Re: [PSUBS-MAILIST] motor seals

["Karl Fuller" <fullerk@voyager.co.nz>]

Hi Gary,
You could have some problems with the motor bearings in the long term. An
electric motor is not normally designed to take an end load on it's shaft as
would be applied if you had strong magnets pulling on one end. You may be
able to replace the bearings with deep groove bearings to compensate for
this. They must have overcome this with trolling motors sold with the
magnetic coupling.
Second is, as you mentioned, there are some problems to be solved if you
want to not lose too much energy on the prop shaft side. As well as the
thrust from the prop working on your Teflon or whatever washer, you also
have the magnet load working against the washer in the same direction. You
mention that there would be some loss of energy caused by the rotating
magnets and the effect of the resistance of the separating plate. All these
losses are starting to add up ! The oil in itself could be 10%.
You can get mechanical seals that are good for 14 Bar or 200PSI from
Johncrane and that is the first site I checked although the smallest was
35mm ID. I'm sure you can get smaller sizes.
Ceramic plate for the 'between magnet ' plate. Not wise I would have
thought. Even a small pressure differential could possibly crack it.
Polycarbonate is great, you can bend it double and it won't break. Acrylic
will shatter.
Good luck,
Karl.
----- Original Message -----
From: Gary R. Boucher <protek@shreve.net>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, August 16, 2000 1:02 AM..
Subject: Re: [PSUBS-MAILIST] motor seals


>      The magnets will not be "slowed" by rotation unless there is some
> conductor in the proximity to allow the fields to generate current.  The
> motor will not have to "work harder" to do anything.  The only headache is
> trying to create the drive shaft going to the propeller.  If done properly
> there will be very little energy loss with the majority of that loss going
> into the bearings and any portion of the coupling that has to rotate in or
> through the water itself.
>
> GB
>
>
> >The loss through heat may be a problem, but something else to consider is
> >that not very small electromagnetic fields get generated too, slowing the
> >magnets down and making your motor work harder to get up to the speed you
> >want generating more fields and causing more headaches than it's worth.
> >
> >Anthony
>
>