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Electric Vehicles – Are They Environmentally Friendly?

Electric Vehicles – Are They Environmentally Friendly?

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- 1. Wali Memon walimemon.com The Electrix 1988 Homda CRX Restored & converted to electric in 2000 Range 40 km Top speed 130 kphWali Memonwalimemon.com 1
- 2. Wali Memon walimemon.comEV Fundamentals Basic Elements of an EV Basic Electricity Energy and Power Batteries, Batteries, Batteries 2
- 3. Wali Memon walimemon.comBasic Elements of an EV Motor Controller Battery Pack Battery Charger Ancillary Electronics 3
- 4. Wali Memon walimemon.comBasic Elements of an EV Block Diagram Ignition Switch Start + 12 V Battery - Advanced Curtis DC Motor Controller 144 V +ve Main Voltmeter Contactor Battery Pack Ammeter 500 Amp 144 V -ve Current Shunt Accelerator - DC/DC + + Converter - Pot Box 4
- 5. Wali Memon walimemon.comBasic 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 5
- 6. Wali Memon walimemon.comBasic 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 6
- 7. Wali Memon walimemon.comBasic 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 7
- 8. Wali Memon walimemon.comBasic 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 8
- 9. Wali Memon walimemon.comBasic 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 9
- 10. Wali Memon walimemon.comBasic 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 10
- 11. Wali Memon walimemon.comBasic 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 11
- 12. Wali Memon walimemon.comBasic Electricity Water Analogy Voltage, Current, Resistance (Ohm’s Law) Serial and Parallel Circuits Electrical Power and Energy 12
- 13. Wali Memon walimemon.comBasic 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 13
- 14. Wali Memon walimemon.comBasic Electricity Voltage, Current, Resistance Voltage - Volts (V) Current - Amps (I) Resistance - Ohms (R) Ohm’s Law: V I= R 14
- 15. Wali Memon walimemon.comBasic 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 15
- 16. Wali Memon walimemon.comBasic 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 16
- 17. Wali Memon walimemon.comBasic 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 17
- 18. Wali Memon walimemon.comBasic 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 18
- 19. Wali Memon walimemon.comEnergy and Power Basic Physics - Mechanical Force, Work, Power Total Energy and Peak Power Relationship to Electrical Energy and Power 19
- 20. Wali Memon walimemon.comEnergy and Power Force, Work, Power Newtons 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 20
- 21. Wali Memon walimemon.comEnergy and Power Force, Work, Power Newtons 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 21
- 22. Wali Memon walimemon.comEnergy 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/sTime (t) 30 sMass (m) 1200 kgAcceleration a = v/t = 0.93 m/s2Force F = ma = 1,111 newtons 22
- 23. Wali Memon walimemon.comEnergy 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 23
- 24. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example (force over a distance): F = 50 N D = 60 m W = 3,000 j 24
- 25. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example (acceleration over time) m 1,200 kg t 30 s Vf 100 kph = 28 m/s a 0.93 m/s2 F 1,111 N d 417 m W 463 kj 25
- 26. Wali Memon walimemon.comEnergy 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) 26
- 27. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example: P = 0.5ma2t m 1200 kg Vf 100 kph t 30 s a 0.93 m/s2 P 15.4 kW 27
- 28. Wali Memon walimemon.comEnergy 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 28
- 29. Wali Memon walimemon.comEnergy 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 29
- 30. Wali Memon walimemon.comEnergy 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 30
- 31. Wali Memon walimemon.comEnergy 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 31
- 32. Wali Memon walimemon.comEnergy 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 32
- 33. Wali Memon walimemon.comEnergy 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 33
- 34. Wali Memon walimemon.comEnergy 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! 34
- 35. Wali Memon walimemon.comEnergy and PowerRelationship 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 35
- 36. Wali Memon walimemon.comEnergy 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 36
- 37. Wali Memon walimemon.comBatteries, 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 37
- 38. Wali Memon walimemon.comBatteries, 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 38
- 39. Wali Memon walimemon.comBatteries, 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 39
- 40. Wali Memon walimemon.comBatteries, 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 40
- 41. Wali Memon walimemon.comBatteries, 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 41
- 42. Wali Memon walimemon.comBatteries, 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 42
- 43. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations Peukert Calculation Rated battery capacity 130 amp-hours C rate for quoted capacity 20 Hours Discharge rate 75 amps Peukert exponent 1.2 Acceptable depth of discharge (DoD) 60 percent Amp-hours available at discharge rate 48 amp-hours Life at discharge rate to specified DoD 0.64 hours Percentage of rated capacity 37 % 43
- 44. Wali Memon walimemon.comBatteries, 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 44
- 45. Wali Memon walimemon.comBatteries, 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 45
- 46. Wali Memon walimemon.comBatteries, 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 46
- 47. Wali Memon walimemon.com Thank YouWali Memonwalimemon.com 47

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