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Ran D. St. Clair · 12-17-2010, 09:40 PM

MMM, Your questions are just the tip of the iceberg. You need a lot more information than I can give you right now, but I will try to get you started.

1. Go buy “Managing 12 Volts” by Harold Barre
2. Post your question on the Escapees forum. There are lots more people with answers there and you will be better off with multiple sources of information.
3. Read my topic “Stealth Camper Build thread, starting with post #34

I suggest you get a fully integrated unit, meaning inverter, battery charger, and transfer switch. That way you won’t have to worry about all of the pieces playing nicely together.

IMHO, you will need 2 large (65 pound) batteries. There’s lots of ways to configure them, lots of brands, etc. They need to be deep cycle batteries, not car batteries.

You need a battery charger capable of 35A, preferably more like 100A. It needs to be multistage with temperature compensation.

2000W is not at all excessive for your inverter. You already did the math on that one.

I know Xantrex has a good reputation. I liked what I read about Magnum Energy. Trip-Lite also makes this sort of thing. There are others but I can’t make an endorsement. My feeling is that you pay higher prices for the name brands, which gives you some assurance that they will stand behind their warranty. Cheaper Chinese knock offs are often made in the very same factory using the same materials and very similar designs, so they might work just fine, but they are probably throw away units if they fail. Then again, repairs after warranty will often cost half the price of the unit or more, so treating them as throw away units probably isn’t so bad. You pays your money and you takes your chances.

You can answer many of your other questions (approximately) with simple math.

A 65 pound battery is good for about 1,200 watt hours of energy, less if you draw it down rapidly. Some of that will be lost in the conversion from DC to AC, and you should never plan to draw your batteries down more than 60%, so practically speaking you might figure 500 watt hours per 65 pound battery.

So, using your question as an example… “How many batteries would it take to run a 2000 watt inverter for 8 hours at 60%?”. That’s 2,000 x .6 x 8 = 9,600 watt hours. Divide by 500 watt hours per battery and you get 19.2 batteries, or 1,248 pounds of batteries.

The method is correct but the assumptions are wrong. You won’t need anywhere near that much energy for a day or two. You need to do some careful math to figure how much energy you actually need. For example, You can make a pot of coffee with about 1,000 watts in about 6 minutes. That’s 1000 watts times 0.1 hours or 100 watt hours. Your LED TV will probably use about 50W so 8 hours of that is 400 watt hours. I would guess your fridge will average about 25W so over 24 hours that’s 600 watt hours. Now you know why RV’s often have propane powered refrigerators. You can buy 12V TV’s and even 12V refrigerators, but ultimately energy is energy and all you save is the efficiency losses of the inverter, which aren’t that bad.

Don’t trust my figures. Do your own research and math, and get some more opinions, cuz I make mistakes sometimes.

12-17-2010, 09:40 PM	#3
Ran D. St. Clair Senior Member Join Date: Apr 2009 Posts: 212	Toterhome electrical info needed MMM, Your questions are just the tip of the iceberg. You need a lot more information than I can give you right now, but I will try to get you started. 1. Go buy “Managing 12 Volts” by Harold Barre 2. Post your question on the Escapees forum. There are lots more people with answers there and you will be better off with multiple sources of information. 3. Read my topic “Stealth Camper Build thread, starting with post #34 I suggest you get a fully integrated unit, meaning inverter, battery charger, and transfer switch. That way you won’t have to worry about all of the pieces playing nicely together. IMHO, you will need 2 large (65 pound) batteries. There’s lots of ways to configure them, lots of brands, etc. They need to be deep cycle batteries, not car batteries. You need a battery charger capable of 35A, preferably more like 100A. It needs to be multistage with temperature compensation. 2000W is not at all excessive for your inverter. You already did the math on that one. I know Xantrex has a good reputation. I liked what I read about Magnum Energy. Trip-Lite also makes this sort of thing. There are others but I can’t make an endorsement. My feeling is that you pay higher prices for the name brands, which gives you some assurance that they will stand behind their warranty. Cheaper Chinese knock offs are often made in the very same factory using the same materials and very similar designs, so they might work just fine, but they are probably throw away units if they fail. Then again, repairs after warranty will often cost half the price of the unit or more, so treating them as throw away units probably isn’t so bad. You pays your money and you takes your chances. You can answer many of your other questions (approximately) with simple math. A 65 pound battery is good for about 1,200 watt hours of energy, less if you draw it down rapidly. Some of that will be lost in the conversion from DC to AC, and you should never plan to draw your batteries down more than 60%, so practically speaking you might figure 500 watt hours per 65 pound battery. So, using your question as an example… “How many batteries would it take to run a 2000 watt inverter for 8 hours at 60%?”. That’s 2,000 x .6 x 8 = 9,600 watt hours. Divide by 500 watt hours per battery and you get 19.2 batteries, or 1,248 pounds of batteries. The method is correct but the assumptions are wrong. You won’t need anywhere near that much energy for a day or two. You need to do some careful math to figure how much energy you actually need. For example, You can make a pot of coffee with about 1,000 watts in about 6 minutes. That’s 1000 watts times 0.1 hours or 100 watt hours. Your LED TV will probably use about 50W so 8 hours of that is 400 watt hours. I would guess your fridge will average about 25W so over 24 hours that’s 600 watt hours. Now you know why RV’s often have propane powered refrigerators. You can buy 12V TV’s and even 12V refrigerators, but ultimately energy is energy and all you save is the efficiency losses of the inverter, which aren’t that bad. Don’t trust my figures. Do your own research and math, and get some more opinions, cuz I make mistakes sometimes.