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
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)
Not much. A bit more than not much at higher cycle rates.
The wireless charger gizmos have cores.
More reinforcement of my knowledge of how dumb you are.
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?
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Do not interfere in the affairs of dragons, For you are crunchy and tasty with barbecue sauce.
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.
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! :)
The power limits of air-core coils relate to
(1) their annoying habit of melting nearby metal items (see "induction furnace")
(2) the breakdown of air when the L di/dt of a single winding exceeds safe values
(3) the mechanical stresses when the repulsion of opposite sides of the coil causes diameter to increase, and attraction of parallel wires causes the coil length to shorten
(3) the nice folk from your local communications commission who come knocking at the door after neighbors complain of RF interference.
One can use self-shielding magnetic parts (like in a Sonicare toothbrush stand) and get good efficiency and repeatability, The drop-on-a-pad solutions have to be less efficient, but if they're smart enough to adjust, might work. I worry that they radiate, though.
More spectrum pollution...
--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)
Rather crappy, i expect..maybe in the 10% efficiency region (or worse).
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.
-- I won't see Google Groups replies because I must filter them as spam
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.
Check out "series resonant converter" and you'll see papers with lots of valuable information in there such as this one:
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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