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