Re: [PSUBS-MAILIST] Pressure compensation

[Subscuba@aol.com]

 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. 

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. 

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

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.

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.

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

Ken Martindale