RE: OLTC update - primary IGBT loss

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Terry,

On 3 Sep 2002, at 13:16, Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Gary,
> 
> There are two factors at work here.
> 
> First, I am trying to make the thing really efficient so I am fretting
> about power losses.  I suppose I could just dump a whole lot more power
> into it but then the over all efficiency might be "only" as good as a
> typical coil. ;-)
> 
> Second, the voltage gain is really high  SQRT (0.492/404e-9) = 1103!!  The
> gain of my big coil is only SQRT(0.075/132e-6) = 24.  Max voltage for
each is:
> 
> 1103 * 560 = 617680
> 24 * 21000 = 504000
> 
> That seems about right from that point of view...

I don't think the equivalent shunt impedance will allow the voltage 
gain to be anything like 1103. The coil Q is a direct reflection of 
the coil's ESR and by a simple equivalence transform, its 
output/shunt impedance.
     I'd say that your proposed method for correcting the problem is 
probably only going to work if you rewind with bigger wire and a much 
bigger topload with a rather modest ROC.

Regards,
Malcolm


> It may be that I was trying way to hard for voltage gain and I over did it
> at the expense of current to drive the streamer.  I may have way too high
> of output impedance.  I am studying all this now so I don't have the answer
> yet.  However, I suspect going to a much larger toroid and pulling turns
> off the secondary (low voltage and higher current) would be a good thing
> (but taking wire off is a whole lot easier than trying to put it back on
> ;-)).  The Q's are sort of low, but they alone should not be a critical
> problem.  If the output impedance is way off, that is a big problem that
> only amplifies the Q losses.  We don't normally worry much about this stuff
> because it is messy and we just hope it's ok.  I seem to have found a case
> where it is all very important!
> 
> Much to ponder...
> 
> Cheers,
> 
> 	Terry
> 
> 
> At 11:48 AM 9/3/2002 -0400, you wrote:
> >Hi Terry:
> >
> >While primary circuit Q has always been viewed as important, I recall many 
> >considered opinions suggesting that secondary Q was not so critical.  
> >Suggestions were made to wind secondaries with Litz wire, and the
prevailing 
> >response was that secondary losses (in disruptive coils) were not worth 
> >fretting over.  Please help me to reconcile this with your secondary 
> >situation.  Is your secondary just outrageously more lossy than a typical 
> >secondary coil?
> >
> >Thanks, Gary Lau
> >MA, USA
> >
> >
> 
> 
>