Odyssey Exide Orbital Extreme Cycle Duty
Optima Yellow Top, Blue Top Gel East Penn
Deka Dominator Flooded Trojan Golf Utility
Vehicle US Battery BB Series NiCd Flooded Sa
ft STM NiZn SBS Evercel Li Poly Kokam SLPB
Note LiFePO4 are recommended, having the
lowest weight but highest initial purchase price.
But they have similar overall cost, and the rest
have safety, toxicity or power issues.
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EV Battery Charging
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Battery Chargers Need Voltage Regulation and
Current Limiting This shortens charge time
without shortening life.
Source Charging Dynasty Valve Regulated Lead
Acid Batteries, http//www.cdtechno.com/custserv/p
df/2128.pdf.
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EV Charger Temperature Compensation is Required
for Safety Excess voltage at higher temperatures
can lead to thermal runaway, which can melt lead
acid modules, explode nickel modules, and ignite
thermally unstable lithium ion cells. Battery
cooling systems are typically employed with
nickel and unstable lithium ion packs to maintain
performance while providing safety.
Source Thermal Runaway in VRLA Batteries Its
Cause and Prevention, http//www.cdtechno.com/cust
serv/pdf/7944.pdf.
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EV Battery Management
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• EV Batteries Need to be Monitored
• All batteries need to be kept within their
  required voltage and temperature ranges for
  performance, long life and safety. This is
  particularly important for nickel and thermally
  unstable lithium ion batteries which can be
  dangerous if abused.
• Ideally each cell is monitored, the charge
  current is controlled, and the driver is alerted
  when discharge limits are being approached and
  then again when exceeded.
• For high quality multi-cell modules without
  cell access, module level voltage monitoring is
  better than no monitoring.
• For chargers without a real time level control
  interface, a driven disable pin or external
  contactor will suffice for battery protection,
  but may result in uncharged batteries in time of
  need.
• Dashboard gages and displays are good, but
  combining them with warning and error lamps is
  better.

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Amp-Hour Counters are More Accurate Fuel Gages
Than Volt Meters
To predict when your batteries will drop below
the minimum voltage, Depth of Discharge should be
monitored.
Open circuit voltage drops only 0.9V between 0
and 80 depth of discharge.
Voltage drops up to 2.7V at 600 amps discharge,
and can take a good part of a minute to recover.
Ideally your fuel gage looks at all of the above
plus temperature and then estimates depth of
discharge.
Data Source MPS 12-75 Valve Regulated Lead Acid
Battery Datasheet, http//www.cdstandbypower.com/p
roduct/battery/vrla/pdf/mps1275.pdf.
Data Source Integrity Testing,
http//www.cdtechno.com/custserv/pdf/7264.pdf.
Note do not use Dynasty MPS batteries in EVs
they are not designed for frequent deep cycling
required in EVs
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• EV Batteries Need to be Balanced
• All batteries will drift apart in state of
  charge level over time. This is due to
  differences in Peukert effect and internal leak
  rates. This will be detected during monitoring
  as early low voltages during discharge, and early
  high voltages and not high enough voltages during
  charge.
• Sealed batteries need to be individually
  balanced, whereas flooded batteries can be
  overcharged as a string, then watered.
• Individual balancing can be done manually on a
  regular basis with a starter battery charger, or
  with a programmable power supply with voltage and
  current limits, but the latter can be expensive.
  And it can be a hassle, and it can be difficult
  if the battery terminals are hard to get to.
• Automatic balancing maximizes life and
  performance. Ideally balancing is low loss,
  switching current from higher voltage cells to
  lower voltage cells at all times. Bypass
  resistors that switch on during finish charging
  only is less desirable but better than no
  automatic balancing.

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EV Battery Pictures
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Optima Blue Top AGM Sealed Lead Acid Batteries
with PCHC-12V-2A Power Cheqs Installed in Don
McGraths Corbin Sparrow
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Valence Module
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Valence BMU
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Valence batteries and BMU connected via RS485
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Valence battery monitoring via CANBus and USB to
laptop
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Valence Cycler 2.4 battery monitoring screen
capture (idle mode 2.8 now available)
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Valence battery monitoring file list
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Valence battery monitoring file example
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Valence battery monitoring results maximum
charge voltage vs. target Troubleshooting
unbalanced cell (dropped from gt90 Ah to 67 Ah
after balancing disabled for 3 months due to late
onset RS485 errors due to missing termination
resistor and unshielded cables)
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Valence battery monitoring results discharge
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Valence battery monitoring results charge and
discharge Troubleshooting bad cell that abruptly
went from gt90 Ah to 25 Ah in less than 1 week
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EV Record Holders
Phoenix Motorcars SUT charged 50 times in 10
minutes with no degradation in 2007 130 mile
range
AC Propulsion tZero drove 302 miles on a single
charge at 60 MPH in 2003, Lithium Ion batteries
Solectria Sunrise drove 375 miles on a single
charge in 1996, NiMH batteries
DIT Nuna drove 1877 miles averaging 55.97 MPH on
solar power in 2007, LiPo batteries
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Future EV Batteries
Stanford University Silicon Nanowire electrodes
have 3X capacity improvement expected for Lithium
batteries
Not technically a battery, but MIT Nanotube
ultracapacitors have very high power, 1M cycle
energy storage approaching Lithium battery
capacity