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[TCML] RE: MOT Measurements (Off-List)



Hello, Phillip,

I'm not sure if we've spoken, before, but I wanted to say that I'm interested in VTTC design, much more than I am interested in solid-state design. I've been looking for a design for a MOT-powered VTTC with a cheap tube, because I can't find anywhere that has any tubes. I've looked on ebay, searched on google, and haven't come up with anything. I'm only fifteen years old, mind you, so I can't go to Teslathons or anything of the nature, because my father doesn't want to drive to another state for a few days.

I was wondering if you might have a circuit diagram that would show a simple driver circuit for a VTTC that you'd be willing to send me. I'm more interested in audio-modulated VTTCs, but you have to start somewhere. Also, I work on my coils for research and pleasure. I'm just hoping that somebody will reply to me about the VTTCs. I haven't recieved any replies, yet, from anybody.

Thank you for your time,

 - Christopher

> Date: Tue, 30 Dec 2008 20:36:53 -0600
> From: pslawinski@xxxxxxxxx
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] MOT Measurements
> CC: 
> 
> Hi Bart,
> 
> I posted some measurements I took of open circuit current draw on two rather
> large MOTs.  I think both of the transformers secondary voltage was around
> 180V with 10V in.
> 
> http://www.flickr.com/photos/pslawinski/2885535771/sizes/o/
> 
> You're quite right about heat being an issue with these transformers.  This
> is especially true when you run MOTs in a VTTC circuit.  I air-cool my MOTs
> now.  The two MOTs I have are huge for MOTs.  Perhaps I can make some more
> detailed measurements of these transformers, but I'd have to have another
> reason to open my VTTC case.
> http://www.flickr.com/photos/pslawinski/3119076877/  The transformers are
> positioned right next to the slits in the side with two fans blowing on
> them.  Even with that the air coming out the other side is still rather warm
> after several minutes of runtime.
> 
> -Phillip
> 
> On Tue, Dec 30, 2008 at 19:08, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:
> 
> > Hi All,
> >
> > I took a a few minutes to measure the characteristics of a MOT I had on
> > hand and I've found the microwave transformer rather odd. All this stems
> > from Herwig Roscher looking at his MOT power supply determining if resonance
> > is or is not a problem for his SISG circuit. Herwig fried his first
> > transformer and posted on the subject, but almost no replies other than the
> > initial emails when the transformer died. This was not a MOT tranny that
> > died, but now he is looking at his new MOT supply. During those brief
> > comments, Terry mentioned the sisg circuit was designed for resonance and
> > possibly that could have played a role.
> >
> > Well, since then, Herwig has been measuring and running simulations for the
> > new MOT supply. I've also made some measurements of my own MOT and came
> > across some interesting observations (well, interesting to me).
> >
> > Basically, I'm looking at the MOT and if the transformer resonance is an
> > issue. Here is a list of my typical measurements for any transformer.
> >
> > Measured dc resistances:
> > L2 R=53.2 ohm
> > L1 R=0.204 ohm (low dc voltage with series resistor for .053V/0.26A).
> >
> > Measured inductances with LCR (knowing this is not real, but just a
> > reference as why it's not).
> > L1 Inductance via LCR = 0.044H
> > L2 Inductance via LCR = 15.75H
> >
> > Measured open and short circuit currents and voltages in 10V increments:
> > Vin      Vout     IpOC      IpSC    IsSC(A)   VA     K
> > 10.14    182     0.178     1.72    0.0960     17     0.947
> > 20.0     365     0.220     3.31    0.1500     66     0.966
> > 30.2     563     0.270     5.00    0.2400     151    0.973
> > 40.2     747     0.310     6.62    0.3200     266    0.976
> > 50.1     928     0.360     8.42    0.4100     422    0.978
> > 60.2    1123     0.430    10.63    0.5300     640    0.980
> > 70.2    1321     0.510    13.46    0.6800     945    0.981
> > 80.0    1476     0.600    16.60    0.8600    1328    0.982
> > 90.1    1681     0.780    24.00    1.1200    2162    0.984
> > 100.0    1812     0.980    29.00    1.3200    2900    0.983
> > 110.1    1971     1.600    36.00    1.6000    3964    0.978
> > 120.2    2071     2.760    43.00    1.8800    5169    0.967
> >
> > I've graphed this data in the following files:
> > http://www.classictesla.com/temp/mot-vin-vout.gif
> > http://www.classictesla.com/temp/mot-scc.gif
> > http://www.classictesla.com/temp/mot-k.gif
> >
> > This MOT does not have specs labeled on it, so I needed to look at turns
> > ratio. For accuracy here, I chose a low voltage midterm value of 50.1V.
> > Turns ratio 928/50.1 = 18.5. For a 120V input transformer, 120 x 18.5 =
> > 2220V out.
> >
> > At the normal 120V input, open circuit primary current is 2.76A, thus
> > primary reactance is 43.55 ohms. Therefore, the following "real" inductances
> > for L1 and L2 can be found:
> > L1 Inductance = 0.1155H (Reactance / (2 * pi * Hertz)
> > L2 Inductance = 39.5H (Primary Inductance * Inductance ratio)
> > Note: inductance ratio is turns ratio squared (18.5^2 = 342.25).
> >
> > I then simulated in Microsim the transformer with L's above and at 0.967 k
> > (and of course the R's) using a linear transformer. I inserted a cap across
> > the loaded side of the MOT and adjusted C until resonance was found.
> > Transformer resonance occurred at 2.75uF. This is equivalent to a 5kva
> > transformer with an impedance in the range of 970 ohms. I verified both 1e3
> > and 1e12 load resistors (resonance is not affected, only the output value).
> > But, was this large C value for transformer resonance real? I then looked at
> > Terry's MOT.
> >
> > I inserted Terry's MOT values as shown in the Piranha schematics in place
> > of my own. Terry's transformer resonance occurs at 1.5uF and is equivalent
> > to a 2.5kva transformer. My MOT is twice the power, and my chosen
> > measurement MOT is rather large (compared to other MOT's I have). So,
> > Terry's MOT resonant C value is no surprise compared to my own.
> >
> > My conclusion here is that unless one is using a very large cap value,
> > there is no transformer resonance issue. Terry's Piranha circuits using
> > 165nF is no where near resonance. There is no need to simulate the full
> > circuit. If the resonance won't occur until 1.5uF in a basic transformer
> > circuit, it certainly won't make any difference when rectification is
> > inserted. I feel confident that transformer resonance with a MOT is not a
> > problem for the LC values which we use in spark gap and ss switching
> > designs.
> >
> > But, the MOT cores are small for the odd inductances. This is really the
> > wierd thing with a MOT. There's no doubt that if a MOT is run in continuous
> > mode at it's "max kva ability", the MOT will heat up tremendously and likely
> > see a heat caused death. But as we are pulsing the MOT, we can certainly get
> > away with some abusive currents (at least for a limited time). MOT's from my
> > measurements seems to be quite the transformer! But due to the core size, I
> > suspect it's "power" is rated for it's thermal capabilities. My particular
> > MOT is probably rated at about 1000W considering it's size.
> >
> > Has anyone else made detailed open and short circuit current measurements
> > of a MOT? I'm curious how my measurements compare?
> >
> > Bart
> >
> >
> > _______________________________________________
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> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
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