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Re: [TCML] GU5B VTTC rebuilt- new CW PSU
I play a bit with the numbers and the results are not very encouraging. starting from the schema:
http://img243.imageshack.us/i/greincwgu.jpg/
The total capacitance at the output is C/2 = 1.5 microF/2 = .75 microF
Considering 2200 V from each MOT, the theoretical output voltage would be 4.4 kv * 1.4 * 2 = 12320 V (I know, the real voltage is lower)
So the energy stored in the output capacitance would be 56.91 J
If I want a minimum 500 W on output, thats a 7.5 microF capacitance, so C (on each side of the doubler) would be around 15 microF.
Let consider the the safe voltage on each C cap would be 4.4 kV * 1.4 * 2 )for safety) = around 10 kV
If I choose to use 400 V electrolitics in serie, I need for each C around 25 electrolitics at 350 microF @ 400 V (so 50 electrolitics in total). That/s almost impossible for me to get..
Another way is to use more MOCs, but for 2 x 14 microF I would need 112 caps....hehehe...good one.
Possible solutions:
- two big 10-15 microF at least 6 kV (I dont have)
- using 6 MOTs to get a tri-phase system and rectifying it - it would give less ripple, but it is a danger for my apartment wiring (I could ran 6 MOTs, for 1 meter sparks from the VTTC, but only with staccato, at low rates)
- using big inductors on the output: this would be possible, using 2 MOT secondaries on each HV leg (4 MOT secondaries in total = around 5.5 * 4 = 22 Henry). This would be possible to experiment with when I get a new, more powerful variac.
vasil
>
>
--- On Mon, 10/18/10, Steve Ward <steve.ward@xxxxxxxxx> wrote:
> From: Steve Ward <steve.ward@xxxxxxxxx>
> Subject: Re: [TCML] GU5B VTTC rebuilt- new CW PSU
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Monday, October 18, 2010, 7:41 PM
> Hi Vasil,
>
> It looks to me like you are not filtering the output very
> much (i see ~1.5uF
> worth of microwave caps on each side of the doubler).
> Im assuming these
> capacitors are about fully discharged on each cycle, and
> maybe only serve to
> ballast the HV supply at this point. For real
> filtering you probably want
> to series up a bunch of electrolytic capacitors to get the
> most energy per
> cost. Consider the energy storage for a CW SSTC of
> similar power level
> might need 500-1000J of energy stored in the filter caps to
> get acceptable
> filtering. A typical microwave cap stores about 3J at
> 2500V, so you have
> maybe 36J or so available, which cant offer much filtering
> for a CW device
> of this power level.
>
> Still, a nice plasma display.
>
> Steve
>
> On Mon, Oct 18, 2010 at 10:38 AM, Liviu Vasiliu <teslina@xxxxxxxxx>
> wrote:
>
> > Hi
> >
> > The new source is ready.
> > I was lucky enough to get these nice HV diodes (75 kV
> @ 100 mA):
> >
> > http://img143.imageshack.us/i/teslahvdiodes.jpg/
> >
> > The new PSU is a Greinacher cascade. The voltage from
> the 4 MOTs is
> > doubled. The cascade capacitors and the filter caps
> reduce ripple. I used
> > ferite beads as RF suppressors on the output HV
> cables:
> >
> > http://img243.imageshack.us/i/greincwgu.jpg/
> >
> >
> >
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