Re: Thruster Construction

["STEVE McColman" <steve_mccolman@hotmail.com>]

>From owner-personal_submersibles@psubs.org Sun Jun 21 18:55:51 1998
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>Date: Sun, 21 Jun 1998 21:48:57 EDT
>To: personal_submersibles@psubs.org
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>Subject: Re: Thruster Construction
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>Steve,
>
>I would think you would need someone who could do a thermal analysis 
for you.
>My opinion is that if you had good thermal contact between the steel 
pipe and
>the motor housing the surrounding sea or fresh water would provide a 
more than
>adequate sink to prevent the motor from overheating. If the motor is 
made to
>run in free air you may have a safety margin for cooling. The answer is 
not
>simple since the cooling depends on the construction of the motor. Some 
motors
>are made with forced air cooling and do not conduct much heat through 
the side
>walls. If this is the case you may have a problem.
>
>I estimate the motor at 12 horsepower draws 270 amperes from 36 volts 
assuming
>92% efficiency for the motor, almost 10KW of power.  I'm interested in 
what
>size your batteries may be  to provide this kind of discharge current. 
If your
>batteries are sized to provide more than a few minutes of operation 
your Sub
>must be fairly large. My question is what size is your Sub? 
>
>Good Luck and have fun,
>
>Ken Martindale 
>


I got my motor and batteries out of an electric lawn tractor.  I have 
six 6-volt deep cycle batteries.
The tractor would run full speed for over an hour so I assume that my 
sub will also run for an hour at full speed.  The batteries themselves 
are quite a bit larger than an average 12-volt car battery, but fit very 
nicely in the back of my sub, which is approximately 14 feet long.  
If anyone has any ideas how I can cool my motor, if it was enclosed in a 
housing, please let me know.


                                 Steve McColman, Vancouver Island


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