Re: [TCML] MOT Measurements

[tesla <tesla@xxxxxxxxxxxxxxx>]

Hi Again all

Did measurements and advise.

Single 600 Watt MOT, magnetic shunts in:

With primary sided shorted (replicates low source Z mains) 200v rms of
secondary excitation causes 100mA to flow.

The modulus of the impedance is therefore 2000 ohms. As the resistive
component is small compared to this the modulus is almost the same as the
Inductive reactance. So from 2pifL=Z L is 6.3Hy

What are the measurement conditions used to give results as high as 40Hy ??

I believe my technique is validly measuring the series output inductance of
an operating MOT as an external voltage generator can replace the one
provided when the Xfrmr is operating. Have I missed something in my thinking
??. I will try the same measurement with an AC excitation of about 1kv to
bring the xfrmr closer to normal operating conditions but I expect this will
lower further the Xl value as saturation impacts
Ta
Ted


----- Original Message ----- 
From: "tesla" <tesla@xxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Monday, January 05, 2009 3:53 PM
Subject: Re: [TCML] MOT Measurements


> Greetings Team
>
> Well in the fist instance I used the resonance graph published recently
> which showed 60Hz resonance with a capacitor of  just under 1.5uF. (close
to
> the value found in an operating MOT, no coincidence here I suspect)
>
> I just solved f=1/(4pi^2f^2C) with
> 60Hz
> C=1.5E-6
> To give that 4.7Hy even if 50Hz environment still close to that value,
would
> not explain the 20 to 65Hy quoted below, I wonder what conditions this L
is
> measured at, I try to measure at high currents in the secondary (ie lots
of
> excitation to test it) so as to test it close to operating conditions. My
> simple L meters measure around 40 to 100Hy on a secondary but I do not
> believe those results
>
> In the past as I'd said I've measured MOTs (600 watt type) with Pri SC I
got
> 6Hy looking back into the secondary, I'll re-check tonite as it was a
while
> ago and advise results giving excitation voltage and resultant current.
>
> Given the magnetising current required I long ago gave up using a meter to
> measure large iron cored trannies and I'm not sure of the test freq
either.
>
> Best
> Ted in NZ
> Message ----- 
> From: "bartb" <bartb@xxxxxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Monday, January 05, 2009 2:23 PM
> Subject: Re: [TCML] MOT Measurements
>
>
> > Hi Ted,
> >
> > Not that high. Terry's MOT measured 65H at L2. My own MOT measured 39.5H
> > (although my MOT is a bit beefy compared). I would expect Herwigs MOT to
> > be no lower than 20H. Your calculated value of 4.7uH is extremely low.
> > How are you basing this value? Herwig is 230V 50Hz power environment.
> > Are you assuming a 120V 60Hz situation?
> >
> > Take care,
> > Bart
> >
> > tesla wrote:
> > > Team
> > > I noted the Value of Secondary L here of 30.4 Hy
> > > I believe this is rather higher than I would expect.
> > > Resonance at 1.5uF/60Hz puts this figure down to around 4.7Hy which is
> > > in close agreement with experiments I've done (magnetic shunts
intact).
> > > Measured Secondary L with Pri Shorted (voltage generator source
> > > situation as per mains input) and Secondary driven with a large 50Hz
> > > AC voltage source and current measured technique
> > >
> > > Thanks, enjoying the dialogue on this matter
> > > Ted in NZ
> > >
> > > SNIP
> > >> - I am not so experienced in simulations as you are. Therefore I
> > >> would like to accept your generous offer to run the simulation with
> > >> my MOT data: no-load-output-voltage = 2232 Vrms, dc-resistance of
> > >> secondary winding = 70 Ohms, calculated secondary inductance = 30,4
> > >> H, all the other parts were copied from Piranha II.
> > >> Take care,
> > >> Herwig
> >
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
>
>
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