RE: MOT Help

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

Original poster: "Loudner, Godfrey by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>

Placing a resistor across the secondary of the MOT used as a ballast will
drop the current flowing through the secondary, and hence  the current
supplied to your 7.5 kV transformer will drop. A resistor will increase the
current limiting effect of the MOT over that of shorting the secondary.  
 
If you place a 1uF cap across the secondary of the MOT used as a ballast,
current will flow through the secondary until the cap becomes fully charged.
When you pull an arc off your 7.5 kV transformer, energy will drain from the
cap and it will charge again. The resulting arc should pulsate. I set up
such a situation to ballast another MOT. When I pull an arc using a 1uF cap
with a build in resistor, you can faintly hear a high rate pulsing. The
resistor is constantly draining energy from the cap, so the current flow to
the arc is continuous. When I pull an arc using the cap with no build in
resistor, the pulsing rate is much slower than with a cap having a build in
resistor. With no resistor, the current flow will momentarily stop when the
cap is charged to peak voltage. I can distinctly hear the low rate pulsing.
The use of a cap does seem to cause a higher voltage output. There must be
some sort of ferro-resonance being produced by the cap. However the use of
each 1uF cap significantly lowered the current output of the MOT that
supplied the arc. The use of a cap, when ballasting a MOT, significantly
increased the current limiting effect over that of shorting the secondary.
The charging current of the cap is certainly much smaller than the current
in a shorted secondary, and hence the current limiting effect on your 7.5 kV
transformer will be significantly increased over that of shorting the
secondary. The pulsing effect mentioned will probably produce very irregular
voltages and currents to be seen by the tank cap. I see no advantages to
putting a 1uF cap across the secondary. 

However the pulsing I saw was interesting. I think I'll parallel up a bunch
of 1uF cap and see what effect this has on the arc. With only one 1uF cap,
the arc is quite feeble (lots of current limiting). I should see bigger
bangs with more caps.

Godfrey Loudner           

> -----Original Message-----
> From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent:	Saturday, October 27, 2001 2:23 PM
> To:	tesla-at-pupman-dot-com
> Subject:	Re: MOT Help
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <Hollmike-at-aol-dot-com>
> 
> Hi all, 
>    I have a question.  What if, instead of shorting the secondary of a
> MOT, one
> simply places the 1uF cap across the termimals?  What effect would that
> have if
> one wished to use the MOT as a ballast for a larger transformer?  Would
> the
> secondary's impedance be 'reflected' back to the primary?  Perhaps a
> fairly
> high value resistor of appropriat wattage rating would do better?   
>    I have a 7.5KV(open circuit) transformer, which I could
> rectify/multiply
> easily, that will pop a 15 amp breaker(120V in) after a few seconds with
> the
> secondary shorted.  I could try it with with an available 20amp circuit,
> but it
> might pop that as well, so I was thinking of using the MOT as a ballast.
> I was
> just wondering how a cap or resistor on the MOT secondary would affect the
> current ballasting. 
> Mike 
> 
> <snip> 
> >
> > Yes, they 
> > do pull as much as 15A from the mains, but there are ways to ballast it
> so 
> > it won't trip the breaker. The easiest way is to find a second MOT,
> short 
> > out its seconday, and connect the primary in series with your other MOT.
> 
> > This will allow you to pull 2-3" beefy arcs from it. 
> 
> 
> 
> 
>