Re: Terry's DRSSTC - The Bridge...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Steve,

At 04:42 AM 12/10/2004, you wrote:
> > Important thought!!!  If we run our DRSSTC at 120
> Hz,  We can take
> > advantage of the AC line high peak currents and
> vastly reduce the size of
> > the filter electrolytic caps...  Why do all
> that "filtering" when we can
> > just run resonate with the AC line too...
>
> Well as I'm sure Dan McCauley will point out... the
> caps are there to provide energy storage just like in
> a photo flash gun. So they have to be able to give a
> number of joules equal to your desired bang energy,
> without the voltage dropping too much.
>
> The peak current drawn by the inverter is so high that
> I think you would be on a hiding to nothing trying to
> draw it straight from the 120v line. Even in a small
> DRSSTC you have peak powers of around 50kW. (the big
> ones are 300+ kW) How much do you think the voltage
> would sag if you plugged a 50kW load into an ordinary
> 120 volt outlet?

I could do it with as little as 470uF of bus caps.  But the waveforms 
looked real ugly in modeling.  While it would be "possible", it would 
create too much trouble and added EMI problems and sync issues to be of any 
use.


> I like your "No GDT" approach and I hope it all works
> well...

That allows one to "play" with the IGBT timing and one can do a lot of 
experimenting with different digital timings.  It also gets rid of the 
issues of trying to make gate drive transformers behave in many different 
situations.  Hopefully, this method will work with any smaller IGBT without 
fiddling.

I wonder if a common lamp dimmer controller would work in place of a variac 
for input voltage control?  It would be nice to get rid of the variac too 
and it may not be too hard in this case to make the input control 
electronic too...  It seems like it all wants to be in one universal "box" 
that could be hooked to a wide variety of coils and just work...

Cheers,

        Terry


> Steve
> C.