AndyS wrote:
Andy writes:

I have been thinking about building a high voltage power supply
for a big amp, and am toying with the idea of using a couple of
microwave oven transformers, which I have on hand.

I plan to use two, with the primaries connected in parallel but
opposing, so that each one will supply voltage, half-wave, to a
diode ring. By doing this, I can have each core grounded like it
is used in the ovens....

So, has anyone else done this and run into any problems that
I may not have forseen ?

Using 1/2 wave rectification on each one will result in big DC currents
in the coils. These DC currents will saturate your cores like nothing else.

If you wanted to do this and be safe you'd want to rewind the primaries
after insulating the core with some appropriate high-dielectric strength
material like Kapton.

If you're in the US you may want to consider using the primaries in
series, and running off of 220V.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

Using 1/2 wave rectification on each one will result in big DC currents
in the coils. These DC currents will saturate your cores like nothing
else.



Hey, Tim -

IIRC, there is only one diode attached to the transformer in my microwave.
That would mean it is half-wave rectified as it comes from the factory. Yes?

Cheers,
John

John - KD5YI wrote:

Tim Wescott wrote:

Using 1/2 wave rectification on each one will result in big DC
currents in the coils. These DC currents will saturate your cores
like nothing else.




Hey, Tim -

IIRC, there is only one diode attached to the transformer in my
microwave. That would mean it is half-wave rectified as it comes from
the factory. Yes?

Cheers,
John

Yes, come to think of it -- yes. Perhaps the core is sized to take it.

I guess the next question is how much harder can you push the system if
you _aren't_ putting DC on the core?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

John - KD5YI wrote:

Tim Wescott wrote:

Using 1/2 wave rectification on each one will result in big DC
currents in the coils. These DC currents will saturate your cores
like nothing else.




Hey, Tim -

IIRC, there is only one diode attached to the transformer in my
microwave. That would mean it is half-wave rectified as it comes from
the factory. Yes?

Cheers,
John

Yes, come to think of it -- yes. Perhaps the core is sized to take it.

I guess the next question is how much harder can you push the system if
you _aren't_ putting DC on the core?


Do they not put a capacitor in series with the transformer secondary, and
then connect this combination to a diode in parallel with the magnetron?
In this way the capacitor would prevent DC in the transformer.

Chris