Copyright - EVCO/Richard Hatherill 2009 1 The Electrix 1988 Homda CRX Restored & converted to electric in 2000 Range 40 km Top speed 130 kph

Copyright - EVCO/Richard Hatherill 20091

The Electrix

1988 Homda CRX

Restored & converted to electric in 2000

Range 40 km Top speed 130 kph


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


Basic Elements of an EV

• Motor

• Controller

• Battery Pack

• Battery Charger

• Ancillary Electronics


Basic Elements of an EVBlock Diagram

Battery Pack

CurrentShunt

144 V -ve

500Amp

144 V +ve

Accelerator

MainContactor

'Ignition'Switch

'Start'

'Pot' Box

CurtisController

AdvancedDC Motor

12 VBattery

+

-

DC/DC

Converter

-

+ -

+

Voltmeter

Ammeter


Basic Elements of an EVMotor

• 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


Basic Elements of an EVMotor

• 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


Basic Elements of an EVSeries 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



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



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



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



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


Basic Electricity

• Water Analogy

• Voltage, Current, Resistance (Ohm’s Law)

• Serial and Parallel Circuits

• Electrical Power and Energy


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


Basic Electricity

Voltage, Current, Resistance

• Voltage - Volts (V)

• Current - Amps (I)

• Resistance - Ohms (R)

Ohm’s Law:V

RI =


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


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


Basic Electricity

Electrical Power and Energy

• Power - watts (W)

• The instantaneous power is equal to the voltage times the current

P = V I

• Transposing Ohm’s law V = I R

• Therefore P = I2R

• This shows that wiring losses square with increasing current


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


Energy and Power

Basic Physics - Mechanical

• Force, Work, Power

• Total Energy and Peak Power

• Relationship to Electrical Energy and Power


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


Energy and Power

Force, Work, Power

• Newton's Second Law: Mass and Acceleration

F = 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 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

Accelerationa = v/t = 0.93 m/s2

Force F = ma = 1,111 newtons


Energy and Power

Force, Work, Power

• WorkWork 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


Energy and Power

Force, Work, Power

• Example (force over a distance):

F = 50 N

D = 60 m

W = 3,000 j


Energy 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


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)


Energy 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


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


Energy and 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


Energy and 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


Energy and Power


• Rolling Resistance ForceFr = 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


Energy and Power


• Aerodynamic Drag ForceFd = (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


Energy and 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


Energy and 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!


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


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


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



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



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



Battery 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 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



Battery 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 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



Battery LimitationsPeukert’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



Battery LimitationsPeukert 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 %

© 2004 John De Armond All Rights reserved.



Battery LimitationsOperating 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



Battery LimitationsThe 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



Battery LimitationsCell 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


EV Fundamentals

End of Presentation

Thank You


The Electrix Experience

The Donor Car



Restoration

Alek’s Auto Body Works



Conversion



Conversion



Conversion



Conversion



Conversion



Battery Monitor



Finished!

Documents

Copyright - EVCO/Richard Hatherill 2009 1 The Electrix 1988 Homda CRX Restored & converted to electric in 2000 Range 40 km Top speed 130 kph