Re: [PSUBS-MAILIST] Pressure compensation

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

I had a friend years ago who was layed-off from the factory we both worked
at because of slow business due to foreign imports.  After a while--with
some pull--he found a job working along side his brother as an electrician
for a local contractor.  One of the first jobs he was involved in was
replacing the lighting fixtures in a grocery store.  Eventually he came into
contact with a live 120v wire while standing on a 10ft step-ladder.  Not
really being an electrician; and not really used to an occasional electric
shock, he jumped off the ladder in a panic and fell through a plate-glass
window costing several hundred dollars.  Of course he was immediatly fired
on the spot.  Hey, the jig was up OK?  Well, not really.  It seems he very
soon filed a lawsuit against the contractor he was working for, and settled
out of court for a sizable amount of capital.  He then split up with his
wife he met at the factory and hooked up with his former High-School girl
friend who--he had much earlier confided in me-- had a father who had mob
ties.  Well, Eddie is now a successful business man that owns and operates a
chain of busy video rental outlets, and a lucrative vending machine
business.
I guess the point I'am trying to make is that 120v is  an arbitrary figure
without the all important amperage figure.  I have personally held onto 120v
from a wall socket without ill effect other than a vibration throughout my
arm up to my shoulder.  Admittedly, the first time was a 'shocking'
experience, but curiousity soon took hold.
I once took a 1-year Vocational course in Heating and Air Conditioning.  The
instructer demonstrated his ability to withstand a 120v shock by holding
onto the bare wires of an extension cord while a student plugged it in.  He
jerked momentarily, but was instantly able to assure us that little
discomfort was present.
Oh yes, 3-phase watch-out! Especially 440.  It will kill you instantly!
No, 120v is little to worry about really so long as you isolate the grounds,
and pay attention to the amperage.
TTYL,
Big Dave

P.S.  While bringing in the barn a wagon load of tobacco as a very healthy
18-year old, I was indirectly struck by a bolt of lightning.  I was knocked
unconscious for a short time, but regained myself after a minute or two with
a strong pain in the chest and weakness in the legs.  I have a lightning
bolt tatoo on my forearm to remind me of the event.  It was a shocking
experience!
-----Original Message-----
From: Gary R. Boucher <protek@shreve.net>
To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
Date: Saturday, August 12, 2000 1:24 AM
Subject: Re: [PSUBS-MAILIST] Pressure compensation


>     It could work if high enough in power.  But you do have the 120 volt
>in water issue.  I feel like it would be easier and more efficient
>(possibly safer) to compensate a trolling motor.  You wouldn't have to
>worry about the brushes wearing out.
>
>>What about using the motor from a submersible pump?  Granted it will no
>>doubt be AC, but you could use a relativaly cheap inverter as long as the
>>amperage was not too high.
>>Big Dave
>>
>>-----Original Message-----
>>From: Gary R. Boucher <protek@shreve.net>
>>To: personal_submersibles@psubs.org <personal_submersibles@psubs.org>
>>Date: Friday, August 11, 2000 11:31 PM
>>Subject: Re: [PSUBS-MAILIST] Pressure compensation
>>
>>
>> >Jon,
>> >     You're right in that the mentioned method is a much better way of
>> >compensating.  I wonder if anyone has ever been successful at using a
low
>> >viscosity oil in a trolling motor.  It would be an interesting
experiment
>> >in the direction of a low cost compensated thruster.  It almost makes me
>> >want to go get a trolling motor and experiment.  I wonder if the
armature
>> >would have too much drag against the oil and how much power you would
loose
>> >in the process.  I would think that cooling would not be a big problem.
I
>> >would suspect that real thrusters for submersibles that are compensated
in
>> >this way have special armatures.  Probably the same oil used in
submersible
>> >pump applications would work.
>> >
>> >GB
>> >
>> >At 08:16 PM 8/11/00 , you wrote:
>> >>On Fri, 11 Aug 2000 22:00:37 -0700, "Gary R. Boucher"
<protek@shreve.net>
>> >>wrote:
>> >>
>> >> >      The trick is having the pressure inside the motor the same as
the
>> >> > outside pressure, or at least close.  If you set the pressure inside
>>the
>> >> > motor at a certain value and ascended the pressure inside is greater
>>than
>> >> > outside.  If you dove beyond the set pressure you have more pressure
>> >> > outside.  One method of pressure compensating a motor is to place a
>>rubber
>> >> > bladder with air in the water close to the motor and run a tube from
>>the
>> >> > bladder to the motor housing.  As the sub dives the pressure on the
>> >> bladder
>> >> > increases and so does the inside motor pressure.
>> >>
>> >>Just as a point of interest...
>> >>
>> >>In deep professional-quality thrusters, they typically fill the
thruster
>> >>housing (and thus the motor) with oil, which makes the whole deal
>>basically
>> >>non-compressable. Instead of using a seal, they use a magnetic coupling
to
>> >>turn the propeller. This gives a thruster that can be used to full
ocean
>> >>depths.
>> >>
>> >>Later,
>> >>Jon
>> >>
>> >>--------------------------------------------------------------
>> >>    Jon Hylands      Jon@huv.com      http://www.huv.com/jon
>> >>
>> >>   Project: Micro Seeker (Micro Autonomous Underwater Vehicle)
>> >>            http://www.huv.com
>> >
>