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Frank Without getting in to a Pissing competition I will quote my
friend who is an electrical engineer “the motor (AC) that has been
selected will handle full load at all speeds, yes without using braking
resistor/dynamic braking.” I am not an expert but I have consulted
several and not one has suggested a DC system in practice will be practical
without manufacturing a Customised purpose specific motor like in conventional
military subs. If you are talking about small DC motors like on the K boats or
Kara then DC is the way to go. The size of the sub Brian has on the drawing
board he will need a 600+ Volts DC for the system to work. That’s a lot
of 2 volt Cells or even 12 or 24 volt cells. Ask Carsten, I believe several
months ago he was making substantial modifications and now requires 600 Volts because
of his choice to go DC and had not yet concluded the make up of his final
system. The problems and expense of a 600Volt system and the cost of
the switching and associated components are huge. For example a 75KW DC motor
is in the range of 28K to 30K (USD) new. The AC equivalent is about 12K and
Reconditioned about 6K. I would also fell less comfortable in a vessel with a 600V DC
system that under certain circumstances may be subject to partial flooding. You
will need room to house all those batteries in water and air tight ‘spark
free’ containers. By all means run your hotel load off 12V DC batteries but DC
setups for 50+ HP can be impractical and cost much more in real terms. I went
through this process with the initial view of wanting a DC only system but I
have modified my design as a result of being prepared to accept that there are
experts with experience in this area that know more than I do. I want a successful
P-sub at the end of the process even if that means that my initial design was
impractical due to my ignorance. Frank if you can design a better propulsion system using 50+
volts DC motors and Diesel Gensets that overcomes the problems and impracticalities
I have described I would be sincerely interested in looking at it and if it is superior
to my current design adopt it as my system of choice. Respectfully (sorry Jay for borrowing your tag line J ) Steve P -----Original
Message----- Just a
quick note.... D.C. motors have more torque at lower speeds, where the power
band of an A.C. motor isn't realized until the optimum speed of the particular
A.C. motor is achieved. The
universal availability of A.C. components doesn't work either, when you
consider the use of different Hertz configurations in foreign countries. D.C.
is D.C......no matter what country you're in. Everybody in the world uses 12
volt chargers.....and batteries the world around are all compatible. My jumper
cables built in Chicago, will connect to my Toyota, carry a charge to my wife's
Volvo, which will get us to my broken down Harley out on Interstate 5, and
getting me back home with time to see Monday's game on my 12 volt T.V. Stick
to D.C. and save yourself a lot of expense and grief. Frank
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