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Re: PT CURRENT LIMITING QUESTION!
Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>
Tesla list wrote:
> Original poster: "Drew Murray by way of Terry Fritz
> Hello all,
> I have a big question about potential transformers, but first I will tell
> you my story.
to start with the flourescent type ballasts are too small to use ( more on
ballasting pole pigs and PT's for current flow requires either 2 methods
... resistive and/or inductive
resistive can consist of some type of heating element such as stove top
heater coils, hot water heater
cores, electric dryer elements... just to name a few. There are also true
resistors but finding resistors
rated for 10 ohms at 5 kilowatt capacities is difficult ( unless you are
rich and can buy them ). These
are run in series with the power to the transformer ( DT or PT ). The down
side to this method is that you
have a voltage drop to the transformer, thus reducing the upper end voltage
out of the transformer.
Inductive methods include ... inductors* , electric welding machines (AC
type 50A draw capacity minimum),
modified transformers ( of a very healthy size 18Kg minimum).
Some of the more popular and easy ways are using a transformer that is
already wound ( such as MOTs) but
this requires one to find such a transformer. The junk yard or an appliance
repair shop(s) are the first
place to look. If you can find an old electric welding machine, this is a
viable option too. Some
modifications will be needed for this to work as a ballast.
some info about inductive devices.....
inductors* ( real inductors) are basically a transformer with one winding (
primary only). when current is
applied to it, the current waveform of the AC signal is shifted 90 degrees
and thus you have a reduced
current at the peak of the voltage waveform. the amount of inductance
depends upon the core size and the
amount of windings on the core and the frequency of the AC signal.( this is
basic minimal info here)..((
there are about 9 million factors involved with inductors ;) )) what
to look for in an inductor for
ballasting a piggie... a core size ( center leg) of about 16" square, the
windings should be about a #10
wire or thicker, and there should be about 100 turns of wire on the core.
If you use MOTs as inductance, you will need about 4 of them, these can be
run in a series/parallel setup
to spread out the current thru them.
you may have something usable right now.... the OBITs holding your boat...
;) if the primaries of the
obits are still good and its just the secondaries that have shorted then
you have several "inductors"
When using transformers as inductors, the primary coil is used as the power
feed and the secondary must be
you mentioned that you have a transformer from an old scope... if this
item matches the description given
above ( core size, wire thickness on the primary) this is also another
option to use for ballasting.