Re: Ballasting Primer (was: Help Me Prepare for a BIG Coil)

["BunnyKiller" <bigfoo39-at-telocity-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:

> Original poster: "Ryan Ries" <spud-at-wf-dot-net>
>
>         I'm going to go pick up my 10kva pig tommorow, and I really need
a crash
> course in ballasting.

Snipperzzz...

Hi Ryan ...

resistive ballasting reduces the voltage to the pig, it also produces alot
of heat
from the resistors ( be it real hi power resistors or hot water heater
elements oven
or stove elements)  in effect, as you approach a lower level of ohms to
produce a
higher current to the pig, the voltage drops which "kinda keeps the
""power"" at a
constant.

Inductive ballasting can take on many forms...
be it as "simple" as a heat resistant tube with an iron core ( the tube is
wrapped in
wire ) and the iron core is slid in and out of the tube for adjustments

an EI core of substantial size with a coil set of 120 wraps of # 10 or 8
wire and air
gaps are left between the E & I part  ( about 1/8" or so )

a dual wrapped EI core ( electric welder core )  where the primary is run
in series
with the pig and the secondary is shorted ( most electric welders use an
adjustable
shunt ((moveable)) that sits between the primary coil and secondary coil which
controls the amount of amperage drawn by the secondary coil the down side
to this
setup is that your run time is limited to very short "on" periods at high
power with
long (10 minute ) off periods to allow the primary coil to cool off

another option to consider is the isolation transformer ( of course it will
have to be
a sizable one 5-8KVA unit if you plan on running 10KVA for extended periods
of time
(( 10 +  minute runs)) )  the "secondary" side is hooked up to the
resistive elements
which can be adjusted a bit more easier than a straight inductive
adjustment...  as
the resistive elements are adjusted on the secondary side the load produced
by the
secondary side is " reflected " "into" the primary side thus drawing the
need amperage
that will supply the pig

another option but it is hard to really get a smooth tune with is the usage
of a large
variac as the current limiter ...  if you turn the adjustment a bit too far
on the
variac you will supply the pig with huge amounts of power and either the
variac will
do a meltdown or the fusing system will go ....

I prefer the isolation type transformer setup altho there is a bit of
bucking to deal
with but it does allow a smoother transition of current flow to some degree


Scot D