Wireless power: Difference between revisions
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Wireless power transmission | |||
The simplest version is a basic case of inductive coupling: | |||
two coils, similar to a a transformer (without a core). | |||
More than a few centimeters and the efficiency is low. | |||
More than that and it's miserable. | |||
But for things you can get to millimeters, | |||
and that don't have to have huge current, | |||
like recharging electric toothbrushes, | |||
phones, | |||
game console controllers and such, | |||
It can also power some devices, such tablet pens and mics, | |||
which then don't have to have any power source. | |||
They transfer AC, so DC devices that want this will need a rectifier and voltage regulation. | |||
The above describes | |||
https://en.wikipedia.org/wiki/Inductive_charging | |||
A fancier version is '''resonant inductive coupling''' [http://en.wikipedia.org/wiki/Resonant_inductive_coupling], | |||
at much higher frequencies (a dozen MHz up to a few GHz) | |||
which can do a bunch of Watts over a few meters without being dangerous in the process. | |||
The efficiency is not great, but much better than the simple variant ~50% at 2 meters. | |||
--> | |||
| Line 6: | Line 46: | ||
* not very much power | * not very much power | ||
* not very long distance | * not very long distance | ||
* | * only moderately efficient, lessened with range | ||
As such, | As such, | ||
| Line 16: | Line 56: | ||
There are three major variants: | There are three major variants: | ||
* '''Wireless Power Consortium (WPC)''' | |||
Wireless Power Consortium (WPC) | |||
: e.g. Qi | : e.g. Qi | ||
: frequency: ~110-200kHz | : frequency: ~110-200kHz | ||
| Line 23: | Line 62: | ||
: inductive | : inductive | ||
* '''Power Matters Alliance (PMA)''' | |||
Power Matters Alliance (PMA) | |||
: frequency: ~300kHz (277 kHz to 357 kHz?) | : frequency: ~300kHz (277 kHz to 357 kHz?) | ||
: power: 3.5W to 15W, planned higher? {{verify}} | : power: 3.5W to 15W, planned higher? {{verify}} | ||
: inductive | : inductive | ||
* '''Alliance for Wireless Power (A4WP)''' | |||
Alliance for Wireless Power (A4WP) | |||
: e.g. Rezence | : e.g. Rezence | ||
: frequency: ~6.6MHz | : frequency: ~6.6MHz | ||
| Line 44: | Line 81: | ||
Range of each of these may be mentioned as 10 meters. | Range of each of these may be mentioned as 10 meters. | ||
However, this is a " | However, this is a "you can ''maybe'' tell a transmission device is nearby" range. | ||
If it manages to transfer anything at all, it most likely has ''absolutely terrible'' efficiency. | |||
You should assume it needs to be nearly touching to be halfway okay efficiency. | |||
| Line 56: | Line 90: | ||
It turns out there is usually a very real difference between | It turns out there is usually a very real difference between | ||
: ideal hardware in lab | : ideal hardware in lab conditions - Minimal distance. Expensive hardware. Good shielding. Good alignment of transmitter and receiver. | ||
: ...and what you will see in reality. | : ...and what you will see in reality. | ||
Assume that that quoted figure from lab conditions, transported to a real-world device, will actually be ''noticeably'' less. | |||
Real-world data (including some official graphs from manufacturers) as well as amateur tests (e.g. charging a phone wired versus wireless) suggests efficiency peaks out at 60% to ''maybe'' 70%, which decreases with distance, poor alignment, and cheap designs. | |||
From an engineering standpoint, that's peak is actually pretty decent. | |||
From an efficienty standpoint, you are typically using ~40% more power compared to just plugging it in in a good case, and maybe twice in a bad case. | |||
Latest revision as of 01:01, 24 April 2024
✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.
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 "you can maybe tell a transmission device is nearby" range. If it manages to transfer anything at all, it most likely has absolutely terrible efficiency. You should assume it needs to be nearly touching to be halfway okay efficiency.
On efficiency
It turns out there is usually a very real difference between
- ideal hardware in lab conditions - Minimal distance. Expensive hardware. Good shielding. Good alignment of transmitter and receiver.
- ...and what you will see in reality.
Assume that that quoted figure from lab conditions, transported to a real-world device, will actually be noticeably less.
Real-world data (including some official graphs from manufacturers) as well as amateur tests (e.g. charging a phone wired versus wireless) suggests efficiency peaks out at 60% to maybe 70%, which decreases with distance, poor alignment, and cheap designs.
From an engineering standpoint, that's peak is actually pretty decent.
From an efficienty standpoint, you are typically using ~40% more power compared to just plugging it in in a good case, and maybe twice in a bad case.