Ian Malcolm wrote:

Ted Edwards wrote:
Ian Malcolm wrote:
Mike H wrote:
If I remember my tranformer theory correctly, the load current in the
lower half of the winding is opposed by the supply current so you only
need a 3.5A rated winding.

Sorry. No go. 7amps is 7amps. If you are getting 7A out of the
transformer, the wire of that half of the winding has to be carrying it.

So riddle me this. Visulize the autotransformer. 24V AC Live at the
top. 0V at the bottom, 12V at the centre tap. Supply connected top to
bottom. 3.5A flows from the supply into the top terminal of the winding
and has to flow back to the supply from the bottom terminal.

On further thought I, too, came to the conclusion that my above
statement was wrong. 3.5A in eac half in opposite directions.

Ted