# Short-range wireless AC-AC power?

#### summersab

Joined Apr 8, 2010
146
So, I took enough EE classes to know about resistors, Ohm's law, and that I needed to major in ME. That being said, I'm curious about wireless AC power transfer. Every Google search I do provides me with info about advances in wireless AC-DC power transfer technology for charging electronics and phones or transferring AC power over long distances using Tesla coils. What about transferring AC power over a distance of <1" to, say, illuminate a standard incandescent bulb using household 110V? How would this be done, and what devices are used?

Thanks!

#### Glenn Holland

Joined Dec 26, 2014
705
So, I took enough EE classes to know about resistors, Ohm's law, and that I needed to major in ME. That being said, I'm curious about wireless AC power transfer. Every Google search I do provides me with info about advances in wireless AC-DC power transfer technology for charging electronics and phones or transferring AC power over long distances using Tesla coils. What about transferring AC power over a distance of <1" to, say, illuminate a standard incandescent bulb using household 110V? How would this be done, and what devices are used?

Thanks!
The principle of a simple transformer can be used to transmit AC power over small distances (like an inch or less) and eliminate the need for a plug-in charger. The primary winding of the charger would produce an external magnetic field and the secondary winding would be in the device to be charged. The AC magnetic field would couple the primary and secondary of the two devices

However a transformer coupling must contain a certain amount of volume and mass and those would be added to the device you want to charge (like a phone). Using a very high frequency (12KHZ. to 24 KHZ. instead of 60Hz. ) will allow the use of a much smaller transformer, but it would still consume real estate in the device under charge.

Transformers are not completely efficient and the air gap between the charger and the device would further decrease the efficiency. For now, the only practical solution is still a connecting cord.

#### GopherT

Joined Nov 23, 2012
8,012

#### ronv

Joined Nov 12, 2008
3,770
Here is a good DIY project with a pretty good description. As people have stated it can be done, but is very inefficient. When I was a kid I had a 1KW ham transmitter and a simple long wire antenna. I could light a 40w florescent held in my hand (ground) buy getting within a few inches of the antenna. Once struck it would stay lit to about 2 feet away.
What is it you really want to do?

#### Glenn Holland

Joined Dec 26, 2014
705
As stated earlier, a Tesla Coil can transmit AC power through empty space.

Griffith Observatory in Los Angeles has a Tesla coil that will light a fluorescent tube 10 feet away, however the power quickly decays off with increasing distance. Therefore, a Tesla coil remains just a novelty with no practical application.

#### MrChips

Joined Oct 2, 2009
22,090
Therefore, a Tesla coil remains just a novelty with no practical application.
They said the same thing about electricity.

#### AnalogKid

Joined Aug 1, 2013
8,687
" ... a Tesla coil remains just a novelty with no practical application."

Road Trip - Let's go to Dayton, dig up Charles Kettering, and see if he has a different opinion.

ak