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Re: DRSSTC thoughts...



Original poster: "Mike" <induction-at-comcast-dot-net> 

Hi Dr. Resonance,
                              Well I did hook one up to a classic coil, used
the 3/8 water cooled tubing as the primary, one turn, also tried two, was
better ratio with one.
The heater was a Lepel 2.5 kilowatt and we ran it with an extra tank cap so
it was in the same area as the secondary with a larger ball as the end cap.
Made a nice discharge, clean, after we filtered the DC plate supply well.
With SCR on the plate transformer we were able to control the power out nice
also. Externalized the Grid /feedback coil so it took up frequency lock with
the secondary.
I was fun, we got a few feet out of it, was more interested in what the
target experiment we made it for was doing so that output was enough. Nice
thing about tubes, they don't get so upset at an unusual load.
When we were done, took it apart and moved to the next project.
You're right though, man, would I love to tie into a 300 or 600 kW machine.
Even the wire in the 2.5 driven secondary got warm, I would have used Litz
wire to wind it if we had plans to run it really long.
We often use Litz wire to cut down RF heating, works well. Place up north of
here makes Litz wire about as large as you wish, I think to at least the
equal of MCM-500 anyway.
Carries RF much better with less heating than standard wire.
Regards,
                 Mike

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, September 29, 2004 10:14 AM
Subject: Re: DRSSTC thoughts...


 > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 >
 > Mike:
 >
 > Ever tried hooking one of your 600 kW induction heater circuits to a
classic
 > Tesla coil (minus the spark gap of course)?
 >
 > It might be an interesting experiment --- just before the secondary melts!
 >
 > Dr. Resonance
 >
 >  >
 >  > Hi Terry, Steve and everyone,
 >  >     About the cooling issues, especially the die's, and whole devices,
I
 > like
 >  > water cooling. Distilled water of course and non-conductive hose, ~1
foot
 >  > per kV in length and then some safety factor. At work we routinely use
it
 >  > cooling the big triodes of induction heaters of 600 kW output class and
 > also
 >  > for the "hockey puck" large SCR's controlling the 480 volt 3 phase to
the
 >  > transformer primary. Leakage to ground is not a problem with good
water, a
 >  > non-iron pump and heat exchanger.
 >  > Even the solid state machines use water cooling, be they the older
"fast"
 >  > SCR type or IGBT type.
 >  > On the larger tube machines at ~450 kHz and down (280 kHz typical on
 >  > thermatool pipe welders) we have no problem with water cooling 22,000
 > volts
 >  > at 30 amp power supplies.
 >  > It does help to have a corona ring /cone the first foot from the water
 >  > jacket (anode) around the feed/drain hoses as they pull away from that
 > water
 >  > jacket to the hose trap / coil wound to get enough feet before hitting
the
 >  > feed and drain manifolds, otherwise that end(s) dielectric heat
somewhat.
 >  > But for that kind of voltage DC and RF, this is not so hard to do and
one
 >  > ring protects both hoses.
 >  > For the power levels spoken of on the coils, a very modest pump and
 >  > exchanger would be very easy to do and is quiet.
 >  > Even the CQK-650 tube, tetrode, is rated at 22 kV, 100 amps anode (CW),
 > 1.77
 >  > output Mw with 900 watts signal grid drive, used on VOA is water cooled
 >  > without problems. Our old tube re-building division used to rebuild
them
 > and
 >  > the smaller CQK-450. Point being water and electricity do mix if done
 > right.
 >  > Regards,
 >  > Mike
 >  >
 >  > ----- Original Message -----
 >  > From: "Tesla list" <tesla-at-pupman-dot-com>
 >  > To: <tesla-at-pupman-dot-com>
 >  > Sent: Tuesday, September 28, 2004 11:13 PM
 >  > Subject: Re: DRSSTC thoughts...
 >  >
 >  >
 >  >  > Original poster: "Steve Ward" <steve.ward-at-gmail-dot-com>
 >  >  >
 >  >  > Hey Terry,
 >  >  >
 >  >  > Some comments:
 >  >  >
 >  >  >
 >  >  > .
 >  >  >  >
 >  >  >  > Dan ­ I see you used the model for streamer loading of 220K +
 > 1pF/foot
 >  > for
 >  >  >  > a streamer load in your SPICE models.  I was just wondering how
well
 >  > that
 >  >  >  > worked for you?  There is some concern that model is just "too
 > simple"
 >  > for
 >  >  >  > some things, so I was curious if it worked well in this case?
 >  >  >
 >  >  > Steve Conner has been battling this one for a long time.  A real
 >  >  > streamer model is the #1 hinderance in simulations i feel.  Its just
 >  >  > hard to get it exact.  And your results can change wildly depending
on
 >  >  > what you used for a streamer model!  Am i gonna see 1000A or
2500A?..
 >  >  > was my question at one time :-P.
 >  >  >
 >  >  >  > I see that super high current IGBTs are really in demand now ;-))
 > But
 >  >  >  > monsters like the fabulous Powerex CM600HA-24H my be too heavily
 >  > designed
 >  >  >  > for "power" when what we need is "current".  It can "officially"
do
 >  > 1200
 >  >  >  > amps peak which is nice but I know we don't need the 4200 watts
of
 >  > power
 >  >  >  > dissipation ;-))
 >  >  >
 >  >  > Yeah exactly.  They also didnt strive to minimize stray L inside the
 >  >  > bricks either.  Greg Leyh wrote an article on this... cant remember
 >  >  > where to find it though.  As we push these IGBTs harder and harder
the
 >  >  > little things like stray L inside the IGBT will add up quick!  And
 >  >  > heck, we'd be doing something bad if we dissipated over 50W per IGBT
 >  >  > (unless it was a REALLY big system).  Even with making 11 footers,
my
 >  >  > IGBTs stay cold to the touch.
 >  >  >
 >  >  >    So I wish to remind of the simple IR IRG4PH50UD.  A lowly
 >  >  >  > 24 amp rated TO247AC IGBT with diode.  But it uses a great big
die
 > in a
 >  >  >  > small package thus it's 180 Amp peak rating ;-))
 >  >  >
 >  >  > Yeah, thats a tough little guy!
 >  >  >
 >  >  >    Note that some people
 >  >  >  > have put a lot more current through them like this one happily
 > eating
 >  > 700+
 >  >  >  > amps :o))
 >  >  >  >
 >  >  >
 >  >  > If only the bigger IGBTs could withstand such abuse.  I only run my
 >  >  > CM300s at 2X their peak rating.
 >  >  >
 >  >  >  >
 >  >  >  > Above about 740 amps, the signal starts "flat topping" do to the
 > fact
 >  > that
 >  >  >  > the gate structure simply cannot support more current no matter
how
 >  > high
 >  >  >  > the gate voltage is.  BTW ­ I note a lot of folks no longer worry
 > much
 >  >
 >  >  >  > about the maximum gate voltage specs :o))
 >  >  >
 >  >  > Seems that 30V or so is common now, at least thats what i always
use.
 >  >  >
 >  >  >    But suppose we just
 >  >  >  > can't find them "cheap" or want new IGBTs without spending
$1300...
 >  > Then
 >  >  >  > using a few of the little IRG4PH50UD IGBTs may start to be a good
 >  >  >  > deal.  They cost $16 a "pop".  If you get $1300 worth of them,
you
 > have
 >  > 20
 >  >  >  > IGBTs per leg at 3600 amps peak "rated" and 14000 amps
"unrated"!!
 > So
 >  > it
 >  >  >  > may be useful to consider a "multi-mini IGBT" (MMIGBT ;-)) array
in
 >  > some
 >  >  >  > cases.
 >  >  >
 >  >  > Yeah, that certianly is impressive.  And it seems that you could
take
 >  >  > more control of problems with stray L.  Then again, how to minimize
 >  >  > inductance on a layout consisting of so many individual devices is
 >  >  > quite a feat!
 >  >  >
 >  >  >   However, Dan's data shows the primary current can almost
 >  >  >  > double during a ground strike!!  That is a critical bit of info!!
 > Do
 >  > the
 >  >  >  > models show that behavior too?
 >  >  >
 >  >  > Ive simulated this in some of my models.  My big coil has active
 >  >  > current limiting to keep things "safe" under these conditions.
 >  >  > Shorter, heavier arcs make things much worse as they present lower
 >  >  > impedances.
 >  >  >
 >  >  >  >
 >  >  >  > Of course, if off the self IGBTs just are not right, check this
 > DigiKey
 >  >  >  > part out ;-))
 >  >  >  >
 >  >  >  > IRG4CC50UB-ND
 >  >  >  >
 >  >  >  > 600V 55A for a buck ;-))  I bet you can find a wire bonder on
E-bay
 > for
 >  > a
 >  >  >  > song (Yipps!! guess not
 >  >  >  >
 >  >  >
 >  >
 >
(http://cgi.ebay-dot-com/ws/eBayISAPI.dll?ViewItem&category=45045&item=384297461
 >  > 1)...
 >  >  >  > Just use the silver epoxy for the pad bonding too...)...  Silver
 > filled
 >  >  >  > epoxy for mounting, and your there baby!! :o)))
 >  >  >
 >  >  > Oooh, now THAT can get interesting.  Talking to Jimmy Hynes, the
idea
 >  >  > came up to make our own bricks with some dies, but instead of
 >  >  > designing for lots of power, design it to withstand very high
 >  >  > temperature transients.  That is, put heatsinking on BOTH sides of
the
 >  >  > die to remove heat even faster.  Or even just some sort of small
 >  >  > aluminum block on top of the dies to wick away heat faster... then
IT
 >  >  > can be dealt with via forced air cooling.  I wonder if they come in
 >  >  > 1200V versions :-).
 >  >  >
 >  >  >  >
 >  >  >  > Also note that the primary cap strings could be distributed
between
 > the
 >  >  >  > IGBTs to force current sharing like the OLTC does if that would
 > help:
 >  >  >
 >  >  > Not sure if there would be much reason for that one, though if we
were
 >  >  > paralleling a bunch of small IGBTs it may somehow work.
 >  >  >
 >  >  >  > Apparently, primary to secondary arcing is a  problem.  This is
 > often
 >  > due
 >  >  >  > to incorrect primary to secondary tuning.
 >  >  >
 >  >  > Or your secondary throwing sparks 3X its length!  Thats when my coil
 >  >  > starts to show some signs of being stressed out ;-)
 >  >  >
 >  >  >    Since DRSSTCs are self tuning,
 >  >  >  > there may need to be a little "tweaking" the that circuit to
better
 >  >  >  > match/lock the primary and secondary frequencies.
 >  >  >
 >  >  > Well, the tank circuit cant tune itself.  I think that is what was
 >  >  > meant.  Tweaking the primary L is what is needed... or just turn
down
 >  >  > the variac a bit ;)
 >  >  >
 >  >  >  >
 >  >  >  > The SPICE models can be used to force all kinds of fun fault
 > conditions
 >  >  >  > too.  Primary to secondary arcs and such are just t timed switch
 >  >  >  > away.  These studies tend to reassure one that such events
usually
 > are
 >  > not
 >  >  >  > too bad and can also find a few real doozies!
 >  >  >
 >  >  > Ooh, i will have to try that out in my next sim.
 >  >  >
 >  >  >  >
 >  >  >  > One may "possibly" be able to use 60Hz resonant primary charging
for
 >  > the
 >  >  >  > DRSSTC like the OLTC used.  That would eliminate a lot of the DC
 >  > charging
 >  >  >  > and giant cap stuff.  But I do note that "I" seem to be the only
one
 >  >  >  > foolish to go that way ;-))  But I have not had any problems with
 > it...
 >  >  >
 >  >  > I dont think *my* line can supply 1200A for even very short periods
of
 >  >  > time.  I think we need these big DC caps there to be a low Z power
 >  >  > supply.  Maybe im wrong...
 >  >  >
 >  >  >
 >  >  >  >
 >  >  >  > It would be neat if there were a fairly off-the-shelf system that
 > could
 >  > be
 >  >  >  > hooked up to any already made coil to get rid of the HV stuff and
 >  > simply
 >  >  >  > convert it to DRSSTC operation right then and there.
 >  >  >
 >  >  > The main problems are 1) tank impedance for DRSSTCs are usually less
 >  >  > than that of a SGTC.  2) operating frequencies can tend to be too
high
 >  >  > for efficient use of a solid state driver using slugish IGBTs
(though
 >  >  > they are indeed getting much faster!).
 >  >  >
 >  >  > I too must think that the days of the
 >  >  >  > spark gap coil are numbered.  Not because there "are" good SSTCs
out
 >  > there,
 >  >  >  > but because the will soon simply be the "best" TCs...  Even "big"
 >  > systems
 >  >  >  > are coming to speed fast!!  The record for a point to point arc
is
 > 59
 >  >  > feet...
 >  >  >
 >  >  > 59' for what???  a solid state system?  I was pretty sure that SGTCs
 >  >  > were beyond those spark lengths for some of the larger systems, but
 >  >  > maybe not?
 >  >  >
 >  >  > Steve
 >  >  >
 >  >  >  >
 >  >  >  > Maybe this all will be a bit of help, forget any parts that are
 >  > obviously
 >  >  >  > stupid :o))
 >  >  >  >
 >  >  >  > Cheers,
 >  >  >  >
 >  >  >  >        Terry
 >  >  >  >
 >  >  >  >
 >  >  >
 >  >  >
 >  >
 >  >
 >  >
 >
 >