Re: DRSSTC - I think I heard Cross Conduction...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Liviu Vasiliu <teslina@xxxxxxxxx>

Come on Terry, blowing IGBTs is the nice thing. After
some time, the streamers become just boring.

teslina
>
>
--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: Terry Fritz
> <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi All,
>
> I got my noise filter caps in and first tried them
> on the remote filter
> buss.  The noise was still tearing off the H-bridge,
> but the filter board
> is an easy place to experiment:
>
> No cap:
>
http://drsstc.com/~terrell/pictures/FilterBuss-nocap.gif
>
> Ceramic cap:
>
http://drsstc.com/~terrell/pictures/FilterBuss-CeramicCap.gif
>
> Mica cap:
>
http://drsstc.com/~terrell/pictures/FilterBuss-MicaCap.gif
>
> The mica cap does just slightly better but probably
> not enough to worry
> about or justify their expense.  The plain old
> ceramics should do just fine.
>
> So before pulling the H-bridge to add the caps, I
> tried the caps across the
> output first to see how well they stop the noise at
> that point.
>
> That caused a different kind of noise...
>
> Sort of a magnum handgun noise.  Sharp super loud
> BANG!!!!  =:O   Hmmmm.  Hey! sounded like cross
> conduction :-(
>
> Of course, if I had thought...  Putting caps
> directly across the output of
> the DRSSTC was a real BAD idea :-P  The first IGBT
> started up and it's
> current went "nice and high!".  When the other side
> came up it all hung on
> and dumped everything into the two cross conducting
> IGBTS!!  A dumb mistake....
>
> But it did give me a chance to test that case :o)
>
> As expected, the little IGBTs blew VERY loudly and
> made a nice
> flash.  However, they did very little collateral
> damage:
>
> http://drsstc.com/~terrell/pictures/BlownIGBT-01.JPG
>
> http://drsstc.com/~terrell/pictures/BlownIGBT-02.JPG
>
> I have not checked the drives yet but they should be
> fine.  A small soot
> smudge on the case wiped right off.  So it appears
> that a full cross
> conduction event did little damage to anything else.
>  The lights did not
> flicker and the scope and such nearby did not even
> blip.  So everything
> reacted just like it should have :-))
>
> I was hoping a simple IGBT set replacement would
> have it right back on
> line.  However, a trace on the bottom exploded too:
>
> http://drsstc.com/~terrell/pictures/TraceBlown.JPG
>
> The trace is vaporized all over the caps (cover them
> with tape next time
> ;-))  The traces that are not blown have intense
> pulse current cutting in
> the corners and cluster cracking...  Probably went
> to may 10's of thousands
> of amps...  The board just cannot be fixed
> reliably...
>
> I kept wondering if I should get another set of
> boards incase but kept
> putting it off incase I wanted to change something
> (which I do).  So It
> will be about a week to get new boards.  I am going
> to tear all the parts
> here apart to see if there is any hidden damage.  I
> will see if I can beef
> up the traces to keep the explosion in the IGBTs
> where it does little
> damage, but the current is enormous!!!   Not sure if
> anything I do would
> help that.  One lead of the IGBT is also "gone".  I
> think it is splattered
> on one of the transorbs.
>
> So my little buss noise experiment did not get
> finished.  Now it is the
> cross conduction test...  But no big deal other than
> having to wait about a
> week to get the new parts.  But I do think the
> ceramics across the H-bridge
> buss is a wonderful thing that should really help
> the noise in the box.
>
> So all you other DRSSTC guys out there can now sleep
> soundly knowing Terry
> finally blew his IGBTs up too :o)))
>
> Science marches boldly on ;-))
>
> Cheers,
>
> 	Terry
>
>
>



		
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