EV Conversion PDRNovember 1, 2004 1 Battery-Powered Electric Vehicle Conversion: (BEVC) Preliminary Design Review November 1, 2004 Presented By: Ryan Bohm

EV Conversion PDR November 1, 20041

Battery-Powered Electric Vehicle Conversion:

(BEVC)

Preliminary Design Review

November 1, 2004

Presented By:Ryan Bohm

1355 N. 400 E. #1Logan, UT 84341


BEVC Project Summary

Project Stage: Preliminary Design Review

Objective: To convert a conventional gas-powered vehicle to battery-powered electric and observe public reaction to electric vehicles as an alternative form of transportation.

Principle: Most commuter vehicles use an internal-combustion engine which is fueled by gasoline. Gasoline combustion engines are inefficient, noisy, require frequent maintenance, and require non-renewable resources to power. Electric motors are virtually maintenance free, quiet, efficient, and can use renewable resources as a power source. A gasoline combustion engine can be replaced by an electric motor.

Project Lead: Ryan Bohm

Finish Date: December 2004


Agenda Welcome / Introduction 1 min. Executive Summary 2 min.

Project ObjectiveGeneral Theory of Operation

Dismantling of Internal Combustion system 1 min.

Drivetrain 3 min.Electric motorCoupling motor shaft to flywheelCoupling motor to transmissionCooling motor

Batteries 2 min.ChoosingBattery racks

Power Brakes 2 min.Vacuum pumpVacuum tank

Power Steering/Air Conditioning 2 min.

Accessory motorMounting bracket


Agenda Heater 2 min.

ChoosingTheory of operationRemoving dashboardBuilding heater housingHall-effect sensor unit

Motor Controller 2 min.SpecificationsMountingCoolingConnectingThrottle controlTach sensorController interface

Battery Charger 2 min.

Battery RegulatorsCharging connector

Accessory Electronics – 12V system 1 min.

Isolation of High-Voltage and 12V system 1 min.


AgendaCircuit Breaker and Main Fuses 1 min.Battery Voltage Monitoring 2 min.

Interfacing with dash gaugesBlock diagramProgramming/calibrating

Current Sensing Unit 1 min.Block diagramProgramming/calibrating

Wiring 1 min.

Conclusion 1 min.


Executive Summary

Ryan Bohm

Utah State UniversityLogan, UT 84321

Phone: 435-755-5754Email: [email protected]


Project Objective

•Convert a 1984 Nissan 200sx conventional internal-combustion vehicle to battery powered electric.•Display to the public the feasibility of battery-powered electric vehicles for short-distance commutes.•Fulfill the requirements for Computer-Engineering Senior Design Project and Utah State University.


Theory of Operation

Battery Bank

Transmission

AdapterController

Motor

Electronics Box

High-Current Cables

Charging Cable

Charger


Dismantling ICE Components

Items to be removed:Gas tankExhaust systemInternal combustion engineFuel linesRear seats

* Care must be taken to mark electrical connections, nuts, and bolts to ensure that parts which will be reused can be properly identified and placed.


Drivetrain: Electric Motor

A series wound DC motor with the following characteristics will be used:

20 HP (continuous rating)Series wound96 Volts (will be run at 144, which is within working range)


Coupling Motor to Flywheel

Motor shaft coupler and adapter plate will be designed and manufactured by Electro Auto. The motor coupler is a critical component of the drive train, through which all torque is transmitted.


Coupling Motor to Transmission

Once flywheel has been attached to the motor shaft, a new clutch is installed. Then the motor can be attached to the transmission.


Cooling Motor

An internal fan pulls air through the motor to keep it cool during operation, but this fan is insufficient at lower speeds or extended high-current situations. An external 12v blower will force air through the motor to keep it cool.


Batteries

The battery is the “gasoline” of the electric vehicle. It must be able to handle large current surges and deep discharges.

This electric vehicle conversion will be designed with quick acceleration and limited range (10-15 miles) in mind. A suitable battery for these conditions must be chosen.


Choosing Battery Type

•Flooded lead acid (Pb) batteries have limited maximum current draw, typically < 500 amps.

•Sealed Lead Acid (SLA), or Absorbed Glass Mat (AGM) batteries such as the Optima Yellow Top or Exide Orbital can handle extreme current draws in excess of 2000 amps.

•12 Exide Orbitals will be used in this conversion.


Battery Racks

Batteries weigh 41 lbs. each. Total battery weight is 492 lbs. Batteries must be arranged for low center of gravity, and low polar moment of inertia for good handling characteristics. To achieve this, 10 of the 12 batteries will be placed in a metal rack built into the rear seat. The rack must be able to contain the batteries in an accident. The remaining 2 batteries will be secured to the electronics rack in the engine compartment.


Power Brakes

The original vehicle was equipped with a power brake booster which was vacuum powered. This vacuum came from the intake manifold of the combustion engine.

For similar driving characteristics and safety, this vacuum must be supplied by another source.


Vacuum Pump

A 12v, 9 amp vacuum pump replace the vacuum provided by the internal combustion engine.

An adjustable vacuum switch will turn on the pump when vacuum falls below the set value.


Vacuum Tank

The vacuum pump alone will only provide about 1 assisted actuation of the brakes. By using a vacuum tank, multiple assisted actuations of the brakes can be made.


Power Steering/Air Conditioning

The original vehicle had both power steering and air conditioning. The decision was made to keep power steering in the electric conversion for safety and convenience reasons. The air conditioning system will also be retained for comfort during hot summer months.


Accessory Motor

The traction motor does not need to idle at stop conditions like the internal combustion engine. This makes powering the AC/PS off of the traction motor undesirable, as there would be no power steering assist when the vehicle was not moving, and the air conditioning would not perform when the vehicle was at a rest.

Consequently, a 1.5 Hp. accessory motor will be used. This motor will run whenever the ignition is in the “On” position and the vehicle has been “started”.


Mounting Bracket

A mounting bracket will secure the power steering pump, air conditioning compressor, and accessory motor. It will be mounted to the front face of the traction motor.


Heater

The original heater core obtains its heat from the internal combustion engine cooling system. A heater is important for driver comfort during cold winter months.

Since there are no appreciable sources of heat in the electric vehicle, an alternate form of heating must be chosen. Several alternatives exist.


Heater Choice

Alternate forms of vehicle heating include the following:Electric elementElectric water heater/pumpFuel-fired heaterPeltier cooler in reverse

Each option has its own advantages/disadvantages. The electric element option was chosen due to recommendations by other EV users for its high-output, quick heat production, and minimum use of existing vehicle real-estate.


2 Gnd L.V.

144vGndH.V.

GndH.V.

Gnd L.V.

1Fan Speed Sw.

Temp. Select

1

2

ControlCircuit

Heater Theory of Operation

The electric heater elements are positioned where the existing coolant-heated core was located. High-voltage DC relays are controlled by a circuit which determines if the fan switch is turned on, and the heat selection control switch is in the half or full on position.

Air Flow


Removing Dashboard

•To replace the existing heater core, the entire dashboard must be removed. •The procedure shown in the vehicle repair manual will be followed. •All electrical connections must be marked carefully to ensure proper reassembly.


Building Heater Housing

The 2 electric heater elements come with a special plastic housing capable of withstanding the high temperature of the element. This housing will be modified to accommodate the elements in a “sandwiched” configuration. An aluminum housing will be manufactured to fit in the footprint of the original heater core.


Hall-effect Sensors

Heater element selecting will be performed by two Hall-effect sensors mounted on the back of the heater element housing box. Magnets are embedded in a control arm which previously opened/closed a coolant valve, and was actuated by moving the temperature control lever.


Motor Controller

The motor controller delivers current to the electric motor. It also controls the motor voltage. The controller should also have the ability to protect against over-revving, self over-heating, and contactor failure. Few options exist for high-current motor controllers in the electric vehicle arena. Curtis, DCP, and CafeElectric DC motor controllers exist with current capabilities of 500 amps or higher. A CafeElectric Zilla Z1k will be used in the conversion.


Controller Specifications

The CafeElectric Z1K has the following features:1000 amps maximum motor currentOver-rev protectionWater coolingContactor monitoringSilent high frequency PWM (15.7 kHz)Upgradeable firmware


Controller Mounting

The motor controller will be mounted inside an electronics box which will reside in the engine compartment. This electronics box will keep moisture, dirt, and dust from the controller and other electronics.


Controller Cooling

The motor controller should be cooled using a pump and small radiator. This allows for optimum performance of the controller. A 120VAC pump will be powered by a small AC inverter. The coolant will pass through the coolant lines to a small radiator.


Controller Connections


Throttle Control

The motor controller throttle input is a 5K Ohm variable resistor (potentiometer). A pre-built unit from Curtis will be used. This potentiometer has a built-in return spring and will connect directly to the existing throttle cable. An additional return spring will be used for safety.


Tach Sensor

To emulate the tachometer generating signal for the on-dash tach and to supply the motor controller with a signal for over-rev detection, a tachometer sensor will be designed.

The controller tach signal must be pulled low 4 times per revolution. The motor controller has an output signal that is connected to the vehicle tachometer which provides the necessary pulses.


Tach Sensor Construction

The tach sensor is a Hall-effect sensor and 2 capacitors epoxied in a copper cap housing. Magnets are embedded in a nylon collar which mounts on the motor tail-shaft.


Controller Interface

Controller parameters such as motor voltage and current can be adjusted through a serial connection to the controller. A Palm IIIe PDA will be used as the interfacing device. A 12v to 3v converter board will be designed to provide constant power from the vehicle 12v system, thus eliminating the need for battery changes in the PDA. The PDA will be mounted within reach of the driver using a cell phone mount.


Battery Charger

The battery charger is an integral part of the electric vehicle. Many charger options exist. More expensive chargers have pre-programmed charging algorithms and require minimal user interaction. Other options are less expensive but require user monitoring and attendance.

For ease-of-charging, a Manzanita Micro PFC20, 20 amp charger will be used. This charger has the capability to interface with battery regulators to avoid overcharging, and will be able to charge the 144v pack in about 2.5 hours.


Battery Regulators

Battery regulators will be used in conjuction with the charger. When charged in series, lead-acid batteries do not charge evenly. Consequently, some batteries may be under-charged, and others over-charged. Battery regulators detect when the battery has reached full charge, and pass current to avoid over-charging. The regulator will also talk to the charger over a network to signal when the battery has reached full charge.

The PCBs and components will be ordered, and the regulators assembled in-house at a lower cost than purchasing pre-assembled.


Charging Connector

The battery charger will plug into the 120 or 240 AC grid using a permanent twist-lock connector located where the gas fueling door resided. All charging connectors will be rated for 20 amps.

A Hall-effect sensor and magnet on the fuel door will send a signal to the motor controller to indicate if the fuel door is open or closed. The controller will not allow the motor to turn if the fuel door is open to prevent driving away with the charging cord connected.

Stationary PlugHall-effect sensor

Magnet


12V System

The existing 12 volt system will remain to power accessory devices such as headlights, horn, radio, and dashboard instruments.

During normal operation, the 12 volt system will be powered, and the 12 volt battery charged, by 2 IOTA DLS-55 DC/DC converters (actually dual-purpose battery chargers), with a maximum rating of 2 x 55 = 110 amps. This exceeds the original alternator output of 60 amps.


Isolation

The 12V chassis ground must be isolated from the 144V system. This is to ensure that through error, or accident, the chassis ground cannot complete a 144V potential loop. The 144V system has no common grounded chassis like the 12V system.

+

-12V

+

-144V

Chassis Ground


Fuses & Circuit Breakers

All load lines will be equipped with fuses and/or circuit breakers. The main 144V feed line will have a fast semiconductor fuse for protection of the system. The 144V line will also have a high-current circuit breaker within easy reach of the driver to disconnect power in case of an emergency.


Battery Voltage Monitor

The existing dashboard fuel gauge will be used to display the battery state-of-charge (SOC). A battery voltage monitor unit will be designed to interface with the dashboard fuel gauge. The battery voltage monitor will calculate the SOC, and will also interface with the low-fuel dashboard light, and charge warning light (previously the alternator error light).


Voltage Monitor Block Diagram

Inputs Outputs

Current (from current sensing unit)

Temp. Sensor

+12V

12V Gnd

HV +

HV Gnd

Bat. Reg. Signal

Low Fuel Light

Fuel guage

Battery Error Light

PIC 16F76High Volt.

PIC 16F76Low Volt.

LM7805

optocouplers

voltage bus

5V

12V

Ω

LM7805

5V

voltagedivider

HV+

optocoupler

voltage divider &Op-Amp

Temp.Sensor

Bat. Reg. Signal Out

Program.Buses


Programming Voltage Monitor

The voltage monitor unit will contain two PIC microcontrollers. These microcontrollers can be reprogrammed in-circuit to change the software. This will be necessary to adjust for errors in the initial program calibrations.

Code for the microcontrollers will be written in PIC C++. A USB In-Circuit Serial Programmer will be used for programming.


Current Sensing Unit

It is useful to see the instantaneous motor current draw while driving the electric vehicle. An analog Hall-effect sensor will be used to detect the magnetic field produced by current flowing in the main power cables. A ferrite core will initially be used to increase the magnetic flux to the sensor; however, this may prove unnecessary with the high currents being used.


Current Sensing Block Diagram

Main HV Conductor Sensor

PIC 16F76

Resistor Network to dash gauge

Programming Bus


Programming Current Sensing Unit

The current sensing unit will be programmed in the same fashion as the voltage monitor unit. It is anticipated that calibrating the unit will require a fairly significant amount of trial and error.


Wiring

With the large amount of wiring required for the electric vehicle conversion, the following guidelines will be observed:

Use existing wiring whenever possibleMake quality connections: Western Union joints, solder all connections, cover with heat-shrink tubingUse only proper gauge of wiresUse high pressure crimping of terminals and lugs on main power lines guageUse rubber grommets whenever wires exit/enter metal orifices


Conclusion

High quality components will ensure reliable operation.A simple user interface and ease-of-driving will allow the vehicle to be driven without special expertise.Attention to details will produce a safe and reliable vehicle.Public reaction will be observed to view the acceptability of electric vehicles for short-range commuting.

Documents

EV Conversion PDRNovember 1, 2004 1 Battery-Powered Electric Vehicle Conversion: (BEVC) Preliminary Design Review November 1, 2004 Presented By: Ryan Bohm