Date: Sat, 8 Jul 2006 15:38:08 -0700
Reply-To: Larry Chase <roadguy@ROADHAUS.COM>
Sender: Vanagon Mailing List <firstname.lastname@example.org>
From: Larry Chase <roadguy@ROADHAUS.COM>
Subject: Re: Norcold refrigerator + modest solar rig, a report [LVC]
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Can you give us a link and/or details on the Group 31 100 amp-hour battery.
Nice set up.
On thing confuses me a bit.
"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."
So if I take an extreme worse case example and say the fridge uses 1.5 amps
per hr over 24 hrs that equals = 36 amp hrs of usage per day.
Although cutting it close, it seems that the 55 amp hr optima would handle
things for one day without problems.
When you then factor in the solar panels at 6-7 amps per hr while charging
in full Sun ... It seems you could run the fridge and recharge the optima in
a good full sun day.
The only problem would be if you didn't have sun for the solar?
And of course that wouldn't give you any room to run additional appliances
like the laptop and such.
- - -
Date: Fri, 7 Jul 2006 16:14:32 -0700
From: "Mike \"Rocket J Squirrel\" Elliott" <camping.elliott@GMAIL.COM>
Subject: Norcold refrigerator + modest solar rig, a report [LVC]
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
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
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
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
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