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 #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
I use a 1kohm 30W resistor for my bank, since after calculating it (972J) i found it would be fine..Then calculated the mosfet, and found that a 600V 1A mosfet is plenty. and well, tested it. and works. Mosfet just sends the power after the resistor to capacitor ground. Slowly discharges, and it does heat a little, but nothing major.
So. 450V 9600uF = 972J, or 972 Watts a second.
450V^2 / 1000ohms = 202.5 Watts.
972 / 202.5 = 4.8 seconds to discharge the whole capacitor bank. Which is roughly true, i know for sure its around 5 seconds after other resistances in wires.
so the resistor gets 202.5 watts...for for 5 seconds, it doesnt heat much at at all, as long as i dont do it a lot. Yes I know this is for something way different, but it should apply for you, to "safe discharge large capacitors"
202.5 / 450V = 0.45 Amps, So I got a 600V 1A mosfet, works.
I did a calc for you, the 800 ohms for fun, and it came to about 80 seconds...to discharge..
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
Luca wrote ...
Just a curiosity: why do you need such huge capacity for a DC power supply?
Regards,
Luca
the capacitor is a smoothening capacitor to smoothen the DC before going into a voltage regulator, and because of the load I am using, I want it to slowly go from the voltage fed to the load to zero, instead of just abruptingly turning off the power. (kind of soft shutdown) but I do not want the capacitor to do this for a long period of time, just the under 2 minutes kind of deal.
also, radiotech, I messured the capacitors with a capacitance meter, and they read 100,000uF (0.1F) give or take a few uFs and before I used these capacitors I "chilled" them (I left then in -10 or so overnight) so the work fine, this approach was recomended by my welding teacher, and It works good for all my capacitors.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
It would be interesting to see how the esr of various electrolytics is affected by keeping them in low temps, like a fridge freezer for about 24 hours if you have some expendable ones to try that on.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
And incandescent bulb is an ideal discharge device. It has high resistance when hot, and low resistance when cold. Therefore the discharge curve is much more linear (read: faster) than the usual long exponential decay curve. As a bonus, they're a visible indicator of voltage level. And best of all the lamps are common and inexpensive.
I discharge my 7kJ capacitor bank into an ordinary light bulb with a light switch. While stored the switch leaves the bulb connected, ensuring a residual charge does not build up while unused.
Cheers, Barry Please accept my friend request because based on your name, city, and thumbnail photo, I'm certain we're soul mates
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
A 100 watt 120 volt lightbulb has a cold resistance of 10 ohms, a teflon coated machine tool shatterproof bulb will retard the expulsion of glass if you manage to burst it electrically.
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.
safely discharge large capacitors?
