[Amps] MW Oven Transformer question

[Will Matney]

What you have where a weld is across the lams is this. If we looked at the cross section of a lamination, the eddy currents would be in a circular pattern inside the area we're looking at though thin it may be, but what we want. The flux would be at a right angle to that flowing through the longitudinal of the lam itself. However flux traveling at the top of those lams where that weld is, the eddy current circling around the flux lines has room now to grow in size because of more area from the weld and which increases eddy currents. In other words, there's no break between the lams and it become a solid mass and the circular eddy pattern can gain in size which is not what you want. That will cause some loss but not a great amount. Now if their was a weld at the top and bottom, it would have a path around. If you put four welds all around it, one on each side, the outer fringe flux traveling in the circle from core to legs and back have to go through those welds where the eddys can increase sort of like putting four resistors in the partial flow of the flux. Partial flow meaning several lines of flux in the outer most of each lam.

Best,

Will


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On 3/21/06 at 7:39 PM John Popelish wrote:

>Tony King - W4ZT wrote:
>> John,
>> 
>> The MOT I used in my tester (<http://tester.gs35b.com>) has welds across 
>> the laminations in four different locations. The transformer gets pretty 
>> hot with no load (shunts removed). Fortunately, my duty cycle on the 
>> tester is very low so it really doesn't matter for this application. The 
>> four lines of weld is why I asked the question.
>
>The path of eddy current is around the flux path.  There are not 
>likely welds across both the outside of the laminations, and also 
>across the laminations inside the hole, to complete a closed path that 
>circles flux.
>
>The only increase in eddy current the welds cause is caused by the 
>flux that actually passes through the weld cross section (at right 
>angles to the long direction of the weld).  If the weld is a small 
>fraction of the depth of the core at that point, this is a small 
>fraction of the total flux.
>
>Rows of weld across only the outside of the laminations are a lot like 
>connecting the negative ends of a lot of batteries together.  It 
>causes no current.
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