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Re: Herrick's s.s. progress & woes



Original poster: Ken or Doris Herrick <kchdlh@xxxxxxxxx>

Brett (& all)-

Good...perhaps this will start a colloquy! (And I take no offense.) I've looked back thru my CAD drawings to remind myself & see that I started coiling about 10 years ago. But my fascination with Tesla coils started as far back as 1939, about the time I started seriously being a techno-nerd ("radio nut" at that time); and in the interim I've had way too much exposure to problems in design, debugging, troubleshooting and component failure--due to my own errors for the most part plus those of others. So my view is somewhat jaundiced.

My "too many parts" and "antenna" complaints stem from exasperations over the years--and not only with Tesla coils, of course. So...onward, solid-staters, if you will; but be prepared for exasperations a-plenty!

KCH

Tesla list wrote:
Original poster: Brett Miller <mailto:brmtesla2@xxxxxxxxx><brmtesla2@xxxxxxxxx>


Ken,

Not to contradict you outright, since I am sure many
of the frustrations you have encountered during your
foray into solid state by way of IGBT brick
experimentation are valid.  Yet, I too have only been
playing with solid state the new year '07, and I have
had a great time.  I've had a few setbacks and angry
afternoons, but nothing that would cause me to warn
newcomers away from the newest frontier of our hobby.
I want to give my opinions on these 5 points...it
might sound like a point by point refutation, but it
isn't hostile.  It simply means that not everyone who
tries Solid State has the same experience.

> Ken Herrick
>
> A P.S:  I repeat for novice readers my take on the
> fundamental
> drawbacks of s.s:

1) Too many parts, a failure in
> any one of which
> could well lead to another, instant and expensive,
> failure;

Many SSTC topologies provide isolation betwen the
driver section and the power electronics.  It is true
that a failure of a single IGBT or MOSFET within a
full or half-bridge can cause a compromise or outright
failure to the other IGBTs or FETs in the bridge, but
this in no way should effect the electronics in the
driver, power supply, interrupter, etc.  I have had
several MOSFETs fail in a class E sstc (only because I
pushed the input power beyond it's rating) and no
other component was lost.  The coil resumed proper
operation as soon as the FET was replaced.  This was a
single MOSFET coil.

>2)  difficulty in making oscilloscope measurements on
> high-voltage,
> mains-referred circuits;

Most people just make those measurements at low
voltage and get the information they need to ensure
proper operation before applying full power.

> 3) difficulty in keeping
> out extraneous
> signals from the scope due to the large EMF
> generated by the (usually
> adjacent) secondary;

Generally you can test most MOSFET and IGBT circuits
using a non radiating test load -- see Steve Conner's
site for a good example (his DRSSTC testing).

> 4) the need to avoid those
> pesky little
> antennas; and last but foremost,

Antennas work great in SSTC circuits that are designed
for them.  When you have a need to lose the antenna
(maybe your sparks are coming too close) there are
other ways to derive feedback that alleviate this
problem.

5) the expenses
> that can be
> repeatedly incurred as a result of design-flubs.

Yes.  VTTCs and well built disruptive coils can be
expensive too, a new Penta-Labs 833C....a 100nf MMC
for your PDT coil.  But ebay has a lot of stuff if you
are persistant.  You can get enough semiconductors to
keep your coil going for months.

So basically, I just wanted to provide some balance.
I'm new to solid state too, but I've really been
having a lot of fun, and success.  There is a sharper
learning curve, but the end result is, I think, more
rewarding.

-Brett

>
> KCH
>
>
>
>


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