Welcome
Username or Email:

Password:


Missing Code




[ ]
[ ]
Online
  • Guests: 25
  • Members: 0
  • Newest Member: omjtest
  • Most ever online: 396
    Guests: 396, Members: 0 on 12 Jan : 12:51
Members Birthdays:
One birthday today, congrats!
MicroTesla (34)


Next birthdays
07/09 Avi (41)
07/09 Jannick Hagen (15)
07/10 Sparcz (69)
Contact
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.
Forums
4hv.org :: Forums :: High Voltage
« Previous topic | Next topic »   

Using SCRs

1 2 
Move Thread LAN_403
Firefox
Mon Aug 04 2008, 12:02AM Print
Firefox Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
I have been browsing SCRs and looking at what I need to build some wire exploders, induction launchers, and the like, but I am unable to understand how you guys pick your SCRs. It seems like more than just the current rating, which to me makes sense as the most important item when you are talking about putting energy into a near short circuit. Someone said that with 60 or 120J, a certain (dont remember which) SCR could handle it, but in a short circuit, it would have slightly exceeded the pulse current rating. So is pulse current rating the most important aspect of the SCR, or is there more to it than that?
Back to top
Myke
Mon Aug 04 2008, 12:09AM
Myke Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
There is peak reverse voltage rating to take into consideration because there will be some high frequency ringing.
Back to top
Hon1nbo
Mon Aug 04 2008, 01:00AM
Hon1nbo Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
also consider the voltage spike coming from the gate of the SCR to the trigger circuit (had SERIOUS problems with this)... Then there is the switching time/voltage (how long until on, and how low E until off).
Back to top
Shaun
Mon Aug 04 2008, 01:58AM
Shaun Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
Well the thing is, the most common use of SCRs by amateurs (and 4hv members) by far is in coilguns. Coilguns will have peak currents that are FAR lower than the applications you discuss (induction launchers/wire exploders) of similar energy. The pulse length will be much shorter in duration, but things still are looking bad for SCRs under those conditions.

Not saying they absolutely can't be used, its just that a 300J coilgun will require a much smaller SCR than a 300J ring launcher. An SCR also has a rather limited dI/dt (relative to a spark gap), which is bad for induction launchers where you need the current to be able to ramp up as fast as possible. Again, SCRs can be used, but once you get higher than a few hundred joules one is almost forced to switch to a spark gap.

To answer your original question, I think the most important rating is Itsm, the non-repetitive peak surge current. Keep in mind, this rating is given for a duration of 8.3ms (half a 60Hz sine pulse). 8.3 ms is quite a while, even for coilguns. So its fairly reasonable that this rating can be overshot by quite a bit before your SCR detonates. Just how far over you want to try and go is up to you...scope+current probe helps here.
Back to top
rp181
Tue Aug 05 2008, 12:40AM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
I talked to some engineers at a power semiconductor company, heres what they said:
All rating usually have about 10% saftey margin, also, pulse rating is for 10ms, for coil gun applications, pulses are less then 1ms. The surge rating exponentially goes up as time goes down, it is safe as long as you keep the pulse short enough for the power, and wait a couple of seconds between shots.
Back to top
...
Tue Aug 05 2008, 01:58AM
... Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I would look at the I^2t 'fuse' rating, since that is what will dictate wether or not you will melt the die. Also very important is the di/dt rating, since you are talking about HUGE di/it for things like ring launcher.
Back to top
Firefox
Tue Aug 05 2008, 04:07AM
Firefox Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Ok, say I was discharging a 450V 2200uF pulse cap into a dead short with an SCR. What determines the rise time and A/us? I know the Io is determined by the voltage of the cap and resistance of the load. Is it a combination of the resistance and inductance of the load, or just the inductance?
Back to top
Myke
Tue Aug 05 2008, 04:15AM
Myke Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Resistance and inductance. The resistance is pretty low but it's still there. Same with inductance. Don't forget the ESR and the inductance of the cap too. Isn't there a calculator out there that calculates the max pulse current when given the resistance, capacitance, and inductance?
Back to top
Firefox
Tue Aug 05 2008, 06:55AM
Firefox Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
I'm not scared of a little paper/pencil and calculator work, so a formula (and perhaps an article/explination on this topic) would be fine too.
Back to top
rp181
Tue Aug 05 2008, 04:52PM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
what is di/dt?
Back to top
1 2 

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob

Go to:

Powered by e107 Forum System
 
Legal Information
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.