Welcome
Username or Email:

Password:


Missing Code




[ ]
[ ]
Online
  • Guests: 35
  • Members: 0
  • Newest Member: omjtest
  • Most ever online: 396
    Guests: 396, Members: 0 on 12 Jan : 12:51
Members Birthdays:
One birthday today, congrats!
Frog_Qmak (34)


Next birthdays
03/01 mostlymacros (46)
03/02 Staff (31)
03/02 Doubl3 Helix (33)
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 :: Tesla Coils
« Previous topic | Next topic »   

SCR power control for an SSTC any ideas?

 1 2 3 
Move Thread LAN_403
Dr. Dark Current
Wed Aug 15 2012, 11:37PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The current pulses of a non-controlled rectifier and a cap are limited by the dv/dt of the mains voltage, which is finite. The current pulses are defined even with no line impedance, no capacitor ESR/ESL and ideal diodes. But if you apply voltage pulses, they have infinite dv/dt. I believe you know the equation for instantaneous current through a capacitor: I = C * dv/dt. I think it should be obvious now and I'll stop here as I don't want to get into an argument...
Back to top
brandon3055
Thu Aug 16 2012, 02:14AM
brandon3055 Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271
Or do the scr's replace the bridge rectifier?

Edit I will mostly be using this to limit current draw in CW mode
Back to top
Goodchild
Thu Aug 16 2012, 04:07AM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
We will have to agree to disagree then, I also don't want to get into an argument. I was simply trying to share what I learned from my experience with building SCR supplies for coils.


Destroyer of mosfets, yes that is exactly how it would be setup. If you plan to use it to limit current draw though I would warn against it. Go with a variac or an interrupter controlled method PWM or mains sysncs such as Dr. Dark current was talking about.

I used SCR supply in past to precharge my coils only, I never used them for any long period of time at < 95%
Back to top
Steve Conner
Thu Aug 16 2012, 06:30AM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The current pulses are worse with SCRs. The reason is that an uncontrolled rectifier does its charging at the peaks of the line voltage, which are quite flat. This tends to flatten and broaden the charging pulses. But a SCR can be fired at any time.

The charging current into a capacitor depends on dv/dt, but in the steady state, the SCR fires as soon as the line voltage gets above the capacitor voltage. So there is no massive pulse, it is just the dv/dt of the line voltage. That is a minimum at the peaks, where regular rectifiers operate, and maximum around the zero crossings. Indeed this is where the controlled rectifier performs worst.

I ran into one problem with my controllers (I have two designs) When trying to charge a big capacitor bank, the system could become unstable at low voltage. The current pulses took bites out of the line voltage big enough to disturb the zero crossing detector.

On the plus side, SCRs are very rugged and don't care about high peak currents. I've blown lots of fuses and breakers with my controllers, but no SCRs. It's always good practice to include a series inductor though, to make sure that the critical di/dt of the SCR isn't exceeded. The inductance needed for this is much smaller than what would be needed to improve the power factor. If you're running a big SCR brick off household wiring, the impedance of the mains wiring may be enough to take care of it.
Back to top
brandon3055
Thu Aug 16 2012, 01:14PM
brandon3055 Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271
Goodchild wrote ...


Destroyer of mosfets, yes that is exactly how it would be setup. If you plan to use it to limit current draw though I would warn against it. Go with a variac or an interrupter controlled method PWM or mains sysncs such as Dr. Dark current was talking about.


Which is right? A or B or am I right that the scr's replace the Bridge
Back to top
Steve Conner
Thu Aug 16 2012, 01:20PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've used B, for a coil where I wanted to run off either SCRs or a variac.

I've also done it with two SCRs replacing two of the four bridge diodes, and a full-wave doubler with both diodes replaced by SCRs. They all worked fine.

I drove all the SCR gates from the same source, using pulse transformers for isolation. You're not really supposed to do that, but it doesn't seem to cause any ill effect. One of the SCRs will just "ignore" the pulses and the other will fire.

A will work but is a waste of two SCRs.
Back to top
teravolt
Thu Aug 16 2012, 02:00PM
teravolt Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
why not just add 1 or 2 or ohms 200w resistor between the cap and diode or a inductor in series withe the AC to cushion the switching periods?
Back to top
Goodchild
Thu Aug 16 2012, 04:41PM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
teravolt wrote ...

why not just add 1 or 2 or ohms 200w resistor between the cap and diode or a inductor in series withe the AC to cushion the switching periods?

An inductor is exactly what you would add to smooth out the current pulses in series with the AC line. What I was saying before lines up with what every one seems to be saying but maybe I'm just bad at getting my info across.

Depending on where the SCR fires in relation to the line voltage the pulse can be very short and large. IF it is fired right at the start however it will act like a regular rectifier.

In the past I have used the SCR in the doubler configuration with 2 cap. It seem to work well.
Back to top
teravolt
Thu Aug 16 2012, 09:54PM
teravolt Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
if you used a micrccontroler a stepped turn on might work to
Back to top
brandon3055
Thu Aug 16 2012, 10:05PM
brandon3055 Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271
Thanks everyone you've been a verry big help now all I need to do is find time to build it :)
Back to top
 1 2 3 

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.