Re: Advice on short duration, high current electromagnet circuit
- From: Jessie <jessie.taylor91@xxxxxxxxxxxxxx>
- Date: Thu, 24 Sep 2009 12:44:05 -0700 (PDT)
Bob Eld wrote:
Maximizing force a magnet produces is a very different thing than maximizing
flux density as I assumed you meant when you said "magnets strength" above.
Sorry, I thought where there is smoke there's fire so they were one
and the same.
You must use an iron core to convey the flux to the pole tips where the test
piece will grab. Your pole tips should "match" the test piece and be more or
less of the same total area or you will be wasting flux. Both the north and
south pole tips should touch the test piece with the largest area available.
This makes a complete magnetic circuit that includes the test piece. The air
gap between the pole tips and the test piece should be minimized. This means
grind or polish the tips absolutely flat or to the contour as the test piece
if it's not flat.
In Year 12 physics what we learnt about magnetism was not very deep,
so please pardon my ignorance.
I know magnetic field strength decays in an inverse square law but
what is the maximum pull strength a modern, well designed resistive
and superconducting electromagnet can achieve on a given ferromagnetic
test mass at various distances (e.g. 1m, 2m, ...)
How can this pull strength be increased?
The same rule about maximizing amp-turns applies as above in the air core
case, but there is no point it going for a flux density larger that about
1.8T, the saturation point of the iron. Because the air gap is so small,
about .002cm with polished pole tips, this flux density is easily reached
with far fewer amp-turns than in the air core case.
But even if a ferromagnetic test mass has been saturated, surely
increasing the electromagnet's field strength will increase the pull
on it?
I'm just trying to see if this problem can be tackled from many
angles.
Design the core to maximize it's area at all points around the magnetic
circuit to the same or larger area as the each pole tip. If multiple pieces
of metal are used be sure to minimize the air gap which is always present
when two piece of metal are in contact by grinding and/or polishing the
contact areas.
Would having a very fine ferromagnetic dust on my electromagnet's
poles (analogous to thermal paste for cooling) help improve the
contact and reduce flux leakage?
Your magnet should be designed with the test piece in mind and need not be
larger than the area of the test piece dictates.
A well designed lift magnet can operate on very low power, maybe 100 watts
or less and pull thousands of Kg when the air gap(s) are very short. There
is no need for capacitive discharge or other gimmicks. Study the way
professional lift magnets are designed and constructed.
Thanks for your input.
Jessie xx
.
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