Re: [TCML] MOT Measurements

["Herwig Roscher" <herwig.roscher@xxxxxx>]

Hi Bart,

> The voltage across the MOT itself is due to the cap value (hope were 
> talking apples and apples and the same Piranha circuit). The resonant 
> value for the MOT was near 1.45uF, so the MOT and total capacitance 
> (2x330nF) is operating in STR at 1/2 it's Cres value
- Now I am a little bit confused: Here you are talking of resonant 
rise and in one of your previous messages you stated: "...My 
conclusion here is that unless one is using a very large cap value, 
there is *no* transformer resonance issue. Terry's Piranha circuit 
using 165 nF is nowhere near resonance...". Yes, we are talking of 
Piranha II.
 
> Regarding the MOV's: If their getting hot within seconds, then their 
> switching all the time. Are you using MOV's across the MOT's secondary 
> winding? If so, what are is the rated turn on voltage?
- After frying the medical transformer I replaced it with the 
original MOT. In order to protect it from overvoltage/kickbacks I 
soldered 4 MOVs S20K625 (connected in series of course) directly 
across the secondary winding. The no-load-voltage of the MOT is 2232 
Vrms. To my surprise they got so hot within seconds that they became 
unsoldered. Then I disconnected the diodes from the tranny and 
repeated the test: no heating at all. To find out the amplitude of 
the overvoltage I added MOVs in series until they stayed cold: 3675 
Vrms!! A note: I used unused MOVs, as used ones could have reduced 
their breakdown voltage. S20K625 means max AC voltage is 625 Vrms.


Bye		Herwig

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