The Wireless Power Consortium has added a new transmitter technology to the Qi specification. This transmitter, called A4, uses two coils to enable a low-cost battery charger with increased freedom to position a Qi-capable phone on the charging surface.

The Qi specification is available as download from the website. You can find the new transmitter as "Addendum 2" inserted at the end of the document.

You can expect more approvals of transmitter technologies in the coming months. Members of the Wireless Power Consortium can get their wireless power technology included in the Qi specification, provided the technology is compatible with all Qi-capable phones and other Qi receivers. The procedure to get a wireless power technology approved is described in an earlier blog entry.

Energy efficiency matters.

We know that consumers love products without a connector, but it is impossible to beat the efficiency of a connector and copper wire. (No, superconductive wires are not more efficient than copper wires. The cost of cooling is prohibitive.)

So what can we do to create efficient wireless battery chargers?

We found that standby power consumption is the key. Standby power dominates total energy consumption for battery chargers that remain connected to mains power. By lowering standby power the total energy consumption is significantly reduced.

How low can you go? At first I thought we would have to trade low standby power against response time. You would expect that a responsive transmitter, searching constantly for new power-demanding receivers, will consume more power than a transmitter that goes to sleep and looks once a minute.

It turns out there is no need to trade response time. I have seen a Qi transmitter with a standby power of only 0.0001 Watt (100 µW) that detects new receivers instantaneously.

In the efficiency analysis that is published on the front page you can see what the effect is on total energy consumption.