Canadian Researchers Create Wireless Charger For Electric Cars 179
An anonymous reader writes "University of British Columbia researchers have developed a wireless charging system for electric cars. It involves a spinning magnet beneath the parked vehicle which turns another magnet in the underside of the car. Charging takes four hours and is about 90% as efficient as plugging in. From the article: '"One of the major challenges of electric vehicles is the need to connect cords and sockets in often cramped conditions and in bad weather," says David Woodson, managing director of UBC Building Operations.
"Since we began testing the system, the feedback from drivers has been overwhelmingly positive."
Four wireless charging stations have been installed at UBC's building operations parking lot. Tests show the system is more than 90 per cent efficient compared to a cable charge. A full charge takes four hours and enables the vehicle to run throughout an eight-hour shift.'"
Existing tech (Score:5, Informative)
This is used all of the time in pumps where you don't want a dynamic seal. You have permanent magnets spun by a motor and inside a sealed case the pump is coupled by a magnetic field.
http://www.proconpumps.com/brands/Magnetically-Coupled-Pump-(Sealless).html [proconpumps.com]
Re:efficiency: 90% of cable? (Score:5, Informative)
Let's see if you're right. A Tesla Roadster has a 50kWh battery. Charging that in 4 hours requires 12500W of power. 10% of that is lost compared to the cable charger. That's 1.25kW of heat in addition to the heat from the inefficiencies of the rest of the charging system and the battery. That's in heater territory, but not enough to significantly heat an uninsulated garage. Problems with molten ice and snow can't be much different from parking a car with a warm engine.
Re:Spinning magnet in the car? (Score:4, Informative)
It's called a "magnetic circuit" [wikipedia.org] (scroll down halfway for an actual diagram). They are used all the time in high-efficiency motors and solenoids. By putting the right type of iron in the right shape around a coil or a permanent magnet, the iron provides a "path of least resistance" for the magnetic field lines and the field that escapes from the iron is small or miniscule.
If you have ever taken apart a mechanical hard drive, you will have found the very strong neodymium magnets used in the head travel motor are attached to a piece of metal--probably an alloy called "mu metal" or similar--and the observable effect is that you can only magnetically stick things to the magnet side, not the mu-metal side. That is because of where the magnetic field lines go: instead of going out one side of the magnet, around in the air, and back in the other side, they go out into the air on ones side and then directly into the mu metal, then through the mu metal and into the magnet. This not only shields the magnetic data on the hard drive platters from the motor magnets, but also greatly increases the efficiency of the motor.
I assume they will do the same thing with this car. There will be a pretty significant "air gap" in the magnetic circuit, which increases leakage, but it is easy to provide iron on the top side of the in-car magnet so that all the field lines are directed downward and away from the interior of the car.
Re:Effects on the family cat? (Score:4, Informative)
Different type of charging system.
The charging system in your references is working via induction - basically a transformer and the energy is transferred through an alternating magnetic field that creates a current in the coil on the car.
The system that's references here appears to use a magnet to spin a magnet on the other side that then spins a generator. I'm not sure exactly how the intensity of the magnetic field would be different because the power is still being transmitted magnetically, but it's going to be at a much lower frequency. The induction charging has a frequency of 40KHz while this would be more like 60Hz.