Wireless charging for electric cars

No more carrying wet and heavy charging cables: wireless charging for electric cars has arrived and these are the cars that offer it

John Evans
Jun 30, 2018

You might be thinking of plugging in to the electric car revolution, but these days you don’t even have to plug in an electric car – the latest will charge wirelessly, like an electric toothbrush.

Park a car with the necessary technology over a pad on the ground, and the batteries will begin charging. Resembling a large set of scales, the inductive charging pad works on the same principle as the toothbrush.

BMW will be first to offer the technology this year in its 530e iPerformance plug-in hybrid car and it’s expected to be followed by Mercedes, which will soon unveil its first mass-market electric car.

Owners will be sold a charging pad to install at home - in a garage or outdoors - but there are already plans to expand the system to workplaces and public charging points.

Wireless power should remove much of the hassle of recharging a modern electric car, removing the need to plug in heavy cables, which are particularly messy to store when they become covered in rain and mud.

Looking further ahead, wireless vehicle charging while on the move may be possible, meaning that you may never have to stop to recharge your electric car. You can't say that about a petrol or diesel vehicle.

  

Which cars have wireless charging?

Drivers that lease the BMW 530e iPerformance plug-in hybrid car will have the option of adding wireless charging to their vehicle - at the cost of higher monthly payments.

Nissan, Renault, Hyundai and Honda are also developing the technology. In America, a wireless charging provider called Plugless has demonstrated aftermarket applications are possible on a range of cars including the Tesla Model S, BMW i3, Nissan Leaf and Chevrolet Volt.

BMW’s package includes one pad that is fitted to the underside of the car, and a second weatherproof one that is placed on the ground and plugged in.

BMW’s system can charge cars at 85 per cent of the rate of a standard home charger, using a cable, enabling the car’s battery to be charged in three-and-a-half hours, which is fast enough if you’re travelling overnight.

Fully charged, the BMW can travel for 25 to 30 miles on electric power before its petrol engine takes over. A full electric car would take considerably longer to charge at this rate but systems that can charge twice as quickly are in the pipeline.

 

Are there any public wireless charging points?

One of the leading companies in the development of wireless car charging is Qualcomm, which has been working on its system called Halo since 2012.

In Britain, it’s partnered with Chargemaster, which is testing wireless pads in a small number of workplace parking spaces and says its cable-based charge points can be adapted to accept wireless charging when demand warrants it.

Chargemaster also supplies wireless charging points to power support vehicles in the Formula E electric racing car series where the alternative, struggling with charging cables, would cost emergency crews valuable seconds.

 

How does wireless car charging work?

It sounds a little like witchcraft: electricity is sent through the air from one charging pad to a second receiving pad in a process that’s only a little less efficient than a standard cable,

The technology is known as inductive charging and is based on electromagnetic energy.

The pad takes mains electricity and sends it through a wire coil, converting it to electromagnetic energy. This travels to a second coil in a pad on the car, where it is converted back to electrical energy and used to charge the batteries.

The distance between the pads is 8cm in the case of the BMW 530e iPerformance, but the technology also works with taller cars such as sport utility vehicles (SUVs), where the distance is greater.

Cars don’t have to be perfectly aligned with the pads, but current technology requires drivers to be position the car’s receiving pad within 15cm of the charging pad on the floor.

To help drivers, BMW has developed a Pad-nav system that’s activate when the car detects a WiFi signal from the charging pad. A birds-eye view camera is switched, displaying an overview of the vehicle inside the car and overlaying blue lines to show the driver where to steer and when to stop.

 

How do you start wireless car charging?

In BMW’s case, you press the car’s Stop/Start button to initiate the vehicle’s electrical system and the energy transfer begins. Once the battery is full, the process stops automatically.

 

How safe is wireless car charging?

Because it’s electromagnetic rather than pure electrical energy, and because there are no exposed contacts, there’s no risk of an electric shock if you touch the pads. In any case, systems such as BMW’s switch off when they detect an object between the pads.

BMW’s pad cannot be installed below ground level but is strong enough to withstand being driven over. Some charge pads can be located below the surface so that apart from a visual marker, you’d never know they were there.

 

How efficient is wireless charging?

Chargemaster says that around 8% of the available energy is lost from Qualcomm’s Halo system as it travels through the air between the two pads.

It says this compares with around 6% through its own cable-based systems.
Claims vary, though. The American firm Plugless says around 10% of the energy its system provides is lost on transfer. BMW says its wireless charging system loses up to 20%.

BMW’s wireless charger takes 3.5 hours, compared with four hours with a basic plug and cable connection. However, the company’s more powerful, dedicated home charging point wallbox, which also uses a cable connection, is faster still at around 2.5 hours.

 

How much does a wireless charger cost?

In the America, prices for the Plugless system, an aftermarket wireless charger, start at around £880.
In Britain, BMW’s new system will only be supplied with new vehicles on a lease deal. A spokesman said the precise monthly leasing cost is being calculated.

Again in the UK, these figures compare with around £779 for one of the cheapest 3.6kW plug-in chargers, including installation, or £279 under the government’s electric vehicle homecharge scheme that contributes a grant of up to £500 including VAT towards the cost of purchasing and installing a home charger.

 

What’s the future for wireless charging?

Last year, Renault revealed that in collaboration with Qualcomm, it had designed a Kangoo ZE that can be recharged on the move, receiving electricity like a Scalextric car,

Called a dynamic wireless charging system, this technology would be perfectly suited to autonomous cars which could then be in use for longer. They could also enter and leave wireless charge points at will.

 

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