Re: Air-core power transfomers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Quick answers...

1) You need a bunch of inductance to store energy in a typical switcher..
gotta have a core, therefore (or a huge aircore inductor/transformer. If
you get your switching frequency up high enough, it's less of an issue
(which is why the industry is pushing to ever higher switcher
frequencies... 20 kHz used to be sort of standard, now, they're pushing 500
kHz, 1 MHz and higher.  The limit is the losses in the switching device and
in skin effect (sound familiar, tesla coilers?)

2) Air doesn't saturate (at least, not at any field we're likely to encounter)

3) Coupling should be as high as possible, for most switchmode power supply
designs.


Tesla list wrote:
> 
> Original poster: "Marry Krutsch by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <u236-at-earthlink-dot-net>
> 
> Hi all.
> 
>         I've been interested in those solid state MOTs ever since someone
here
> mentioned them.  Since discarded microwaves are scarce around here
> (that, or someone is beating me to them ;-)), I wanted to make one
> myself to power a DC coil, and to feed smoother power to magnetrons.
> 
>         Anyway, I've got plenty of wire, but no ferrite for the core.  Can I
> make an air core "MOT"?  What are the potential problems with this?
> Should I let the inductive reactance of the primary limit the current,
> or should external limiting be used?  Does air "saturate" the way iron
> does?  I'm thinking that operation at 50 kHz or so is good.  And now the
> stupid question:  Does the primary (drive coil) need to be wrapped
> around the secondary (driven coil)?  I thought that coupling would be
> better in this case, but really don't know.  Thanks for any help.
> 
> Winston