Installing a Power Inverter

There may still be cruisers out there that light their way with oil lamps, use a bucket instead of a head and sail without a motor, but in 18 years of cruising we have not met them. Today, most cruisers are like us, preferring to take the comforts and conveniences of life ashore with them when they cast off the dock lines to sail off into the sunset. Long ago we made the decision to cruise in comfort and not turn our sailing trips into a camp out on the water. This meant we would need a means to power our small appliances, power tools and entertainment devices. There is more than one way to accomplish the same end depending on the level of your power consumption and what your budget might be. For us the requirements were simple. The cost needed to be kept down, the system needed to be as simple as possible, and we needed to be able to install and maintain it ourselves. Additionally, it should not interfere with our piece and quiet, or that of our neighbors. OK, maybe not so simple after all.



There are as many options to accomplish this as there are boat owners. For us, this meant that we would forgo the big energy hogs, like heat and air conditioning, while at anchor and concentrate on the creature comforts. We have had a TV on board for as long as we have lived on a boat. It is great for plain old entertainment and receiving news and weather. By adding a VCR, and now a DVD player and satellite TV receiver, we are always up on current events and always entertained. In addition, we have small appliances like a coffee pot, microwave, small battery chargers for tools, cell phones,  and power tools. There would be two options for us, either install a small generator, or have enough battery capacity and install a 12 volt to 110 volt inverter. The inverter seemed to meet our criteria and since we already had a sizable battery bank for cruising, it made the decision an easy one.

In sizing an inverter, the power requirements for running the appliances and tools have to be carefully calculated. This is done by determining the total wattage you will need for the possibility of running several or even all of your appliances and tools at the same time. Although this will not be the case most of the time, it will save having to remember to turn something off before turning something else on. For our purposes, we determined that a 2000 watt inverter could handle our needs easily and we chose the ProMariner because of past good experiences with their equipment. Major power consumers like the hot water heater and AC/Heater would not be used to conserve the amps the inverter would need from the batteries. Keep in mind that the amps pulled from the batteries to run the inverter will need to be replaced, but that is for another article.  Many inverters come as inverter/charger combinations. We choose the inverter and charger separately for a couple of reasons. Should the charger fail, we would not be without the inverter. Conversely if the inverter failed we would not be without the charger. The combination units are also much more expensive than buying the stand alone units separately and we had a variety of choices between manufacturers to determine the best charger and the best inverter for our needs.

The installation is much more straightforward than one might expect. There are some basic electrical standards to follow to make the system safe and efficient and these are provided by most manufacturers in their installation manuals. The first step is to find a dry, well ventilated area that will give you easy access, but out of the way enough that it will not be intrusive. The first consideration might be the engine compartment, but many units will not work well or can be damaged when installed in a high heat environment, especially if the inverter might be used at the same time the vessel is under power. We chose the inside of a small cabinet near the electrical panels within a short distance of the battery banks. This location kept the wiring runs as short as possible, minimizing the need for larger cables. Next, determine the locations for the transfer switch and control panel. This means drilling holes somewhere and running wiring, so the areas should be easily accessible both inside and outside as well as free of other wiring and obstacles.

When determining the wiring size, the total possible amperage flowing throw the wiring and the round trip
distance from the inverter to the power source, the battery banks, and back to the inverter needs to be calculated. The amperage can be substantial and some manufacturers have a limit to the distance for installation purposes. Sizing the cables properly is critical, as is proper fusing of the cables to the battery bank. For our needs we ran a #2 cable from the inverter to a 250 amp T-style fuse, within ten inches of the battery connection, to the positive side of the house battery bank. A #2 cable was run from the negative connection on the inverter directly to the negative post on the house bank. We chose to make the connections directly to the battery bank instead of to a switch to connect and disconnect the 12 volt to the inverter. This eliminated a possible source of failure or loss of voltage through a switch and gave us a clean, straight connection to the 12 volt system.

Making the connections to the inverter was done with the inverter outside of the cabinet it would be mounted in to allow for long enough wiring to be able to remove the entire unit and easily work on it if necessary. The battery cables were run and proper eye connections crimped on, but the connections to the batteries were not done until all of the installation process was completed. All of the 12 volt cables were secured with heavy duty straps and the fuse holder securely mounted with easy access. Our fuse holder came with a plastic cover that eliminated an accidental short circuit.

Once the 12 volt wiring was complete, but not yet connected, it was time to work on the 110 volt side of the installation. For absolute safety, we not only turn off the circuit breakers on the boat and on the dock, but we physically unplug the shore power cords from the boat. The choice to connect the inverter into the boats 110 volt system can again be done in several ways. Dedicated outlets can be wired directly into the inverter, but these will only work if the inverter is on. Or the inverter can be wired to directly feed the AC panel for the boat. Even directly feeding the panel can be done in several ways - feeding only certain circuits, or feeding the entire panel. How it is done affects the complexity of the installation. For our purposes we choose to feed the entire panel using a transfer switch to go from shore power, to off, to inverter. The inverter should never be allowed to feed the electrical panel or any outlets at the same time as the shore power so the transfer switch is a must for safety. The boat is set up with two shore power feeds, one for the AC panel and the other strictly for the reverse cycle heat and air conditioning system so we would not be accidentally trying to run the air conditioning or heat off the inverter. The water heater and 110 volt battery charger were on the panel but we figured we should be smart enough to be sure the breakers were off for these two when we turned the inverter on. Even if we briefly forget to turn these breakers off, no harm would be done with the size inverter we chose.

I would add at this point that a good working knowledge of a boats 110 volt system and installation is essential to be able to complete a safe, secure installation. If one does not have those skills, a qualified installer should be hired to assure there are no problems in the future. Improper installations in the AC side of the boat can cause all kinds of problems from minor to severe. One of the reasons we choose this inverter was that it allowed us to easily hardwire the 110 volt output from the inverter. Many of these units require the AC output to be wired to a plug which is attached via an outlet on the front of the unit. This plug can work itself loose. You can take others apart and hardwire them, but this is not our favorite solution. The proper size standard marine grade, black, white, green, 110 volt wiring was run from the inverter, to the transfer switch, to the AC panel.

We also needed to move the wiring from the shore power inlet to the transfer switch. Great care must be taken to not reverse the hot and neutral, black and white wires at any point along the installation path from either the inverter or the shore power to the AC panel. The green earth ground from both the shore power inlet and the inverter was run through our already installed galvanic isolator. Another feature of this particular inverter is the ability to remove the on/off power indicator from the front of the unit and install it remotely near our electrical panel. Other units that do not have this feature may have a separate remote panel that can be installed. This is much more convenient than going into the cabinet each time we wanted to turn the inverter on and off.

With all of the wiring run and the AC side connected, the inverter switch in the off position, all AC breakers off and the transfer switch in the off position, it is time to connect the DC side to the batteries. With the positive fuse in place, the positive cable should be attached to the house battery bank. Finally, the negative cable should be attached to the house bank and at this time the inverter may make an initial beep or a slight spark may be seen as the negative cable is attached. Depending on which unit is being installed, this is normal. Testing the unit should be done one step at a time, keeping the shore power disconnected at all times. First, turn on the inverter switch and if there is a power indicator light or lights, be sure you have enough voltage in your battery bank. Check over all connections, look and feel for any over heating, and be alert for odd smells. If at any time something feels warm or does not operate properly, shut everything down and disconnect power. Be sure all AC breakers are off including the main breaker. The transfer switch should have a light indicating power on the inverter side and none on the shore power side at this point. A good switch will also have a reverse polarity light, and a note at this point is in order.

Not all inverters are alike and many are designed for the RV market. I have seen many inverters that are not designed for boats that once switched on will show reverse polarity when there, in fact, is none. Be sure to verify whether this is the case before you make your purchase and go through the lengthy installation process. With the inverter powered up and the transfer switch on and not showing reverse polarity, turn on only the main breaker. You AC panel voltage gauge should show a minimum of at least 110 volts of power from your inverter. Anything less than this means something is amiss, such as too small wiring from the batteries, and needs to be corrected. If the voltage looks good, turn on a breaker to your outlets and turn on something that is plugged into those outlets. If all works well and no problems are indicated, add additional loads for test purposes. At this point it is a good idea to leave the loads on for a period of time and check the draw on the batteries. If the battery drain is excessive, some troubleshooting will be required, but remember, a fully loaded inverter will draw a fair amount from your batteries. If you have done your installation properly, you are on your way to many happy hours of silent power, at least until you need to recharge those batteries.

Once the inverter is tested and all is OK, the switches, including the main breaker on the AC panel, should be shut off, the transfer switch turned to the off position, and the inverter switch turned off. Plug the shore power cord back in and turn the shore power circuit breakers on the dock to the on position. The transfer switch should show power on the shore power side and no reverse polarity lights. Turn the main breaker switch on the AC panel to the on position and turn on your AC breakers one at a time until all of the breakers you use are on. Check over all of your switches, breakers and connections carefully. Remember this is live 110 volts, and if all is well you can button it all back up. The complete installation should be easily done over a weekend or even in one long day if you have the skills and equipment. The next time you are at anchor you can enjoy all of the conveniences of home without all of the noise of a running a generator.