Re: [PSUBS-MAILIST] motor seals

["D. Blake" <dblake@bright.net>]

Hey Gary:
WOW! you were not exaggerating about the strength of these magnets.  I found
a surplus supplier on the net:
http://www.wondermagnet.com/dev/magnet37.html
Here's what they had to say about one of their larger magnets:

ITEM #37
Price: $35.00 ea.
dimensions: 1.5" diameter, 1" thick
We have a fair number of these large magnets in stock. These are Nickel
plated.
These magnets are not available through our online form, and are not for the
general public; we will sell these only for use by legitimate commercial or
industrial/research applications. To order these, please send us an email or
call (877) 944-6247. These magnets are not available for purchase through
our web site.
We take these precautions because, due to their size, these magnets require
extremely special handling. Gloves and eye protection must be worn at all
times. Folks who are unfamiliar with magnets of this strength are likely to
wind up hurt. We generally prefer to sell smaller items, so we would like to
sell these quickly and we would be glad to offer substantial quantity
discounts on large orders.

© 2000 ForceField
toll free (877)944-6247

A better item for our purposes would probably be
http://www.wondermagnet.com/dev/magnet45.html

TTYL,
Big Dave


-----Original Message-----
From: Gary R. Boucher <protek@shreve.net>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Tuesday, August 15, 2000 9:24 AM
Subject: [PSUBS-MAILIST] motor seals


>     I have an idea, not an original one I will admit, but I have some
>thoughts on magnetic coupling.  I played around with the idea of using
>magnetic coupling to make my scanning sonar have no seals, leakage, etc.  I
>purchased several rare-earth magnets from a surplus vendor.  Some of the
>new permanent magnet motors use these and most people can not imagine how
>powerful they can be.  I literally hurt my hand a couple of times when I
>got two of them in close proximity and they came together with my fingers
>in the middle.
>     I believe there may be a way to engineer a coupling with these
>high-strength magnets.  A couple of thoughts on that; these magnets are so
>powerful that when I took a piece of aluminum plate 3/16 inch thick, tilted
>it on a 45 degree incline, and released one of the flat magnets it creeped
>slowly down the aluminum.  This was due to the fact that the very strong
>mag flux moving through the aluminum (conductor) created currents in the
>metal opposing the flux created by the magnet.  This effect will drain
>energy out of any coupling system where metal is used between the
>magnets.  The faster the rotation, the more energy lost.  If the magnets
>are placed on either side of a flat plate for the coupling you have the
>additional problem of using a flat, non-metallic plate to withstand the
>water pressure.  I believe that a tube of non-metallic material perhaps PVC
>or fiberglass (not composite - carbon fibers conduct!) could be used.  This
>could withstand the pressures because of its geometry.  Also, I believe
>that the rotating components could be "potted" in an epoxy or even
>fiberglass or composite.  With the rotating components, you would not have
>to worry about small currents as you would with the housing, since both
>systems are turning at exactly the same RPM.  Metal could also be used for
>these components.  What ever was used for the rotating magnet holding
>system, you would have to balance it to minimize vibration.
>     If both motor and propeller magnets are rotating at the same speed
>there will be very little loss of power except for the drag of the water
>around the prop side magnet.
>
>Gary Boucher
>