How the Tesla Roadster Works

        Auto | Concept Cars

Image Gallery: Electric Cars The Tesla Roadster is fast, fancy, handles like a dream and goes like a rocket, but it's virtually silent. Find out what else sets it apart from gasoline-powered cars. See more electric car pictures.
Image © 2006 Tesla Motors, Inc. A­ll rights reserved.

When you climb into the seat of a high-performance car that costs six figures, you expect certain things: acceleration that pushes you back into the seat, top-end stereo equipment, road-hugging handling, the throaty roar of a powerful engine and a big budget for the high-octane gas needed to fuel it. Well, the Tesla Roadster has almost all of those aspects covered. It's fast, fancy, handles like a dream and goes like a rocket, but it's virtually silent and it'll never burn a single drop of gasoline. Tesla's first production car is also the world's first high-performance electric car.

Unlike a traditional gasoline-powered car, the Tesla Roadster doesn't contain hundreds of moving parts. It's powered by just four main systems:

  • The Energy Storage System (ESS)
  • The Power Electronics Module (PEM)
  • An electric motor
  • A sequential manual transmission
The Energy Storage System is located in the rear of the vehicle.
The Energy Storage System is located in the rear of the vehicle.
Imag­e © 2006 Tesla Motors, Inc. A­ll rights reserved.

In place of an internal combustion engine, the Tesla Roadster sports a bank of batteries -- the Energy Storage System (ESS). In developing a power source befitting such a high-performance car, Tesla went with technology proven in the laptop computer field -- rechargeable lithium-ion batteries. The Roadster contains 6,831 of them. They weigh about 1,000 pounds in total, and Tesla claims that they provide "four to five times the energy-density stores of other batteries" [ref]. The batteries fit into 11 sectors with 621 batteries each. A separate computer processor controls each sector to make sure all of the charging and discharging is handled smoothly.

The Power Electronics Module (PEM) is a power inverter and charging system that converts DC power to AC power using 72 insulated gate bipolar transistors (IGBTs). This results in a marked increase in power output compared to first-generation electric cars. Under peak acceleration, the batteries can crank out 200 kW of energy -- enough to light 2,000 incandescent light bulbs.

In addition to controlling charge and discharge rates, the Power Electronics Module controls voltage levels, the motor's RPM (revolutions per minute), torque and the regenerative braking system. This braking system captures the kinetic energy usually lost through braking and transfers it back into the ESS. The efficiency and integration of the battery, PEM and motor systems is between 85 and 95 percent, allowing the motor to put out up to 185 kW of power. Aluminum heat dissipation fins and a rear-mounted ventilation port keep the power transistors from overheating.

The Roadster's charging port
The Roadster's charging port
Image © 2006 Tesla Motors, Inc. All rights reserved.

You can recharge the Roadster in two different ways. An electrician can install a recharging station in your garage. This 220-volt, 70-amp outlet allows for a full recharge in 3.5 hours from a completely dead battery. Tesla likens charging your car to charging your cell phone; you can plug it in at night and have a fully-charged car in the morning. There's also a mobile kit that allows recharging at any electrical outlet, no matter where you are. The length of time it takes to charge using the mobile kit depends on the outlet configuration that you're using (110-volt or 220-volt).

Although auto owners have been driving around for decades with tankfulls of volatile, flammable gasoline in their cars, having 1,000 pounds of batteries behind their head gives some people pause. The recent recalls of lithium-ion batteries used in laptop computers have increased those fears. Tesla has gone to great lengths to ensure the safety of the Roadster's energy system. First, the battery system was extensively "catastrophe tested," which involved heating individual cells until they burst into flames. Each cell is isolated enough from adjacent cells to prevent any damage to them. If one cell overheats, it will not start a chain reaction explosion.

A host of sensors detects acceleration, deceleration, tilt, temperature and smoke. If one senses an abnormal event, like a crash, it immediately shuts down and disconnects the power system. Similar anti-fault protections and sensors are part of the charging system [ref].

Tesla Roadster Motor and Other Features

The Roadster motor.
The Roadster motor.
Image © 2006 Tesla Motors, Inc. All rights reserved.
The Roadster has just three gears.
The Roadster has just three gears.
Image © 2006 Tesla Motors, Inc. All rights reserved.
The Roaster cockpit.
The Roaster cockpit.
Image © 2006 Tesla Motors, Inc. All rights reserved.

The heart of the Tesla Roadster is its 3-phase, 4-pole electric induction motor, which weighs just 70 pounds. Tesla's claims and independent testing show that the Roadster can reach 60 mph in about four seconds and its speed will top out somewhere around 130 mph. But the Roadster's performance isn't just about speed and acceleration. The unique properties of an electric motor give it a huge advantage over a combustion engine in terms of torque, force that tends to rotate or turn things, and power band, the range of operating speeds under which the engine operates efficiently. The Roadster can generate large amounts of torque even at very low RPM, and the motor can always turn out major horsepower. It can reach over 13,000 RPM, something very few large combustion engines can do. The Tesla Web site includes the following: "A favorite trick here at Tesla Motors is to invite a passenger along and ask him to turn on the radio. At the precise moment we ask, we accelerate. Our passenger simply can't sit forward enough to reach the dials" [ref].

That kind of motor response eliminates the need for a complicated transmission, so the Roadster has just three gears -- two forward gears and one reverse gear. Shifting is manual, but there's no clutch. That also means there's no stalling or "jerk" when you shift between gears.

The Tesla Roadster can go a lot faster than previous electric cars, but perhaps more importantly, it can go a lot farther. The Roadster's estimated range is 250 miles on a single charge, at least 100 miles more than General Motors' EV1, which could go almost 150 miles under optimal conditions.

Most of the hype surrounding the Roadster is about its status as an electric vehicle. But while earlier electric cars tended to be cramped and lacking in features, the Tesla Roadster looks and feels like a sports car. In addition to basics like heated seats, a stereo with CD player, ABS brakes and dual airbags, the Roadster has a few unique features:

  • A unique PIN to start the car and prevent hot-wiring
  • A Homelink transceiver you can program to control radio-frequency controlled devices such as your community gate and garage door
  • A dock connector for your iPod
  • Electrically-controlled door handles (there's no mechanical lock, which makes it more difficult to break into the car)

Since it's a convertible, the Roadster comes standard with a soft top. Options include a hard top as well as features like a full leather interior and a satellite navigation system.

Tesla Motors and the Future of Electric Cars

Image courtesy Sony Classics                          The GM EV1
Image courtesy Sony Classics The GM EV1

The Tesla Roadster and the Tesla company have an unusual history. The company has almost no connection to the traditional American auto industry, and its founder had no experience in the auto industry when he decided to create the world's first high-performance electric car. Martin Eberhard and his business partner Marc Tarpenning founded a company based on a portable eBook reader. Frustrated at the mainstream auto industry's inability to create an effective electric car that had mass appeal (he often refers to early electric cars as "punishment cars"), Eberhard decided to create one himself.

The Tesla Roadster's chassis is a heavily-modified version of the Lotus Elise chassis.
The Tesla Roadster's chassis is a heavily-modified version of the Lotus Elise chassis.
Image courtesy Group Lotus PLC Image © 2006 Tesla Motors, Inc. All rights reserved.
The Tesla Roadster's chassis is a heavily-modified version of the Lotus Elise chassis.
The Tesla Roadster's chassis is a heavily-modified version of the Lotus Elise chassis.
Image courtesy Group Lotus PLC Image © 2006 Tesla Motors, Inc. All rights reserved.

Instead of creating an entire car and all its systems from scratch, Eberhard took advantage of outsourcing, which made the various elements easy to acquire. After netting $60 million in investment funds, (including over $30 million from Elon Musk, co-founder of PayPal), the new company chose a design from England-based Lotus.

The Tesla-Lotus partnership works well for several reasons. Lotus' Hethel, England facility is well suited to producing cars in small runs. This allows Tesla to basically manufacture cars to order, rather than building thousands and spending money to warehouse the overstock. Also, the Tesla Roadster is based on the Lotus Elise -- they look superficially similar and have the same basic chassis (though the Roadster's chassis is heavily modified) and other parts. This added to the savings. While most of the Roadster's parts and systems, such as the stereo, the brakes and the battery chargers are off-the-shelf, final assembly happens at Lotus facilities.

Tesla claims that the Roadster offers double the efficiency of popular hybrid cars, while generating one-third of the carbon dioxide.
Tesla claims that the Roadster offers double the efficiency of popular hybrid cars, while generating one-third of the carbon dioxide.
Image © 2006 Tesla Motors, Inc. All rights reserved.

Are Electric Cars Finally the Next Big Thing?

Tesla's business plan recognizes that innovative technology is often very expensive and that the very rich are usually the first people to adopt it. Once prices come down, the technology can move down into the market. That's why Tesla's first car is a high-end sports car only made in limited numbers. However, Tesla has set its sights on a 2008 release of a four-door electric sedan (codenamed White Star). The Roadster seems to be a success within its limited production numbers -- the first 100 limited edition "Signature Series" Roadsters sold out, and the next run of 100 is ready for pre-orders. A fully-loaded Roadster will cost $100,000, with a $75,000 down payment required to reserve one.

Electric cars will probably always be more expensive than cars that use combustion engines. The savings comes when you look at its the fuel costs and environmental impact. An electric car has zero emissions and doesn't add to pollution. Driving an electric car a mile costs a fraction of what it costs to drive a gas-powered car a mile. Critics rightly point out that the energy to power an electric car still comes from somewhere -- in this case, a power plant that provides energy to the electrical grid. Shifting the source of the energy from oil to coal doesn't necessarily make it any cleaner.

Tesla and other electric car proponents respond that electric cars are more efficient for several reasons. First, generating power at a power plant, even a coal power plant, is more efficient and creates less pollution than millions of small combustion engines creating the power. Plus, some of our electricity comes from cleaner power plants like hydroelectric plants, wind farms and solar cells.

In an interview with Wired.com, Eberhard claimed that the energy in a gallon of gasoline could drive an electric car 110 miles. Comparing average gas prices and electricity prices, the Roadster could go 150 miles for the price of one gallon of gas. Tesla reports twice the efficiency of even the greenest hybrid cars.

For lots more information on the Tesla Roadster, Tesla Motors, electric cars and related topics, check out the links on the next page.

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More Great Links

Sources

  • Davis, Joshua. "Battery-Fueled Car Will Smoke You." Wired News, July 19, 2006. http://www.wired.com/news/wiredmag/0,71414-2.html?tw=wn_story_page_next2
  • "Electric Ride." http://blog.wired.com/teslacar/FF_162_tesla3_f.jpg
  • Tesla Motors http://www.teslamotors.com/engineering/how_it_works.php?js_enabled=1
  • Wald, Matthew L. "Zero to 60 in 4 Seconds, Totally From Revving Batteries." New York Times, July 19, 2006. http://www.nytimes.com/2006/07/19/business/19electric.html?ex=1158206400&en=dd66218d2c708a9d&ei=5070
  • "Tesla Roadster Photo Album." http://blog.wired.com/teslacar/index.album?i=19