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 eddy
s 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
*********** REPLY SEPARATOR ***********
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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