Demonstrated Success: Porsche 914 BEV
The team's first project began in late 2006, when MIT Professor Yang Shao-Horn and Dr. Quinn Horn of Exponent donated a 1976 Porsche 914, motor, charger, and controller. The Porsche was converted into a battery electric vehicle (BEV) using 18 U-Charge® XP Lithium Phosphate batteries donated by Valence Technology. From the beginning, EVT students designed this lithium-ion conversion with two underlying objectives: to establish the vehicle's usefulness for research and to maximize the system's safety. The Porsche 914 BEV has similar driving performance to the original vehicle, with the added advantage of regenerative braking. The vehicle is street legal, and EVT team members can often be seen driving around the Boston area on test drives or on the way to local outreach. Video from our latest test drives is available here
Timeline
- November 2006 – Conversion begins based on Electro Automotive Voltsporsche conversion kit
- June 2007 – Major hardware components installed; Emmanuel Sin wins mechanical engineering’s Peter Griffith Experimental Thesis Award for his work on the conversion
- October 2007 – Vehicle electronic system redesigned (deviating from kit) to improve safety and account for the Lithium-ion batteries and the AC induction motor
- February 2008 – Six additional batteries installed, bringing pack voltage to 230 V (nominal); motor and battery controllers re-programmed to use 18 batteries
- March 2008 – First successful test drive
For more information about the early stages of the conversion, see Manny Sim's 2007 BS thesis, "Electric Conversion of Porsche 914."
Battery Pack and Battery Management
The battery pack comprises 18 lithium-ion phosphate batteries, produced and donated by Valence Technology. They are arranged in series for a total nominal voltage of 230.4V and a capacity of 100 Ah (at C/2). Each battery has its own built-in computer that monitors the battery's conditions. The battery management system, a separate computer, communicates with each of the 18 battery computers and can be used to control the high voltage circuit, shutting it off in case any problems occur.
Motor and Motor Controller
The motor is a 3-phase AC induction motor from Azure Dynamics and has a peak power of roughly 55kW and a maximum speed of 12,000 rpm. The motor controller inverts the DC voltage from the battery to AC voltage for the motor and demands a torque from the motor based on the input from the accelerator pedal. Unlike an internal combustion engine, the motor can provide full torque at zero speed, and it has a much wider speed range than an engine. For ease of conversion, the team retained the stock manual transmission. The motor and controller are also used for regenerative braking.
Charger
The on-board charger is a Zivan NG3 which converts 230VAC to DC voltage to charge the battery pack. It can be plugged into a standard clothing dryer (230VAC) outlet, but is current limited by the power rating of a 120VAC outlet, taking roughly 8 hours to charge the battery pack. With the proper charger and power supply, the Valence Li-ion battery pack could be charged in as little as 2.5 hours.
Data Acquisition and Display
Data buses from both the battery management system and motor controller are logged via an NI CompactRIO that was donated by National Instruments (NI). This provides valuable information about the currents, voltages, torques, speeds, and temperatures seen by the vehicle components during driving. In addition, the data acquisition system records all fault and limit conditions, warning the driver when motor power is limited and providing a powerful diagnostic tool. The CompactRIO also controls an NI touch screen which display valuable real-time information about the motor and batteries to the driver.
Specifications
| Specification | Original Porsche 914 | MIT Porsche 914 BEV (estimated) |
| Fuel Economy (mpgge) | 22 (tank-to-wheel) 18 (well-to-wheel)+ | 180 (battery-to-wheel)+ 65 (well-to-wheel)+ |
| 0-60 MPH Time (sec) | 14 | 16* |
| Continuous Top Speed (mph) | 110 | 100 |
| Range on full charge (miles) | 400 | 100* |
| Vehicle Mass (lbm) | 2,100 | 2,500 |
