Almost all of the equipment in your rig runs on 12VDC power. Most if not all of the lights, the electronics for the Fridge, stereo, heater, etc. all run on 12VDC. If you are plugged into 110VAC in a campground the converter that is provided in your rig converts the 110VAC shore power into 12VDC to run all of these native 12VDC devices. If you are not plugged in, power is provided by the battery or batteries in your rig. In addition to providing the 12VDC power, the converter also acts as a battery charger, albeit a typically less intelligent battery charger than you need.
There are typically a couple of exceptions to the 12V rule: the giant Air Conditioner mounted on top of your rig, the microwave oven in your kitchen and perhaps a television. These are all 110V devices that will only function if you have your rig plugged into 110V power. They all have large power requirements (with the exception, perhaps, of the TV). In addition to these standard items in your rig you may have also brought along other typical household devices like a coffee maker and toaster. Again, these are typically large power users that require huge amps to run.
Back to some electrical power basics. Remember that watts (power) equals volts times amps ( P = V * A ). If you have a 1200W device, like a toaster, and you run that on 110V you need approximately 11A for that device. If you want to run that same 1200W toaster on 12V you will need 100A instead. 100A is a lot of amps requiring very large cable to safely work. The difference in wire size? 100 amps requires wire about 1/2 inch in diameter. For 11 amps, that wire size can be less than 1/10 inch in diameter. I have over simplified the discussion about wire size but it is illustrative if not completely, technically, accurate.
Wire size is why, way back when, higher voltage alternating current (AC) was chosen rather than lower voltage direct current (DC) for most of our daily household electrical requirements. The size of the wire required in our homes is significantly smaller, and thus less expensive, at the higher voltage. In Europe they chose 220V AC to further reduce their wiring requirements and in some cases we use 220V in our homes to power big things like our ovens and stoves. These higher voltages were chosen to reduce wire sizes. Why not even higher voltages? What, you want to kill yourself? 110V shocks are sufficient and usually not fatal. Higher than that? Not so much…
But in an RV, having a portable source of 110V alternating current is expensive (and noisy and I think you know what I think about generators). Enter the use of 12V wet cell batteries. Batteries are relatively inexpensive and are also very efficient sources of electricity. Unfortunately, they provide DC power at relatively low voltages. Thus to provide lots of watts they need to provide lots of amps. And they can only run those relatively small, low power devices, like lights, efficiently and without destroying themselves. Drawing high current from a battery for long periods of time will destroy it.
Enter the inverter. An inverter is the opposite of the converter, inverting 12V DC into 110V AC. This is done using magic provided by a large, heavy, box. OK, it isn’t magic so much as a bunch of electronics and some transformers cleverly concealed in a box. An expensive box if the number of watts you want to create is large, say large enough to run your microwave. I should mention that you will never, realistically, invert enough battery DC into 110VAC to run that giant air conditioner on your roof. Don’t think about it, don’t try it. If you need air conditioning, plan on parking someplace that has 110VAC.
There are basically two different kinds of inverters: Modified Sine wave and True Sine wave. The differences are fairly arcane but relevant. The more sensitive the device is to power, the more likely it is that you need True Sine inversion. As you can imagine, True Sine is more expensive. Most, if not all, electronic devices, like TVs, gaming stations, computers, really like True Sine. Toasters, curling irons, etc., can live with Modified Sine. You should probably rule out Modified Sine. Modified Sine is less expensive but less flexible.
Inverters come in all shapes and sizes and prices. Here is the key: if you are not going to try to run a large device, like the microwave, or a toaster, then think about getting a relatively small, True Sine inverter of sufficient size to run the device. I have a 300W, True Sine that measures about 6″x4″x2″ that will run my TV just fine. Cost about $100. It has a fan and makes some noise but it does what I need it to do. It plugs into a convenient 12V cigarette lighter outlet next to the TV. The TV then plugs into it. There are a bunch of choices for inverters of this size. Spending a little more buys you a better inverter in most cases.
We also have a 2000W Magnum 2012 True Sine Inverter to run the big things. That bad boy cost about $1700 and weighs 43 pounds. It will run, ONE AT A TIME, the microwave, toaster, hair dryer, curling iron, crock pot, TV and DVR, etc. It lives in the battery/solar/inverter compartment at the front of our rig. It is wired into the 110V electrical system in the rig. It also has a very precise battery charger so if your rig is plugged into 110V shore power, it can be used to correctly charge the batteries. We don’t often use it to do this as we have solar to provide battery charging. It is a sophisticated piece of equipment. Installing the inverter and electrical wiring to support it cost about half of what my total system cost! Just to be able to run those pesky 110V devices.
In order to support this large inverter, my system required four Trojan T105 6V batteries. If you try to run a large inverter using a smaller battery bank, you will fry those batteries. Period. If you do not use large enough wire on a short enough run between the battery bank and the inverter, you will fry the wiring (and perhaps your rig). Period. We’re talking #3/0 or larger wire. That is wire as fat as your thumb. If you are spending $1700 on an inverter and $700 on batteries, why would skimp on wire? Duh.
If you are contemplating a large inverter, read this:
Subjective, objectivity is what I call HandyBob’s notion of inverters. You might as well benefit from his experience. DO NOT BUY JUNK. Period.
What’s the bottom line? If you have the need to run those pesky 110V devices while in your RV, you need an inverter. You should only buy what you need! If you only want to run your TV then you can get away with a stand-alone small True Sine inverter. You will save money and you will save your batteries. All inverters draw power whether or not they are providing power to a device. The larger the inverter the more power you waste. If you are not using 110VAC turn the inverter off or unplug it!