Noob electrical question

[eddie1261]

I am fairly sure that I know the answer, but I need to ask anyway. I assume that there is an inverter of some kind that when I am running on house batteries rather than shore power the 12v in those batteries should be converting to 120v and my outlets and such should work. That's just what I think though.

Everything works fine when I am plugged into my house electrical or when the generator is running. Am I wrong in assuming that those two 12v batteries should be converted to 120v and power those outlets. Maybe not for long, but they should. Or am I wrong in making that assumption? Are those 12v batteries supposed to power only the 12v lights and such? Believe me, I have looked and looked through every book I have. The thing is that I don't know if I have ALL the manuals and all that came with this thing 17 years ago.

Normally I would be very sheepish about asking what to you experienced folks are likely really stupid questions, but you folks are better than an RV reference library!! I just wish life had a fast forward button and I could move ahead in time to the place where my house is sold and I am out on the road. I have been doing ordering stuff, envisioning stuff, then sketching it, then building it.... I did touch base with a handyman dude in my area who will (and can) do what I need done to get my house listed and we have a meeting this week. It's time to do some traveling!! I am not a very patient person, but I have a timetable and must stick to it. Plan your work and work your plan.

[gjhunter01]

On most RV's the 12v system of lights, refrig, W heater, and furnace is powered directly from the 12v batteries. The batteries are then charged from a built in 12v charger powered from the house or 120v power. If you disconnect the house power, your 12v system should still work until the batteries run down. The 120V system will not work off the 12v battery unless you install a inverter. Just unplug your shore 120v power cord and see what is working in the RV.

Greg

[Big Greg]

If you have a converter in your RV the 12v batteries will not be supplying 120v AC. 

If you have an inverter in your RV then you will have 120v supplied from the 12v batteries. 

Greg

[eddie1261]

Yeah those replies kind of cemented what I thought. I do not have an inverter. I will have one to power my electronics after the solar install in spring but I wondered about the house 120v outlets between now and then. The 120v outlets do NOT work when my shore power is disconnected. All I really do in the RV right now (parked in the driveway) is take my dog out there for an hour every now and then so she can start getting used to the scents and the layout (she is blind and it's all scent and feel for her now), and do small things to prepare, like I have built the wood frame that would lock my computers into place, lowered the table top to where it works for my short self, measured up for the spice rack I need to buy (or build)... that kind of stuff. And of course learning how stuff works. And now I know that what I am seeing with the electricity is what I should be seeing.

Thanks all!

[Lou Schneider]

Make a list of what you want to power from an inverter and their power draws.  It makes no sense to buy a 3000 watt whole house inverter (and the extra batteries needed for it) if all you need is a couple of hundred watts to run a TV and DVD player, a PC and monitor and an ink jet printer.

I get along just fine with a $40 Harbor Freight 750 watt modified sine wave inverter.   It won't run the microwave, but it handles everything else I want to run on it.  Pure sine wave inverters of similar size are available for 2-3 times as much.  The key is to mount the inverter close to the batteries, then extend the 120 volts to where you want it.

It's more efficient to use 12 volt adapters to charge anything that uses a USB or Lightning cord.  I use a Wagan Tech USB Power Hub and tapped power for it from a 12 volt light over my worktable.

[Kirk W]

12 hours ago, eddie1261 said:

I assume that there is an inverter of some kind that when I am running on house batteries rather than shore power the 12v in those batteries should be converting to 120v and my outlets and such should work. That's just what I think though.

The answer to this comes in two parts. Pretty much all RVs today have a converter. It converts the 120V power that comes from either shore power or a built-in generator into 12V-dc to supply loads of the RV and when some power is left to charge the batteries. The inverter, which makes 120V-ac power from battery power is standard in some newer RVs but was rarely so in past years and even today isn't always offered. With your RV, there is little chance it has one unless some previous owner installed it. 

12 hours ago, eddie1261 said:

Am I wrong in assuming that those two 12v batteries should be converted to 120v and power those outlets.

You are wrong. Even if your RV had an inverter it would be very unlikely to be wired to supply all of your 120V outlets because the battery power is so very limited. Since you have only two batteries, using an inverter to power very much will deplete them very quickly. Your appliances and things in the RV which have low power requirements are supplied by the 12V from your batteries to enable you to use them without shore power or the generator, but some of those will draw down your batteries pretty rapidly. The biggest power hog in most RVs that do not have an inverter is the furnace blower. It heats with propane but uses the battery to move that heat. The refrigerator uses propane also to replace the energy used by 120V when you do not have shore power. 

It is very important to understand that power is current multiplied by driving force, or in other words amps multiplied by volts. That means that even with no conversion loss, a 120V device that draws only 2A from shore power will eat up 20A of your batteries. If you plan to use much from an inverter, the first thing that you need to do is increase your battery capacity. 

10 hours ago, Lou Schneider said:

It's more efficient to use 12 volt adapters to charge anything that uses a USB or Lightning cord.

I completely agree with this. Keep in mind that an inverter isn't 100% efficient so that means that if you need 2A of 120V you will actually be using at least 21/22A from your batteries. We lived for nearly 12 years in a gasoline-powered motorhome similar to yours and we did just fine without any inverter. Of course, we also didn't do a lot of dry camping so solar was not needed either and what little need we did have for 120V we solved by using our built-in generator. That was mostly for a coffee maker and TV. You can get both of those in 12V-dc versions as well and we also bought a 12V power cord for each of our laptop computers.  

When you go off-grid as you desire to do, both solar and an inverter become the best answer, in my opinion, but even then the best way to live well is by good power management. Based on what you have said thus far, I strongly suggest looking at adding at least 2 more batteries very early in your transition.

[eddie1261]

Here are my plans and steps I have already taken as far as power.

I plan to buy a 265w solar panel, just the right size to fit on my roof without a lot of exotic work. A couple of rails for the panel to bolt to. I MAY add a suitcase solar that would add another 120w  they I would deploy when I stop. That will run to a Blue Sky i3000e Charge Controller. From my research, that is the one I think I like the best. That will go to one 100 amp hour lithium battery (to start - they are $1000 each). I am going with lithium for several reasons. I don't want batteries that weigh more than I do. If I buy 85-90 pound batteries, I will need help to lift them, and I am all by myself here. The lithium I am buying is 32 pounds. Also, there comes into play the "don't use it beyond 50%" rule. I can take lithium all the way to 0% if that should ever happen and it will not damage it. They guarantee 4000 cycles, and if they guarantee 4000, I anticipate I can get 5000. Do that math. 4000 cycles is 11 years. That takes me to age 77. Also, they need no attention. I don't want to have to remember to be popping caps of batteries like I would have to do with flooded lead acid batteries. So lithium will be it despite the amount of email I have gotten from people telling me how long their lead acid batteries lasted and that lead batteries cost so much less. Money is not my concern. "Install and forget" is my goal. One less thing to deal with. Once the financial picture allows it, I will add a second battery.

For consumption, a 1500 watt inverter is what I will use, though I could get by with less. I like to have room for expansion. I have already taken readings on every device that will go into the RV and use solar power with my Kill-A-Wall meter. (TV, computers, monitor, keyboards and studio monitors. I play and write songs.) After creating a spreadsheet with all that information, I then started creating usage scenarios and setting up formulas in that spreadsheet. For example, the "Watching TV at night" scenario is "inverter, TV, streaming computer, repeater, and laptop". The formula for that scenario adds up the amp draw per hour and multiplies it by 4, 5 or 6 hours. There is another for "general computing", which is reading email, surfing to get my news, editing video, etc. That one contains inverter, repeater, computer and monitor. Another is "writing music", which contains inverter, computer, powered monitors and a synthesizer. And so forth. That one battery at full charge will do me fine TO START WITH. 6 months later I will add that second battery. Kitchen stuff, like the blender and the food processor will only be used when the generator is running, so never on solar. (Can't do without my Cuisineart!   I like to cook too much.) I applied the same concept to data vs wifi and metered how much data I use to stream TV on my cell data. (It's ugly!) SO I will probably pretty much do most of my stopping where my wifi repeater can see an access point where I can get wifi. I live online too much but it is how I live, so..... Been a nerd since the early 80s!

The main thing this is going to require from me is changing how I do things. Right now in a house, as I pour my iced tea from a gallon jug, the fridge door stays open for the 30 seconds or so it takes me to get the jug, fill the big glass half way, then get the water jug and fill it the rest of the way. (I water down 50-50 my sugar free Arnold Palmer iced tea!)  I can't do that in the RV when the fridge is already cold from being on genny, though by then the gas will be fixed, and not powered by 120v (in boondocking situations). I need to get in and get out fast. Things like that will take me a while to adjust to as I have been doing it that way for decades, but I'll be fine. If I plan to boondock a lot I will probably add a small Dometic fridge that I can power from solar and use that for water and tea, and dog food.

There is a lot of "spending" in this plan, and while I am not rolling in dough, I also have no desire to be the richest corpse in the graveyard, so unlike a lot of folks who squeeze a nickel until the buffalo bleeds I buy what I need/want. I am not leaving money to anybody when I die, though the animal shelter where I got my last few dogs will be happy when I go..... my small insurance policy and any profits from my estate go to them. They should see about 50k when I die. And for all the joy I got from them over the years, 50k doesn't even start to cover it!

So those are my general plans, and I welcome observational criticisms pointing out anything I missed. General things, electrical, communication... anything.

[vermilye]

One suggestion - Since you plan to power audio equipment as well as musical instruments, I'd plan on a sine wave inverter rather than the less expensive modified sine wave.

Also, while it may not be a problem in your situation, lithium batteries are not happy being charged at sub freezing temperatures...

[eddie1261]

Absolutely pure sine wave inverter. And the day my RV life begins, I will be avoiding  cold weather as much as possible! This year will make 66 Ohio winters. Enough!!

Thanks for your input.