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

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Brett Miller <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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