Re: Terry's DRSSTC - input DC rectifier and filter stuff

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

To follow up...  The models say that having very close 10uF poly 
capacitance right at the IGBTs will happily take care of things even if 
fairly high inductance (10uH) lead wires go back to the main electrolytic 
filter caps.  Basically, say 10kV of RF divides between the 15nF primary 
cap and the big 10uF close poly caps.  The poly caps see 15nF/10uF of the 
voltage which is 15 volts.  I think having poly caps right at the IGBTs is 
a real winner!!  Their ESR is only 4m ohm per cap which is vasty better 
than the electrolytics.  Once the coil fires, you could actually remove the 
electrolytics from the circuit with nill effect since the poly caps take 
all the high frequency load.  They do 500 amps peak so no problem 
there.  My poly caps are CD 940C6W4P7K  600V 4.7uF metalized poly that I 
had left over from the OLTC.

This should eliminate Dan's heavy copper buss work in the DRSSTCII design 
and make using "just big wires" ok.  It may also help some of the glitching 
and noise Dan reported seeing.  In general, I really hate to run 200kHz at 
say 300 amps through electrolytics.  Adding these poly caps simply bypasses 
that current to cap types that love that stuff ;-)

Of course, you still certainly need the big electrolytics to supply stable 
far lower frequency juice to the whole mess.

Happy to see your report of 550kHz out of IGBTs!!!  I have never heard of 
them being run that fast in any situation!!

Cheers,

        Terry



> Hi Steve,
>
> I will have about 10uF of poly caps at the bridge too to block HF 
> stuff.  The leads will be thick and short too.
>
> Some resistance in that path helps things too, but inductance needs to be 
> watched for sure.  I finally am getting some good system models working so 
> I'll check that stuff out more.
>
> Cheers,
>
>         Terry
>
> At 10:58 PM 12/2/2004, you wrote:
> > Hey Terry,
> >
> > Nice looking PCB ;-).
> >
> > Are you planning on mounting another lytic right on the H-bridge
> > itself? or are you just going to keep your output connections from
> > that board very short?  Im sure you realize that any inductance
> > between the lytics and the H-bridge means voltage spike at high
> > currents... better keep those inductances down!!
> >
> > Good luck with this project.  I started working with even smaller
> > coils, and have a DRSSTC running at 550khz ;-)  It throws out some
> > cute 6-7" streamers at about 50W or so :-).  I will post details to
> > the TCML when i get the final version built.  But the fact that it
> > worked well at 550khz suggests that you really *can* build a DRSSTC
> > driver for just about any (resonably sized) secondary out there, just
> > have to use the right IGBTs ;-).
> >
> > Looking forward to seeing your project working!
> >
> > Steve
> >
> >
> > On Thu, 02 Dec 2004 21:07:33 -0700, Tesla list <tesla@xxxxxxxxxx> wrote:
> > > Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
> > >
> > > Hi,
> > >
> > > Got the filter parts in today and built it up...
> > >
> > > http://hot-streamer.com/TeslaCoils/MyCoils/DRSSTC/PC020019.JPG
> > >
> > > It can take a full IGBT nuclear "cross conduction and cool explosions
> > > event" (CCCEE) on the output while keeping the AC line side safe and
> > > happy.  Prolly holding $300 in R&D there ;-))
> > >
> > > 6 x 9 PC card that packs "70 TIMES" the energy of most TC primary
> > > caps!!!  It could kill an elephant dead (unlike Edison, I won't verify 
> > that)...
> > >
> > > I think I will stick it, the breaker, line filter, and discharge circuit,
> > > and a 300V meter in a nice rack case...  Another $300!!!
> > >
> > > This ain't cheap stuff!!...  But blowing $3000 of computers ain't cheap
> > > either...  I now have 4 computers on my desk...  Do this stuff al the time
> > > at work...  But "I don't care there"...  When repairs are on "my 
> > nickle", I
> > > do care ;-))
> > >
> > > It could also power my "waiting" OLTC that has never been "really" put to
> > > the test...  Big hefty AC to DC filters that pack lots of capacitance seem
> > > to be in great need nowdays ;-))
> > >
> > > I think big brass output bolts and wing nuts on the back of the rack
> > > case...  Like 3/8 to 1/2 inch...
> > >
> > > I am looking for a 0-300VDC Simpson meter in excellent to new
> > > condition...  Newark has them in stock for $95...  If anyone has them
> > > cheaper (in stock) I am interested ;-)
> > >
> > > Cheers,
> > >
> > >        Terry
> > >
> > >