JB's Electric Porsche 944
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Why an electric car?
Building an electric car was a wonderful challenge and combination of many things that I enjoy working on. Power Electronics, Batteries, Electric Motors, and Microcontrollers all come together. While the range is short (30-40 miles) the performance is great with a high-voltage battery system and a high-current motor controller.
The main challenge of this project was building a motor controller from scratch. The controller is capable 240 Volts and 1200 Amps (motor or battery) that's 288 kilowatts! The batteries and clutch are really the limiting elements in the car right now, not the controller.
In addition to the general fun of building this project it is also fun to drive with quick acceleration. My commute is only about 5 miles and the round-trip is easily within range while still driving the car like a Porsche. And of course there are the standard EV benefits of being quiet, emission-free, and rechargeable in the garage. I am now also purchasing 100% green energy from the Palo Alto Municipal Utility so the car is truly a zero emission vehicle being recharged by a mix of solar, wind, small hydro, and geothermal energy.
Project Details
The Motor Controller:
Features: Programmable current limit 100-1200 motor amps, automatic over-temperature current limit cut-back, water-cooled copper heat sink, low-loss IGBT modules, and motor overspeed limit.
Processor: Microchip PIC 16F877 This small yet powerful microcontroller runs at 5 MIPS and 20MHz with 8kb of onboard program FLASH memory. It also has two onboard 10-bit PWM generators, eight 10-bit ADC channels, and a UART interface.
Microchip Home PagePower Components: IGBT Modules, six 500 Amp 600 Volt modules used (International Rectifier, GA500TD60U), Fast recovery diode modules, four 560 amp modules (International Rectifier HFA280NJ60C), Filter capacitors, six 450 volt 1000uF high ripple current, low ESR, screw-terminal caps (Mallory CGH102T450V3L), Heat sink, custom built water-cooled copper cold plate, isolated DC current transducer from LEM international.
Coolant System: The water cooling system uses a small 12V DC pump for circulation through a small plastic reservoir and an oil-cooler radiator. These radiators can be found at just about any auto parts store and are a good size. The pump is made by ShurFlo (model number 2088-423-344). It circulates around 2.8 gpm with a quiet 3-chamber diaphragm pump and permanent magnet motor. The current draw is between 2-3 amps. West Marine sells a wide variety of these pumps at competitive prices.
The Motors:
Two, 8" Advanced DC motors belted together and driven in series by the motor controller. One motor has a custom coupler that was machined to mate with the flywheel/clutch pressure plate. This motor is directly in line with the driveshaft running back to the transmission. On the outside of the coupler is a synchronous belt sprocket. This allows power to be transferred from a motor mounted above, through a Goodyear Eagle PD belt, into the same coupler and clutch.
The Batteries:
Twenty 12V, deep-cycle Optima "yellow-top's" (D750S) for a total system voltage of 240 and a total pack weight of about 850 pounds. Peak power (at 9 kw per battery) ~180 kw.
Optima Battery Home PageBattery Mounting:
6 batteries in front of the motors roughly where the radiator used to be in front.Other Components:
DC-DC Converter: A custom modified Power-One power supply. This allows for an input of 240VDC with a continuous DC output of 40 amps at between 11-14 volts (adjustable). There were no commercial DC-DC converters available that took an input voltage this high. The converter is used to keep a small sealed lead acid battery topped off for load surges.
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Site Last Updated On: April/29/2006
