ارشيف احداث عام 2009

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Eric Tischer woke up one Saturday and decided to build an electric car. The decision was just that easy. The project wasn't.

It helped that he's a gearhead. Tischer is the kind of guy who can take an engine out of a Mazda RX-7, stuff it into an MG Midget and wind up with something that runs. Converting his 1991 Volkswagen Passat to run on electricity took 11 months and cost about $20,000. Much of the time was spent figuring out how to build the inverter / motor controller. Much of the money was spent on batteries.

Tischer has put about 150 miles on the car so far. It hasn't got much range and he says it handles like a boat, but it has been reliable. He gave us a rundown of the buildup and some specs on the car.

Tischer converted a '91 VW Passat with a blown engine. He found it on Craigslist for $1,800. The Passat is a bit big for a conversion, he says, but it's aerodynamic and attractive. That counts for a lot. "It's just a professional looking car with a beautiful interior, and something I enjoy having as a daily driver," he said.

Photographs by Eric Tischer

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The engine came out in a few hours. The Passat has loads of room under the hood for an electric drivetrain and a pile of batteries, and the throttle-by-wire system simplifies the conversion. The engine was junk, so Tischer, a 31-year-old graduate of Chico State University, gave it away on Craigslist.

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The liquid-cooled Siemens motor came out of a Ford Ranger EV and cost Tischer about $1,250 shipped to his door. The three-phase AC unit is rated at 90 horsepower. Mating it to the five-speed transmission required fabricating an aluminum adapter plate and a coupling between the motor's helical gear and the clutch.

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Homemade motor mounts secure the drivetrain to the chassis. "The AC motor has a very flat torque curve from zero speed up to about 3,000-4,000 rpm, and from 3,000 4,000 up to 10,000, it is constant horsepower," Tischer says. VW tucked the Passat's steering rack well out of the way, so there's nothing to get in the way.

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Power comes from 24 Optima 55 Ah batteries Tischer bought at CostCo. Eight are mounted under the hood. Tischer says he typically drives 20 miles to work, about half of that on the freeway at 65 mph, then recharges for 3.5 hours at 10 amps, 230 vac. "This is roughly 7.2 kilowatt hours," he said, "and the battery pack is rated at 16 kilowatt hours, so 20 miles uses roughly half the battery capacity."

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Four more batteries are mounted under the car where the gas tank used to be. Tischer says he spent about $8,000 on batteries and the charger. He's using a Manzanita micro PFC-20 charger that can draw up to 20 amps at 240 volts.

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Tischer designed a battery management system to prevent overcharging. As each battery reaches 14.4 volts, the circuit sends excess power into a resistor to keep the battery from overcharging as the others continue charging. The circuits cost him $6 apiece to build. Beefy 4/0 gauge cable and crimp lugs tie it all together.

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The trunk houses 12 more batteries – six are stashed under that white cover in the spare tire well – and the electronics that keep the car going. The green box is the Manzanita charger. The gray box on the left is the custom-made inverter / motor controller (more on that in a moment). The black box is a homebuilt insulated-gate bipolar transistor stack.

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Tischer designed his own inverter / motor controller because the unit used to control the Siemens motor is no longer available. The inverter converts the 312 volts direct current from the battery pack to 230 volts alternating current for the motor. It runs in "sensorless vector control" mode, which allows Tischer to control the amount of torque generated by the motor. Full throttle means 100 percent torque. Half that amount is good for 65 mph on flat ground. Tischer gives a detailed explanation. (.pdf)

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Tisher has put about 150 miles on the car so far. After five months of troubleshooting, he's got it running "quite well" and has hit a top speed of 87.3 mph.

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Tischer says the Passat can easily carry 1,000 pounds, so it had no trouble handling the weight of the EV drivetrain. The motor weighs 120 pounds and there's 960 pounds of batteries aboard. That's roughly what the pack in the Tesla Roadster weighs.

"I've never driven a gas-powered Passat," Tischer said, "but I'm sure it doesn't feel like a boat like mine does. Stiffer springs in the back would definitely help. The ass end is sitting pretty low right now."

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