Eric, I had a simillar idea a few months back when I needed a spot
welder. The main thing with using a microwave xformer based welder
is the power output, the "big" xformers are rated for around 1500 VAs.
That's O.K. for spot welding thin sheet metal & thats what the plans
available on the web seem to be aimed at, such as

http://www.5bears.com/welder.htm


1/4" brass is probably more than a single transformer home built will
handle. As a comparison, commercial units rated for spot welding
3/16" steel are rated around 2500 VAs w/ a 250 V primary. I ended up
buying a unit off of Ebay, they seem to go for about $70. Thats
probably a lot cheaper & certainly quicker than trying to roll my own.

If you're trying to butt weld the brass as I suspect then I really
have no idea how much juice you'll need but you're certainly talking
about a lot more than you'll get from a m/w trans. or the 70 bucks on
Ebay.

Howard.

On Tue, 13 Jul 2004 18:02:35 -0700, Eric R Snow
wrote:

Greetings to all the microwave oven scroungers,
I have a job coming up that requires soldering the corners of brass
frames. These frames are made of 1 1/2 x 1 1/2 x 1/4 brass angle. In
the past I've used a torch to heat the brass. This leads to a little
distortion. This can be troublesome because the brass expands so much
that it moves the joint even though everything is clamped. The parts
must then be straightened when cool. Because of the application and
fit the frames must be straight within .010" in 36". I saw some
resistance soldering units in a catalog and the description of how
they operate says that only a small area is heated and gets to heat
fast. This would be ideal. However, the ones I saw were too small and
the price too large for me. But I've got several microwave
transformers and they seem like they might be perfect. A rough
calculation from the specs and pictures given in the catalog leads me
to believe that they output about 12 volts open circuit. Some have
variable outputs. So I have a few questions:
1) Does 12 volts sound reasonable? Would a different voltage be
better?
2) Is DC better than AC? Does it matter?
3)What would be good ways to limit the current? Would a lamp dimmer on
the input side of the xmfr work? Wouldn't that also lower the voltage?
Would that matter?
4) I have a timer that pulses a relay on and off. I can set the length
of the pulses. Sort of what a lamp dimmer does but much longer pulses
(1 second and up) and the voltage would be the same out as in. But the
brass would average the heating. Would this work almost as well as
lowering the current? Better?
Any other input is much appreciated.
Thank You,
Eric R Snow,
E T Precision Machine