Class 1 Fundamentals 19 May 09

The Electrix1988 Homda CRXRestored & converted to electric in 2000Range 40 km Top speed 130 kph

Electric Vehicle Council of OttawaFundamentals of Electric Vehicles Conversion Course

Class 1 20 May 2009EV Fundamentals

EV FundamentalsBasic Elements of an EVBasic ElectricityEnergy and PowerBatteries, Batteries, Batteries

Basic Elements of an EVMotorControllerBattery PackBattery ChargerAncillary Electronics

Basic Elements of an EVBlock Diagram

Basic Elements of an EVMotorAC MotorsHigher efficiencyNo brushesComplex drive electronicsGenerally not suitable for amateur EVs

Series Wound DC MotorStator and rotor in seriesStator and rotor fields add, so torque goes up as square of currentHigh starting torqueSimple drive electronics variable currentNot suitable for regenerative brakingMost popular for amateur EVs

Basic Elements of an EVMotor

Shunt Wound DC MotorStator and rotor in parallelStator winding has high resistanceTorque increases linearly with currentCan be used for regenerative braking

Compond Wound DC MotorCombination series and shunt woundHas advantages of bothComplex drive electronics

Permanent Magnet and Brushless DC MotorsSimilar performance to shunt wound motorsHigh efficiency

Basic Elements of an EVSeries Wound DC Motor

Stator and rotor have very low resistanceHigh current hence high torque at low speeds

Motor generates back EMF (voltage) as it speeds upHigher battery voltage allows more current at higher revs hence increased power

Potential motor runaway at low loadDo not apply voltage when not in gear or with clutch disengaged

Basic Elements of an EVController

For Series Wound DC MotorModern solid-state variable current motor driveVery High PowerUp to 150 VoltsUp to 500 Amps75 KilowattsRequires large heat sink with good air flow for cooling

Basic Elements of an EVBattery Pack

Practical pack voltage - 96 volts to 144 voltsMultiple 6, 8, or 12 volt batteries16 x 6 volts = 96 volts16 x 8 volts = 128 volts12 x 12 volts = 144 voltsHigher voltage = more cells (2 volts per cell)144 volts = 72 cellsRange limited by weakest cell

Basic Elements of an EVBattery Charger

On-board chargerInput - 115 or 230 volts ACSingle pack charger or individual charger per batteryInterlock to prevent starting EV with charger plugged inBattery pack must be vented while charging explosive hydrogen released

Basic Elements of an EVAncillary Electronics

Battery voltage and current metersBattery monitoring systemBattery venting and coolingBattery heaterCar heaterCharger for auxiliary 12 volt batteryVacuum pump for brakes

Basic ElectricityWater AnalogyVoltage, Current, Resistance (Ohms Law)Serial and Parallel CircuitsElectrical Power and Energy

Basic ElectricityWater AnalogyVoltage - water pressureCurrent - water flowResistance - pipe diameter (smaller diameter equals greater resistance)The higher the water pressure, the greater the water flowThe smaller the pipe diameter, the less the water flow

Basic ElectricityVoltage, Current, ResistanceVoltage - Volts (V)Current - Amps (I)Resistance - Ohms (R)Ohms Law:

Basic ElectricityVoltage, Current, ResistanceCurrent increases as voltage increases and resistance decreasesVoltage sometimes referred to as electro-motive force (EMF)Back EMF was discussed earlier in relation to DC motors

Basic ElectricitySerial and Parallel CircuitsBatteries may be serial or serial/parallel connectedSerial connection increases voltageParallel connection provides more currentBuddy pairs of batteries are sometimes used with lower capacity batteries to increase range

Basic ElectricityElectrical Power and EnergyPower - watts (W)The instantaneous power is equal to the voltage times the current P = V ITransposing Ohms law V = I RTherefore P = I2RThis shows that wiring losses square with increasing current

Basic ElectricityElectrical Power and EnergyEnergy - joules (J)Energy is power integrated over time (watt/hours)Energy is used to overcome wind and rolling resistance, to accelerate, and to climb hillsAssuming a relatively constant battery voltage, the total energy from the battery pack is proportional to the total current drawnImportant when calculating required battery pack capacity

Energy and PowerBasic Physics - MechanicalForce, Work, PowerTotal Energy and Peak PowerRelationship to Electrical Energy and Power

Energy and PowerForce, Work, PowerNewton's First Law: Mass and InertiaAn 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

Energy and PowerForce, Work, PowerNewton's Second Law: Mass and AccelerationF = maWhere 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

Energy and PowerForce, Work, PowerExample: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 kgAccelerationa = v/t = 0.93 m/s2ForceF = ma = 1,111 newtons

Energy and PowerForce, Work, PowerWorkWork is the product of the net force and the displacement through which that force is exertedW = FdF is in newtons, and d is in metersThe unit of work is the newton.meter or jouleWork is an alternative word for energy

Energy and PowerForce, Work, PowerExample (force over a distance):F = 50 ND = 60 mW = 3,000 j

Energy and PowerForce, Work, PowerExample (acceleration over time)m 1,200 kgt 30 sVf 100 kph = 28 m/sa 0.93 m/s2F 1,111 Nd 417 mW 463 kj

Energy and PowerForce, Work, PowerPowerPower is the work done divided by the time used to do the workP = Fd/tThe unit of power is the joule/second or watt(1 kW = 1.34 HP, 1 HP = 746 W)

Energy and PowerForce, Work, PowerExample: P = 0.5ma2tm 1200 kgVf 100 kpht 30 sa 0.93 m/s2P 15.4 kW

Energy and PowerTotal Energy and Peak PowerThe total energy (or work) is the sum of the energy required to:Accelerate and climb hillsOvercome rolling and wind resistance

Energy and PowerTotal Energy and Peak PowerExample: Our 1,200 kg EV accelerating to 100 kph up a 5% grade hill.Acceleration ForceFa = maW 1200 kgVf 100 kpht 30 sa 0.93 m/s2Fa 1111 N

Energy and PowerTotal Energy and Peak PowerGrade ForceFg = W g G (for typical grades)W = vehicle weight in kg g = gravitational force G = Percent gradeg 9.8 m/s2Grade 5 %Fg 588 N

Energy and PowerTotal Energy and Peak PowerRolling Resistance ForceFr = Cr W g cos fCr = 0.007(1+ (v/30.5)) W = vehicle weight in kg g = gravitational force f = angle of inclineCr 0.0134 f 2.86 degrees (0.05 radians)Fr 120 N

Energy and PowerTotal Energy and Peak PowerAerodynamic Drag ForceFd = (Cd p A V^2)/2Fd = drag force in NewtonsCd = coefficient of drag p = air density (1.29 kg/m2 @sea level) A = frontal area in sq m Va = average speed in m/sCd 0.3 P 1.29 kg/m2 A 1.39 sq m Fd 52 N

Energy and PowerTotal Energy and Peak PowerPropulsion ForcePropulsion Force = acceleration + grade + rolling resistance + aerodynamic dragFa 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

Energy and PowerTotal Energy and Peak PowerTotal EnergyTotal Propulsion Force = 1871 NFrom before, distance = 417 mW = Fd = 779 kjPeak PowerP = W/t = 779/30 = 26 kW (35 HP)Note: This would be the power delivered to the wheels!

Energy and PowerRelationship to Electrical Energy and PowerAssume efficiency is 80%Total EnergyW = 779 kj = 217 whIf V = 144 voltsThen Ah = 217/(144 x 0.8) = 1.9 AhPeak PowerP = 26 kWA = 26 x 1000/(144 x 0.8) = 226 Amps

Energy and PowerTorqueTorque is rotational energy (work) in newton.metersWheel torque is the applied force in newtons multiplied by the wheel radiusMotor torque is the wheel torque divided by the transmission ratioPower is proportional to torque multiplied by RPMP = n.m x 2 x RPM/60

Batteries, Batteries, BatteriesBrief 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

Batteries, Batteries, BatteriesLead Acid BatteriesMost common type is flooded:Liquid electrolyte - must be kept horizontalCan tolerate deeper dischargeCan be over-charged to equalize cellsRequire periodic topping up with distilled water

Gell Cells:Gelled starved electrolyteSealed - can be mounted on sides if requiredLower capacity, lower tolerance to deep dischargeMustnt be overcharged

Batteries, Batteries, BatteriesLead Acid BatteriesSpiral Wound:A form of absorbent glass mat (AGM) battery where the plates are wound in a spiralVery rugged and can tolerate high rates of dischargeNot available in very high capacities so sometimes connected as buddy pairsExpensive

Batteries, Batteries, BatteriesBattery CapacityRelationship 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 scenarioFrom spreadsheet:For a typical 20 km highway trip in the Electrix:Total Energy = 3 kwh = 21 AhPeak power = 30 kW = 206 A

Batteries, Batteries, BatteriesBattery LimitationsQuoted 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 hoursThe actual capacity drops exponentially as the discharge rate is increasedPeukerts Law can be used to estimate actual capacity at a given discharge rate

Batteries, Batteries, BatteriesBattery LimitationsPeukerts Law

t = H(C/IH)kH is the hour rating that the battery is specified againstC is the rated capacity at that discharge rate, in AhI is the discharge current, in Ak is the Peukert constant, (varies between 1.1 and 1.3)t is the discharge time, in hours

Batteries, Batteries, BatteriesBattery LimitationsPeukert Calculation

Rated battery capacity 130 amp-hoursC rate for quoted capacity 20 HoursDischarge rate 75 ampsPeukert exponent 1.2 Acceptable depth of discharge (DoD) 60 percentAmp-hours available at discharge rate 48 amp-hoursLife at discharge rate to specified DoD 0.64 hoursPercentage of rated capacity 37 %

2004 John De Armond All Rights reserved.

Copyright - EVCO/Richard Hatherill 2009

Batteries, Batteries, BatteriesBattery LimitationsOperating Temperature RangeBatteries are specified at 78O F (26O C)The safe operating range is about 15O to 35O CThe optimum operating range is about 20O to 30O CToo low a temperature reduces capacity, increases DoDToo high a temperature decreases life, increases failure rateBatteries are like babies - dont drop them, dont let them get too hot or cold, feed and water them, and keep them clean

Batteries, Batteries, BatteriesBattery LimitationsThe Weakest LinkA 144 volt battery pack consists of twelve 12 volt batteries in seriesThis is really seventy-two 2 volt cell in seriesWhich ever cell discharges first determines the capacity of the pack if you have one weak cell your pack capacity will be reducedOnce a cell is fully discharged the other cells are forcing current through it - which can cause futher damageCell matching must be maintained to prevent premature discharge

Batteries, Batteries, BatteriesBattery LimitationsCell MatchingInsist all batteries in a pack are from the same production batch and have not been sitting around in stock for too longBatteries should be kept at the same temperatureDifficult to do, especially with multiple battery boxesCells within a battery should remain fairly matched if an equalizing charge is performed regularlySeries (bulk) charging can cause batteries to get out of balanceCharger per battery ensures all batteries are fully charged

EV Fundamentals

End of Presentation

Thank You


The Electrix ExperienceThe Donor Car


The Electrix ExperienceRestorationAleks Auto Body Works


The Electrix ExperienceConversion


The Electrix ExperienceBattery Monitor


The Electrix ExperienceFinished!


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Class 1 Fundamentals 19 May 09