Re: MOT-PSU

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Herwig and all,
                   I have a cautionary note about attempting 
to deduce a transformer's turns ratio:

On 21 Aug 00, at 7:24, Tesla list wrote:

> Original poster: "Herwig Roscher" <herwig.roscher-at-gmx.de> 
> 
> 
> Jim Lux wrote to the list:
> 
> > Step 1.. measure the turns ratio at no load by putting a known voltage in
> > and measuring the voltage out.  Often, you put 110VAC on the HV winding,
> > and measure the LV winding.
> 
> Jim,
> 
> I've performed this method and found a clear difference between the 
> voltage ratio measured "forward" and the voltage ratio measured 
> "backward". Shouldn't be, but exists.......

Be aware that the high voltage winding can exhibit resonances 
(well both do actually) but the resonance/s in the secondary 
can occur near the test frequency due to the large inductance 
and self-capacitance in the secondary and if this winding is 
loaded merely with a scope probe i.e a megohm and a few pF, 
its Q can be quite high. Placing the generator or mains across 
the high voltage winding and measuring across the low voltage 
winding should yield the most accurate result.

Regards,
Malcolm

> > If you can measure the power factor or real power consumed, 
> - I shall use the setup you suggested.
> 
> > Step 2... short the secondary with an ammeter. Apply power to the primary
> > with a variable voltage source until you are drawing the rated current.
> - The problem here is, that on the faceplate of the MOTs (if any!) 
> there's no "rated current". In some(!) cases the manufacturer states 
> the voltage and/or the power - that's it.
> 
> > More at http://home.earthlink-dot-net/~jimlux/hv/xfmrmeas.htm
> - I've visited your pages and found a lot of useful information, I'll 
> read through thoroughly. Thank you, Jim.
> 
> Regards
> 
> Herwig
> 
> 
> 
> 
>