Transcript Class_1_Fundamentals_19_May_09

The Electrix
1988 Homda CRX
Restored & converted to electric in 2000
Range 40 km Top speed 130 kph
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Copyright - EVCO/Richard Hatherill 2009
Electric Vehicle Council of Ottawa
Fundamentals of Electric Vehicles
Conversion Course
Class 1 – 20 May 2009
EV Fundamentals
EV Fundamentals
• Basic Elements of an EV
• Basic Electricity
• Energy and Power
• Batteries, Batteries, Batteries
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Basic Elements of an EV
• Motor
• Controller
• Battery Pack
• Battery Charger
• Ancillary Electronics
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Basic Elements of an EV
Block Diagram
'Ignition'
Switch
'Start'
+
12 V
Battery
Curtis
Controller
Advanced
DC Motor
144 V +ve
Voltmeter
Main
Contactor
Battery Pack
Ammeter
500
Amp
144 V -ve
Current
Shunt
Accelerator
+
DC/DC
Converter
+
-
'Pot' Box
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Basic Elements of an EV
Motor
•
AC Motors
– Higher efficiency
– No brushes
– Complex drive electronics
– Generally not suitable for amateur EVs
•
Series Wound DC Motor
– Stator and rotor in series
– Stator and rotor fields add, so torque goes up as square of current
– High starting torque
– Simple drive electronics – variable current
– Not suitable for regenerative braking
– Most popular for amateur EVs
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Basic Elements of an EV
Motor
•
Shunt Wound DC Motor
–
–
–
–
•
Stator and rotor in parallel
Stator winding has high resistance
Torque increases linearly with current
Can be used for regenerative braking
Compond Wound DC Motor
– Combination series and shunt wound
– Has advantages of both
– Complex drive electronics
•
Permanent Magnet and Brushless DC Motors
– Similar performance to shunt wound motors
– High efficiency
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Basic Elements of an EV
Series Wound DC Motor
•
Stator and rotor have very low resistance
– High current hence high torque at low speeds
•
Motor generates back EMF (voltage) as it speeds up
– Higher battery voltage allows more current at higher revs hence increased
power
•
Potential motor runaway at low load
– Do not apply voltage when not in gear or with clutch disengaged
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Basic Elements of an EV
Controller
• For Series Wound DC Motor
– Modern solid-state variable current motor drive
– Very High Power
• Up to 150 Volts
• Up to 500 Amps
• 75 Kilowatts
– Requires large heat sink with good air flow for cooling
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Basic Elements of an EV
Battery Pack
•
Practical pack voltage - 96 volts to 144 volts
•
Multiple 6, 8, or 12 volt batteries
– 16 x 6 volts = 96 volts
– 16 x 8 volts = 128 volts
– 12 x 12 volts = 144 volts
•
Higher voltage = more cells (2 volts per cell)
– 144 volts = 72 cells
– Range limited by weakest cell
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Basic Elements of an EV
Battery Charger
•
On-board charger
•
Input - 115 or 230 volts AC
•
Single pack charger or individual charger per battery
•
Interlock to prevent starting EV with charger plugged in
•
Battery pack must be vented while charging
–
explosive hydrogen released
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Basic Elements of an EV
Ancillary Electronics
•
Battery voltage and current meters
•
Battery monitoring system
•
Battery venting and cooling
•
Battery heater
•
Car heater
•
Charger for auxiliary 12 volt battery
•
Vacuum pump for brakes
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Basic Electricity
• Water Analogy
• Voltage, Current, Resistance (Ohm’s Law)
• Serial and Parallel Circuits
• Electrical Power and Energy
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Basic Electricity
Water Analogy
• Voltage - water pressure
• Current - water flow
• Resistance - pipe diameter (smaller diameter equals greater
resistance)
• The higher the water pressure, the greater the water flow
• The smaller the pipe diameter, the less the water flow
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Basic Electricity
Voltage, Current, Resistance
• Voltage - Volts (V)
• Current - Amps (I)
• Resistance - Ohms (R)
Ohm’s Law:
V
I=
R
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Basic Electricity
Voltage, Current, Resistance
• Current increases as voltage increases and resistance decreases
• Voltage sometimes referred to as electro-motive force (EMF)
– Back EMF was discussed earlier in relation to DC motors
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Basic Electricity
Serial and Parallel Circuits
• Batteries may be serial or serial/parallel connected
• Serial connection increases voltage
• Parallel connection provides more current
• “Buddy pairs” of batteries are sometimes used with lower capacity
batteries to increase range
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Basic Electricity
Electrical Power and Energy
• Power - watts (W)
• The instantaneous power is equal to the voltage times the current
P=VI
• Transposing Ohm’s law V = I R
• Therefore P = I2R
• This shows that wiring losses square with increasing current
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Basic Electricity
Electrical Power and Energy
• Energy - joules (J)
• Energy is power integrated over time (watt/hours)
• Energy is used to overcome wind and rolling resistance, to
accelerate, and to climb hills
• Assuming a relatively constant battery voltage, the total energy
from the battery pack is proportional to the total current drawn
– Important when calculating required battery pack capacity
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Energy and Power
Basic Physics - Mechanical
• Force, Work, Power
• Total Energy and Peak Power
• Relationship to Electrical Energy and Power
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Energy and Power
Force, Work, Power
• Newton's First Law: Mass and Inertia
An object at rest tends to stay at rest, and an object in
motion tends to stay in motion in a straight line at a
constant speed
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Energy and Power
Force, Work, Power
• Newton's Second Law: Mass and Acceleration
F = ma
Where F is force, m is mass, and a is acceleration (F and a
are vectors).
If m is in kg, and a is in m/s2, then F is in newtons
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Energy and Power
Force, Work, Power
• Example:
What force is required to accelerate a 1200 kg EV from 0 to 100 kph in 30 seconds?
Final speed (Vf)
100 kph = 28 m/s
Time (t)
30 s
Mass (m)
1200 kg
Acceleration
a = v/t = 0.93 m/s2
Force
F = ma = 1,111 newtons
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Energy and Power
Force, Work, Power
• Work
Work is the product of the net force and the displacement through
which that force is exerted
W = Fd
F is in newtons, and d is in meters
The unit of work is the newton.meter or joule
Work is an alternative word for energy
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Energy and Power
Force, Work, Power
• Example (force over a distance):
F = 50 N
D = 60 m
W = 3,000 j
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Energy and Power
Force, Work, Power
• Example (acceleration over time)
m
t
Vf
a
F
d
W
1,200
30
100
0.93
1,111
417
kg
s
kph = 28 m/s
m/s2
N
m
463 kj
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Energy and Power
Force, Work, Power
• Power
Power is the work done divided by the time used to do the work
P = Fd/t
The unit of power is the joule/second or watt
(1 kW = 1.34 HP, 1 HP = 746 W)
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Energy and Power
Force, Work, Power
• Example: P = 0.5ma2t
m 1200
Vf 100
t
30
a 0.93
P 15.4
kg
kph
s
m/s2
kW
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Energy and Power
Total Energy and Peak Power
• The total energy (or work) is the sum of the energy required to:
– Accelerate and climb hills
– Overcome rolling and wind resistance
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Energy and Power
Total Energy and Peak Power
•
Example: Our 1,200 kg EV accelerating to 100 kph up a 5% grade hill.
•
Acceleration Force
Fa = ma
W 1200 kg
Vf 100 kph
t
30 s
a
0.93 m/s2
Fa 1111 N
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Energy and Power
Total Energy and Peak Power
• Grade Force
Fg = W g G (for typical grades)
W = vehicle weight in kg
g = gravitational force
G = Percent grade
g
9.8 m/s2
Grade 5 %
Fg 588 N
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Energy and Power
Total Energy and Peak Power
• Rolling Resistance Force
Fr = Cr W g cos f
Cr = 0.007(1+ (v/30.5))
W = vehicle weight in kg
g = gravitational force
f = angle of incline
Cr 0.0134
f 2.86 degrees (0.05 radians)
Fr 120 N
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Energy and Power
Total Energy and Peak Power
• Aerodynamic Drag Force
Fd = (Cd p A V^2)/2
Fd = drag force in Newtons
Cd = coefficient of drag
p = air density (1.29 kg/m2 @sea level)
A = frontal area in sq m
Va = average speed in m/s
Cd 0.3
P 1.29 kg/m2
A 1.39 sq m
Fd 52 N
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Energy and Power
Total Energy and Peak Power
• Propulsion Force
Propulsion Force = acceleration + grade + rolling resistance
+ aerodynamic drag
Fa 1111 N Acceleration
59%
Fg 588 N Grade
31%
Fr 120 N Rolling Resistance 6%
Fd
52 N Aerodynamic Drag 3%
Total Propulsion Force 1871 N
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Copyright - EVCO/Richard Hatherill 2009
Energy and Power
Total Energy and Peak Power
• Total Energy
Total Propulsion Force = 1871 N
From before, distance = 417 m
W = Fd = 779 kj
• Peak Power
P = W/t = 779/30 = 26 kW (35 HP)
Note: This would be the power delivered to the wheels!
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Energy and Power
Relationship to Electrical Energy and Power
• Assume efficiency is 80%
• Total Energy
W = 779 kj = 217 wh
If V = 144 volts
Then Ah = 217/(144 x 0.8) = 1.9 Ah
• Peak Power
P = 26 kW
A = 26 x 1000/(144 x 0.8) = 226 Amps
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Energy and Power
Torque
• Torque is rotational energy (work) in newton.meters
• Wheel torque is the applied force in newtons multiplied by the
wheel radius
• Motor torque is the wheel torque divided by the transmission ratio
• Power is proportional to torque multiplied by RPM
P = n.m x 2 π x RPM/60
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Batteries, Batteries, Batteries
Brief Introduction
(will be covered in more detail later in course)
•
Lead acid batteries are the most practical for amateur conversions
•
Nickel cadmium are available, but are expensive and have other problems
•
Nickel metal hydride are generally low power and expensive, but could
provide good performance
•
Lithium ion provide best performance, but at a high price and are not
easily available
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Batteries, Batteries, Batteries
Lead Acid Batteries
• Most common type is flooded:
–
–
–
–
Liquid electrolyte - must be kept horizontal
Can tolerate deeper discharge
Can be over-charged to equalize cells
Require periodic topping up with distilled water
• Gell Cells:
–
–
–
–
Gelled starved electrolyte
Sealed - can be mounted on sides if required
Lower capacity, lower tolerance to deep discharge
Mustn’t be overcharged
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Copyright - EVCO/Richard Hatherill 2009
Batteries, Batteries, Batteries
Lead Acid Batteries
• Spiral Wound:
– A form of absorbent glass mat (AGM) battery where the plates
are wound in a spiral
– Very rugged and can tolerate high rates of discharge
– Not available in very high capacities so sometimes connected as
“buddy pairs”
– Expensive
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Batteries, Batteries, Batteries
Battery Capacity
Relationship to Total Energy and Peak Power
• An earlier example was from an Excel spreadsheet that calculates
total energy and peak power required for a typical EV trip
scenario
• From spreadsheet:
– For a typical 20 km highway trip in the Electrix:
• Total Energy = 3 kwh = 21 Ah
• Peak power = 30 kW = 206 A
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Batteries, Batteries, Batteries
Battery Limitations
Quoted Versus Actual Capacity
• The nominal capacity of a battery is quoted at the C/20
rate, i.e. the ampere hours delivered if discharged
100% over 20 hours
• The actual capacity drops exponentially as the
discharge rate is increased
• Peukert’s Law can be used to estimate actual capacity
at a given discharge rate
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Batteries, Batteries, Batteries
Battery Limitations
Peukert’s Law
t = H(C/IH)k
H is the hour rating that the battery is specified against
C is the rated capacity at that discharge rate, in A·h
I is the discharge current, in A
k is the Peukert constant, (varies between 1.1 and 1.3)
t is the discharge time, in hours
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Batteries, Batteries, Batteries
Battery Limitations
Peukert Calculation
Rated battery capacity
C rate for quoted capacity
Discharge rate
Peukert exponent
Acceptable depth of discharge (DoD)
Amp-hours available at discharge rate
Life at discharge rate to specified DoD
Percentage of rated capacity
130
20
75
1.2
60
48
0.64
37
amp-hours
Hours
amps
percent
amp-hours
hours
%
© 2004 John De Armond All Rights reserved.
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Batteries, Batteries, Batteries
Battery Limitations
Operating Temperature Range
• Batteries are specified at 78O F (26O C)
• The safe operating range is about 15O to 35O C
• The optimum operating range is about 20O to 30O C
• Too low a temperature reduces capacity, increases DoD
• Too high a temperature decreases life, increases failure rate
• Batteries are like babies - don’t drop them, don’t let them get too
hot or cold, feed and water them, and keep them clean
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Batteries, Batteries, Batteries
Battery Limitations
The Weakest Link
•
A 144 volt battery pack consists of twelve 12 volt batteries in series
•
This is really seventy-two 2 volt cell in series
•
Which ever cell discharges first determines the capacity of the pack – if
you have one weak cell your pack capacity will be reduced
•
Once a cell is fully discharged the other cells are forcing current through
it - which can cause futher damage
•
Cell matching must be maintained to prevent premature discharge
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Batteries, Batteries, Batteries
Battery Limitations
Cell Matching
•
Insist all batteries in a pack are from the same production batch and have
not been sitting around in stock for too long
•
Batteries should be kept at the same temperature
– Difficult to do, especially with multiple battery boxes
•
Cells within a battery should remain fairly matched if an equalizing
charge is performed regularly
•
Series (bulk) charging can cause batteries to get out of balance
•
Charger per battery ensures all batteries are fully charged
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EV Fundamentals
End of Presentation
Thank You
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The Electrix Experience
The Donor Car
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The Electrix Experience
Restoration
Alek’s Auto Body Works
Copyright - EVCO/Richard Hatherill 2009
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The Electrix Experience
Conversion
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The Electrix Experience
Conversion
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The Electrix Experience
Conversion
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The Electrix Experience
Conversion
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The Electrix Experience
Conversion
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The Electrix Experience
Battery Monitor
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The Electrix Experience
Finished!
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