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DRSSTC Primary strike failures

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Bennem

Mon Mar 10 2008, 03:15PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

I was wondering if any of you DRSSTC guys have had many IGBT failures when
the coil arcs to either the strike ring or the primary coil?
I have read about some guys like Terry Fritz adding a 'Protector' which consisted
of a 2.5uF cap in series with a ten turn inductor on each his H-bridge outputs,
enabling his over current to 'catch' and stop the coil before destruction of his IGBT's.
I have also read of some guys adding a cap on both the + and the - of their buss supplies to earth, helping with this problem.
I also see that some guys coils can take racing sparks between primary and secondary coils without bridge failure whilst others just have to have a 'wisp' of a spark touching their primary
and boooom.....the bridge blows!
I demo'd my coil at this years Nottingham Teslathon which was working great untill a
spark curled around and sneaked its way between two strike rings and hit my primary,
blowing half of my full bridge of HGT1N40N60A4D IGBT's
( i'm not a 100% sure if the arc hit the primary as the video of its destruction is not all that clear)

Any thoughts?

Mel.

HV Enthusiast

Mon Mar 10 2008, 03:18PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Yes.
Thats why a strike rail is required.

Bennem

Mon Mar 10 2008, 03:41PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

EastVoltResearch wrote ...

Yes.
Thats why a strike rail is required.

I installed two strike rings.....i guess a third can't hurt.....lol

Austin

Mon Mar 10 2008, 05:00PM

Registered Member #1169 Joined: Wed Dec 12 2007, 09:16AM
Location: Portland OR
Posts: 251

This is most likely a dumb question.... but why can't someone just shield or enclose most of the primary in like a copper box or something?

Mates

Mon Mar 10 2008, 05:09PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Do you use TVS? They should help with problem too...

HV Enthusiast

Mon Mar 10 2008, 07:41PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Austin wrote ...

This is most likely a dumb question.... but why can't someone just shield or enclose most of the primary in like a copper box or something?

Because it will act like a shorted turn (donut shaped as hole for secondary is required)
Very bad.

Bennem

Mon Mar 10 2008, 07:53PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Mates wrote ...

Do you use TVS? They should help with problem too...

Yes.....i use TVS,
though i haven't used them across the gates as i've used back to back zener diodes,
i think i saw Steve Connor once post that some TVS have greater capacitance than the IGBT
you are driving, so i used zeners instead across the gates, but i see that Dan McCauley uses
both zeners and TVS in his miniBrute circuit.

Mel

bob golding

Mon Mar 10 2008, 08:12PM

Registered Member #1084 Joined: Mon Oct 29 2007, 08:58PM
Location:
Posts: 28

hi mel,
just from looking at your setup it doesnt seem wise to have a strike rail as low as your bottom one. could attract arcs to the primary,rather than prevent them. i havent built a soleniod type primary so dont have any experience of primary strikes to them but i would get rid of the bottom strike rail and lift the top one up a bit. of course the arcs will go were they want whatever you do. having the breakout point on the top will help as well. i dont have any experience of DRSSTC's yet ,but it looks as if the spark propagation is very simular to a SGTC.

bob

Bennem

Tue Mar 11 2008, 09:24PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Bob,

Thanks for the tip,
i shall try a different strike rail arrangement...

Mel

Tom540

Wed Mar 12 2008, 02:28PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

Hey Mel,

Ive never had an IGBT failure from striking the primary but i did have two MMC failures from this.
I use tvs's across each IGBT from collector to emitter.

Now I separate my MMC into 2 parts so that I half the caps are on one side of the bridge output and half on the other. I then have a string of tvs's from the primary side (the top of the primary) of the MMC to earth ground. Works perfectly. The TVS string is set for just under the caps rating and doesn't negatively effect performance. With no strike rail. Maybe worth a try for you.

-Tom

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