Re: Air-core power transfomers

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "Marry Krutsch by way of Terry Fritz <twftesla-at-qwest-dot-net>"

<u236-at-earthlink-dot-net>
 
> 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?


	Poor efficiency/power handling.
	Transformer needs to be bigger as a result.
	Could be made to work, i guess.


> 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?


	No.
	Or (for calculation purposes) it STARTS saturated & Stays
	saturated.

> 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)?


	Reduces cooling, arguably increases coupling.

> I thought that coupling would be better in this case,


	Transformers work by moving the energy into a magnetic
	field, then recovering it.  Use of a core allows this
	to be done in more compact form.  Controlling the
	mag field shape via the core means the coils can
	be more freely located, keeps the field strength
	somewhere useful.  Cores are inapropos for some
	applications, where HF or LF cause eddy current
	losses, sometimes special materials (ferrite) can be
	used.  An air core transformer will need to be
	physically larger.


	best
	dwp

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	Vernor Vinge
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	-me