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New HBT info for Doug
Original Poster: Doug Brunner <dabrunner-at-earthlink-dot-net>
I bought a 100' spool of 10-gauge a little while ago. Problem is, unless I
have a LOT of secondary windings to go with it, the inductance will be really
low and
it'll waste a huge amount of energy in hysteresis losses. I'm going to try
to put as many secondary windings on as I can, maybe 6400 or 10000 if I'm
lucky
and can rip open some unused transformers.
Another question: if I were to put in an external inductive current
limiter, would that be a big power loss (as in would I be losing a large
fraction of the
power I put in to the limiter, rather than my coil)? Is a variac a better way
to go
(if current starts to get too high, turn down the voltage), or is doing
something like
that unsafe?
Hi there again Doug,
You will lose a little power using a limiting inductor. However it will be
less (a LOT less) than using a resistive limiter. A resistive load not only
drops the voltage (which an inductive load does not, at least not on such a
large scale), but also gives off heat. The higher the VA the higher the losses
and the more heat is produced. A lot of Teslaphiles use oven elements and you
know what that means. They can boil themselves a cup of coffee while running
their coils. Your variac idea posses one big problem. You know what would
happen if you ( in case of emergency or excitement) were to turn it in the
wrong direction. Bye, Bye xformer. If I where you I would use an inductive
ballast to limit your total current and a variac for fine tuning. This way you
can ramp the variac up to full w/o having to continuesly watch the ampere
meter. Another idea would be to use the variac alone if you can make a good
and postive dead stop at the max voltage/current you will be able to use on
your xformer. You would have to find the position experimentally.
W/o knowing what VA rating you want to build I can´t tell you if AWG 10 is too
big or too small fo the primary.
I wouldn´t relish your idea of using several different transformers for a wire
source, thou. I´ll tell you why. First of all you would need to find several
transformers of the same type to keep the wire gauge the same. Just because
the tranformers VA is the same, doesn´t mean the wire gauge will be the same.
This depends on how much the xformer manufacturer overrated his design. The
next problem you have is joining the wires, when you run out of the first
spool. You can solder this, but:
a.) the wire will be thicker here
b.) You will have to polish up this joint (sharp edges enhance corona and arc
overs)
c.) You´ve got to insulate this joint really good.
My last argument for not re-using wire is of physical nature. The wire will be
kinked at the edges of the turns where it was originally wound. You would have
to have a lot of luck if these kinks would "fit" your new core. It´s a lot of
work to smooth out these kinks. The wire is more or less strained at these
kinks, really inviting it to break at a somewhat heavier pull, while winding
the new job.
If I were you I would:
a.) Decide on my needed VA rating
b.) Try to find an old welding xformer from stick welder (etc)
c.) Leave the primary alone.
d.) Calculate my new number of turns and wire gauge for the HV I need.
e.) Insulate the new winding very good after each wire layer, core, etc.
f.) Go for a small width and a larger heigth for the secondary coil form.
g.) Try to put the primary in the middle of the core and split the secondary
in two.
h.) CT the secondary to cut down the insulation loading.
i.) Make a test run w/o oil at 25% and 50%. If all goes well pluck ´er in
oil.
Never make a HBT for an exact VA rating, when choosing the secondary wire
size. Go bigger. It won´t hurt and it does give you a comfortable safety
margin.
Coiler greets from germany,
Reinhard