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From: Harry James (no email)
Date: Fri Jul 11 2003 - 17:50:04 EDT
I have have been thinking a lot on this, and I have come to the
conclusion that an AC gen. set is not the way to go on a family cruiser.
About 2-3 years ago I started seeing adds for DC generator sets in some
boating mags. I was scornful of this approach at first, but after a
lot of reading and cogitation I have developed a concept on electrical
supply that fits my me anyway.
I talked with one of the small NW suppliers of a DC Gen. set and he gave
this concept of how it should work. The plan is to keep the generator
running for long periods of time at low output, rather than a high
output alternator charging a large battery bank and then shutting down
At low RPM's the generator is very unobtrusive, almost inaudible. The
battery bank can be a lot smaller. Think of it as a small water storage
dam with a variable demand. The DC gen. acts as a refilling stream at a
steady but low rate, the Battery "dam " has to only be big enough to
supply power through the peak loads of the day plus you can up the
refilling rate if you have to. He told of one on land customer living in
Yakataga on the AK Gulf Coast who kept his Gen. running non stop (except
for oil change of course) for 5 years with no problems at a 800 Rpm
output and a steady 10 amps. Some of the suppliers of these DC
generators attach a water maker also, for further savings in stowage
space and weight. All the makers of these units with one exception that
I have discovered so far use a small light weight Kubota with heat
exchanger and water lift muffler. The exception is whispergen,
A New Zealand made unit that uses a Sterling cycle generator, that
supplies both heat and power. This is the unit that I first ran across
that got me interested in the idea of DC generation vice AC. There is a
German web site for the European distributor of the Whispergen, Victron.
They have a position paper on what I have been talking about written
much better and very convincing. Go to the Manuals link and read the
"Electricity on Board and other off grid applications
<http://www.victronenergy.com/BookRVA/ElectricityonBoard20030212.pdf>"
What would I do? I would get one of the small air-cooled Hatz diesels
and build a frame for it out of angled aluminum, add a 70 amp marine
alternator, encase it with sound proofing with a baffled inlet with a
close fit to the engine fan case, the exhaust would be in the baffled
air outflow. I would consider an electric fan capability for cool down
after shutdown. This unit, which I think I could construct to weigh less
then 120 lb., could be mounted under cockpit seat or wherever. If I
didn't have the time or inclination to mess with a home built outfit I
would buy one of the commercial DC generators. I would run everything
that I could off of DC power, with a large inverter to take care of the
rest. I would also have a couple of large solar cells to keep things
going in case of generator failure or time when the boat is unoccupied.
If money was no object, I would take a look at the Whispergen, which is
pretty speedy.
Some of the units sell with full automation, which I would avoid as
electrical stuff fails so easily cursing in salt water. I would get a
high quality battery bank monitor however.
HJ
sail_nutter wrote:
>I am currently working on the electical systems design for a new
>sailing catamaran that will be built over the next year. Space and
>weight are at a premium, but the boat will be somewhat power hungry
>(Instrumentation / Aircon / Heat / Entertainment etc.)
>
>After originally specifying a 12KW A/C genset to provide power for
>Aircon, battery charging, reverse cycle heating, and general A/C use -
> it has been suggested that I look at a DC system with inverters to
>supply general A/C use.
>
>The gains appear to be subtantial: Simpler systems, much lighter
>weight equipment and more efficient generating power being the main
>ones.
>
>I was wondering if any group members had any personal experience
>recommending (or warning against for that matter) a DC system, or
>could point me in the general direction of any reviews of such
>systems on the web or otherwise.
>
>Thanks in advance.
>
>
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