If you stick with just DC power and not AC/DC power the reliability factor
is much greater. The wiring becomes much more intense. The KISS principle comes
into play here as well as the money
Carl
D.
----- Original Message -----
Sent: Tuesday, October 31, 2006 7:22
PM
Subject: Re: [PSUBS-MAILIST] diesel
electric
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: <personal_submersibles@psubs.org>
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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