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Re: Bi-Polar DRSSTC

Original poster: "Dr. John W. Gudenas" <comsciprof@xxxxxxxxxxxxx>

Hi Chris
Thank you! I believe you have shed some analog thinking into my digital brain.
Several list members have been able to build DRSSTC coils that operate for long duty cycles. (I ran my DRSSTC for three hours at low BPS at a stable component temp.) However, the only consistent design factors (with equivalent current limiting feedback circuits that are controlling the bridge) seem to be associated with different techniques that keep more than sufficient clean power always handy for the IGBTs (obviously robust IGBTs) on the bridge (i.e. keep short leads, low inductance etc). What you are doing, clearly works. If we start from there, your inference on the large decoupling capacitor bank with a somewhat remote but clean DC always available makes sense. I think you verified your system design when you blew the IGBT's. Pushing the bit rate may be the acid test for a well designed power source, delivery and bridge. Of course, all this may be completely obvious to anyone who uses these high power transistors on a daily basis, but I am just starting to understand how critical this aspect is in DRSSTC
design. Especially for high BPS and long runs.
Thanks again.

John W. Gudenas, Ph.D.
Professor of Computer Science

On Jan 4, 2007, at 9:07 PM, Tesla list wrote:

Original poster: "Dr. Spark" <<mailto:azdrspark@xxxxxxx>azdrspark@xxxxxxx>

Hi John,
No I have not had an opportunity to scope out what the bit rate is, I just
push the interrupter till the IGBT's can not switch. Next time I run, I
will mark the knob and scope it.
 I am using Siemens IGBT's. They are rated at @200A, 1200VBVce,+-20V Vge.
It is a full bridge @ <http://www.drspark.org/images/new%20engine2.jpg>http://www.drspark.org/images/new%20engine2.jpg and <http://www.drspark.org/images/newengine1.jpg>http://www.drspark.org/images/newengine1.jpg and using solid cooper bus.
What save me are two things I think? One is I am running a great deal of
decoupling @ <http://www.drspark.org/images/newcaps11.jpg>http://www.drspark.org/images/newcaps11.jpg. (I cooked my old
one.whooooops) I ran the coil once without these caps and blew two IGBT's
right out of their socket (I am running wild primary currents with only a
little more than one turn on the primary). Also I am running pure DC
source, which are four big filter caps @
<http://www.drspark.org/images/bpcap3.jpg>http://www.drspark.org/images/bpcap3.jpg on the rectifier. With no
doubler, the power into the bus is very clean. All the decoupling may not
be a good thing on most DRSSTC's, as may cause issues with all those leads
increase inductance and could cause more bad than good, but this design
worked well for me.

You have to see this coil run in person, as video just does not do it
justice, man is it loud!

What I am looking at now is this effect on the output @
<http://www.drspark.org/images/closebp3.jpg>http://www.drspark.org/images/closebp3.jpg and

I like the way it sprays sparks off the stingers. That is a lot of energy
trying to get off.

Best Rgs,
Christopher @ <http://www.drspark.com>www.drspark.com

-----Original Message-----
From: Tesla list [<mailto:tesla@xxxxxxxxxx>mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, January 02, 2007 10:05 PM
To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
Subject: Re: Bi-Polar DRSSTC

Very nice work Chris.
I have a few questions after watching your video.
1) Have you scoped the controller circuit to see
what BPS you are running the DRSSTC at? It does indeed scream!

2) What IGBTs are you using? I couldn't tell if
it was a half bridge or full bridge.

This is of interest to me because when I run my
DRSSTC at that screaming BPS I usually, (and
quite undramatically) blow my IGBT's.
I can run for an hour at lower BPS.  Yes, I do
push the coil and IGBT's and certainly duty cycle
is a factor, but there may be more going on too.

Great video and it was nice to meet you at Cheesehead.

John W. Gudenas, Ph.D.
Professor of Computer Science

John W. Gudenas, Ph.D.

Professor of Computer Science