dry camping

[Pete Masterson]

The primary drain (through the inverters) is the power to the
refrigerator. It will limit your ability to operate off the grid with
an all-electric coach. (My '95 is all electric.) Newer refrigerators
are perhaps a bit more economical to operate than the 22 cu ft 2-door
Amana that I have in my coach -- but you're likely to experience the
similar power drain.

For example, I have 6 model 4D AGM-type house batteries. These have
about 220 amp hours each. So, 6 x 220 = 1320 amp hours. However,
that's an overstatement of what's available, as you can't deplete the
battery more than 50% for standard wet cell or by more than 60% for
AGM batteries. So that would mean there's between 660 and 792 amp
hours available from the battery to power all the 120 volt systems
that are serviced by the inverters. (I have two, 2500 watt
inverters.) Also, don't forget that the inverters cause a loss (10%
or more) while changing the 12 vdc to 120 vac. Don't forget that amps
X volts = watts. So, a 1000 watt refrigerator is about 8.3 amps at
120 v per hour. Convert that to 12 vdc, and its about 83 amps. With
the inverter loss, that's about 95 or 100 amps (per hour while the
refrigerator is running)... so that suggests about 6 to 8 hours or
perhaps 10 hours of operation (since it doesn't run 100% of the time)
just for the refrigerator. Add the microwave (high draw, but short
period) plus the various lights and the 12 volt stuff... and then you
can see that the batteries are kind of limiting!

Here's where you have to do some math. First figure out the
approximate hourly draw in amps of each appliance that runs on 120
volts. Don't forget that _some_ of the lights run on 120 volts and
are powered by the inverters. Of course, all 12 volt items and
appliances also draw from the batteries. So, you also have to figure
out what 12 volt appliances you have operating. Do not ignore the
draw from the Microphor toilet compressor nor from the air-system
auxiliary compressor, if you have one (I don't) along with various
signal lights, etc. etc. -- well, to be honest, there's a _lot_ of
load on a 'bird and without a source to recharge, the batteries can
be drawn down to a dangerous level in just a few days, even when
everything is "off."

So, back to the refrigerator -- the practical situation is to make
sure your house batteries are fully charged. If you have an isolation
switch to "turn off" everything, it would help. Anyway, when you
think your batteries are fully charged, isolate them (and unplug
shore power), then check the voltage. (This is the "resting"
voltage.) For AGM batteries, it should be about 12.9 to 13.0 volts
(wet cell batteries are different). Then, turn on the isolation
switch (apply the normal load) -- wait and hour, remove the load, and
check the voltage. 12.4 volts is 50% depletion and 12.25 volts is 60%
depletion -- do not let the volts drop below 12.25 volts!!! ---this
is "resting" voltage measured from the battery terminals.
Measurements drawn from other locations (e.g. a fuse panel) are
likely to be much lower due to line losses.)

My experience has been that "boondocking" isn't especially practical.
I can shut down the generator in the evening, but I usually need to
restart after about 12 hours or so. So, if I shut down at 8:00 PM,
I'll usually need to start the generator by about 8:00 AM the next
morning to avoid causing any damage to my batteries. This has caused
a fair amount of heart burn when I've stayed in a CA state park that
had a generator operation ban between 8 PM and 10 AM ... those two
hours were nail biting time and I had to shut down any/all items that
made demands on the batteries.

My plan (the next time I boondock) is to pull the breakers on the
inverters perhaps at 10 PM or so, and see how the batteries are the
next morning. The refrigerator won't warm up much during the night,
if it is not opened and if we're in a reasonably cool location.

I've compared notes with another all-electric Blue Bird owner (just
this past weekend at the Lone Star Birds rally in Kerrville, TX) and
I'm of the impression that my voltage drain seems to be on the high
side (so I may need to further explore possible reasons).

The reality is that you can probably turn off the generator in the
evening then turn it back on in the morning without major problems.
You can run the generator for 3 hours or so to bring the batteries
back up to full or near full charge. Then you can shut down the
generator for a few hours, then run it for 3 or 4 hours until the
time you wish complete quiet at night (or until any required shut
down time occurs).

The coach can be off the grid without the generator for periods of
several hours -- but it will need to have power to recover the
batteries rather more often and/or for longer periods than coaches
that have LP gas appliances.

See Poop Sheets by Phred at:
<http://www.phrannie.org/phredex.html>
#5 has a thorough discussion of "electrical stuff."

Pete Masterson
'95 Blue Bird Wanderlodge WBDA 42
aeonix1@...
On the road at Lubbock Texas following a great weekend with the Lone
Star Birds at Kerrville, TX.



On Dec 1, 2007, at 2:08 PM, medpro28 wrote:

> Just purchased a 2005 LXi and need some advice on dry camping. I cook
> in bbq contests and sometimes no power or 110 only. Dealer says I
> will
> have to use the generator all the time. Although the unit is all
> electric, will not use the stove top or microwave while camping.
> It is
> hard to believe I can't dry camp any length of time and then use
> generator to keep batteries up.
> Is the dealers advice right or does anyone have thoughts or
> suggestions?
>
> Jerry Smith
> 2005 450 LXI