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Re: [PSUBS-MAILIST] diesel electric
Ahh, so a bit more complicated than it would seem ! I wonder what what Carsten's set up is ? If I could read German a little bit better I'm sure his schematic would tell me. I've been meaning to get my German friends to translate some of his web site !
Brian
----- Original Message -----
From: "Stephen Pearce" <sjpearceqld@bigpond.com>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, October 31, 2006 17:10
Subject: 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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