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 #2727
Joined: Tue Mar 09 2010, 02:39PM
Location: Montevideo - Uruguay
Posts: 33
Hello all. I want to know the flashover voltage in air for normal carbon resistors of high ohmic values as used in electronic circuits, from 1 / 4 W, 1 / 2 W, etc. (through hole resistors, no surface mounting). Is difficult to find this data. Does it change much this voltage if the resistance is immersed in an insulating medium such as vegetable oil? Thank you very much
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
youwont be able to find this type of data. you should run your own experiments with a NST + Variac, then destroy some resistors. also, the resistance will change a great deal (additional sintering) as the flashover voltage is typically 10-15 times greater then the spec'ed max voltage. beware if you series to many youll get other problems too.
flashover is typically not important to know, other limiting factors are.
If our search function here on the forum were not so shitty, i could have found my thread for you, but i have class now.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The regular 1/4W type, only about 250-500V. 250 is usually what it says on the datasheet. They mean it, I have had them break down and destroy my tube amp circuits.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve McConner wrote ...
The regular 1/4W type, only about 250-500V. 250 is usually what it says on the datasheet. They mean it, I have had them break down and destroy my tube amp circuits.
whats spec'ed and what they will flashover at are two completely different questions.
And yes, I too would say they self-destruct quite easily, taking other circuitry with them.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
The actual flashover voltage varies with humidity and even more with contamination. For a quick estimate look up datasheets for similar devices !
Then there's the question of safety, if this is for a Marx etc. then a fault will not harm you, if it's for a meter etc. then you don't want to be at the end of a chain of resistors that may flash over and connect you to eht.
If you thoroughly clean the resistors (e.g. wash with alcohol) and immerse them in oil the voltage rating will increase massively (>10x) to the point that dissipation will probably be the limiting factor. Potting in epoxy, resin, wax etc. also increases voltage ratings.
Registered Member #2727
Joined: Tue Mar 09 2010, 02:39PM
Location: Montevideo - Uruguay
Posts: 33
Thank you for your answers. I know what to expect working with HV. I´m going to make a 100 chain resistors to measure almost 50 kV, but I will be looking at the voltmeter at a very prudent distance while the circuit are energized. And I know about the five golden rules about working with voltage. Anyways, I'll test some resistors, to verify the they can stand the voltage. Can anyone give me a reference PDF for common resistors ?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I have had sparks jumping across a 0.6 watt resistor, might have been good 5kV and the resistance was still the same after the "test", though I don't remember the resistance value...
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.
Flashover voltage for normal resistors
