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RE: [PSUBS-MAILIST] diesel electric
Brian
>From memory you are going to require more than 35 HP which is about as
large as low voltage (<120VDC) off the shelf DC motors get.
Before you make a decision you may want to quote DC motor prices in the
KW (HP) range that you will require for your particular project. The
voltage required also climbs significantly over certain outputs (400
VDC+) and will require components that cannot be purchased off the shelf
so easily. This may also apply to high voltage DC Gensets. Most DC
Gensets are just AC rectified to DC anyway from what I have discovered.
One other advantage of AC is that parts are cheaper and globally
available off the shelf. My understanding is that some AC motors can
also deliver greater torque at lower rev's when compared to DC motors.
Maybe some list members may have a different view.
Regards
Steve P
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brian Cox
Sent: Wednesday, 1 November 2006 10:23 AM
To: personal_submersibles@psubs.org
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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