[Amps] MW Oven Transformer question

[John Popelish]

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.