Re: ballast formula

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

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "James T by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jamest2000-at-att-dot-net>
>
> Hi Deano,
>  Thanks for the response. That is just what I was looking for. I think i
> need those drawings to
> figure out the mean length.
> Whenever you get a chance to scan those pages would be great. There should
> be a clickable email
> next:
> mailto:jamest2000-at-att-dot-net
>
>  I think the MU(permaebility) should be around 60,000. Does that sound right?
>
> Thanks James
>
> Tesla list wrote:
>
> > Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> <deano-at-corridor-dot-net>
> > Hi James,
> > I have an old text book with some of that stuff in it.  It says:
> > L = N^2*mu*A/10^8*l
> > (L equals N squared mu A over ten to the eighth l)
> > where L is in henries,
> > and   N = number of turns
> >       mu = permeability of core (in English units)
> >       A = area of core in square inches
> >       l = mean length of core in inches
> > The mean length would be {twice the length of the center leg (with the I
> > part on there) plus twice half the width of the core} plus [the
perimeter of
> > one window} / 2.
> > Trying to draw pictures with words is not my strong point. If you want, I
> > can scan the pages and email them to you.
> >
> > later
> > deano

Hi James....

if you plan to use a transformer for ballasting, there are a few things to
consider looking
for. The EI core should be of a healthy size , the center leg should be
approximately a minimun
of 9-10 square inches of area.
the primary winding should be made of a #8 wire ( #10 will work for short
term runs (( 20 secs
on 2 min off). the secondary wire size is determinded by the winding ratio.
( if the
transformer is a welding type transformer, the secondary has very thick
wire, very few turns.
if it is a voltage increasing (( NST MOT OBIT)) transformer, then you will
find small gage wire
on it with many turns usually thousands of turns)

if the transformer you plan to use is too small for the current you plan to
pump thru your
Tcoil transformer, the primary in the ballasting transformer will meltdown.
( example - Tcoil
to run at 40 amps, ballasting trannie rated for 20 A, ooops ...  hot
ballasting trannie. in
this case the maximun Amps to be allowed into Tcoil trannie is 20 A)

the problem with using transformers to ballast Tcoil trannies is that the
ballasting
transformer is subject to saturation problems, and that results in a
runaway condition that
allows the amperage to shoot sky hi.

if you have an amp meter ( which can handle 100A + )  you can do a quick
test to see just how
much the ballasting trannie is rated for ...  connect the primary to your
supply voltage (
check secondary voltage to determine the possible amperage delivery (( also
the size of the
secondary wire thickness is a hint as to how much amperage is to be
delivered by the secondary
the thicker the wire the higher the delivered amperage)) example - 120V in
12V out, primary
wire about a #16, secondary wire about a # 6, expect about 50 amps on the
secondary side, 5
amps on the primary side. once you have connected the primary to the supply
voltage and checked
the secondary voltage you have your winding ratio available. next step ...
disconnect primary
voltage , connect the secondary leads to each other ( short the secondary
side) and reconnect
the primary to the supply voltage ...  2 things will happen where ,  either
the fuse will blow
or it wont, if it doesnt then check the amperage drawn by the primary. this
amp reading will be
the nominal rating of the transformer, and that is about what you will be
limited to as a
ballasting current to your Tcoil.


Scot D