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New DRSSTC, secondary to primary arcing is OK!

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LAN_403

Reaching

Wed Aug 13 2008, 06:32PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

One of my big coils i build for a big energy company is now emc tested, like any device which is for show and enetertainment etc. they added such a filter on the ground path and the coil succeeded the hard test, and there is no additional rf ground or something.

Mathias

Wed Aug 13 2008, 06:40PM

Registered Member #1381 Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74

Reaching wrote ...

One of my big coils i build for a big energy company is now emc tested, like any device which is for show and enetertainment etc. they added such a filter on the ground path and the coil succeeded the hard test, and there is no additional rf ground or something.

Some kind of LCL T-filter or what?

Alexandre

Wed Aug 13 2008, 06:40PM

Registered Member #1228 Joined: Tue Jan 15 2008, 01:08AM
Location: Curitiba, Brazil
Posts: 162

Nice coil Steve!!!!!!

teslacoolguy

Wed Aug 13 2008, 07:50PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

I noticed that on the pcb layout the cathode of the led is not connected to anything. I am assuming that the led is just a power light and i can connect it to the - trace that is right next to it.

Ken M.

Thu Aug 14 2008, 01:01AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Hey Steve I imagine by filter you mean an rf filter like most people here use to reduce the rf picked up by the power lines being carried into the low voltage circuits, unless most rf, emi or whatever theyre called, unless they have the ground going straight through the casing and into the plug, I'd sa they don't work to well using house ground. Considering thats how I grounded out my minicoil and if there was a stereo on in any other room in the house they would pick up that signal and amplify it to with an audible range.

HV Enthusiast

Thu Aug 14 2008, 01:43AM

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

Nice work Steve. Your on your way to becoming an expert on EMI.
If you go into power electronics in the industry, this is a tremendous asset to have as 99.99% engineers have zero clue in this area.

That being said, you should definitely pick up the following book and add it to your library.

Its the bible as far as EMI design is concerned.

http://www.hottconsultants.com/book.html

http://www.pentodepress.com/books/noise.html

Steve Ward

Thu Aug 14 2008, 05:32PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I noticed that on the pcb layout the cathode of the led is not connected to anything. I am assuming that the led is just a power light and i can connect it to the - trace that is right next to it.

Oh gosh, hit "ratsnest"! Might need to include that instruction on the website, it fills in all the ground plane areas, of which that LED and other components connect without traces.

If you go into power electronics in the industry, this is a tremendous asset to have as 99.99% engineers have zero clue in this area.

I just got an offer for being a power and control systems R&D engineer for an aerospace firm

. I think when i told them that i had the same IGBT bricks the guy had on his desk, except i run them at higher frequencies and currents than they did, he was set

.

Im gonna try to get ahold of that book, thanks for the suggestions! Id imagine they will have some literature at this place too, since we arent just born with it in our heads. Many of these EMI problems became much more clear in my mind after looking at this problem, Im glad i did it. And now i have a wickedly robust coil that can spit out 43" sparks from an 11" resonator

.

One last tidbit of useful information for people building coils of similar geometry (this coil is basically a direct rip of Dans Minibrute, but i think that was also kind of a rip of my DRSSTC-3, which wasnt all that original anyway...). Take a sheet of plastic, something that exceeds the total outer diameter of your strike rail by say 2" (so you have 1" of overhang), cut a hole in the center to pass the secondary though, and set this sheet of plastic on top of the strike rail/primary. This will, at least in my case, completely eliminate arc-over between the strike rail and secondary, even at full voltage with no breakout point! I should mention Bert (also a forum member) recommended this to me in the past, and i didnt think it would be that useful, but wow! I think it helps because the plastic is placed perpendicularly to the electric field lines, and as having a higher dielectric constant, it helps spread out any sharp E-field distortions over the surface of the plastic, so you dont get corona forming as easily. Now this is opposed to putting plastic parallel to the E-field lines, where it merely provides a better surface path for the arcing to take place!

Right now im using just a 1/16" thick PP sheet, but ive also tested using 1/4" polycarbonate sheet on one of my larger coils, it worked great too. You could probably even use cheap 1/10" thick acrylic sheet from the hardware store in a pinch, but that stuff is tricky to cut a circle in without destroying it!

Bennem

Thu Aug 14 2008, 05:58PM

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

Steve Ward wrote ...

And now i have a wickedly robust coil that can spit out 43" sparks from an 11" resonator

Hi Steve,

Excellent coil!!

Are you now running at 240 volt mains input for 43 inch spark output?
What ferrite beads have you used on your GDT primary?
Thanks for the plastic cover tip.....i'll try that one

Mel

Steve Ward

Thu Aug 14 2008, 06:37PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Are you now running at 240 volt mains input for 43 inch spark output?

Nah, 140VAC, so about 200VDC maximum on the bridge. I had to lower the secondary so that the start of the winding is about 1" below the top primary turn. JavaTC said this is like .165 coupling coeff. Then i had to further detune the primary, all the way to the end (9 turns) to push some extra spark out of it.

EDIT:

What ferrite beads have you used on your GDT primary?

Ive used both regular shaped toroids, and wound the cable through 2-3 times, or the long tubular beads found on most EMI suppression stuff (i think i got mine from computer monitors), and just slide it through there once, they seem to have much higher permeability and this is probably the preferred method.

Tom540

Tue Aug 19 2008, 06:54AM

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

This is all really weird. My coils would survive strikes to the primary all the time but what was getting destroyed was the MMC but it wasnt right away. Then I added the TVS primary protection to save my MMC. I'm now wondering if the primary strikes are effecting your MMC.

Also on a side note I build up some half bridge coils and they would die every time when hit with primary strikes. Took out both igbt's. Never happened on a my fullbridge. I even had a strike directly to full bridge PCB and still nothing. Don't think I'll be using half bridges anymore.

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