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Re: Transformer Design

Original poster: "PotLuck by way of Terry Fritz <twftesla-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Hi Ben,

VA = ( CS / 0.16 )^2


VA = (6 /0.16)^2
VA = (37.5)^2
VA = 1406

The formula above is for transformers with laminations of the E and I

I've just completed a power transformer,  8500vac per secondary -at- 425ma
though I got 1/2 amp out of it under load with no excessive heating.
Actually it barely got warm after about five minutes. Core section was a
shade over 15 square inches. The "Core" is the leg that the coils are
wrapped on only, not ALL legs.

It's under oil also. But you may want to consider the work involved. Took me
almost 3 months to complete the thing. And tightly winding the #8 magnet
wire primary took a large rig to do. Also, EACH secondary took 44 layers at
an average of 80 turns/layer of #25 wire with kraft paper soaked in
polyurathane between layers. Care MUST be taken with insulation to prevent
flashover between layers and arcing to the core or primary. It's a LOT of
work. May be better to save your nickels and dimes to get a PT from Ebay. :)

Rick W.
Salt Lake City

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, May 13, 2002 8:39 PM
Subject: Transformer Design

> Original poster: "Ben McMillen by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hello all,
>   Yesterday evening I took some time to begin the design of
> a new power supply for TC work. I'm planning on using the
> core from an old power transformer that was being thrown
> out. It's a 3 phase tranny rated at 240/260/280V input 3
> phase. Output is 17 -at- roughly 280 amps. The name plate is
> marked 4.8KVA. I went to this site for design information:
> http://members.tripod-dot-com/~schematics/xform/xformer10.htm
> After working through some of the numbers, I got rather
> confused working out the VA ratings of the core. Accordint
> to the chart given on the webpage, for a core area of
> 6in^2, I should get a VA of about 900VA. Since there were
> three secondaries and primaries, I multipy that by 3 to
> come up with 2.7KVA. So where does the 4.8KVA marked on the
> name plate come from? If I divide that by 3 I come up with
> 1.6KVA per core. Is something different for 3 phase? How
> does core area relate (in mathematical terms) to VA
> ratings? Could someone direct me to a webpage with
> appropriate formulas? I want to do this by the numbers..
> The core of this beast measures 9 1/2 inches by 11 inches
> and weighs about 80lbs.(quite hefty) Each leg has a core
> area of 6 in^2. I was hoping to wind the primary for
> 120/240V operation and place it on the center leg. The
> secondaries will each be 7.2KV (on the outer 2 legs of the
> E core) (center grounded to core) for a total of 14.4KV.
> Does anyone see a problem with this? How would I go about
> configuring the primary for 120/240V operation? (in the US)
> Thanks for any help! I'm hoping to use this PS with an 8"
> coil ;)
> Coiling In Pittsburgh
> Ben McMillen