"Frank" wrote in message
...
On Fri, 10 Dec 2004 18:59:18 +1300, Adder wrote:

In article in nz.tech on Thu, 09
Dec 2004 00:52:43 GMT, Repeating Rifle says...
in article , wave at wave@waving wrote on 12/8/04
2:38
PM:

Have spent over 2 hours trying to find out if most or all microwaves
do true
variable power output as opposed to the traditional cycling on & off
to
attain different power levels, panasonic call this inverter
technology, they
make it sound like they are the only ones that do it, have not been
able to
determine if this is so yet, I searched webpages as well as the
newsgroup
archives but frustratingly I could not find the answer to what I
would have
thought would be a common question.


I was intrigued by this and other posts on the subject. Here is what I
conclude off the top of my head. I may be wrong in part. It sure is
difficult to glean specific information from the Panasonic web pages.

The inverter substitutes high frequency electronic switching and a
SMALL
transformer for a much heavier magnetic transformer to provide the high
voltage necessary to operate a magnetron. The switching also allows
varying
the voltage applied to the magnetron. In turn, that varies the
magnetron's
output level. A conventional transformer's output voltage is not easily
changed. The down side is that efficency is reduced somewhat,
especially at
low cooking level. That is, a larger fraction of the electrical power
you
pay for ends up heating things other than food you are trying to heat.

Running transformers at high frequencies, what the inverter does,
reduces
the size and weight required to handle large powers. The cost of
electronic
devices such as transistors has dropped as manufacturing techniques
improved. Magnetic components such as transformers have not dropped
much, if
any, in price. To a large extent, cost and size for these components
vary
together.

This is how all switchmode supplies (like in your PC) work. Transformers
can be made much more efficient at the higher frequencies. It's probably
the reason why aircraft power runs at higher than ordinary mains
frequency.



That is to get Smaller Transformers, war time planes use 80hz, and IBM
main
frame computers I think from memory used 400hz



I thought large aircraft almost universally used 400hz?