Re: AC vs DC and Toroid Question

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

Original poster: "Steve Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>


 >
 > Hello everyone,
 >
 > I have a relatively large secondary coil-about 2500 ft., 12.5" dia, 50"
high.
 >   Have a small (14 dia duct pipe toroid but planning a larger one.
 >
 > I have several questions, please:
 >
 > 1)  Given a .15 mfd primary capacitor, a rotary spark gap, and a set of
four
 > 120v/7500v neon transformers in parallel producing 240 ma together, would
 > there be a performance difference (1) operating the system AC versus  (2)
 > rectifying the current to produce DC, and slowing the spark gap down to
 > allow the
 > capacitor to charge fully between firing ?

If you size the capacitor properly and use a sync rotary spark gap running
at 120pps, the capacitor _is_ fully charged at every firing point. The
performance in this case would be identical to if you used DC. The polarity
of the capacitor charge doesn't seem to matter.

AC systems that use an asynchronous gap do behave in the way you described:
some of the bangs will be undersized or missing. This isn't usually a
problem with pole pig and MOT systems. Neon transformers are different;
under certain conditions they can produce oversized bangs and burn
themselves out, so you should only use a sync rotary or static gap with
NSTs.

However, if you did rectify the output from the NSTs, you could probably use
an async rotary safely.

 >
 > 3) The program also indicates a power factor correction capacitor of 291
mfd.
 >   Is this to be at 500v or is a higher voltage recommended.  Do these
really
 > make a difference on transformer performance ?
 >
The PFC cap only needs to be rated for 120V AC. But be aware that PFCs don't
give you any extra power, all they do is cause the system to draw less
current from the line. If the AC outlet you'll be using can supply enough
current there's no need to bother with PFC.

Steve C.