Date:         Thu, 22 Jun 2006 08:09:07 -0700
Reply-To:     Michael Elliott <j.michael.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Michael Elliott <j.michael.elliott@GMAIL.COM>
Subject:      Norcold results (long)
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I installed a Norcold DC0040 into Mellow Yellow and during this week's
shakedown trip, I monitored its performance.
First, generalities: it kicks butt on the Dometic 182R. Despite all the
tweaks and modifications I made to the Dometic, it never held cold below
50F when the outside temperature climbed past 80F. This reefer, on the
other hand, is rock-steady at all times, even at 90F outside.

The one issue that concerned me is battery draw. Before putting Mellow
Yellow to bed at the end of camping season last year, I finished
installing the solar setup. I now have two BP Solar 45W panels that I
can haul anywhere within 40 feet of the van where there's sun, and a
Blue Sky Company Solar 2000E controller to stuff the electricity
generated by the panels into the Optima aux battery. Even so, if the the
consumption of the reefer (along with this little notebook that we use
to watch movies on, and the stereo system I installed . . . oh yeah, the
fluorescent lamps I installed, too) . . . well, if running all these
things depletes the battery quicker than I can charge it back up, then I
will need to re-configure my setup.

I had read that the Norcold draws 2.5 amperes when it is running, and,
according to . . . someone, I don't recall if it was the mfgr's website,
or some other Vanagon list member who said this, but anyway . . . I have
read that the reefer runs about 5 to 10 minutes per hour. At 10 minutes
per hour it comes to 0.4 ampere-hours (2.5/6) so I reckoned my Optima
would do nicely.

Theory. Reality turned out to be somewhat different. I noticed during
the afternoon that the reefer ran a lot. I was busy setting up camp so I
didn't make an effort to log its on and off times, but I estimate it ran
50% of the time. I didn't really use much in the way of other
power-consuming accessories. A blip of the coffee bean grinder to make
myself a cup of drip Ethiopian Fair-Trade organic coffee, a minute @
250w with the mini food-processor to make my lunch. It's a couple days
away from the longest day of the year, so besides one LED reading lamp,
and the car stereo (with subwoofer amp off it draws about 0.3A), the
only appliance I ran after dinner was the reefer.

The Norcold was still cycling on and off when I went to bed. If you put
things just so on the stove top they won't rattle too much, which leaves
only the mild brrrrrr sound of the compressor. At 3am I was awakened by
the squeal of the low-battery alarm. I peered at the voltmeter . . .
don't remember what it said, exactly, being farsighted and groggy, so I
just turned off the reefer and hit the aux battery main shutoff. Figured
I'd sort this out in the morning. I adjusted the alarm to go off if the
battery hits 10.7 volts; according to Optima's tech support, their
yellow top batteries don't want to get discharged below 10.5V.

Of course I tossed and turned for a while, questioning my assumptions,
wondering if I had a defective refrigerator, whether the solar charging
system will be able keep up with this energy-consuming monster, and
wondering whether the food in the reefer would be lukewarm in the morning.

I noted a few things this morning. First, I had left the inverter on
when I went to bed. It doesn't draw much when idling, but it has its own
low-battery alarm, and it triggers at a higher voltage than the one I
installed. So I might have been hearing that one. Second, the battery
voltage was sitting at 11.7V, when I got up, which is normal bounceback
unloaded bounceback voltage. Third, it was 38F inside the reefer. Didn't
lose any appreciable heat.

So I made some coffee (had enough juice to grind another batch of beans,
left the reefer off, then went outside to place the panels in a spot
where I could see I would have sun a bit later in the morning. As the
sun started to hit the panels, I watched the ammeter in Mellow Yellow go
from zero to over 6 amps of charging current.

The Norcold does draw, as claimed, 2.5A. But it runs a lot more than the
five to ten minutes per hour claim I had heard. Another interesting
quality is that it does not seem to be thermostatically controlled,
i.e., the knob on the front does not set the internal temperature.
Rather, the knob seems to determine how long the compressor runs. I
recorded the start/stop times of the compressor during two hours of
operation. The first run was between 10am and 11am. The the outside
temperature was 85F. I set the knob to the minimum "1" position. The
compressor started every 10 minutes, exactly, and ran for 3 minutes,
then shut off for seven minutes. The internal temperature ranged between
40 to 41F. The second run was between 12 noon and 1pm. By this time, the
outside temperature had climbed to 88F and the temp inside the Norcold
had gone up some, so for this run, the knob was set to "3," the
manufacturer's recommended normal position. As before, the compressor
started every 10 minutes, exactly, then ran for 6 minutes before
shutting off.

This behavior contributed to the middle-of-the-night discharge of my
house battery: whether it needs to or not, this reefer turns on every 10
minutes.

FOLLOWUP: I am mistaken: the Norcold does demonstrate thermostatic
control. I put a warm liter bottle of water into it and the internal
temp climbed to 48F,  then I turned it to "3" and it ran for 30 minutes
to bring it down to 40F then shut off. I guess the thing likes to keep
to a 10-minute cycle when doing maintenance cooling.

How many ampere-hours are needed to run this thing? Certainly more than
0.4Ah, which is based on 10 minutes of operation every hour, or a duty
cycle of 17%. When set to "1' the duty cycle is 30%, when set to "3" the
duty cycle is 60%. 30% of 2.5A is 0.75Ah, and 60% is twice that. So a
reefer set to "3" will, over the course of a 24-hour day, require 36
ampere-hours. But as last night suggested, it does not need to be on all
night long to keep things cold. Tonight I will shut it off at bed time
and see how cold things are in the morning.

So, if you want to take advantage of the superior cooling ability of the
Norcold, you should consider mounting a thermal sensor in the reefer so
you can monitor its interior temperature and adjust by hand, as needed,
to conserve power. Plan on either plenty of battery capacity to run it
for more than a day or so, unless you can stuff power back into the
battery, either with an external generator, by driving for a while, or
other means, such as a solar rig, like I have.

Another consideration I had about this reefer was its noise level. The
Dometic was, near as I could tell, dead-quiet. It possesses no moving
parts, unless you count liquid and gas. Once in a while the rear fan
would kick in during a hot afternoon, but at night, it made less noise
than Mrs Squirrel's breathing, and she's pretty quiet. The Norcold, on
the other hand, has a compressor, with oscillating bits of metal hurling
about.

This thing is quite audible. It makes a "brrrrrrrrr" noise like a Magic
Fingers bed. Is it intrusive? That depends on who's doing the listening,
how light a sleeper they are. That unexpected evening solicitor's knock
on the front door might be a disturbance to me, but for another person
it might be a welcome opportunity to spend a few minutes with a stranger
who is selling something which might be of possible interest. I can hear
this reefer, but by pushing around on the front, sides, and top of the
sink cabinet, I can tell that it could be made to run a lot quieter if I
can figure out what bits are vibrating in sympathy and anchor them.

Summary: I'm a little disappointed by how power-hungry the Norcold
DC0040 is. But Mrs Squirrel and I only camp when it is sunny and nice,
so I expect to count on plenty of Mr Sun's rays to keep the Optima full.

Next morning follow-up: the battery barely made it through the evening,
even under minimal usage. I think the cheap Harbor Freight trickle
charger that I had hooked to the battery while Mellow Yellow sat under
its cover during off-season may have damaged it. I shut the reefer off
at bedtime, and the internal temp was 52F this morning.

--
Mike Elliott