Daniel May

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Team
Dr. Marshall Molen - Advisor
Brandon Holbrook
Daniel May
Web Site Slave Microcontroller Analog Sensors
Graphics Algorithms Relay Switching Web Site
Brandon Gore
Heath Massey
Interfacing Power Supply Charging Circuit OpAmps
Software Master Microcontroller Interfacing
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Project Introduction

• Simple Concept
• Hybrid Electric Vehicles (HEVs) use batteries as
  a source of power for the electric motor.
• The electric motor acts as a generator to
  recharge the batteries.

• General Information
• Batteries are charged by applying reversed
  current.
• While the battery is being charged, the voltage
  across the battery terminals increases.
• While the battery is being discharged, the
  voltage across the battery terminals decreases.
• Amount of charge on a battery is called State of
  Charge (SoC)

Discharge
Charge
-
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Approach
Battery Module
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Batteries

• Nickel-Metal Hydride (NiMH)
• 2600 mAh
• 12 Volts (Nominal)
• Our prototype uses 4 to achieve 48 Volts

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Battery Analyzer from West Mountain Radio

• Automatically charge / discharge the batteries
• Monitors and records temperature, current,
  voltage, Amp-Hours
• Used to compare against our readings

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Battery Voltage During Discharge
Expected Voltage Curve Measured Value
Our batteries behave very close to ideal
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Monitoring Circuit Critical Battery Measurements

• Voltage
• Batteries can output a maximum of 15 Volts
• An OpAmp used to divide by 3 steps it down to 5
  volts for the PIC A/D
• Temperature
• An NTC Thermistor decreases resistance as
  temperature increases
• A voltage divider varies the voltage as
  temperature fluxuates

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OpAmp V/3 Voltage Measuring Circuit
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Results OpAmp Circuit
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Temperature Monitoring Circuit
Resistance is governed by the following equation
Therefore, at room temperature (T300K)

• If placed in series with 200 Ohms, expected
  voltage is 4 Volts
• Results
• When measured by the PIC, the network did give 4
  Volts
• Network obeyed this equation up to 80 degrees C

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Relay Circuit Switching Charge Modes

• BJT Allows a 5 Volt, low-current PIC Output to
  drive a 12 Volt, high-current Relay

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Software Slave Microcontroller

• Change Since Midterm
• PLD ? PIC18F242 Microcontroller
• I2C is very complex, difficult to emulate
  ourselves
• PIC has built-in I2C Controller
• Analog readings can be directly measured with
  PICs A/D Converter, instead of complex and
  inaccurate resistor thresholds

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Software Master Microcontroller

• Written in C
• Automatically switches the system from charging
  to discharging modes based upon SoC calculations
• Will safely shut down the system if any error
  conditions occur

• Change Since Midterm
• Atmel AT89 ? PIC18F458
• Both have comparable hardware features
• Consistent programming language / environment
  with Slave PIC18s

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Diagnostic Software

• Displays connected Battery Packs
• Displays all monitored characteristics (voltage,
  temperature, SoC)
• Can manually Stop / Start the system
• Can manually switch the system between Charging /
  Discharging

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The Prototype
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Goals for Design II

• Continually refine charging algorithm
• Incorporate current readings into SoC
  calculations
• Consolidate hardware onto PCBs
• Increase prototype size to 23 packs for HEV and
  verify operation

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Acknowledgments

• Dr. Raymond Winton
• Dr. Marshall Molen
• Philip Conley
• Dr. Marion Hagler
• Dr. Bob Reese
• Tom Vaught (DRS Technology)
• Stephanie Holbrook

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Answers