Re: variable electromagnet
From: D Akers (digikey_at_webtv.net)
Date: 12/30/04
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Date: Wed, 29 Dec 2004 21:34:18 -0500
"i would like to build a variable electromagnet that is directly
connected to a computer controlled (220v AC) dimming unit. i suppose
that dimming the electric current will lower the magnetic field and thus
its attractive force? the (somewhat creative) goal is to gradually
attract light weight suspended metal parts depending on the dimming unit
output.
- is this possible? if so, could you give any tips what to do or where
to look?
- dangerous? (e.g. to nearby computers or other electric equipment)
- what would be the range of such a electromagnet? the suspended objects
will be very light but some object-magnet distance should be kept."
___________________________________
Re;
Not sure about the AC dimmer control part; but I would suggest that you
use a full wave rectifier to provide DC current to the magnet coil. I
would also recommend that you use a soft iron core to minimize magnetic
"memory". You can scavenge them from discarded AM radios; they are used
in the "antennae coil". They are also found in some large inductors.
Assuming that would be meet your needs. Just remember that the magnetic
field strength will be proportional to the number of turns of wire you
wind around the core and the magnitude of the DC current flowing through
it. The more turns the greater the field strength. Thus, even a very
small current can create a powerful field with a large number of turns.
The "range" of the field will depend upon it's shape and that in turn
depends on the geometry of the coil/core assembly. If the ratio of the
length to diameter is greater, then the range of the field will be
greater.
You may also need a power resistor between the rectifier and coil to
provide the current control you desire. The characteristics of the AC
controller will determine this.
Yes, strong DC magnetic fields can do strange things to the electron
beam of cathode ray tubes; but they usually recover during the auto
degauss at start-up.
I hope that helps in some way...
-Dan Akers
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