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Old 02-05-2013, 03:58 PM   #1
DJW
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2004 25' Safari
Lafayette , California
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What charges/runs/drains what when?

Hello all, I'm sure this is covered somewhere, but my "search' attempts have failed me.

Is there a quick guide to where the electrons go?

My basic question is about the relationship between my tow vehicle (TV) and the the Airstream (AS).

1) If towing, does the power switch in the AS need to be on "Use" (not "Store") for the trailer batteries to charge?

2) When parked, with the TV connected, will using AS electrics drain the starting battery on my TV?

3) Approximately, what is the amp/hr drain on the batteries when running the refridge on propane? (assuming it is already cold)

4) Approximately, what is the amp/hr drain when running the AS furnace (on propane).

Thanks in advance. Heading out next week on my first "no power" camping adventure for 3-4 days.

AS= '04 Safari LS TV= '07Toyota Tundra 5.7
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Old 02-05-2013, 04:59 PM   #2
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2005 19' Safari
GLENDALE , AZ
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See responses below:

1) If towing, does the power switch in the AS need to be on "Use" (not "Store") for the trailer batteries to charge?

Answer: On our 2005 19-foot Bambi, the "power switch" seems to change on it's own, as necessary. I suspect that that it should be in the USE position when you are towing, so that the batteries will charge. However, it seems to change automatically when we switch from shore power, and hook up the umbilical connector to our 2008 Tundra. Since installing a marine battery isolator switch about a year after purchasing our Bambi (in 2005), I completely ignore the "store" switch.

2) When parked, with the TV connected, will using AS electrics drain the starting battery on my TV?

Answer: For newer Tundras, the charge line that goes to your Airstream is only connected to your truck battery when the ignition is on. So, when the engine is turned off, your trailer does NOT draw power from your vehicle battery. Specifically, for your 2007 Tundra, you do NOT need to disconnect the umbilical connector while parked.

3) Approximately, what is the amp/hr drain on the batteries when running the refridge on propane? (assuming it is already cold)

Answer: When running on propane, the current draw for the refrigerator is very low, as 12 volts only powers the electronic controls and propane burner igniter circuitry. We have boondocked for up to a week running on trailer batteries only, and the refrigerator is not what draws the batteries down. The highest 12-volt drains are the furnace blower, 12-volt appliances (e.g., television, and other 120-volt AC appliances powered by an inverter), and non-LED (i.e., incandescent) interior lights. The lowest drains are the refrigerator and hot water heater, when they are operating on propane. So, basically, you don't have to worry about the refrigerator running your batteries down, unless you leave it ON while in storage.

4) Approximately, what is the amp/hr drain when running the AS furnace (on propane).

Answer: I don't know exactly what the current drain on the furnace blower motor is. However, the blower will drain the trailer batteries significantly overnight in cold weather. If you adjust the thermostat to a comfortable setting like you would at home, it's likely that your batteries will be mostly depleted by morning. You can reduce this drain by turning the thermostat to 50-degrees F or OFF, at bedtime. If you camp for more than a couple of days, you may wish to consider recharging your trailer batteries daily by running the TV engine (which could take several hours), or using a generator or solar panels.
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Old 02-05-2013, 05:01 PM   #3
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Quote:
Originally Posted by DJW View Post
1) If towing, does the power switch in the AS need to be on "Use" (not "Store") for the trailer batteries to charge?
Most likely. Different models were wired differently... but your electric jack and break-away switch likely need this switch to be on "Use" as well.

Quote:
2) When parked, with the TV connected, will using AS electrics drain the starting battery on my TV?
Not unless someone did a hack job wiring your tow vehicle. Typically, if the ignition isn't on, the 12 V line from TV isn't hot either. Unplug if you're nervous .

Quote:
3) Approximately, what is the amp/hr drain on the batteries when running the refridge on propane? (assuming it is already cold)
Depends on the unit; ours is basically 0, some may be 1 amp or so.
Small in any case.

Quote:
4) Approximately, what is the amp/hr drain when running the AS furnace (on propane).
Lots - between 10 and 15 amps when the furnace runs. The colder it is, the less the charge in the batteries and the more power you'll need . Many people find forced air furnaces impractical for boondocking.

One thing I've found really useful for boondocking (besides solar panel;s ) is a Trimetric battery monitor, which provides both very accurate ammeter and voltage readouts as well as an integrating amp meter which provides a very handy and accurate % charged readout.

Trimetric 2025RV Battery System Monitor

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Old 02-05-2013, 05:26 PM   #4
DJW
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OK, thanks! This makes much sense.

Quick notes- We never run the furnace at night- too noisy. Usually just run for 10-15 minutes when we wake up to kill the chill. Should be OK on this one.

Our "Super Jack" is wired, via a fuse, directly to the batteries. So is the #@%# little light for the jack, which got left on once and drained the batteries...

The break away brake circuit also seems to be wired directly to the battery, which makes sense.

I have a small array of solar panels that in full sun will charge at about 0.5 amps. So, if I leave it connected all daylight hours, I should be fine with just the reefer, occasional hot water and brief furnace, and one light to read by at night.
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Old 02-05-2013, 05:41 PM   #5
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When I left my trailer plugged into my TV for a couple of days while parked in a friend's driveway during a visit, and using the trailer normally during that time (but not starting the TV at all), it did draw down the trailer battery. That battery failed, requiring replacement, and so it also drew down the TV battery, so that I needed a jump when we were ready to leave. Now I faithfully unplug when parked. All of the wiring is as supplied by the factory. My 12v supply socket pin registers current even if the TV is not running, so you may want to confirm that yours is not powered all of the time.
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