Re: 48kW DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Hooper, Christopher AZ" <christopher.az.hooper@xxxxxxxxx>

Hi Steve,
Good input but what about looking cool to be able to pull a rack at a 
thon. He he

Rgs, ch
--------------------------
Sent from my BlackBerry Wireless Handheld


-----Original Message-----
From: Tesla list <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx <tesla@xxxxxxxxxx>
Sent: Sat Dec 03 10:17:12 2005
Subject: RE: 48kW DRSSTC

Original poster: Steve Conner <steve@xxxxxxxxxxxx>


>Anyway, commercial product (not 833C
>compliant) is allowed to fail and will someday. Electron tunneling will
>put small holes in silicon no mater what you do (run at spec), and
>someday a path to metal will happen.

If you ever run your DRSSTC long enough for this to happen, I'll eat
my hat, and any other items of clothing I might have on at the time.
Assuming I haven't died of old age that is. I'm no reliability
expert, but as far as I understand, if the device is run within its
ratings, systematic failures like this should not happen for >100,000 hours.

There isn't much work done on reliability of IGBTs that are pushed
outside their ratings (well not in the public domain anyway- maybe
you know some "trade secrets" that I don't) but I'm willing to bet
that that 100,000 hour figure drops like a stone as soon as you go
outside the datasheet peak current. I don't know why it would, but I
just have that feeling. After all, if the devices were capable of
taking higher peak currents with good reliability, then the
manufacturer would print that bigger number on his spec sheet to make
the device look better.

So I reckon it all comes down to the same tradeoff as Terry Fritz
explored with MMCs. He discovered that you can run the capacitors
outside of their AC voltage rating. It shortens their life
drastically, often to less than 100 hours. But that is still plenty
enough for hobby Tesla coil use. We discovered that you can run IGBTs
outside their peak current ratings, but the life implications are
nothing more than a "Bad feeling" just now. That is in opposition to
the case with MMC caps, where there is even an equation to tell you
how long they will last at a given overvoltage. If someone could
figure out a similar equation for overcurrented IGBTs, it would be
worth a NoPig Prize ;-)

Steve Conner
http://www.scopeboy.com/