[Amps] RE : MW Oven Transformer question

[Will Matney]

Jos,

A man could put to in a container and pot them but heat don't escape that easily this way I don't think. Some say potting makes them cooler by making it like a heatsink. However, in calculating the heat loss in transformers, insulation thickness has everything to do with it, including the outside layer of paper. Then you have the hot spot for each winding which is at the mean turn of each coil, and down in the center of the coil from top to bottom. That heat has to escape and every bit of insulation causes this heat to raise, not lower. Peter Dahl even uses a black die in his varnish which is supposed to help dissapate the heat. Most people think it's something other than varnish, or it's potted, but he did have it on his website at one time what he done. Actually, I think you can buy that now pre-mixed. That's the way I've been taught and is what's in every book on the subject. I'd just as soon see a couple mounted on a common base, and connected together like we're talking, out in mid air so they can breathe.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 3/21/06 at 10:54 PM hermans wrote:

>Hello Will,
>
>I have never seen a micro oven transformer from close, so I ignore its
>dimensions.
>Nice idea to construct some POTTED HV or HP transformers for the HAM
>world for cheap and make some money ! 
>A win win operation for both parties.......
>What say Will.
>
>73 Jos on4kj
>
>
>-----Message d'origine-----
>De : amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] De
>la part de Will Matney
>Envoyé : mardi 21 mars 2006 19:30
>À : amps at contesting.com
>Objet : Re: [Amps] MW Oven Transformer question
>
>
>Gerald,
>
>My guess by seriesing two will drop the flux density in each to around
>10 kilogauss as each will have 1/2 the line voltage across it. That's
>well below the bottom of the knee and in the linear region. It will
>raise the power capability X2 also, but I can't say how much without
>knowing the core dimensions. Two this way though will run as good or
>better than a lot of off the shelf linear transformers because of the
>low flux density. This means the efficiency is really high, probably 95%
>for a rough guess.
>
>Best,
>
>Will
>
>
>*********** REPLY SEPARATOR  ***********
>
>On 3/21/06 at 2:22 PM TexasRF at aol.com wrote:
>
>>Thanks Will and John; I now have an understanding of the heating issues
>>with 
>>the MOT. It appears that these transformers are really a poor choice
>for  
>>continuous operation such as a filament power source. Two transformers
>>with the  
>>primary and secondary windings series connected will work and for
>testing
>>the 
>>traveling wave tubes is the quick method to be used.
>> 
>>Many thanks for your help in my continuing education!
>> 
>>73,
>>Gerald K5GW
>> 
>> 
>> 
>>In a message dated 3/21/2006 11:10:15 A.M. Central Standard Time,
>>craxd1 at verizon.net writes:
>>
>>If you  want to add turns to the primary (if there's enough room, and 
>>should be with  the secondary removed), you can do a simple test to see
>
>>how many turns to add.  First, use the formulas I published last week 
>>about figuring the
>>core size and  number of turns to find the correct number of turns for
>the
>>core 
>>size you  have. Next, connect the primary to 120 Vac and wind a 10 turn
>>coil 
>>secondary.  Take that secondary voltage and divide it by the 10 turns.
>>That 
>>will be the  turns per volt. Last, wind the extra turns you've found
>you
>>need by 
>>the  formulas and the known turns per volt. One good thing on this
>>transformer 
>>in  question, the primary is on the inside. If on the outside, you'd be
>
>>screwed on  removing the secondary.
>>
>>Best,
>>
>>Will
>>
>>*********** REPLY  SEPARATOR  ***********
>>
>>On 3/21/06 at 11:42 AM John Popelish  wrote:
>>
>>>TexasRF at aol.com wrote:
>>>
>>>> Not what I hoped  to hear but I appreciate the good info!
>>>
>>>If you have a supply  of this kind of landfill, you might put two
>>>similar units side by  side, wire the primaries in series (effectively
>
>>>halving the volts per  turn, so eliminating the saturation problems). 
>>>Then you can knock the  shunts out and wind a similar secondary on
>each 
>>>(doubling the number  of turns to compensate for the half primary 
>>>voltage) and wire those  two secondaries in parallel.  This gives you
>a 
>>>reasonably  efficient transformer (that won't overheat without a fan) 
>>>with about a  kVA rating.
>>>_______________________________________________
>>>Amps  mailing  list
>>>Amps at contesting.com
>>>http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
>>_______________________________________________
>>Amps  mailing  list
>>Amps at contesting.com http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
>>
>>_______________________________________________
>>Amps mailing list
>>Amps at contesting.com http://lists.contesting.com/mailman/listinfo/amps
>
>
>
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps