Re: Where can I find...

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Matt,

Tesla list wrote:

> Original poster: "Matt Woody Meyer by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <meyerml-at-stolaf.edu>
>
> Does anybody know where I might be able to find a reliable but still
> inexpensive motor for a SRSG?  1800rpm should be fine.

Nope. But you can modify an asynchronous motor by grinding flats on the
armature. Check Terry's
personal web page at www.hot-streamer-dot-com for instructions.

http://hot-streamer-dot-com/TeslaCoils/Misc/syncmot.zip

> I've noticed that many of the larger coils use a resistive ballast... is
> this something that you only need for a distribution transformer, or do some
> use it with NST's also?  I'm running 2 12kV/30ma and one 15kV/60ma
> transformer, all in parallel.

Resistive ballast are sometimes used with potential and distribution
transformers in series with an
inductive limiting scheme to keep the thumping down which can occur when
pumping some hefty current.
It's not a requirement and can be just a point of loss in the system as the
resistive component is
prone to getting hot unless it's a really high watt device.

> Lastly, I am considering "borrowing" one of our department's variacs instead
> of buying one of my own.  I know that while tuning the coil, it's not the
> best idea to run it at 100%, however, after the coil is in tune, is it still
> better to have a variac to ramp up the HV, or is it safe just to "throw the
> switch" once the coil is tuned?

Either or. Sure it's nice to ramp up the voltage, especially with higher
kva, but many simply flip a
switch.

> I've heard of using a "bleeder resistor" to discharge the capacitor after
> coil use.  I've never heard of this, what exactly is it?

The cap can sometimes have a charge left on it which can give you a nice
jolt. Removing this charge is
a safety precaution.

>  For a simpler solution, it also works to directly bridge the capacitor
terminals also,
> right?

If you mean by bridge 'to short across', then no. Yes, it will discharge
the cap, but can also damage
the cap. The bleeder slowly discharges the current (slow as compared to a
dead short).

> and lastly...
>
> Just out of curiosity, how does the TC designer program go about calculating
> arc length?  9.7 feet seems a bit much from the coil I'm working on :)

JavaTC shows 5.4 feet at 12kv/120mA, which uses John Freua's spark length
formula:
1.7 x sqrt(input watts). This is an optimum length. Most coilers have
losses in the system from one
thing or another which drops the actual sparklength. A few coilers have
exceeded the length predicted,
but only a few. These would be considered low-loss or efficient coils (by
efficient I mean power in vs.
sparklength, nothing more and nothing less). Consider a predicted
sparklength as an approximation and a
possibility.

> This is all I can think of at the moment.  Thanks again for all your help,
> ><>Matt

Take care,
Bart