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Re: Self-built power transformer

I *think* I've got that problem figured out. There will be 5 windings on
top of
each other, so the primary can take 30A. I've calculated the inductance for
that primary at 101.7687875 mH (it's wound on commercial iron).That gives an
inductive reactance of 38.37 ohms at 60Hz. Not exactly a short circuit.

Tesla List wrote:

> Original Poster: Keith Maddox <kmaddox-at-burgoyne-dot-com>
>
> Hold on!!!  There are some careful calculatations than need to be done
> before you undertake this.   I can tell you from the start that 40 turns of
> 24 awg for your primary is far too few.  This will look essentially like a
> short circuit to 120VAC.  I suspect you need more like 320 turns but 24 awg
> is quite small also.  Let me give you some basic starting figures.
>
> Take your average 15kv 30ma NST.  It usually has about 303 turns of 14 awg
> wire on the secondary and about 17,000 turns on each donut secondary.
> >From your description, I know very little about your core.  Even the core
> has to be carefully matched to your application. The secondary sees roughly
> 1/2 volt per turn as does the primary.  The easiest way to do what you are
> trying to do is to use the existing primary, since it will already have the
> right Inductive Reactance (XC) for 60Hz 120V, for this core.  If you want
> to see how many turns the primary has, wind 10 turns around the primary
> while it is in the core and power it up.  Put a volt meter across the 10
> turn secondary and do the math.
>
> There is nothing wrong with doing some experiments with this but I'd use a
> variac, an amp meter, and seperate voltage meter on the secondary, power it
> up slowly ect.   Its a great way to learn!  As you apply power, you'll
> notice that (with 40 turns) the current will rise sharply as you go past a
> certain point.  This is because there is not enough "Back EMF" due to XC
> being too low.  I suspect you'll see this at around 20 volts or so.
>
> Good luck
>
> -Keith
>
> Tesla List wrote:
>
> > Original Poster: Doug Brunner <dabrunner-at-earthlink-dot-net>
> >
> > I'm currently building a power transformer for my coil, and I'd like to
> > get some reactions on it. It's wound on a 15" long, 1" diameter
> > commercial iron core with 1600 turns of 32 AWG magnet wire for the
> > secondary, and 5 windings, 8 turns each, of 24 AWG (they're on top of
> > each other) for the primary. I'll probably wind a second primary so I
> > can run it on 240V as well as 120V. The whole thing will be immersed in
> > motor oil. Please reply with your opinion--I want to be sure it won't
> > fry on me when I power it up.
> >
> > --
> >            --Doug Brunner
> >                 <dabrunner-at-earthlink-dot-net>



--
           --Doug Brunner
                <dabrunner-at-earthlink-dot-net>