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RE: Mot DC Ps

Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>


When I looked at this the first time around I must have not been paying
close attention. I missed the connection between the two filter caps and the
lower two diodes. This is the same rectifier circuit used in the off line
rectifier in computer power supplies. When the connection is there, the
circuit is a full wave doubler and the lower two diodes do nothing. The PIV
rating of the diodes needs to be 2*1.4*VRMS. When the connection is not
there, the circuit is a full wave bridge rectifier with a PIV requirement of
1.4*VRMS. However in the diagram it shows two microwave oven diodes in
seriesed for each diode position, so you are covered there.

I tried a full wave doubler made with one MOT last summer. (6.5KV filtered
DC output) I first tried resistance between the PSU and the static gap, but
it burned up real quick. You need to have a lot of wattage for resistors to
work. Then I tried a charging choke made from the secondary and core of
another MOT, stripping several layers from the inside and the outside of the
winding to make room for insulation. It worked, but only a few seconds. I
suspect the choke ringing killed the diodes. Perhaps a charging choke with a
dampening resistor would work, and the filter can't hurt. (I didn't have one
on mine)


> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Sunday, February 18, 2001 8:50 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Mot DC Ps
> Original poster: "Luc by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <ludev-at-videotron.ca>
> Hi Chuck
> Tesla list wrote:
> > Original poster: "Charles Hobson by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <charles.a.hobson-at-btinternet-dot-com>
> >
> > Hi Luc,
> >
> > I looked at your web page gif:
> http://pages.infinit-dot-net/luc2/mot_dc_ps.gif
> > It was a pleasure to see such a well drawn schematic. Several
> comments on
> > the circuit though:
> >
> > 1. I can not see the need for the two lower sets of diodes
> connected across
> > the 2.2uF capacitors. They don't appear to be doing anything.
> The P.I.V. on the diode is equal at the peak V of the transfo, with out it
> it's equal to 2X the peak V of the
> transfo and you have a little gain on the current ( around 5% ).
> >
> >
> > 2. I bread boarded your bridge circuit and applied a low A.C.
> to it to test
> > it. Yes, it doubles the voltage. I then removed the diodes I mentioned.
> > Voltage doubling still occurred.
> >
> > 3. I don't think the circuit can be regarded as a full wave rectifier.
> English is not my natural language when I said full wave I mean double
> alternation .
> > The
> > 2.2uF on the right charges to the peak value of the two MOT's in series
> > (around 6kV) via the two top right diodes during 1/2 the ac
> cycle. Then the
> > left 2.2uF capacitor charges to the peak ac value through the top left
> > diodes to  6kV during the other half of the ac cycle..The 2.2uF
> caps  with
> > their 6kV in series deliver the  12kV to the load.
> >
> > 4. This is still a pretty hefty 12kV dc power supply. I would
> be concerned
> > about the 500k ohm power control. If you are after dc voltage control, I
> > think a conventional variac controlling the voltage to the MOT primaries
> > would be a better option:
> > .i e. safer to operate, efficient, etc.
> I choose this way because I plan to use this power supply with a RSG 20 to
> 800 bang /sec. the cap on the PS will
> always be charge at the maximum available ( less 60 Hz ripple ) and the
> resistance will help to decouple the PS
> cap from the tesla circuit.  Any way I have both: resistance and variarc.
> Operation will tell me what is the best
> set-up.
> >
> >
> > 5. I may be stepping into a mine field here by saying the 120
> Bangs is not
> > applicable with a DC power supply. I think DC charging,
> resonant through an
> > inductor, or RC through a resistor, of your Tesla Coil primary
> capacitor is
> > more appropriate. Bangs per second would be limited or
> determined by the  RC
> > time constant or the LC resonance.
> This is why I build this PS,  I want to use it at different rate of bang.
> >
> >
> > 6. Finally, I don't know your background or experience Luc, so I feel
> > obligated to say that your power supply can be very lethal have
> 12kV  with
> > plenty of current behind it. Good luck, take care and carry on.
> Tx I take it like a mark of friendship. I'm near 50 years old, I start to
> fool around with electricity  at 8 Years
> old ( get shock more often than I like ) I learn to be cautious almost
> frightened by high voltage  and I was in
> charge of the engineering section of the film department of a national TV
> station for 10 years. I have the same
> reaction then you when I read post of teens playing with MOT or PIG.
> >
> >
> >  Chuck
> If you have more comment please post it
> Luc Benard