# Re: Self-built power transformer

```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.
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