Date: Fri, 7 Jul 2006 16:14:32 -0700
Reply-To: "Mike \"Rocket J Squirrel\" Elliott" <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Mike \"Rocket J Squirrel\" Elliott" <camping.elliott@GMAIL.COM>
Subject: Norcold refrigerator + modest solar rig, a report [LVC]
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Hi all,
Three weeks ago I reported here how my newly-installed Norcold DC0040
refrigerator drained my under-seat Optima battery before dawn.
In brief: I was mistaken to think that the Norcold would run only 5 to
10 minutes an hour. I don't know where I got that impression. A more
accurate value is between four to six minutes out of every ten minutes
in my conditions of 85F ambient temp (same inside the van), or a duty
cycle of between 40 to 60%. When running, the Norcold draws 2.5A, so
that comes to 1 to 1.5 amp-hours per hour during my warm daylight hours.
Fewer at night when it's colder outside and inside.
I received numerous helpful suggestions from several Vanagon.com folks,
including, some tech-heavy, battery fundamentals and energy management
responses from Dennis Haynes and David Beierl. To summarize from all the
helpful folks:
1. The run time I got from my Norcold is about what should be expected
from this unit. So if I want to use it, I better have sufficient power.
2. The Optima battery is simply too small to count on for overnight
running, despite my careful nighttime energy managment.
3. Something beefier, like a Group 27 or 31 deep-cycle would kick the
Optima's butt. This is what I was told.
The only remaining problem would be whether my modest solar rig could
keep up with the demand.
So, I pulled the Optima and moved a bunch of my tools under the seat,
and installed a deep-cycle Group 31 100 amp-hour house battery under the
bench seat, with 4 gauge wire run to it from the charging relay. Then
Mrs Squirrel and I went on a three-night camping trip in the Cleveland
National Forest. I was deeply concerned that unless I ran the engine to
add amps back into the house battery, I would be running out of
refrigeration before dawn. "Great," said Mrs Squirrel, "nothing like
running the engine for an hour or so on an already hot day." Yeah, I know.
Here's what happened: On the first day, we set up camp at 2 pm. Mellow
Yellow's alternator is set to 14.0 volts, so I knew that I had not fully
charged the house battery, but was close.
I set up the solar panels and within two hours the controller dropped
into its low-current absorption voltage mode of 14.8 volts, indicating
the battery was fully-charged. When we went to bed, I noted that the
battery voltage was 12.7 volts, unloaded (no current being drawn from
the battery). Overnight, the temps dropped to the mid-50's, so the
Norcold was only operating for a couple minutes out of every ten.
(I still marvel that the reefer [means "refrigerator" in parlance]
reliably comes on every 10 minutes, regardless of the setting on the
dial. The more you turn the knob clockwise, the colder the reefer will
get inside, and once it has reached that point, the compressor will turn
off. Wait 10 minutes and it will turn on again, and run as long as
needed to keep the temp where you set it, then shut off . . . until
another 10 minutes has passed. Have to get a service manual to see if
there is clock in the thing).
Anyways, in the morning, the unloaded voltage of the house battery was
12.5 volts. I set up the solar panels to point toward where the sun
would strike them once it cleared the trees, and left camp at 8:30 on a
bicycle ride to the general store to buy some soft drinks (2.5 miles
steady 7% climb up to the store, 2.5 miles steady "Look ma -- no hands!"
downhill back from the store). When I returned, at 10:30, the voltage
was 14.8 and the controller has switched into low-current absorption
mode. The two 45-watt BP solar panels had brought the battery back to
fully-charged in about 2 hours.
The panels are wired to a Blue Sky 2000E MPPT solar controller, which
handles battery charging, as well as squeezing every available amp out
of the panels. It works brilliantly. Under good conditions, the
controller can eke 6 to 7 amps out of the pair of panels. The output of
the controller is high enough to easily power the Norcold while
continuing to dump current into the battery. I watched the battery
ammeter switch from a charging current of 6 amps to 3.5 amps when the
reefer kicked in. Around noon, it became overcast as moist air from the
Sea of Cortez was hoisted over the Laguna Mountains by a southeasterly
wind, and turned into thunderheads. Lightning, thunder, wind, hail, and
rain ensued, a good time was had by all. During this time, the output
from the panels dropped to nothing and the Norcold, running a 50% duty
cycle in the 80F temperatures, ran off the battery. At 5pm, the clouds
dissipated, and by 6:30pm, the battery was full again.
That's pretty much how it went: a couple hours of full sun in the
morning is all it took to bring the battery back to full charge, and
during the day, the panels mainly loafed in absorption mode, increasing
power as needed to power the reefer or other loads. At no time during
the day did the battery do anything more than provide ballast duty and
help hold Mellow Yellow to the ground.
On our final night, we watched a movie on my notebook computers, which
draws about 4 amps per hour, so call it 8 amp-hours. Add in, say, a 25%
duty cycle on the reefer over a 12-hour 7p to 7a period of time, which
amounts to 7.5 amp-hours, for a total of around 16 amp-hours. In the
morning, with panels cranking out 7 amps AND operating the reefer at
(say) a 40% duty-cycle as the day warms up (1 amp-hour load), that
leaves 6 amps for battery charging, or about 3 hours (18 amp-hours) to
fully recharge it.
The bottom line is that this modest solar rig is more than capable of
keeping up with my electric load -- as long as there is sunlight. If the
sun goes away . . . well, we don't camp much if it stays gloomy for too
long. So we're very pleased.
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR
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