Qi (inductive energy transfer)

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Qi (Chinese word for " life energy ", pronunciation : [ ˈt͡ʃiː ]) is a proprietary standard of the Wireless Power Consortium for wireless energy transmission by means of electromagnetic induction over short distances. According to the WPC, the Qi standard, which was founded in 2008, is supported by over 1000 different devices and has over 200 companies among its members. Powermat is a similar, but incompatible and competing standard of the Power Matters Alliance with Qi .

In Germany, wireless charging received more public attention for the first time with the introduction of a new product line from the large furniture manufacturer IKEA . The first provider of smartphones (apart from the Palm Pre in 2009) was the South Korean manufacturer Samsung , whose Samsung Galaxy S III , which appeared in 2012, could be upgraded with Qi. Inductive charging was more widespread thanks to its permanent integration into the Nokia Lumia 820 and 920, which were introduced in autumn 2012 . With the iPhone 8 and iPhone X introduced in September 2017, Apple smartphones also support Qi for the first time. Qi quick chargers with an output of 7 to 15 watts are also currently on the market, which brings the charging time closer to that of USB chargers.

Technical specifications

Representation of inductive energy transfer through Qi

Qi uses a resonant inductive coupling between the transmitter and receiver. Sender and receiver exchange data in order to ensure optimal energy transfer. The transmitter modulates the transmission field. The receiver uses a technology similar to RFID to transmit data to the transmitter. Due to the typically high magnetic coupling of the coils, high power can be transmitted without exceeding EMC limit values.

  • Transmission frequency: 87 to 205 kHz ( long wave )
  • up to 5 watts (Baseline Power Profile) or up to around 15 watts (Extended Power Profile)
  • Data transmission between sender and receiver at 2 kilobits per second

advantages

  • The device only has to be put on
  • The standardization means that the charger and the device to be charged do not have to come from the same manufacturer
  • As a result, one charger is theoretically sufficient for several devices to be supplied
  • The fact that the socket is no longer necessary results in electrical and mechanical effects
    • no wear and tear of plug contacts due to plugging and unplugging,
    • better protection against ESD discharges ,
    • no mechanical weak points due to a socket recess,
    • No ingress of dust or water, so use in harsh environments or a higher IP rating is possible,
    • In the coordination between PCB layout and housing design, there is no need to align the positioning of a socket.

disadvantage

  • The devices must remain in close spatial contact during energy transfer. For example, it is therefore difficult to use a cell phone during the charging process. Some Qi chargers, such as that of the Google Nexus 5, use magnets to hold the charger on the device.
  • The efficiency of approx. 0.6 of a loose inductive coupling is always worse than when using a cable - the energy depreciation is higher and the charging speed (with the same power consumption as a wired charger) is lower.
  • Qi chargers are usually more expensive than conventional chargers.
  • Disturbance of long wave broadcasting
  • Increased heat generation due to eddy current losses (see also efficiency above) compared to wired charging, which means that components such as the accumulator either age faster or the charging power has to be reduced.

Web links

Individual evidence

  1. ↑ https://www.wirelesspowerconsortium.com/about/
  2. ↑ https://www.heise.de/newsticker/meldung/Ikea-laedt-Smartphones-kabellos-2611721.html
  3. ↑ Christian Just: These smartphones can be charged wirelessly . In: THE WORLD . April 18, 2015 ( welt.de [accessed March 20, 2018]).
  4. ↑ a b c The Qi Wireless Power Transfer System, Power Class 0 Specification (ZIP file with three PDFs)
  5. ↑ Nexus wireless charger, Google . Retrieved January 21, 2014.
  6. ↑ a b Stiftung Warentest: Inductive charger for smartphones in the quick test , test.de from May 2, 2013