Researchers at the Stanford School of Engineering have developed a system capable of charging batteries for electric cars while they are in motion, similar to the induction charging used in cell phones. The system, although still being tested on electric cars, already works to recharge robots – which will be useful to reduce downtime and increase productivity in factories, for example.
The project started three years ago when Shanhui Fan and Sid Assawaworrarit developed their first system based on wireless charging. In summary, in this type of charging, electricity is transmitted through a magnetic field that oscillates at a frequency capable of creating resonant vibrations in the magnetic coils of the receiving device.
This resonant frequency changes if the distance between the source and the receiver is changed even on a small scale – which works very well for cell phones, as they stand still while receiving the charge. Knowing this, the pair incorporated an amplifier and a feedback resistor into the system to allow it to adjust the frequency automatically if there was any distance.
However, the system used a lot of energy to make these constant corrections, so that only 10% of force was transmitted as energy to the car. After adjusting this problem by changing the amplifiers, the pair reached the current configuration of their charging system, which has no less than 92% transmission efficiency.
With this update, the system is able to transmit 10 watts of electricity over a distance of up to 90 centimeters. But, according to Shanhui Fan, tens or hundreds of kilowatts can be sent to an electric car and the charging capacity can be easily expanded.
The scientist pointed out that this technology is fast enough to refuel an electric car, even if it is at high speed, since wireless transmission takes only a few milliseconds. Shanhui Fan pointed out that the only limiting factor would be the speed with which the car’s batteries can absorb energy.