Wireless charging charges ahead

Delivering energy wirelessly is attractive for numerous reasons, but its limitations can’t be ignored; the technology can demand close proximity with little tolerance for misalignment, introducing device size limitations, in addition the amount of power than can be transferred can preclude its use with more power-hungry devices.

Of course, while well established the technology is still in its early stages, relatively speaking. It’s going to take some time before inductive power transfer is as ubiquitous as the humble standard cell battery or AC/DC adapter. Standardisation can sometimes be seen as a doubled-edged sword in emerging markets, particularly where more than one exists, as is the case with wireless charging; it can often force component manufacturers to support all at the same time, inevitably adding cost and complexity. However, the recently announced merger between two of the standards in questions - Alliance for Wireless Power (A4WP) and Power Matters Alliance (PMA), based on magnetic resonance and inductive coupling respectively - could significantly simplify the landscape. The organisations have signed a letter of intent to merge the two bodies by June 2015; described as ‘key milestone’. It is hoped that the merger will reduce market confusion, presenting fewer standards (and therefore lower complexity/cost for manufacturers).

The merger has been proposed as a ‘logical direction’ to unify the wireless charging market, but it still leaves the Wireless Power Consortium and its ‘Qi’ standard (based on inductive coupling) as a prevailing alternative. According to Ron Resnick, President of the PMA, there is a chance for further consolidation in the future, he commented: “We remain open to all options for the future.”

The popularity of the Qi standard is evident; IDT recently announced that its wireless power chips have been designed in to the Cube remote control from 4MOD Technology, based on the Qi standard. 4MOD’s CEO, Laurent Stephan, said: “Wireless charging is an important part of the Cube user experience, and we wanted to make sure we got it right. IDT’s success in developing wireless power products for a broad range of applications made choosing a vendor an easy decision.”

We need more power!

The division within the industry and end-market isn’t stopping its pioneers from forging ahead, and one of the more recent developments is a significant increase in the amount of power that can be transferred. Freescale recently announced a 15W Qi-compliant wireless charging solution which increases the amount of power that can be transferred wirelessly by three times. “Today’s mobile products offer a broader range of features, functionality and form factors than ever before, requiring developers of wireless charging systems to accommodate larger batteries and enable faster recharge speeds,” commented Denis Cabrol, Director of Global Marketing and Business Development, MCU Group, Freescale.

Toshiba Electronics Europe has also increased the amount of power its solutions can support, to a 10W version that remains Qi V1.1 compliant. It boost the power output from 5V/1A to 7-12V/1A. Marcus Schorpp, Field Application Engineer, Toshiba, explained that the need for more power was always apparent: “Even at the time when WPC Low Power standardisation development started, the need for higher power was already in demand and the need for a Medium Power standard was emphasised.”

The reason is apparent to anyone with a smart phone; portable devices are becoming more power-hungry. “The capacity of batteries in smart phones, tablets and other rechargeable battery powered devices increases steadily,” added Schorpp. “Since the acceptable charging time of a device is a ‘constant’, regardless of the battery size, charging currents need to increase to meet with consumer expectations.”

“Bosch Power Tools recently introduced a wirelessly chargeable battery for their professional battery powered cordless drills, with the ability to charge a relatively large battery in a short time. I strongly believe that we will see more and more devices on the market that will need t be charged with much more than 5W; even the automobile industry is interested in wireless charging hybrid of full EVs.”

Realistic limits

Toshiba recently developed a 7kW wireless power transfer system for EVs, which raises an interesting question; what limits wireless charging, the standard or the technology? “Predominantly in the traditional applications of mobile phones it’s the size or volume available for wireless power receiver systems; the coils are the largest part of that,” explained Schorpp. “Larger coils would offer higher charging currents, but consumers ask for thinner, more compact phones. Higher power transfer also requires thicker ferrites and shielding in the phone, and other power receiving devices, which is often in conflict with the consumer demand for smaller devices.”

As with most things, the market will ultimately decide; it’s not improbable that we experience a period of cross-over, as Schorpp explained: “It may be a matter of time until the first standard C-sized or even A, AA or AAA sized rechargeable batteries will be available with wireless recharging. It would be nice for the user if they could recharge those batteries on a wireless power plate that could also be used to recharge their phone. But with rechargeable batteries the cost pressure is very high, and the available product volume is very limited - the volume required for the wireless charging system would reduce the batteries’ capacity quite a bit.”

Schorpp pointed out that Toshiba is a member of WPC, A4WP and PMA but is currently only mass producing products compliant with the WPC standard and believes the A4WP/PMA merger is a positive move, but added: “It remains to be seen how long it will really take to merge both in to a single standard and develop products that comply with both technologies; resonant and inductive coupling.” According to Schorpp, it is also important to note that the WPC is in the process of developing a resonant power solution. Ultimately, the future direction of wireless charging may depend less on the smart phone and more on emerging applications.