Design for Prius C PlugIn Conversion Objective Add

Design for Prius C Plug-In Conversion

Objective Add an additional battery and charger to compliment the Prius C’s existing hybrid drive system to improve overall efficiency

Outline � Will roughly follow what is known as the “contactor method” already proven in full-sized Prius conversions � Li. Fe. PO 4 pack as extra battery with higher voltage than hybrid battery to avoid using a DC-DC converter � Connected to Hybrid Drive system in parallel with original hybrid battery � Battery connection controlled by an electrically controlled contactor � Contactor controlled by an Arduino microcontroller � Arduino monitors state of charge, current, voltage and cell under/over voltage and sets state of the contactor

Build Steps � Get Arduino to read the CANbus, specifically the State of Charge (SOC) of the Prius’ battery � Build the hybrid battery pack, including Battery Monitoring System � Build the interface board between Arduino and the battery as well as instrumentation and control to include Li. Fe. PO 4 battery current Relay for charge control Main contactor control � Display system for hybrid pack information Display hybrid pack SOC Warning for system faults � Incorporate Li. Fe. PO 4 pack battery charger � Develop Arduino code for system control

Arduino and CANBus �CANBus Shield gives Arduino the ability to read and log CANBus data �Reading of CANBus is necessary to find the Hybrid Battery’s SOC to know when to open and close the contactor between it and the Li. Fe. PO 4 battery to prevent over/under charging

Arduino and CANBus �I have already developed and Arduino sketch (program) to read and log CANBus data

Arduino and CANBus �No publicly available data identifies PID codes for Prius C’s unique attributes �Reverse engineering was necessary to find the Hybrid Battery’s SOC on the CANBus

Battery �Li. Fe. PO 4 chemistry chosen due to proven use in full-EV conversions Long cycle life Flat discharge curve High power/weight �Hybrid battery is 144 V nominal �Li. Fe. PO 4 nominal voltage will be 154 V to allow for low-rate charge of Hybrid battery when connected in parallel � 48 Cell, 20 AH GBS Batteries, 3 KWH pack

Battery Management System �To provide Li. Fe. PO 4 cell under/overvoltage (UCV/OCV) protection and alarm as well as inter-cell balancing, a Battery Management System(BMS) is necessary �Ready made systems for full-EV conversions are expensive (~$1000 for my application) and redundant to capabilities inherent to Arduino

Battery Management System �Maxim MAX 11068 IC chosen for my application Provides UCV/OCV alarms Total pack voltage Inter-cell balancing Pack temperature Two wire interface (I 2 C) to Arduino to provide alerts �MAX 11068 Evaluation Kit (~$250) will be used to reduce time and cost in producing PCB

Interface Board �A small PCB will be necessary to support several interface features Provide 12 V Battery power to Arduino and interface systems Transistor interface to activate contactor Allegro Micro. Systems ACS 758 IC chosen to measure bidirectional current for Li. Fe. PO 4 pack Relay for controlling Li. Fe. PO 4 battery charger Relay for sensing if AC is still plugged in

Display System �A small LCD will be mounted in view of the driver to provide information about the system Li. Fe. PO 4 pack voltage, current, SOC State of contactor Warning for system faults

Battery Charger �Elcon PFC 1500 chosen �Mounted onboard to allow for charging away from home �Will recharge a fully discharged pack within three hours via 120 VAC

Safety Features �Numerous software and hardware features Software trip of contactor ▪ OCV/UCV ▪ Abnormally high charge/discharge current ▪ Over-temperature Hardware ▪ Fuses for main cabling ▪ Barrel switch near driver to allow for manual disconnection of Li. Fe. PO 4 pack ▪ Inertial switch to trip contactor in event of a crash

Pseudo-Code �Initialization Determine SOC of Hybrid battery Verify system health �If Hybrid SOC <80% and Li. Fe. PO 4 pack healthy (>20% SOC, no OCV/UCV or over-temp) Shut main contactor �If Hybrid SOC >90% or any fault detected Open main contactor �SOC for shutting and opening contactor will be modified after initial testing to optimize use of stored energy in Li. Fe. PO 4 pack

Performance Estimates �Stock Prius C advertises ½ mile on EV only mode 0. 9 KWH NIMH pack, max DOD 45% �With addition of 3 KWH Li. Fe. PO 4 pack, max 80% DOD, up to 6 additional miles in EV only mode �In blended mode, full sized Prius conversions have resulted in >80 MPG during normal commuting �Due to smaller vehicle size and larger proportional pack size, expect as good or better than 80 MPG

Conclusion Follow my progress at: http: //www. 100 mpgpriusc. com