To Qi, or not to Qi, that is the question (that was actually)

About Wireless Power Transmission

Because we wanted to create a design centered around aesthetic for our device, we chose to implement wireless charging for our battery.

There are plenty of ways to implement WPT. First of all there is near-field power transmission and far-field power transmission.

For our project, we will focus on a near-field power transmission. In this field, one of the most common technique is inductive coupling. But it is not the only one : capacitive coupling is an interesting technique for our project.

Capacitive coupling VS inductive coupling

Because inductive coupling is based on converting AC current to a magnetic field, there is a high risk that it will cause strong interferences and perturbations with the magnetic fields of the marbles, thus complicating our control over our device.

Regarding this point, capacitive is interesting because relying on a different medium to transfer energy i.e. not a magnetic field. Alas, the major problem with capacitive coupling is that there’s poor documentation on the subject and therefore is hard to implement.

In the end we choose to go for inductive coupling which is very well documented with the advantage of having many organizations working on the subject.
To counter undesirable effects of inductive coupling, we plan to implement electromagnetic shielding.

Qi standard and the Wireless Power Consortium

The Wireless Power Consotium is one the biggest and most important entity working on WPT. They established the Qi standard which is currently in version 1.2.3, with the specification downloadable here.

At first, when looking how we were going to implement Qi compliant WPT we looked for easy implementable solutions like the Würth Elektronik development kit after seeing a similar solution suggested by our comrades working on LitSpin.
Unfortunately implementation of the said kit would be too much space consuming and we would end up with a much thicker device than expected thus possibly ruining the aesthetic aspect.

Because of that and the fact that implementing by ourselves the Qi compliant receiving part of the WPT chain might involve an unknown quantity of unexpected work, we looked for other solutions which weren’t necessarily Qi compliant.

Long story short, the chinese components we could have used as a replacement would mean forgetting interoperability between transmitter and receiver. Therefore after discussing about this with Alexis, we decided that it’d be more safe to stay on the Qi standard as the specifications on the chinese components were vague. Moreover, using the Qi standard we’ll easily be able to order a Qi compliant power transmitter, already packed and beautiful like this one (this one has bad reviews but it’s just an example of the aesthetic we’re looking for).

How to Qi

We will be working on the Mobile Device part of the Wireless Power Charging | Source : P9415 datasheet

The research for Qi-compliant Wireless Power Receiver IC ended up being longer than expected because the components category name isn’t consistent throughout websites. In the end, and after going through pages and pages of datasheet we found this device that we need to further discuss with Alexis before order.

Particularly we need to know what’s behind the two arrows between Receiver and Load on the above image.

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