Hi Will,
No holes in the lams except the one for the secondary termination rivet.
The numbers are worse than you imagined.
The core cross section is 3.5cm x 6 cm.
The primary is wound with (approx.) 103 turns #14; .33 ohms DCR, 34 mHy
inductance. Even with the mag. shunts removed, it takes quite a bit of idle
current.
The secondary is wound with #27; 95 ohms DCR.
The above numbers figure out to about 40 Watts coppper loss, and over 20K
gauss in the core which is likely another 40 Watts loss at 1KW. Eeek!
Inspires a new meaning for ICAS: Inappropriate Consumer Appliance Service.
I think if I was going to rewind one for something I'd add at least 20 turns
to the primary and only run the thing at 750 watts or so to stay within
"amateur" ICAS.
73 & Good morning,
Marv WC6W
-- "Will Matney" <craxd1@verizon.net> wrote:
Marv,
Well, they're getting cheaper, no screws now! Does the lams still have the
screw holes or are they solid? A 1/8" fillet weld wouldnt be too hard to cut
out. The problem with welds here is causing eddy currents that are higher than
normal thus running the losses up. At one tune per volt and about 12
kilogauss, it would use about a 5 square inch core and be rated at about 1KVA
or just under. I'd say though they're running it higher than 12 kilogauss,
maybe 15-16. The easiest way to tell the turns per volt is if there is any room
between the coil and the cores outside legs, snake in some wire, and do a 10
turn winding on the outside of the coil. Any size small wire will do. Then,
power up the primary and read the voltage of the 10 turn coil. Take that
reading and use it to figure the turns per volt with the line voltage. I use 10
turns so it's easier to figure it math wise. At least on this one, the
secondary connection to the core was easily cut, some aren't. The shunt can be
driven out with a hammer and a block of wood or a punch. The shunt was used as
a current limiter type of arrangement if I recall, or something to that effect.
On a power transformer for an amp, it would not be needed or wanted. It's a
shame how they've cheapend everything to cut manufacturing costs using welding
on a core.
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/13/06 at 12:50 AM wc6w@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@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@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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>
>
>
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