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Wireless battery charger (Receiver POQiRX) [130168-2]

Status: Finished
June 24, 2013

In order to make use of the POQiRX, it is strongly recommended that a BLiVIT be in conjunction with this project.  The receiver can be used in a standalone configuration, but the BLiVIT has a space allocated to mount the receiver as a daughter board.

The receiver, plus coil assembly, and thermal sensor permit reception and control of the transfer of electrical energy from a compatible transmitter, using the Wireless Power Consortium's Qi specification.  Qi is the chinese character (pronounced "chee") which means "Life Energy".  This seems apropriate.

The Qi system permits up to 5 watts effective radiated energy through an "air-coupled inductor", comprised of two coils separated by 1-2mm distance.  This assembly is nearly identical in function to any number of transformer devices familiar to electronics hobbyists.  The transmitter for this project uses a 50mm diameter round coil, while the receiver uses a much smaller 32x40mm oval coil.  The receiver also uses finer gauge wire, but more turns of the coil, which compensates for the smaller dimension.

[Will insert here some first-year physics discussion and formulae regarding the induced electrical current in an ideal coupled inductor, and some notes about the materials selection from the WPC.  It is not yet determined if this should go as far as showing Maxwell's equations, as that particular rabbit hole goes very deep.]

The most efficient power transfer will occur if the two coils are centered precisely.  The POQiTX transmitter (project 130168-1) can be housed in a specially designed enclosure which includes depressed holes which fits the four mounting screw covers on the BLiVIT enclosure, for example.

One of the other salient issues with wireless power transmission is inadvertant disruption of the magnetic field, caused by metallic objects between the two coils.  There is enough radiated power flowing between the two halves of the inductor that a coin or other small metal object can become significantly heated and become a hazard.  The bqTesla devices in the transmitter and receiver prevent that by detecting the disruption and using a progressive fallback and retry mechanism to automatically turn off the magnetic field until unimpeded use can resume.

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