Pop in once a month to recharge your batteries: With electric cars come new energy stations, says Hugh Aldersey-Williams

IN THE cleaned-up California of the near future, you will be able to refuel yourself and your electric car in one stop. State laws requiring the big manufacturers to ensure that 2 per cent of their new cars record zero exhaust emissions by 1998, have galvanised efforts to develop battery-driven vehicles.

Hughes Power Control Systems, a division of Hughes Aircraft in southern California, is developing charging stations for the Impact electric car that General Motors plans to introduce in 1995. At first, buyers will have to rely on a home charger, for garage or kerbside use. But gradually chargers will be installed in car parks, and when enough electric cars are on the roads - perhaps as early as 1996 - the 'energy stations' will start to replace petrol stations.

So far, only electric technology is capable of yielding zero car emissions; and in terms of the whole energy cycle, it is more efficient to generate electricity from a fossil source than to burn petrol in millions of inefficient combustion engines.

Notwithstanding its unfortunate name, the GM Impact vehicle has overcome one of the two main drawbacks of the electric car: its low speed. The Impact is reported to have outpaced the sporty Mazda MX-5 in acceleration tests, and has a respectable cruising speed of 65 mph. Range has been the other big problem. The Impact can travel 120 miles on full charge, less than half as far as a petrol car, but sufficient for most uses (the average Los Angeles round-trip is 40 miles).

The Hughes charger employs magnetic induction; it has no moving parts and no direct electrical contact. The user inserts a plastic-sheathed, hand-held coupler coil into a slot in the car body, just as one would a petrol nozzle. As a strong current flows into the coupler coil, a secondary one enters the coils wound around ferrite cores in the car.

The currents and voltages are vast: energy is transferred at a rate of more than 6kw in standard operation and 25kw in a rapid- charging mode. The induction process is said to be highly efficient, but the considerable heat it generates requires heat sinks and vents around the car-charging slot.

The strong magnetic field associated with the induction process is shielded but may cause interference. Mark Roemer, a mechanical engineer with the California consultancy Ideo, which designed the charging station and coupler, says: 'It would not demagnetise a credit card, for example, but it is potentially a problem for radios and telephones, so we are devoting a fair amount of effort to containing (electromagnetic) emissions.'

The Hughes device, which makes quick charging possible for the first time, is an important boost for electric car appeal. 'In order to compete with the petrol car, you have to offer people unlimited mileage,' Dick Bowman, of Hughes, says.

The Impact uses standard lead- acid batteries: 32 of them, weighing more than 400kg (882lb), although some of this burden is alleviated because the electric motor weighs much less than a combustion engine.

The quick-charge inductive- coupling system enables the batteries to be charged selectively. It recognises that not all cells of a battery discharge equally, and so it chooses, electronically, which ones to recharge, when and by how much. The result is that 60 per cent of the battery capacity - equivalent to an 80-mile journey - can be charged in just 15 minutes. 'We believe you can do this once a month without a deterioration of battery life,' Mr Bowman says. At first, drivers will recharge their batteries in such places as shopping-centre car parks. The subsequent energy stations, however, will have to solve the problems of keeping drivers, and their families, amused while they wait a quarter of an hour for the recharging to be completed.

All-American amenities are envisaged. Video terminals will display credit-card transactions at unmanned stations, but they could also screen news, traffic reports, advertisements and televison programmes. And as the cars take their fill, drivers may find it hard to resist the temptation to recharge their own batteries.

(Photograph omitted)