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 #3323
Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116
Thanks for reminding me about your FEMM section, now that I have got FEMM working on my computer, this is a really useful page, mostly for how you have explained things so clearly.
Registered Member #3323
Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116
Here the variable PSU is, customs charged me nearly £20 for VAT and handling D:
Any suggestions/errors? By the way, the PSU has a switch in built, that one there is just for show. Tell me if more details are needed. This was made using XCircuit.
Registered Member #3323
Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116
Today, I am quite sure that when I tested the PSU above, at school the multimeter possibly wasn't connected to the PSU output terminals particularly securely and a pretty big puff of white smoke forced its way out and since the blue LED indicating that the voltage was being regulated is now not lighting up.
I tested it at home before and it worked fine then... D:
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Navrit Bal wrote ...
Any suggestions/errors? This was made using XCircuit.
The SCR is drawn with an unusual symbol. Normally the triggering goes from gate to cathode, and the SCR is a three-terminal device. Okay maybe that's just how XCircuit wants to draw it, but I just thought I'd check.
Cheers, Barry SHAMPOO WARNING: I figured out why I've gained weight. The shampoo I use in the shower that runs down my body says, "for extra volume and body." Going to start using Dawn dish washing soap. It says, "dissolves fat that is otherwise difficult to remove."
Registered Member #3323
Joined: Sun Oct 17 2010, 03:19PM
Location: West Midlands, UK
Posts: 116
I know I haven't posted recently, but I have been working on the coilgun quite a lot over the past 2 weeks and I'm near a firing test. Everything has been tested separately all that is left is the circuit as a whole.
I have been discussing this with Mr Abdullah and he was saying that the anti-parallel diode might cause massive suck-back. Since basically every other coilgun design which I have seen uses an anti-parallel diode, I was wondering whether anyone else has anything to suggest on this.
Using I can see what he means, however since the inductance would be changing throughout and energy would be lost by various means, surely it would therefore be more complex than that. Can anyone offer an opinion on this as well?
EDIT: Also I just tested at 5V and 50V, and when I tested at 5V the voltage jumped up to 9V and stayed there. At 50V when I turned the switch on, there was no voltage change at all. The SCR worked as expected when it was not connected with the exact same triggering circuit. Why is is that Barry's Mk 2 + 3 work but mine does not, for this section, they are identical...
With another test at less than 9V, the voltage did not jump up again as before...
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Navrit Bal wrote ...
I have been discussing this with Mr Abdullah and he was saying that the anti-parallel diode might cause massive suck-back. Since basically every other coilgun design which I have seen uses an anti-parallel diode, I was wondering whether anyone else has anything to suggest on this.
If you compare two identical coilguns, one with an anti-parallel diode and one without, you will find that the diode extends the time that current flows in the coil. The amount of time increase is longer for very-low-resistance coils.
The first question becomes: Is it a problem that timing becomes longer with a diode?
Generally speaking, you can adjust the timing through several means, so the bottom line is that once your coilgun is working you'll tune it up for best performance. You will be testing with various voltages, projectile length, projectile mass, and probably even the number of turns on the coil. I think you'll keep adjusting it until you don't get the DSE (dreaded suck-back effect). So, no, the effect of a diode upon timing is not a problem.
The next question is: Is an anti-parallel diode really required?
This is where opinions may reasonably differ. It is well-known that electrolytic capacitors may be damaged if their voltage goes negative. To avoid damage we should design something to avoid the situation; adding an anti-parallel diode is the cheapest and easiest solution by far. Solutions include a V-switch design, a diagonal half-bridge design, and other more complicated designs.
My own approach is to not use anything to prevent negative voltages. My thinking is that the situation is very temporary; if my capacitor gets a negative voltage it will decay to zero in a short time anyway through the coil resistance. It's a conscious part of my experiments. I am hoping to find out if this is short enough to avoid damage. Indeed, I really want to learn how long these electrolytic caps will survive when mistreated this way. So far none of my caps have failed, but then again I've only use low energy shots and haven't yet hammered them into their limits.
Bottom line is that electrolytic capacitors will last longer in coilguns with an anti-parallel diode. How much longer is uncertain.
Navrit Bal wrote ...
Using www.falstad.com I can see what he means, however since the inductance would be changing throughout and energy would be lost by various means, surely it would therefore be more complex than that. Can anyone offer an opinion on this as well?
I didn't fully understand the Falstad link, sorry. I like to use this RLC simulator and turn on "capacitor voltage". But then again my simulator doesn't show the effect of a diode. (One of these years I should fix that, lol.)
You can ignore the change in inductance; simply changing inductance alone does not change the total energy in the system. You can ignore the energy that's converted to kinetic energy; the conversion rate is so low (a few percent) that other effects are much more dominant.
Navrit Bal wrote ...
EDIT: Also I just tested at 5V and 50V, and when I tested at 5V the voltage jumped up to 9V and stayed there. At 50V when I turned the switch on, there was no voltage change at all. The SCR worked as expected when it was not connected with the exact same triggering circuit. Why is is that Barry's Mk 2 + 3 work but mine does not, for this section, they are identical...
With another test at less than 9V, the voltage did not jump up again as before...
It sounds like you have some kind of circuit problem going on. If the capacitor voltage stays high, then there's likely a problem in the SCR or its triggering. Try temporarily replacing the coil with a simple resistance. An ordinary light bulb works great for this test, even at 300+ vdc, you should see it briefly light up and go dim, and measure zero voltage at the end.
It can also be very helpful to build a small test jig for your SCR. This is a good way to tell if the SCR works at all, which is otherwise really quite hard to figure out. A simple test stand could be a 12v automotive battery in series with the SCR and an ordinary light bulb. When triggered, the light should glow dimly and stay on until you disconnect the battery.
Cheers, Barry Sitting in front of my computer, sculpting my forearm muscles.
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.
Coilgun Questions
So, no, the effect of a diode upon timing is not a problem.