RE: Possible transformer rewind?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Loudner, Godfrey by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>

Hello Rick

Well I don't see anyone else answering your question, and I made a big goof
the last time I answered someone's transformer  question. But I think I'm
right this time. There should be no problem with your 2.3" x 6.4" cross
section. It would be cosmetically nice if the cross section were square, but
that is not necessary. One benefit of stacking the two cores together is
that it will take fewer primary and secondary turns to reach 15 kV. Now you
will have more window space to fill with insulation. I believe that proper
insulation is the greatest problem in making homebrew HV transformers. I
indirectly know someone who is a retired transformer builder, and he has in
house training manuals for building HV transformers. But he won't let me
study or copy the manuals as he considers them to be top secret. I'm sure
they contain some interesting tricks of the trade.

Godfrey Loudner   

> -----Original Message-----
> From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent:	Sunday, November 25, 2001 11:03 AM
> To:	tesla-at-pupman-dot-com
> Subject:	Possible transformer rewind?
> 
> Original poster: "Rick Williams by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>
> 
> Hi list,
>  
> Must be my time for transformers. :)
> Got two trannys at a yard sale today. Husband died and the wife sold all
> his
> ham radio equipment. Except for these 2 trannys. Got both for 20 bucks!
>  
> And very sizable ones at that, identical, 38 lbs, dry (not potted) "E"
> frame
> type. Each has 2 primaries, 120vac. Has 3 secondaries, two 120vac out -at- 8
> amps
> each and one 10vac -at- 6 amps. The current ratings were taken from the wire
> size
> of each secondary. The cross-section of the middle leg of the "E" is 7.36
> sq
> in. Using the formula VA = ( A / 0.16 ) ^ 2 I get 2116 VA. That's about
> right
> for the currents indicated by the wire size.
>  
> Cross-section ... Width = 2.3 in. Length = 3.2 in.
> (length is determined by the number of laminations)
>  
> VA = ( A / 0.16 ) ^ 2
> VA = ( 7.36 / 0.16 ) ^ 2
> VA = 46 ^ 2
> VA = 2116
>  
> These look like some kind of isolation transformer with a secondary for a
> 12
> volt supply or step-up / step-down transformers. 
>  
> I already have an isolation transformer for my scope and never really had
> any
> use for isolation elsewhere nor do I have need for step-up or step-down. 
>  
> So I'm "thinking" of rewinding them. I've wound trannys before and know
> what
> I'm in for, somewhat, since I've wound many low voltage high current ones.
> The
> hardest part has always been aquiring the laminations or making them. I
> can
> join all the laminations from both trannys to form one large one. The
> cross-section would be 14.72 sq in.
>  
> VA = ( 14.72 / 0.16 ) ^ 2
> VA = 92 ^ 2
> VA = 8464
>  
> Even with losses of a little over 10% I may be able to squeeze out 7500
> VA.
> Wire isn't a big issue and neither is the time involved since I can now
> wind a
> custom tranny. Primary 240 vac .... Secondary 15kv -at- .5 amps comes to
> mind. So
> far it looks like the coils needed should fit fine with room to spare for
> the
> insulation necessary. (polypropylene sheeting 1/8" to 3/16" thick)
>  
> But I'm concerned about the shape the cross-section would be at 2.3" x
> 6.4"
> I've generally tried to keep the cross-section as square as possible on
> homebrew trannys.
>  
>  
> Rick Williams
> Salt Lake City
> 
>