The Ford Ecostar was an experimental electric car in the form of a small delivery van. A sodium-sulfur battery in the floor of the cargo area stored power for a 75 horsepower (56 kW) electric motor under the front hood. The Ecostar introduced the road-and-leaf logo now used on a number of Ford products.
Just over 100 Ecostars were produced, and used in fleet tests between 1992 and 1996 with over 1,000,000 miles (1,609,344 km) driven. The Ecostar averaged 94 miles (151 km) on a full charge, and demonstrated 155 miles (249 km) miles range in one test. However, on several occasions the battery burst into flame during recharging. For this, and several other reasons, Ford lost interest in the sodium-sulfur battery and turned to fuel cell concepts instead.
The product niche appeared to be a useful one and has led to a number of similar designs. The Citroën Berlingo électrique was almost identical in looks, performance and range. Ford is re-entering the market as well, with an electric version of the Transit Connect.
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Ford developed the sodium-sulfur battery technology in 1965,[1] but had not developed it commercially. Development was later picked up in Europe.
The Ecostar was introduced as a purely experimental effort, to help develop all aspects of electric vehicle design from engineering to supplier development to market development. A "prototype-of-the-prototypes" was completed with lead acid batteries in 1992, and introduced with the comment that future models would include the new battery technology. Several similar models followed and were lent out for test drives with favorable results.[2]
A total of 80[1] to 105[3] "production-prototype" sulfur-powered Ecostars were hand-built starting in 1993, and used in fleet trials with a number of customers starting the next year.[4] At the time, the cost of the battery was a significant $46,000. However, the vehicles were hand-built at a cost of $250,000, so the battery cost was not representative of a production version.[5]
The tests ran for 30 months. Throughout the tests there were problems with the system, including two vehicles that burst into flame while charging.[6] The sulfur in the battery was flammable, a serious safety risk. ABB introduced a new version of the battery, but was unwilling to guarantee performance beyond one year.[7]
In late 1997, Ford announced a partnership with Daimler-Benz and Ballard Power Systems to introduced car-ready fuel cells,[8] and their experiments with the sodium-sulfur batteries ended.
The Ecostar's chassis was based on the Escort Van produced by Ford's Halewood Body & Assembly factory outside Liverpool. This was essentially a European Escort Mk V with a raised cargo area forming a 2-door panel van. Fully equipped, it weighed 3,100 pounds (1,406 kg).[3]
A significant portion of that weight was its 780 pounds (354 kg) sodium-sulfur battery, which stored 37 kWh.[3] Using the Federal Urban Driving Schedule, this gave the Ecostar a range of 100 miles (161 km).[3] The sodium-sulfur technology was invented by Ford in the 1960s,[9] but the battery for the Ecostar was built by ABB Group in Heidelberg, Germany.[3] In order for the battery to work, it had to be maintained at a temperature of 600 °F (316 °C), which keeps the sulfur molten.[9]
To avoid heat loss, and to insulate the cabin from its heat, the battery was stored inside a double-walled stainless steel vacuum bottle. This allowed it to stay warm overnight, and keep its temperature constant even during cold weather, when traditional batteries are less responsive. The container was mounted below the floor plan of the cargo area, which gave the vehicle a low center of gravity that give it well-liked handling.[9] One complaint, however, was the lack of power steering.[10]
The battery powered a three-phase electric motor located under the hood in the area normally used for the gasoline engine. The motor delivered only 75 hp, low for a vehicle of this size, but up to 143 foot-pounds of torque, numbers typical of a much more powerful gasoline engine. This was better torque than the Ford Escort GT, for instance, whose 1.8 litre four-cylinder engine delivered 127 hp but only 114 ft-lb.[10]
One drawback of the sodium-sulfur battery is its relatively slow discharge rates, which limited the amount of power that could be drawn from the battery during acceleration.[9] Drivers described it as "sedate", while Ford estimated its 0-60 mph (0-100 km/h) acceleration at about 16.5 seconds. While slow by car standards, this is similar to other small European delivery vans of the era, like the Volkswagen Eurovan.[3]
While cruising the motor used only 8 kW to maintain speed,[11] about 6 horsepower (4 kW). This speaks to the motor-to-wheel efficiency of the electric drivetrain, as well as the 50 psi low-drag tires.[10] However, the long quoted ranges referred only to driving, not accessory systems. These added considerably to the load; the electric heater burned 5 kW, and the air conditioner 6 kW.[11] In real-world driving, using either would significantly impact range.