Air core xformer -- max power xfer?

[D Yuniskis]

Hi,

How much power can one expect to *reasonably* (i.e., in
a *small* appliance) transfer using small-ish coils
separated by a good fraction of an inch?

E.g., how do these "wireless charger" gizmos work?
Or, how *well* do they work? (recognizing that
they tend to operate over closer distances).

Thx,
--don

 

[Archimedes' Lever]

Hi,

How much power can one expect to *reasonably* (i.e., in
a *small* appliance) transfer using small-ish coils
separated by a good fraction of an inch?

E.g., how do these "wireless charger" gizmos work?
Or, how *well* do they work? (recognizing that
they tend to operate over closer distances).

Thx,
--don

Not much. A bit more than not much at higher cycle rates.

 

[Archimedes' Lever]

Hi,

How much power can one expect to *reasonably* (i.e., in
a *small* appliance) transfer using small-ish coils
separated by a good fraction of an inch?

E.g., how do these "wireless charger" gizmos work?
Or, how *well* do they work? (recognizing that
they tend to operate over closer distances).

Thx,
--don

The wireless charger gizmos have cores.

 

[Archimedes' Lever]

Frequency of operation is a big factor for
power transformers but more so for
air cores isn't it? Isn't that why a lot of
military stuff still uses 400 cycle power?
I always thought that was to reduce
the size and weight of transformers.
(a portability advantage)

More reinforcement of my knowledge of how dumb you are.

 

[Archimedes' Lever]

Poke around with Google. There have been some developments in the
'wireless power' field, including some products.

A fraction of an inch is nothing. They're talking about GHz RF systems
that can power small devices (5V, maybe up to 100 mA IIRC) across a
room. The efficiency isn't high, but for small loads, who cares?

As long as it doesn't take 20 watts to push that half watt.

Otherwise, I think we have enough RF immersion in life. And yes, that
is the word I want.

 

[D Yuniskis]

Hi Paul,

Poke around with Google. There have been some developments in the
'wireless power' field, including some products.

A fraction of an inch is nothing. They're talking about GHz RF systems
that can power small devices (5V, maybe up to 100 mA IIRC) across a
room. The efficiency isn't high, but for small loads, who cares?

Well, I'm looking at a *good* fraction of an inch (e.g., closer
to an inch than not!). And, power levels a fair bit higher.
A cursory run through the math says I should be able to get
a few watts (3-5) at reasonably high efficiency (60-70%). Of
course, depends on coil sizes, quality of components, etc.

I haven't yet looked into what the consequences re: emissions
might be :<

And, I'll have to recheck my math with firmer parameters.

Maybe I'll poke around tomorrow and see if I can find any
products "on a shelf" that I can examine...

I'll also have to make some time to see what google turns
up. Always a bit of a game trying to figure out what search
terms to use!

 

[Fred Abse]

A fraction of an inch is nothing. They're talking about GHz RF systems
that can power small devices (5V, maybe up to 100 mA IIRC) across a
room. The efficiency isn't high, but for small loads, who cares?

More spectrum pollution...

 

[Kevin McMurtrie]

Hi,

How much power can one expect to *reasonably* (i.e., in
a *small* appliance) transfer using small-ish coils
separated by a good fraction of an inch?

E.g., how do these "wireless charger" gizmos work?
Or, how *well* do they work? (recognizing that
they tend to operate over closer distances).

Thx,
--don

The wireless chargers use resonant coils. It works well enough when
there's almost direct contact but efficiency drops off quickly with
distance.

How much power can be transferred depends on safety issues. Resonant
coils are also used to make inductively heated crucibles and high
efficiency electric stovetops.

 

[Joerg]

Hi Paul,


Well, I'm looking at a *good* fraction of an inch (e.g., closer
to an inch than not!). And, power levels a fair bit higher.
A cursory run through the math says I should be able to get
a few watts (3-5) at reasonably high efficiency (60-70%). Of
course, depends on coil sizes, quality of components, etc.

That depends on the circular area you are allowed to occupy. IOW, a
large diameter and a long distance is favorable, small diameter and long
distance is not so good.

I haven't yet looked into what the consequences re: emissions
might be :<

And, I'll have to recheck my math with firmer parameters.

Maybe I'll poke around tomorrow and see if I can find any
products "on a shelf" that I can examine...

I'll also have to make some time to see what google turns
up. Always a bit of a game trying to figure out what search
terms to use!

Check out "series resonant converter" and you'll see papers with lots of
valuable information in there such as this one:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.21.6350&rep=rep1&type=pdf