Quote:
Originally Posted by GMB
Quote:
Originally Posted by kalee20
Suppose you wind the primary, and then put on a single turn of foil which you earth. And then start winding the 240V secondary....
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That's why you don't do it like that. Safety transformers have separate bobbins so we just need to add enough screening so that the secondary cannot "see" the mains and you can get a good result. Actually it may be enough to earth the laminations if the bobbins are far enough apart. |
That 'separate bobbins' construction style is pretty much the standard design for old-style copper-and-iron wall-wart transformers.
[It's great for us technical-frobber types because it means you can rewind the secondary without disrupting the primary-windings].
The windings-on-top-of-each-other-with-a-grounded-interwinding-screen only works in situations where you have a ground available, making the design rather hard to implement in countries like the UK and loads of European countries where 2-pin mains sockets are the norm.