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Brian, You need to do a little basic electrical calculations (I had to refresh
my memory and quickly found a calculator on the web). For best
efficiency, say you use 460 VAC at 66 A and guessing a power factor of 1 (can
be a lower decimal), you will need 52.6 Kw to run the motor. This is
under ideal conditions, not taking into account power losses, hotel loads, and
the massive starting current surge. Please do your basic homework instead of asking us to tell you
something isn't possible. 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 Sean, I'm
starting to think more and more about building a sub around the power plant
rather than the other way around. For one thing a friend of mine just
gave me a brand new 50 hp motor which is wired for 208 - 230 / 460
it is 132 / 66 amps that is starting and running I
think. It is set up where it will power a third leg for 3
phase. I think I would use a gear box to vary the prop speed, that
way the motor could run in its most efficient speed. My idea
is to get a 25 - 35 Kw diesel generator as the power plant. Do you think this
would be do-able? would I lose a lot of efficiency when I try to
power the motor through an inverter from the batteries? Brian ----- Original Message ----- From: "Sean T. Stevenson" <cast55@telus.net> To: < Sent: Tuesday, October 31, 2006 20:54 Subject: Re: [PSUBS-MAILIST] diesel electric > This really depends on what sort of power levels you're talking
about. > In high power applications, DC stuff is both expensive and hard to
come > by, but it does have some advantages. In DC motor control,
maximum > torque is achieved by always applying the full rated voltage of
the > motor, but varying the duty cycle (pulse width modulation).
In AC motor > control, the AC power source is rectified to DC and then inverted
back > to AC at a controlled variable frequency to control speed.
In the case > of multiple motors, it is easier to synchronize two or more shafts
to > the same RPM in an AC system. AC components are generally
smaller and > cheaper than their DC counterparts. > > To make a swooping generalization, I would assert that AC systems
are > well suited to large subs, while DC systems are better suited to
small > (typical psub) subs. > > -Sean > > > Brian Cox wrote: > > Sean, >
> Thanks,
that was exactly what I was asking. I wasn't clear on whether or not to
use an AC system since that is how many generator systems are sold. But
it sounds to me like it would be better to use a DC generator to power DC
motors and to charge the batteries which are DC power. Would there be any
advantage to using AC other than availability? For instance, are AC
motors easier to control electronically as far as using a speed controller? > > > > Brian > > > > > > ----- Original Message ----- > > From: "Sean T. Stevenson" <cast55@telus.net> > > To: < > > Sent: Tuesday, October 31, 2006 09:25 > > Subject: Re: [PSUBS-MAILIST] diesel electric > > > > > > > >> You need to determine your power requirements, and
design/assemble a system > >> accordingly. It is not necessary to have your
diesel engine mechanically > >> coupled to the prop shaft(s), although theoretically this
will give a bit of an > >> efficiency gain since you don't need to convert
mechanical to electrical power > >> and back again. If you do this you need to be close
to the prop shaft, and have > >> some sort of clutch arrangement to switch between the
diesel engine and the > >> electric motor(s) to drive the shaft. Running
electric power only to the prop > >> shaft allows you to place the diesel engine anywhere you
want within the vessel > >> (i.e. low, with mechanical and acoustic isolation).
Modern generator and > >> converter efficiencies are good enough that the
efficiency loss from doing this > >> is not significant, and it gives you much more
flexibility. Next, you need to > >> decide whether you want AC or DC motor(s).
Generators typically output AC, > >> which needs to be rectified to DC to drive a DC motor
controller, and to supply > >> battery charge circuits. AC can directly drive an
AC motor controller. The > >> batteries themselves are DC, so their output can either
be regulated to drive a > >> DC motor controller, or inverted to drive an AC motor
controller. > >> > >> To start, determine the required shaft power, and add the
power requirement of > >> your system and house electrical loads. Taking the
efficiencies of all motors, > >> converters, etc., into account, you should be able to
work back to find how much > >> power your engine needs to output. You need an
engine with slightly more output > >> than this, since the worst case scenario is that it will
be providing propulsion > >> and house power, while simultaneously charging depleted
batteries. > >> > >> Next, size your batteries according to the desired dive
duration, taking into > >> account the manufacturer's specifications on discharge
extent vs. life (i.e. > >> discharge to 80% before recharge will make a battery last
much longer than > >> discharging to 60% before recharge), and also the
conversion efficiencies of the > >> required inverters, rectifiers or motor controllers. > >> > >> If I understand your question correctly, a "regular
diesel generator" is a > >> combination diesel engine and AC generator unit?
While this could be used to > >> drive an AC motor, or with a rectifier circuit to drive a
DC motor, using a > >> separate engine and motor/generator set gives you greater
versatility since you > >> can convert from electrical to mechanical power or vise
versa. Having a > >> separate small generator (actually engine/generator
combination) dedicated to > >> battery charging is not necessary, but might be nice from
a redundancy > >> perspective, since in the event of a main engine failure
you could still charge > >> your batteries and get home on battery propulsion. > >> > >> All of these components can be purchased off-the-shelf -
much cheaper if you > >> find them on the used market. In any case, start
from your sub design, find > >> your power requirements, and then put together a system
to suit. > >> > >> -Sean > >> > >> > >> Quoting Brian Cox
<OjaiValleyBeeFarm@dslextreme.com>: > >> > >> > >>> Hi All, >
>>>
One thing that I am not really clear on, maybe somebody > >>> will know, is if I'm going to put a large diesel
electric power plant in > >>> my large sub ( something like Carsten's) can I
just use a regular > >>> diesel generator and then regulate the power to
charge the batteries > >>> with electronics or would it be better to have a
specific generator for > >>> that particular job. > >>> > >>> Can the same generator that is used for charging the
batteries also be > >>> used to power the sub? > >>> > >>> Can this set up be purchased of the shelf or does is
need to be custom > >>> built? > >>> > >>> Thanks > >>> > >>> Brian > >>> > >>> > >> > >> > > > > > >
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