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.

Ted


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. The 7A load
current flows out of the centre tap, through the load (Gunner's bridge
rectifier and pump motor) and back to the bottom terminal. Now remember
that the total current into any point must sum to zero so half of that 7
amps *MUST* go up the bottom half of the winding.

OK its a special case for 2:1 autotransformers but it *DOES* only need a
3.5A rating to supply 7A without overloading which would make a really
big difference to Gunner as it would be easier to source *and* to cram
in there.

Finally, this sort of stuff is not unrelated to my day job :-) You wont
see much from me about the best way to rebuild a lathe, make an
interrupted cut or whatever way of making chips is the topic of the
day.,because I have very little machine tool experiance, but if it is
electronics related (note: NOT US mains wiring) I try to return
something for all the good stuff I've read lurking here.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
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