----- Original Message -----
Sent:
Wednesday, November 01, 2006 10:53
Subject: RE:
[PSUBS-MAILIST] diesel electric
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., Bahamas
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-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org] On Behalf
Of
> ShellyDalg@aol.com
> Sent: Wednesday, 1 November 2006 4:43
PM
> To: personal_submersibles@psubs.org
> 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
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 D.
>
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