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Re: Self-built power transformer (some design parameters)



 Hi Mike, All 

My comments are spread throughout the text.
 
  Suggested parameters for a 1KW transformer:
   Primary wire size:  #10 AWG

What !!!?? Are you kidding ? AWG 10 for a 1KVA xformer?! AWG is 0.1019" in
diameter. I think this is waaaay toooooo large. I believe normal house wiring
is somewhere around AWG 10-12 (or even AWG 14?) in America. What gauge would
you use for..... say a 10kVA pig or even a 25kVA? That would be copper bars!!
(Something like AWG 000 or AWG 0000) I use AWG 14 for a 7.5KVA xformer, so I
think a minimum AWG gauge of somewhere around 17-19 would be quite big enough
for a 1KVA xformer. Take a look at some 1.65kVA MOTS. They donīt use AWG 10!!

        Primary turns:  132

This sounds okay, (for AWG 17-19) could be more tho, if you really use AWG 10.
Otherwise your "little" xformer will pull substantial amounts of pure
magnetizing current.

 Core cross section: 2.5" x 2.5"

The cross sectional area of the core is usually defined as the CSA of the
largest leg. Is this what you mean? or do you mean the whole xformer core?

The core I plan to use (for my 7.5kVA xformer) has a CSA of 2.75" x 2.36". It
was originally used in a stick welder with a 8kVA output.
 
 SNIP 

 Quite a large chunk of iron. (Don't forget that five 8-turn windings in
parallel is not equivalent to one 40-turn winding of larger wire.)

Yes, Mike this is true, very true. Your second comment is of utmost importance
to Doug. 
But I think you hit yourself with this comment. Five parallel eight turn
windings CANNOT be equal to a 40 turn winding. Ohms law would tell you that it
would only be a fifth of an 8 turn winding or 1/25 of a 40 turn. The AC law is
similar. In series they would be similar to a 40 turn winding, but not exactly
the same because of:

a.) The different wire size (you mentioned)
b.) The losses involved, which shouldnīt be easy to calculate, BTW.

SNIP
 
Sorry, Didnīt mean to hit you that hard.
 
Coiler greets from germany,
Reinhard