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Mod #10: Power Inverter

Posted By Mark Corgan On June 14, 2008 @ 6:11 am In electrical, featured | 30 Comments

This mod often stirs spirited debate in the RV community on the “bang for the buck” argument. Oftentimes, the question will arise on how to run a coffee pot or a microwave without a generator or other 110 VAC power source to the RV. On the one side, you have those who prefer to just use a good old coffee percolator over an open flame. On the other side, there are those who would prefer some of the conveniences of home when camping, i.e., running the microwave. On the third side, there are those who just want to run a TV/DVD or charge their 2-way radios. Whatever the case may be, there are a multitude of ways (and costs) to accomplish what you want. Since inverters come in all shapes, sizes, and efficiencies, choosing and installing the right one can be a daunting experience. So let’s start with a few of the basics and work up to some examples.

Mod Difficulty:

A power inverter uses direct current (DC) power to produce alternating current (AC) power, like in your home. In an RV, an inverter is connected to the battery and provides 110 VAC for running appliances, like a coffee pot, microwave, or electronics like a TV, satellite receiver, computer, or cell phone charger.

Depending on what you want to power, there are many sizes available, from 50 watts all the way up to 5000 watts. These sizes, or ratings, determine how much power can be supplied by the inverter. For example, if you want to power a typical 4-cup coffee maker which has a power consumption rating of 800 watts, then an inverter rated for 1000 watts is a good choice. Another example is an LCD flat panel TV/DVD combination, which has a very low power consumption rating of around 100 watts for a 19 inch size. You only need a low-power inverter of around 150 watts if this is all you want to run.

Inverters use 2 differing ways to generate AC power: modified sine wave and pure sine wave. The former, for the same power rating, is generally much less expensive than the latter. If you want to power sensitive electronic gear, like a laser printer (don’t laugh, some full-timers do it on the road!), or even a microwave, the pure sine wave inverter is the proper choice. Most other devices and appliances will work well with a modified sine wave inverter but there are some that are very finnicky or don’t work at all, like the digital control on an electric blanket or mattress warmer.

Inverters also can be packaged with a battery charger and automatic transfer switch built in, though these types are quite expensive and are generally reserved for the mid-to-high level trailers and motorhomes requiring high power delivery. This is very convenient way to have many components packaged into one form factor, eliminating some of the wiring work required when using separate components.

So now that you have a little background on inverters, let’s take a look at a few example installations. First up is the low-power install (see image) meant to power an LCD TV. Simply plug the inverter in to the 12-volt receptacle (typically found near where the TV is mounted) and plug the TV in to the inverter. Yup. That’s it. Since the power requirements are less than 150 watts, the 12-volt receptacle has adequate wiring to carry the power required.

Next up is a mid-power inverter powering a coffee pot (or anything else less than 1000 watts). This type of installation is a little more detailed. Because of the high input current requirements (nearly 100 amps!) to produce 1000 watts of AC power, the inverter must be directly wired to the battery, rather than through the 12-volt receptacle as described above. Typically, this means that the inverter should be placed within 5 feet of the battery (but not in the same compartment) to avoid voltage drop from the battery to the inverter, resulting in poor inverter performance. Large gauge cables, 4 gauge in this case, should be used for DC connections to the inverter through a 150 amp fuse.

AC wiring is as simple as plugging the shore power cord in to the inverter. This will power the entire RV so it is essential that the converter, refrigerator, air conditioner, and electric water heater breakers are all turned off at the AC distribution panel, especially the converter. The converter, when supplied AC power, will begin charging the battery. This will in turn deplete the battery supplying power to the inverter, which is supplying power to the converter to charge the battery. It becomes an endless loop and will run the battery dead in no time.

There are other AC wiring options so you don’t have to remember to turn off certain breakers. It involves wiring in a sub-panel, which is a panel of AC breakers separate from the main AC distribution panel, that is dedicated to circuits in the RV you want to power. A transfer switch, which ensures that no 2 AC power sources can be connected to the RV at the same time, is required as well since the inverter will be “hard-wired” to the AC distribution panel. This type of installation isn’t for the faint of heart. If you don’t have the skills required, have a certified electrician assist or do the job for you.

Finally, there is the whiz-bang super duper high-power inverter/charger/transfer switch combination installation. This is the creme of the crop and is typically found in either higher-end motorhomes or in RVs whose owners can afford to not have to worry about powering anything. Inverters in the 2000 to 3000 watt range are used to power anything from a convection microwave oven to a washer and dryer. Some are even wired to run the air conditioner in a pinch, though not for very long.

The type of inverter described above will have a remote control panel to manage and monitor many electrical parameters, such as battery status, AC information, inverter mode, charger mode, and overall system information. These can be adjusted to meet the demands of your particular installation, particularly battery charging. Adjustments can be made for battery types, charging times, and temperature-compensated charging.

At this power level, a large battery bank is required, typically consisting of 6 to 8 6-volt golf cart deep cycle batteries. As detailed above, the inverter must be very close to the battery bank and have cabling of sufficient size to handle the input current requirements. 4/0, or “four-ought”, which is over a 1/2″ thick, should be used at this power level, along with a 300 to 400 amp inline fuse in the positive cable. A competent RV electrician or very knowledgeable RV enthusiast should be consulted to provide the design and installation.

Warning: Always follow the inverter manufacturer’s installation guidelines, paying close attention to proper wire sizing. Installing an inverter requires understanding of safe electrical practices and electrical safety code. If you don’t have the necessary skills, get a qualified electrician to do the wiring. Don’t take chances with safety! I guess I cannot emphasize this enough having cooked one inverter myself.

ModMyRV recommends these parts for this mod:

Power Inverters
XANTREX XM1000 Pro Series Iinverter 1000 Watt
Go Power! GP-SW1500-12 1500-Watt Pure Sine Wave Inverter
2000W Inverter/charger High-efficiency - 12V Dc Input; 120V Ac Hardwired Input
Go Power! 50 Amp Transfer Switch
Go Power! TS-30 30 Amp Automatic Transfer Switch
Power Bright 0-AWG6 Power Cables for Inverter
Power Bright 0-AWG3 Power Cables for Inverter

General Reference
The 12-volt Side of Life


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