4. Evaluation In order to ensure that our system meets the design constraints, each sub-system will be tested in its entirety. The figure below illustrates the fundamental design. The microcontroller and PICS are software based, and the battery packs, monitor circuits, and power supply are hardware components. Testing proper functionality of all these components is important since the system will be handling large currents (up to 250 amps) and large voltages (up to 300 volts). These can pose as potential risks to the driver of the car, and care will be taken to ensure that our system is as safe as possible. Figure 4.1 Design Concept Testing and Simulation Equipment 1. Computerized Battery Analyzer 2. Digital Multi-meter 3. Voltage Source 4. PSpice 5. High Resistant Load 6. MaxPlus 7. RS232 Interface 8. Thermometer 9. MatLab 4.1 Test Specification-Simulation Simulation is needed to obtain realistic values to compare with calculated or theoretical values. The realistic values will be used to determine the accuracy of the design. 4.1.1 Monitoring Circuit The battery monitoring circuit observes two characteristics of the batteries namely the state of health (SOH) and state of charge (SOC). This circuit will be drawn and simulated in PSpice to obtain expected values of the different components of the circuit. Voltage and current readings at key location will be Microcontroller PICS Monitor Circuits Battery Packs Power Supplyanalyzed for comparison with calculated values. Accuracy of the design will be assessed by the variation in calculated and simulated values. Procedure: 1. Draw circuit in PSpice 2. Analyze the simulated voltage and current 3. Compare simulation results with expected values 4.2 Test Certification – Hardware The system’s hardware consists of the battery packs, the monitor circuits, and the power supply. Each will be tested in order to ensure proper functionality. 4.2.1 Battery Packs The battery packs will be individually tested using the Computerized Battery Analyzer (CBA). Temperature, voltage, and current of the battery packs will be measured as they discharge; this data will be imported to a computer through a universal serial bus. After each battery pack completes a discharge cycle, the data will be displayed to the screen graphically via the CBA software package. These results will be used to qualify the manufacture’s specifications; as well as, produce measurements to compare with theoretical characteristics of nickel metal hydride batteries. Procedure: 1. Place single battery pack on the test bed. 2. Configure battery pack and CBA. 3. Connect CBA and laptop computer together. 4. Discharge battery with 5.6  load. 5. Interpret graphical data. 6. Repeat for loads of 2.9, 1.9 , and 1.4 . 4.2.2 Monitor Circuits The monitor circuits will be tested by testing three different sub-circuits: the voltage measurement circuit, the current measurement circuit, and the temperature measurement circuit. Three tests will ensure that the values measured will be readable by the A/D converter on the PIC. 4.2.2.1 Voltage Measurements Since the nominal voltage across the battery packs is 12 volts, and the voltage range for the A/D is 5 volts, the voltage across the battery packs will have to be scaled down in order to be read properly by the A/D. The monitor circuit will accomplish this using a simple voltage divider. In order to test this, a voltage source will be used to simulate the battery pack. Procedure: 1. Set voltage source to 12 volts. 2. Apply voltage to voltage divider. 3. Measure reduced voltage and verify that it is 5 volts. 4. Set voltage source to 6 volts. 5. Measure reduced voltage and verify that it is 2.5 volts. 4.2.2.2 Current MeasurementsThe system will measure high currents using a Hall Effect current sensor. This sensor will be able to accept high currents (up to 400 amps) and convert them into a smaller current that can be read by the A/D on the PIC. Procedure 1. Apply 5 amps to current sensor. 2. Measure and note output current. 3. Apply 10 amps to current sensor. 4. Measure and note output current. 5. Verify that differences in output currents are proportional to the differences in input currents. 6. Repeat for consecutively higher currents 4.2.2.3 Temperature Measurements The thermistors will be tested by simply varying its temperature and measuring the corresponding resistance. Procedure 1. Verify that room temperature (25ºC) resistance is 800. 2. Increase temperature and verify that resistance increases as well. 3. Increase temperature to 50ºC and verify that resistance is 1.6k. 4.2.3 Power Supply The power supply will be tested by testing its two output voltages: 12 volts and 5 volts. Procedure 1. Couple 5 volt output to multimeter. 2. Verify that power supply provides 5 volts. 3. Couple 12 volt output to multimeter. 4. Verify that power supply provides 12 volts. 4.3 Test Specification – Software The software portion of this project is responsible for monitoring the temperature of the battery array as well as voltage levels for individual battery packs. The PIC18 microcontrollers take the temperature and voltage measurements and send the data back to the central AT89 microcontroller. The AT89’s software uses the data to make the decisions about when to switch to charging or discharging mode. The central controller will communicate to the individual PICs using unique addresses on an I2C data bus. 4.3.1 Verification of System Initialization Each time the battery system powers up, the main controller must determine which battery packs are connected to the system. The AT89 controller will traverse a list of possible addresses attempting to communicate with the PIC18 devices located at each battery pack. Procedure: 1. Connect AT89 controller to power supply2. Connect several PIC18 devices to the communication array and power supply 3. Power up the system and allow initialization 4. Check test output to determine if proper communication occurred between connected PIC18 controllers at the specified battery pack locations 4.3.2 Verification of Addition or Removal of Battery Packs The battery system being designed is expected to be very versatile. Some of its versatility comes from its ability to vary the number of battery packs in