Re: ballast core

["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: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<CTCDW-at-aol-dot-com>
>
> Hello folks!
> I havetwoe quick questions...using a straight core of laminations. Like a
> huge 'I' part of an EI core, what would be the smallest cubic inch size I can
> use to ballast a 10kVA pole transformer? I'm planning on about 300 turns of
> #8 wire.
> The other question is...is there a way to figure the tap points besides trial
> and error? I would like to have set taps at 1,2,3,4.........10kVA. OR>>>
> would it be better to wind the coil on a bobbin and move the core in and out
> of the coil?
>
> Thanks for any insight, or experiences!!!
>
> Chris W

Hi Chris....

do you have the E portion of the core? if you do use that section, it will
allow
you to control the current down to the lower end you want. A "brick" type
inductor
is hard to control as far as getting accurate steps in current progression.

the best "tapable" inductor i have seen so far is an old 1256D core that
has been
rewound. The problem with "tapping" a multilayer winding is that it becomes
difficult to wind each consecutive layer over the previous tap point. ( it gets
really lumpy).

the problems with desiging an inductor are...

saturation ( with a 50A draw you need about a minimum of 12" sqr of core
area to
avoid saturating )

wire heating...  for 50A use 2 #8's for a multilayer coil ( i used 3 #10's THHN
solid Cu.)

# of windings... 180 -250 turns seem to produce the Heneries needed for
20-50A of
control


If you are using a variac to control the voltage to the transformer, make the
inductor limit the current to the max capacity of the variac  e.g. 2 1256D's in
parallel = 56A have the inductor limit to 60A, this way you wont fry the
variac at
the upper limits.

One of the better variable home made inductors I have made so far consists
of an E
core ( 13.5" sqr area ) with 200 turns of # 10 THHN. To make the adjustments, I
slide the windings upwards ( off of the center leg) by 3/4"-1.25". This
increased
the current from 15A to 40A. Other methods include increasing the distance
between
the E and the I  ( increasing the air gap) for increased Amp flow.

Also, what I have found is that while trying to control current and still
maintain
a high voltage output is similar to controlling the voltage at a set inductance
level. So basically controlling current on the fly is redundant.



Scot D