Skip,
Some basics: First divide marine refrigeration into two classes, engine
driven and electric. Engine driven systems on sailboats are always
holding plate systems. The compressor can process a lot of BTUs in a
short time while the engine is also charging batteries or propelling the
boat which makes them very efficient. They are great if you are on board
most of the time and the alternator is your primary battery recharging
system. You can freeze the plates as you charge and/or motor. The down
side is that you can't leave the boat for more than a couple of days to
explore an island and box temps tend to oscillate.

Electrically powered systems have one primary advantage: with good
controls, shore power, a lot of solar panels or a wind generator and
lots of wind they can be made to operate unattended. This can be a
distinct advantage if you are off the boat for more than a day or two.

They can be further divided into AC and DC systems. AC systems are
usually a motor driving either an automotive or small commercial
compressor either directly or through a belt. They are closely akin to
engine driven in that they normally use a holding plate and can freeze
the plates almost as fast but away from shore power the engine usually
must be running to generate the power needed to run the motor which
means it has the same limitations plus not being quite as efficient away
from shore power due to losses in the alternator, battery charging and
inverter.

DC systems can be divided further into holding plate and evaporator
systems and the compressors into discrete compressor/motor assemblies or
hermetically sealed compressors. The discrete compressors are similar
to the AC system being linked to the motor either directly or via a belt
and usually freezing a holding plate. There is a practical limit to DC
of 1 1/2 HP motor so they are not as powerful as AC or engine drives.
They also tend to be noisy.

Hermetic DC systems usually drive an evaporator and are more closely kin
to a domestic refrigerator. Most are based on one of the Danfoss
compressors which are gradually getting more efficient. They cycle on
and off all the time and will therefore maintain a more constant box
temperature and, with solar panels or other alternate charging source
can operate constantly while the boat is not in use but they can consume
20% to 40% more energy.



Skip Gundlach wrote:

I may even have it from somewhere before, but the recent conversations on
reefers brought it to mind:

Someone on these lists built a direct drive 12V compressor for
refrigeration. My recollection has it connected to cold plates. It was
designed to do what an engine drive would do, but not run the engine. At
the time I saw it, it was new. If they're reading, I'd be interested to see
a report on its efficacy.

How much power did/does it take to operate? Was the size of the compressor
notably less than one on the engine, and if so, what is the relative run
time? In the end, are you happy with the outcome? If not, or even so, is
there anything you'd have done differently if you were doing it again?

Thanks.

L8R

Skip (and Lydia, by proxy), thinking of how to use the lovely cooling system
on the boat without running the engine or the AC air-cooled system, either


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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