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Carsten, On the nuke boats we used what they called a Motor-Generator Set (MG)
that was an AC unit that could run as a motor or a generator and a DC unit that
would due the same. When drawing off the batteries, the DC motor would turn
the hard connected AC generator to produce AC power. It worked the opposite
way to charge the batteries (say in your case, you wanted to charge batteries
from shore power instead of listening to the din of the diesel running). Very
reliable, when the USS Guittaro sank at the pier during new construction due
poor trimming policies, the AC lights could still be seen glowing through the
submerged open hatches…power being provided by the MG sets! Think we may
have spoke of this previously. R/Jay Respectfully, Jay K. Jeffries Andros Is., It is the mark of an educated mind to be able to entertain a thought
without accepting it. - Aristotle To run a AC-Motor from a DC battery needs a special frequency drive which can handle the high difference in voltage between nearly empty and full DC battery. For example : DC battery empty = 344 Volt DC battery full = 400 volt Most frequency drives are programmed that way that the quit if voltage is 10% lower than nominal Voltage.. 400 -40 V = 360 Volt My problem is that I have a DC-Motor/Generator which load and run from the DC battery - no problem - but all the secondary system like air compressors and bildge pumps runs on AC.. so I need a AC- Network This required a frequency converter - and this seems is not off the
shelf. There seems some available in the e-car market, the UPS-market and the solar-energy market which can handle that.. regards Carsten "Stephen Pearce" <sjpearceqld@bigpond.com> schrieb: > 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 :-) ) > > Steve P > > > > -----Original Message----- > From: owner- > [mailto:owner- > ShellyDalg@aol.com > Sent: Wednesday, 1 November 2006 4:43 PM > To: > Subject: Re: [PSUBS-MAILIST] diesel electric > > 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 > 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 D. > ************************************************************************ ************************************************************************ ************************************************************************ The personal submersibles mailing list complies with the US Federal CAN-SPAM Act of 2003. Your email address appears in our database because either you, or someone you know, requested you receive messages from our organization. If you want to be removed from this mailing list simply click on the link below or send a blank email message to: removeme- Removal of your email address from this mailing list occurs by an automated process and should be complete within five minutes of our server receiving your request. PSUBS.ORG 603-529-1100 ************************************************************************ ************************************************************************ ************************************************************************ |