On Thu, 17 Sep 2009 11:55:59 -0500, brian whatcott wrote:

JIMMIE wrote:
On Sep 16, 8:46 pm, brian whatcott wrote:
Andy GD1MIP wrote:
Hi I am building a (240volt in) 13.8 volt (out) PSU ...
the transformer must have a secondary of 16.5 volt.

I have a Talema branded toroid I want to use, its spec is as follows
(from maker)...
73 Andy
Now that the ideas are cooking.... consider this. 1100 watt defunct
microwaves can be had for the asking.
They have a particular transformer core design that makes it easy
to
saw off the 1 KV secondary, and with the generous core window, you
could wind 18 to 20 turns of wire good for 10 amps. The turns per volt
is not much over 1 tpv.... And you have a decent rectifier diode for
the spares box too....

Admitted - a bandsaw in the workshop makes a 15 minute job out of this
transformer hack.(if you don't nick the primary)

Brian W
KA5WOG

Brian, I have done this with old uwave transformers, the ones I could
knock out the magnetic shunt with a hammer and punch, but on the newer
ovens the shunt is a weld. Will these still work?

Jimmie

I left the magnetic bypass leg in the core on the one I used for a spot
weld source. Its a security blanket against core saturation due to the
magnetron,I reckon.

Brian W

I _think_ that shunt serves to limit the secondary current and therefore
protect the magnetron.

I should go through the math on that...

--
www.wescottdesign.com