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naok

Sat Oct 16 2010, 12:55PM

Registered Member #3128 Joined: Thu Aug 19 2010, 12:23PM
Location: Tokyo,Japan
Posts: 17

hi all!
Thank you for the other day.

I have another problem now.
My primary send out spark.
And,STB16NF06 Nfet on gate driver break down,when secoundry stream atack to primary.

what is problem?

Electronics H-bridge of 40N60 mini-brick IGBTs.
Tank Cap 7 parallel strings of 2 series .15uF 2kV caps (942C series by CDE).
Primary 10 turns of .25" cu tube. 2" spacing between turns, tapped at 3.5 turns.
Secondary 6.5"x22" winding of 30awg magnet wire. Double coat of epoxy for protection.
Toroids 23.2"x6".
Best Spark 33" point to point.

BPS 80
on Time 180uSec

Dalus

Sat Oct 16 2010, 01:31PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

Well over-coupling is the problem. This causes a too high voltage rise in the bottom part if the secondary and thus allows it to break out from there. If you don't use a protection scheme for the bridge (not coupled to ground via a coupling capacitor) it will develop a potential over the GDT strong enough to break down the insulation. So your gate drivers get destroyed by the high voltage.

HV Enthusiast

Sat Oct 16 2010, 02:32PM

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

Well, where is your strike rail? The plastic disk is nice and all, but you really need to have a grounded strike rail somewhere in there at least along the perimeter of the outside of your plastic disk for the arc to go to, otherwise it will just go around the disk (like you have pictured) and end up striking the primary.

Killa-X

Sat Oct 16 2010, 03:38PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

EastVoltResearch wrote ...

Well, where is your strike rail? The plastic disk is nice and all, but you really need to have a grounded strike rail somewhere in there at least along the perimeter of the outside of your plastic disk for the arc to go to, otherwise it will just go around the disk (like you have pictured) and end up striking the primary.

How much does that help though? I had this issue, mine was going from primary to secondary. If you put a strike rail, does it really help that much to prevent it, so i can go much higher feed? Mine travels like 4 inches. Instead of going AROUND the disc, it goes through the disc, where I have like 5mm thick of hot glue!

My coil must be made right, I had times where I didnt see/haer it flashing over, and found on the vide, it was flashing over every break. good ones too, nothing blew...everything was fine.

Dalus

Sat Oct 16 2010, 07:51PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

A strike rail only helps to minimize the problems from topload to primary sparks. Secondary base to primary arcing needs to be stopped first, so lower coupling first. Protect the H-bridge with a coupling cap to ground. Shield the primary with a strikerail.

HV Enthusiast

Sat Oct 16 2010, 10:14PM

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

Killa-X wrote ...

EDIT - Yes, i was referring to Case 3 from topload to primary strike.

Well, right now you have a problem where the arc is going completely around the acrylic disk and then striking the primary. A strike rail isn't going to prevent primary strikes 100%, but it will help if it is done correctly and certainly the path i would choose if i had to correct the issue you are having. I would put it right on the perimeter of the disk.

And as always with high voltage, "it will find a way."

Others on this site have had great results with those plastic disk shields. So maybe they could chime in and provide their own advice and suggestions.

Luca

Sat Oct 16 2010, 11:55PM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

I agree, overcoupling is the main cause.

Rise your secondary some in from the base of the primary coil until strikes from secondary coil stop. You should also achieve longer sparks from the toroid (with your setup, with the right coupling and tuning you should achieve at least 50in sparks)

Obviously, a strike rail is also a good idea...

Regards,

Luca

Killa-X

Sun Oct 17 2010, 05:01AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

EastVoltResearch wrote ...
And as always with high voltage, "it will find a way."

Always true. Even if you have all things cleaned up. If it wants to flash over, it WILL flash over. Even if it means getting through the acrylic tubing by breaking it down. Always something to remember. Thanks for suggestions!

naok

Sun Oct 17 2010, 07:25AM

Registered Member #3128 Joined: Thu Aug 19 2010, 12:23PM
Location: Tokyo,Japan
Posts: 17

Thank you all!

I tryed to use strike rail.
So,Secoundry stream never struck to primary coil!

Now,Does primary-Secoundry still have over-coupling?
I want to have nice couple

,if secoundry stream make progress.
Should I have more long distance between secondary and primary?

teravolt

Sun Oct 17 2010, 07:08PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

do ytou have a picture or video while running

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