Nick Wildwood
Hell California
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Joined: 04/16/2008
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In general I'd say that you can listen to the radio all you want. Use only one light and you can have it on for the whole time. Other than that I could only give you a wild guess depending on how conservative you are.
You need to set up a spread sheet to do your load calculations. Your batteries are probably at least 85 amp hours each. You should be getting 4 amp hours of charging out of your solar panel every hour. That's about 48 amp hours per day max.
The heater fan uses a lot of power. Conserve on that. Lights with two bulbs also use twice as much power so use the single bulb switch when possible.
The spread sheet will let you play around with the numbers and you can see that you can watch TV for an hour a day if you don't use the heater. You can play the stereo all night and take a shower if you don't use lights, etc...
Columns on the spread sheet (typed into row 1):
A - Appliance (includes lights and anything else that uses power)
B - watts
C - (Length of) Time (used)
D - watt hours (similar to man hours)
E - amp hours
Formula for Column D is: '=B2*C2' copy to all rows
Formula for Column E is: '=-D2/12' copy to all rows*
If the appliance runs through an inverter bumping it up to 110volt the formula for Column E is: '=-D2/10' because of the inefficiency of the inverter.
After you list all of your lights and appliances you need to add back in your solar panel just like an appliance except instead column E does not have the minus sign: '=D24/12' (D24 means there are 24 items listed. This will vary so use the appropriate number for that row.)
Next list your batteries and just enter the correct amp hour rating in the box for column E.
Last enter Total in column A and enter this formula in the box for column E: =SUM(E2 26)
Compare the total available in the batteries with the total use. If use is lower then your batteries should be fully charged. If use is higher it is ok because you are not staying out there forever and if you come home with dead batteries that's ok. Many people advise not to drain them more than 50%.
Hope this helps.
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nny12972
NY
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Joined: 10/25/2006
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There isn't a "general" answer to your OP!
Suggest you Google and understand "The 12 Volt Side of Life."
Use one of the solar links to get the info & worksheet for determining YOUR "likely" available 12V power.
J
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profdant139
Southern California
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Joined: 11/14/2005
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The whole battery thing can be very daunting for those of us who are not experts.
I think it helps to monitor the state of your battery, so you can tell how much power you use each day or if you need bigger batteries or new batteries (or if you can really use more power than you have been using and not make your poor wife walk around in the dark needlessly, lit only by a candle and have her say bad words like mine used to do till I got two group 27s but that is another story . . . .)
So anyway, using a simple multimeter (very cheap), I touch the terminals with the probes and read the number every morning to see how much juice is left, according to the following chart which I am told is reasonably accurate:
100% 12.7
90% 12.6
80% 12.5
70% 12.3
60% 12.2
50% 12.1
40% 12.0
30% 11.8
20% 11.7
I have never let the batteries get below 12.1, and we boondocked for five days on one battery recently and never got below 12.2 on that battery. Some folks install meters in their RVs. I just use a portable unit.
I also bought a hydrometer for a few dollars at my local Napa Auto Parts, and it gives me even more precise readings (plus it will tell me if I have a bad cell). But that is probably overkill.
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wayne_tw
South Dakota/Georgia
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Joined: 07/21/2007
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Geneyes wrote:Thanks, I guess I am not looking for a specific answer, but more of a general, around this much kind of answer. In general, running a couple of lights at night, running the water pump once in a while to rinse dishes, maybe play the radio, how much time do I have, in general, 12 hours, 24 hours, 48 hours of intermintent usage, what am I looking at here?
My guess with the solar actually getting sun and working you can do all of the above without concern. The solar should replace any current drawn out of the batteries.
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nny12972
NY
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Joined: 10/25/2006
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With all due to respect to all replies....
Metering and/or checking battery condition during and/or following 12V usage, is like putting a mean dog outside the hen house after the fox has been there.....while metering MAY/CAN lead you to some general appliance usage limitations, as well as future battery choices & charge need necessities, it doesn't tell you what you can or can't do BEFORE you go....
KNOWING what each appliance/lamp uses, and how much you use them, still has it's variables, but it makes it a whole lot easier to add up expected usage, and then subtract that from available 12V battery capabilities......
Understanding the basics, and using the worksheet (or your own) is a much better approximate comparison of what you use, how long batteries will "last", and the battery and charging options available to meet YOUR individual needs.
"The 12 Volt Side of Life" tells you how to do it all.
J
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MNtundraRet
Bloomington, MN
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Joined: 12/06/2007
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The easiest way is to test it at home and see how long it will last. Since everyone's needs are different, this way works best for your current system. You will be able to plug in and recharge batteries at end of test. If unable to do at home, just head to a nearby park with an electric site to test.
Mark
Mark & Jan "Old age & treachery win over youth & enthusiasm"
2003 Fleetwood Jamboree 29
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Rubiranch
Salt Lake City, UT
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Joined: 03/09/2004
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smkettner wrote:Minimum lights(use flashlights and battery lantern when possible) and no heater and you will be fine. Measure voltage each day to keep track of usage.
I think smkettner is right on the money.
If it was me, I would isolate the two batteries and just run off one at a time. Then when the first one runs down you still have a fully charged one to finish the trip and will be better at judging if you need to cut back your electron consumption.
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profdant139
Southern California
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I should add that I did the "mock test" method suggested by Mark -- while the trailer was in the driveway, I hooked up a fully charged battery and turned on a bunch of lights and kept monitoring the battery status all day, to see how fast it would run down. Our real-life usage turned out to be considerably less, not surprisingly -- we are out of the trailer most of the day (hiking and biking and whatever), and we are very careful in our usage during the evenings.
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tpi
Southern CA.
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Joined: 02/22/2005
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If your batteries are in good condition and fully charged, I don't think you'll have problems with a few lights as needed at night, the water pump, powering the refrigerator electronics and a few other small loads. On my trailer with all lights lit there is at least a 40 amp load- so don't light it like a shopping mall.
If you're running the furnace extensively in cold conditions all bets are off. A furnace warm-up in the morning should be ok.In the summer in most locations a few good blankets should do.
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windriderjr
Massachusetts
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Joined: 03/20/2007
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I'm a nerd and did all the calculations for battery consumption for my TT and found I could go for a long time (3+ days) on my single 85 amp-hr battery as long as I didn't run the furnace or bathroom fan.
Then i went camping 
DW didn't like the idea of being ultra conservative with the electrons. She wanted to watch tv at night like at home or in places with hookups. So I was faced with the classic "It looked good on paper" situation. The answer for us was to not worry about the juice and just run the generator for a couple of hrs each day to recharge the battery. I installed a 400 watt inverter for the tv/dvd player. Now DW is happy and I'm happy. battery power is not our limiting factor now, the gray water tank is
DW and I in our Gulfstream Amerilite 21MB
Chevy Silverado 2500 HD - Duramax Diesel 6.6L - Allison Tranny
"We can categorically state that we have not released man-eating badgers into the area." - Major Mike Shearer - British Army - Basra, Iraq
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