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RE: [TCML] Pig SISG: Destroying the Indestructible
Phil:
Just got back in town and read your posts on this subject.
Based on your data/observations I have the following theory as to the
failure mode. I can think of no other mode that can explain your results,
but someone else might.
Failure theory goes like this: A streamer strike destroys the 25 V TVS and
leaves it dead short. With the TVS dead and shorted, there is no possible
way for the IGBT to fire because the potential between gate and emitter will
always be zero. Next the Sidacs trigger at 300V the full primary current
flows thru the Sidacs because the IGBT is unable to fire and remains in the
off state. This causes the Sidacs to overheat, likely short, and catch fire
as you observed. You even turned off the coil and back on again to continue
this process. Soon, the Sidacs are completely destroyed and go open
circuit. As soon as this happens, the IGBT sees a voltage in excess of its
1200 Volt rating and is destroyed and shorted. Now the coil will continue
to operate albeit at a lower SISG threshold voltage because one or more of
the SISG circuits have been destroyed.
This explains how (1) SISG circuit could be destroyed. Not sure how this
leads to all circuits on one board being knocked out unless the initial
strike took out all (4) TVS on the board associated with the (4) SISG
circuits.
Recently, I was surprised to see much discussion on TCML about a strike rail
not being necessary or even a hindrance. I did not post on that subject,
but I think you have demonstrated the importance of having a strike rail to
prevent damage to the primary circuit.
Mark Dunn
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of FIFTYGUY@xxxxxxx
Sent: Tuesday, March 25, 2008 8:29 PM
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] Pig SISG: Destroying the Indestructible
In a message dated 3/25/08 7:56:19 P.M. Eastern Standard Time,
bartb@xxxxxxxxxxxxxxxx writes:
>Very cool! Who knows maybe a marginal component caused the section to
>fry or maybe you are riding the fence! Probably riding the fence.
I still think I'm riding the fence on peak current through the SISG. The
"best guess" seems to be pulses past 800A are not good.
>Have you any photos of your board(s)?
Not of the bad one. The boards are populated pretty close to the
"standard" setup explained on Mark Dunn's site.
FWIW, I put together a little Web page with some pics on it:
_http://members.aol.com/fiftyguy/highvoltage.html_
(http://members.aol.com/fiftyguy/highvoltage.html)
Not very useful for this crowd, but what the heck. My setups are just
ugly prototypes. But I think I've learned a lot more than if I'd invested
my
limited free time in making works of art.
-Phil LaBudde
Center for the Advanced Study of Ballistic Improbabilities
**************Create a Home Theater Like the Pros. Watch the video on AOL
Home.
(http://home.aol.com/diy/home-improvement-eric-stromer?video=15?ncid=aolhom0
0030000000001)
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