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 #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
More turns = greater resistive losses = more heat
No, do the math
Take a given coilform, so constant winding length per turn, constant total winding area, and constant volume = constant weight of copper wire. To simplify things, assuming the filling fraction is constant with wire diameter, as it's not a material but a practical factor, and very slowly varying at that.
Assume a number of turns N.
Winding length proportional to N wire area proportional to 1/N
so resistance proportional to length/area or N^2
Power can be written P=I^2.R, so I=sqrt(P/R)
therefore I proportional to sqrt(P)/N
magnetic field is proportional to I.N, the Ns cancel to give sqrt(P)
I'll leave it as an exercise for the reader to show exactly how the constant of proportionality between field and sqrt(power) is related to the weight of copper used (hint, as spend on copper goes down, spend on energy goes up for a constant field, no surprises there then).
In answer to the question in first post, the best way to build a very strong electro-magnet is to use DC, an iron core, and then sufficient copper and power to saturate the iron. Once you are well into saturation, extra power is just pissing in the wind.
I recently helped my son with a physics project, building a small air-core electromagnet for linearity testing of a linear Hall element. I discovered that the 25mm dia, 25mm long bobbin would take 2watts continuous, but would take 200 watts for the few seconds required to take a reading for the same temperature rise. So if you can be disciplined enough to demonstrate your magnet 5 seconds on, 15 minutes off, you can use a very small coil to get the iron into saturation. Even a 30 second power pulse would allow you much greater power than continuous, and 30s would seem like continuous to your awestruck onlookers.
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
Wow! I am impressed by all of the responses. I took the primary from a microwave oven and wired it in series with a 60w bulb and ran 132vac from a variac through it and nothing happened. No reaction to iron or neodymium. When the primary is still attached to the iron core it makes a loud thump and then a 60hz hum when powered on but, still no reaction to iron objects. When exposed to neodymium the hum stops though.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Electromagnets don't work with AC, you need a unidirectional flow of current inorder to create a magnetic field. With AC all you get is a magnetic field that flips back and forth at 60hz...
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
aonomus wrote ...
Electromagnets don't work with AC, you need a unidirectional flow of current inorder to create a magnetic field. With AC all you get is a magnetic field that flips back and forth at 60hz...
No, electromagnets work just fine with AC. Surely you're aware of ac-driven solenoids and doorbells and the like. An oscillating magnetic field attracts iron very much like a steady magnetic field.
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.
Designing 2kW electromagnet
