If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #4762
Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93
Hi everyone. I'm building typical "big DRSSTC" now, and while designing the full-bridge (based on CM300DY-24NFH) decided to use these interesting capacitors (EC UL4-15418K 20.0±10%), which are quite cheap on Ebay and are (AFAIK) the ultimate solution of the low inductance bridge design. With their 20 uF @ 800VDC rating and literally zero distance between them and IGBT module terminals, it seems that they are the best available option for this application. But I've never seen them in successful construction (like Steve Ward's, Eric Goodchild's and others), only Aerovox snubber caps (2 uf 1000V), which, I believe, come from the same Ebay seller and for the same price, but due to their 10 times lower capacitance are, surely, not so good as these 20uf caps. So what's the answer, why everyone (at least everyone who uses surplus components for big DRSSTCs) don't use these? Maybe there's something I just don't know about them?
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Do those holes go all the way through? If so, then yes, you will have equal if not lower inductance between the caps and igbt's. The "tabs" used in the aerovox caps have little inductance themselves, but allow copper buss bars to be easily mounted without a cap blocking them. the tabs sit the caps off to the side, increasing L, but don’t get in the way. typically the bus caps sit directly on to of the igbt's, not snubbers. Reason?
After powering this coil at 800VDC for extended periods of time, I experienced an IGBT failure (note that this was the first failure in over a year). The IGBT that failed also had its TVS string come disconnected (though the TVS's were not damaged). So I began to investigate what was going on here, and found a significant oversight in my original design. The problem, as expected, had to do with voltage transients. I turns out that the inductance between my large electrolytic capacitors, and the bridge, along with the decoupling film caps located on the bridge, had a resonant frequency of around 40khz! My rail voltage was ringing up to 160% of the input voltage, so at 800VDC input, this would have presented 1280V across the 1200V IGBT devices... yikes! Here is a picture of the output from one of the half-bridges in this condition:
Steve’s coil resonated at ~40khz: the same frequency that his dc bus resonated at. Just make sure they have extremely low esl's, and keep inductance low between the bus caps and the igbts's because the snubbers by themselves aren't going to resonate. The 'lytics may however.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've also had this problem. My coil operated at 220kHz and the DC bus structure ended up resonating with its snubber caps at around 440kHz. I had to tinker with the values of the snubber caps to move the resonance away.
I think it is better to just use electrolytics and work at minimising the inductance. Because of their high capacitance, the resulting resonant circuit has a very low resonant frequency and also very low Q.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Snubbers are nice, but I don't feel using tens of microfarads of brute-force snubbage is the way to go. According to Powerex, one should always use a laminated bus structure between the bus caps and the bricks to minimize inductance. See (note that the example bus inductance calculation doesn't apply to DRSSTC's since they are not hard-switched! but it gives a good indication of how important a low-inductance bus is). Back to the OP's question, those snubbers are fine. I've used them in a large induction heater, and I've seen them used in a big (10KW+) coil.
Registered Member #4762
Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93
Well, I'm not using these as snubbers (40uF snubber capacitance would destroy IGBT bricks in a moment), but as DC bus capacitors, along with proper electrolytics (2 series + 2 parallel EPCOS 6800uF 400V) across C1 and E2 IGBT module terminals. Thanks for answers and for bridge self-resonance issue, will have to check it before launching at full power. Here's the bridge design, if anyone is interested
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
zrg -
Aluminum bus bars? If so, you need to make sure that all your bolted connections are very tight to maintain nice low-resistance contact. And, make sure that they are bare aluminum, and not clear anodized.
Registered Member #4762
Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93
Have been testing the first coil for several days. Seems to work fine, w/o any heating of the bridge or MMC (they remain cold even without a cooler). About 2 meters sparks, with OCD set to 800-900A. Steve Ward's driver and interrupter are really a salvation for DRSSTC beginners. If I could get enough room and power to throw 1000A+ into the bridge, and enough funding to purchase remaining parts and arrange all the electronics into a box, I shall start the thread in Projects section, I think.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Through-hole-mount bus film caps (CM300 & CM600 direct mounting)
