Conductive and Inductive Wireless Charging Smartphones

[jack_92]

I have read many articles on inductive charging technologies and only a few on conductive ones. I was wondering whether it would be more efficient to charge a smartphone wirelessly leveraging the inductive principle or the conductive one. In particular, I was interested on understanding the best way to charge wirelessly two smartphones by sharing their battery levels. Hence, in this way, the most charged smartphone would transfer some of its charge to the other one. This might be very helpful especially in "emergency" situations when you're out for example.

[Keith]

The only difference between inductive and conductive charging is lack of physical connection. They all start (unless you charge from a battery) with an A.C. source passing through a transformer, the ratio of turns between the primary and secondary coils sets the charging voltage and electronics then control the charging. Inductive charging simply has the primary and secondary coils physically entirely seperate rather than just electrically separated, such that the power supply is in one device and the charging circuitry in the other. It's advantages are only electrical safety, sealing out water, etc, and lack of wear on plugs/ sockets.

The issues come from the fact that physical separation reduces efficiency and requires more careful design and optimised frequency for the A.C. component. An even bigger issue occurs if your power source is a battery as it has to be converted to A.C. first, passed through the inductive link and back to D.C. again further reducing efficiency. Some means of turning the charge source on/off is also required or it would be a continuous drain.

Doesn't to me sound like good use of the available battery in a mobile phone, certainly not compared with (say) having a small portable top up battery that can be plugged into the phone.

[jack_92]

Thank you for the careful analysis and explanation. I therefore guess that inductive, though being electrically safer, it may be less efficient and moreover what about the potential losses of watts in the process and their impact on people? Personally, I believe that a wireless conductive solution might be the design and development of covers with both metal strips and metal points that would enable two devices in contact to share battery charge. These strips would be connected to the battery via USB. However, some concerns might arise regarding the fashion of these covers. 

Definitely better the inductive technology, as nowadays we already have smartphones where this tech is already embedded and hence we "only" have to add the transfer circuit necessary to make the energy flow from the battery to the other device in the cover (this is the idea to guarantee the highest compatibility). In this case, since the 2 devices have to be in close-vicinity I believe that the inefficiency related to the distance can be partly mitigated while there may be a more severe issue of overheating. Additionally, I guess in both solutions there must be a communication protocol between the two devices such that it is possible to ensure the flow of charge only one-way from the device with the highest level to the other one. 

I agree with your point about the convenience of having a small portable top up battery but the idea on which I am doing research is more about giving everyone one more opportunity to charge their phone. As cables and top up batteries might be forgotten, we believe that if it were possible to find such a wireless solution, this would make our lives "better". This is also the reason for which, we think that inefficiencies (to a certain extent) have to be accepted as this will not be the ordinary way to charge your smartphone but rather an emergency one. 

Since I am quite new to the topic but eager to learn about it, I hope you can help me to address these issues.