RE: status report

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>


Justin:

I agree with Steve Y. on this.  My DC unit has 1.5uF filter capcitor
banks between each DC leg and ground.  The DC legs are +/- 6KVDC.  The
1.5 uF is obtained by stringing (14) 450V 22 uF caps in series(so I have
a total of 28 caps for both legs).  This provides sufficient DC
smoothing(for me anyway) - ripple under 1 KV.  Each cap has a 1.2 mohm
bleeder resister across it.  Power supply is (4) MOTS series secondary,
parallel primary.  Pictures of the retifier board with the filter caps
can be found at http://www.teslaboys.com/Tesla05/T05Power/index.html
See the rectifier board about halfway down the page.

A DC Tesla power supply allows one to vary the tank capacitance and
primary inductance(# of turns) without changing the power supply.  For
me this meant I could test from a 4 turn primary up to a 12 turn primary
while varying tank capacitance to match secondary resonant frequency.
Turned out 8 to 10 turns gives me 60"+ streamers whereas they are
shorter outide that bound.  Thus the system can be optimized.

With a AC coil it is not possible to make the tank capacitor value
independent of the power supply.

For in depth info on DC resonant charging systems see Richie Burnett's
site.

Mark


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wednesday, December 28, 2005 5:30 PM
To: tesla@xxxxxxxxxx
Subject: Re: status report


Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Justin,

I disagree with David's claim for the need of big (dangerous) filter
caps. You can choose the amount of AC ripple you are willing to tolerate
on your DC output (e.g. 10%), then calculate the filter cap based on the
DC load your setup will draw (e.g. 0.25 amp).  The equations and "how
to" may be found in the Power Supply section of Radio Amateur's
Handbooks.  You can get used ones from Ebay and other used book
dealers--lots of good info for coilers.

I run a DC coil that performs quite well,
and the filter cap is only 0.67 mF at 18 KV (which is still dangerous)
made up of 24 microwave oven caps in series-parallel.

That aside, DC resonant charging gives you a lot more "fun factor"
because you can control break rate and power fairly independently.  But
to get the most fun out of DC, you need a rotary or triggered spark gap.
And if you design your system right, you don't need to ballast your HV
transformer.

I would not recommend using a NST to run a DC system.  NSTs are designed
to run mostly at lower voltages, once the gas filled (neon) lamp is
conducting. With a DC system, you are likely to be running your NST
without a proper load at times which will lead to insulation breakdown
inside the NST.  Best to go with MOTs or a Potential Transformer.  I use
an oil immersed MOT 6-pack which works just fine. --Steve Y.