[Amps] Microwave Oven Autopsy

[Mike]

Got a couple of microwave oven xfmrs.  Would like to build a hi-pot 
tester using one of these.  Any reason one couldn't be used with a 
quadrupling circuit?

At 01:28 AM 3/13/2006, Tony King - W4ZT wrote:
>I used a transformer almost identical to this one in my GS-35B tube
>tester <http://tester.gs35b.com>.
>
>It has the welds nicely done connecting all the lams together. Even
>after driving the shunts out the transformer is quite lossy. Even with
>no load it gets quite warm when you apply primary voltage. I did drive
>the magnetic shunts out. They were also paper wrapped and were fairly
>easy to drive out.
>
>This transformer had one end of the secondary soldered to a lug that was
>under a screw driven straight into a hole in the lams.  I took that
>connection loose, slipped a short length of Teflon tube over the loose
>wire and then soldered it to a solder lug that I put under the original
>screw.  It put out 2200 VAC no load and with a full wave bridge produced
>3000 VDC with 56uF capacitance.  Unfortunately, the voltage dropped
>quiet a lot under load. With 450 mA load, the output HV will drop to
>about 2150 VDC.  Not a big deal for what I'm doing but not so good for
>an amp.
>
>73, Tony W4ZT
>
>
>wc6w at juno.com wrote:
> > Hi Will,
> >    This one has four 1/8" wide welds down the opposing 
> sides.  And yes, it has the shunts but, they are encased in 
> transformer paper so, I'd guess that they could be easily driven 
> out without disturbing anything else.  No screws what so ever.  The 
> lams are even welded to the mounting frame in four spots.  The 
> "cold" end of the secondary was soldered to a lug which was riveted 
> to the lams -- I necessarily disconnected that wire for the hi-pot check.
> >
> >    It looks like it's wound at about 1 turn per volt.   As the 
> core wouldn't practically dissassmble, the only easy rewind would 
> be for a filament transformer.  The secondary could be sliced out 
> by a careful guy and rewound with a bundle of large wires in 
> parallel making a KW filament transformer... for say a 
> 4CX5000/10000?   Or twenty 813's?  :-)
> >
> > 73 & Good afternoon,
> >   Marv WC6W
> >
> > **********************************
> >
> >
> > -- "Will Matney" <craxd1 at verizon.net> wrote:
> > Marv,
> >
> > Did you check to see if one of the windings was connected to the 
> core, and if the core had a shunt in it? That is what most have 
> that I've seen. Another thing that really ticks me about their 
> manufacture, and a few other transformers too, is they weld the 
> lams together. They put a weld right down one side of the lams, 
> front to back, one bead about 1/4" wide. That makes them a bit*h to 
> use for a rewind. A person with a mill, or be good with a disc 
> grinder can remove the weld. Also, the shunt needs to be driven out 
> with a hammer. This is really good though as it gives you more 
> vertical window area for a new coil. What gets me though is why 
> weld them and still use screws to hold the lams together?
> >
> > Best,
> >
> > Will
> >
> > *********** REPLY SEPARATOR  ***********
> >
> > On 3/12/06 at 11:57 PM wc6w at juno.com wrote:
> >
> >> QST
> >>  Yesterday, I acquired a 2004 vintage Sharp microwave oven, from the
> >> "alley exchange", which was light (weightwise) enough that I thought it
> >> might contain a switching power supply.
> >>
> >>  Upon examining the unit, I found that the incredible lightness was due
> >> to its construction with frame metal of soda can thickness, and that it
> >> contained a conventional transformer manufactured by one Digital Power
> >> Communications Co, Ltd.
> >>
> >>  There was an article in QEX about 10 years ago that discussed the use of
> >> these microwave oven transformers in plate power supplies.  It advised
> >> against using them in a conventional full wave bridge but, rather used
> >> them in an unorthodox half wave connection.
> >>
> >>  Examining the transformer at hand, it appeared that the insulation was
> >> uniform over the full length of the secondary.
> >>
> >>  I disconnected the "low side" secondary lead from the frame and
> >> hi-potted the secondary (also the primary just for science...) up to 4KV,
> >> referenced to the frame, with zero leakage.
> >>
> >>  This suggests that one of these transformers might be employed in a
> >> "normal" connection for a low voltage (2500V) KW input amplifier.   Or a
> >> pair of identical units in parallel for a 2KW input amp.
> >>
> >>  Caution, this suggestion MAY NOT hold true for other makers of this
> >> style of transformer.
> >>
> >> 73 & Good afternoon,
> >>   Marv WC6W
> >>
> >>
> >> P.S. -- The magnets from the magnetron assembly make great refrigerator
> >> magnets!
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         73,
         Mike, K4GMH