Wireless power
tl;dr:
- not very much power
- not very long distance
- only moderately efficient, lessened with range
As such,
- it's not used on beefier devices,
- it has mostly ended up as a convenience e.g. in mobile devices.
There are three major variants:
Wireless Power Consortium (WPC)
- e.g. Qi
- frequency: ~110-200kHz
- power: order of 5 Watts (planned higher) (verify)
- inductive
Power Matters Alliance (PMA)
- frequency: ~300kHz (277 kHz to 357 kHz?)
- power: 3.5W to 15W, planned higher? (verify)
- inductive
Alliance for Wireless Power (A4WP)
- e.g. Rezence
- frequency: ~6.6MHz
- power: order of 5 Watts (planned higher)
- range: up to 5 cm (for decent efficiency; can work at more), allowing e.g. under-desk mount
- resonance
On range
Range of each of these may be mentioned as 10 meters.
However, this is a "its effects are measure to be above zero" range.
At that range it is not going to transfer any real power, and if it does anything at all it most likely has absolutely terrible efficiency.
Assume it needs to be near-touching to be halfway okay efficiency.
On efficiency
It turns out there is usually a very real difference between
- ideal hardware in lab condtions - Minimal distance. Expensive hardware. Good shielding. Good alignment.
- ...and what you will see in reality.
Assume that that quoted figure from lab conditions, transported to the real world, will actually be noticeably less.
Real-world data (including some official graphs from manufacturers) and amateur tests (e.g. charging a phone wired versus wireless) suggests efficiency peaks out at 60% to maybe 70%. From an engineering standpoint, that's not too bad.
Yet that's trying to get it to work decently. That increases with distance, poor alignment, and cheap designs,
So at best, you're going to use ~40% more power than just plugging it in.
It's not too hard to en up with twice the power of plugging it in would take.