Re: [PSUBS-MAILIST] Pressure compensation

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

-----Original Message-----
From: Subscuba@aol.com <Subscuba@aol.com>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Saturday, August 12, 2000 9:49 AM
Subject: Re: [PSUBS-MAILIST] Pressure compensation


> I use a pressure compensated Minn Kota trolling motor (with the normal cup
>seal) on my sub. The pressure compensating device is a simple SCUBA
>regulator. I have had no leaks or  problems yet. I adjusted the SCUBA
>regulator to provide a slight positive pressure to the air spaces in the
Sub.
>It does use some air which I supply
>from a small tank (about 30 cubic feet). The air from most SCUBA shops is
>fairly clean and dry. With the pressure compensation my depth is limited by
>other concerns. My sub is a wet sub which makes it simpler to get out.


The external motor pods of a 1ATM could be designed not unlike a miniature
wet-sub and make good use of such a system.

>I thought about using oil but was concerned about two problems:
>
>1) Some oils will dissolve the insulating materials used in the
construction
>of the motor.
>
>2) The brushes which carry 50 amperes in my case would be exposed to the
oil
>and would, I believe, contaminate the rotary connection made by the
brushes.
>I think the brushes would not function very long. Even use of Fluorinert
>wouldn't prevent this problem since decomposition of the Fluorinert would
>occur.

Use of an oil that is typically used in refrigeration compressors--or in my
mind submersible pumps--would have to remain O2 free to prevent corruption
of the extremely delicate magnet wire sheath.  O2 mixed with the oil creates
an acid that attacks the windings.

>Besides all the above, I don't like the problems associated with the mess
of oil.


No mess if the unit is entirely sealed from outside elements which would
necessitate a magnetic coupling to the prop-shaft.  This idea of magnetic
coupling has tremendous implications for our concerns.  Why not we
investigate this technology to the fullest extent possible?  With over a
hundred psub members, we could collectively overcome almost any obstacle.

>Whoever posted the suggestion that 120 volts was safe is misleading. Under
>certain conditions even 12 volts can be fatal. Factors such as skin
>resistance and current paths through the heart are complex enough, but 120
>volt AC or DC can definitely be fatal. Generally shock hazards are due to
>currents through the heart which in turn are driven by the applied voltage.
>The subject is fairly complex and I don't understand it all even though I
>design high voltage power converters.

I was simply conveying my own personal experiences with electricity along
with some other information to put it all in perspective probably for those
who enjoy deconstructionist theory ie. I was 'framing'.  Still, never do
this at home!

>My sub uses a battery bank of 36 volts. When the skin resistance is reduced
>by exposure to sea water, 36 volts is not something I want to be exposed
to.

Then isolate your grounds.

>Good luck to the builders and dreamers, we need both.



>Ken Martindale
>
>