Wireless energy transfer, an idea

[neazoi]

Wireless energy transfer dates back to Tesla. It uses LF/VLF radio waves for the purpose. Since there are high powered transmitters involved, the risk of health effects (allthough not proven?) is possible.
I was thinking of another way and I would like your oppinion about it.

It is as simple as this: A permanent magnet, spins by the use of a local motor, creating a rotating magnetic field; this is the transmitter. A remote coil picks up this rotating magnetic field and converts it to AC; this is the receiver.
Very simple, like an "open" motor generator, isn't it? And there are no considered health effects from a rotating magnetic field as far as I know (patients use MRIs as a safe alternative to the X-ray machines).

Searching on this idea on the net, to see if someone else have thought it, I found that a university has used what they called "magnetic gears" to remotely charge an ellectric car. The car parks above a rotating magnet, which causes another magnet inside the car to rotate at the same speed and this rotates an internal car motor. This is basically an ingenious magnetic gear indeed.

My idea does not use a second magnet, thus minimising moveable parts (but more inefficient though), it just uses a coil to directly pick up this rotating magnetic field.

Just for fun, how does it sound to you? Have you found anything similar published before, after all it is a very simple idea for someone not to have thought it already.

 

[FvM]

The fact that very high (multiple T) magnet fields are used inside a MRT device don't mean that they are tolerated elsewhere. EMC regulations also have limit values for low frequent E and H fields. Don't need to discuss now if they are primarly intended to protect technical devices or human health.

Secondly, the sketched "wireless" coupling devives undergo laws of physics, their maximum power and efficiency can be calculated applying theory of electrical machines. I fear you are underestimating the principle limitations that apply in the dicussed design cases.

 

[neazoi]

Secondly, the sketched "wireless" coupling devives undergo laws of physics, their maximum power and efficiency can be calculated applying theory of electrical machines. I fear you are underestimating the principle limitations that apply in the dicussed design cases.

That's true, I have not made a research on the topic, just thinking.
What are the limitations apart from the distance to the rotating magnetic field and the pick-up coil number-of-turns/size? I do not see why this would not work, of course efficiency of energy transfer drops dramatically with increased distance, but this is also the case with magnetic loop transmitters.

By the way, it works indeed, I have just found a patent about it http://www.google.co.in/patents/US6331744

It can also be used with two electromagnets as well that change polarity, instead of a mechanically rotating magnetic field, clever..

 

[Dan Mills]

Two electromagnets that change polarity? That has a name you know.... Transformer sounds familiar for some reason......

Actually you can create a rotating field far more easily with a simple three phase feed and a suitable arrangement of coils, and it will be magnetically completely indistinguishable from the field created by a motor spinning a magnet (Just acoustically quieter and with no bearings to wear out).
All of the usual considerations for efficient coupling of an EM field across an air gap apply in the usual way to this scheme.

Just because it could be gotten past the US patent office does not (unfortunately) mean it is an original idea or that it is not stupid.

Regards, Dan.

 

[neazoi]

Two electromagnets that change polarity? That has a name you know.... Transformer sounds familiar for some reason......

Actually you can create a rotating field far more easily with a simple three phase feed and a suitable arrangement of coils, and it will be magnetically completely indistinguishable from the field created by a motor spinning a magnet (Just acoustically quieter and with no bearings to wear out).
All of the usual considerations for efficient coupling of an EM field across an air gap apply in the usual way to this scheme.

Just because it could be gotten past the US patent office does not (unfortunately) mean it is an original idea or that it is not stupid.

Regards, Dan.

I like your last point!
I just could not see why they did it with the "magnetic gears" https://www.gizmag.com/remote-magnetic-gears-charging/24771/ it seems idiot to me.
Thanks for the replies

 

[jiripolivka]

Wireless energy transfer dates back to Tesla. It uses LF/VLF radio waves for the purpose. Since there are high powered transmitters involved, the risk of health effects (allthough not proven?) is possible.
I was thinking of another way and I would like your oppinion about it.

It is as simple as this: A permanent magnet, spins by the use of a local motor, creating a rotating magnetic field; this is the transmitter. A remote coil picks up this rotating magnetic field and converts it to AC; this is the receiver.
Very simple, like an "open" motor generator, isn't it? And there are no considered health effects from a rotating magnetic field as far as I know (patients use MRIs as a safe alternative to the X-ray machines).

Searching on this idea on the net, to see if someone else have thought it, I found that a university has used what they called "magnetic gears" to remotely charge an ellectric car. The car parks above a rotating magnet, which causes another magnet inside the car to rotate at the same speed and this rotates an internal car motor. This is basically an ingenious magnetic gear indeed.

My idea does not use a second magnet, thus minimising moveable parts (but more inefficient though), it just uses a coil to directly pick up this rotating magnetic field.

Just for fun, how does it sound to you? Have you found anything similar published before, after all it is a very simple idea for someone not to have thought it already.

EFFICIENCY IS THE KEY!
Have you ever tried to look in a car alternator or toy motor? You should notice that such devices need to have an "almost" closed magnetic circuit to operate.
Try to open the gaps, and even one millimeter causes a grave drop in efficiency.
All this knowledge was acquired in the half of 19th century, BTW.

 

[FvM]

When you operate a rotating magnet or a fixed coil supplied by an AC current without a closed magnetic circuit, the field extents far into the vicinity and can't be concentrated at the receiver.

Different effects can be caused:
- in case of high frequent fields, part of the energy is radiated into free space, emitted as radio wave. This effect can be neglected for low frequencies, e.g. below 100 kHz
- the field can absorbed by objects, particularly extended metallic parts by generating eddy currents
- the field strength must be considerably increased compared to a closed magnetical path to transmit the same power
- even if the field is not absorbed or radiated, the reactive power required to generate it causes losses in the transmitter

If you look at the "remote magnetical gears" photo, it's eye-catching that the transmitter and receiver device are mounted with much empty space arround it. Consider what happens if you mount it in an electrical car's bottom, with a floor panel and other metallic parts around. Be sure that the efficiency is seriously affected by eddy currents.

 

[neazoi]

Thank you all for your replies!