Marv,
20 kilogauss is even over the maximum flux density of Hipersil or M-6 which is
17 and recommends 15. M-2, the best is still 17 kg. I'd say that transformer is
running into stauration under full load, and runs hot as a firecracker. In
microwave ovens, even on high power, the tube is on for maybe a minute, than
off so long, and then on again. The lower powers, this delay is even slower.
I've noticed this while mine has been heating a meal, listening to it kick on
and off over the fan noise. Since they're pulsing the power, they're giving the
transformer time to cool down a little with help from the fan. A 1-3/8 x 2-3/8
core is only 3-1/4 square inches and is way to small for 1 KVA, maybe 500 watts
at the most. What size of mocrowave was this in watts?
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/13/06 at 6:32 PM wc6w@juno.com wrote:
>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!
>>>
>>>
>>>
>>>
>>>
>>>*
>>>
>>>
>>>________________________________________________________________________
>>>Try Juno Platinum for Free! Then, only $9.95/month!
>>>Unlimited Internet Access with 1GB of Email Storage.
>>>Visit http://www.juno.com/value to sign up today!
>>>
>>>
>>>_______________________________________________
>>>Amps mailing list
>>>Amps@contesting.com
>>>http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
>>_______________________________________________
>>Amps mailing list
>>Amps@contesting.com
>>http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
>>________________________________________________________________________
>>Try Juno Platinum for Free! Then, only $9.95/month!
>>Unlimited Internet Access with 1GB of Email Storage.
>>Visit http://www.juno.com/value to sign up today!
>
>
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
>
>
>________________________________________________________________________
>Try Juno Platinum for Free! Then, only $9.95/month!
>Unlimited Internet Access with 1GB of Email Storage.
>Visit http://www.juno.com/value to sign up today!
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|