Electrical Systems

The vast majority of boats on the water today depend on electricity. Unfortunately, too many of those boats are operating with unbalanced and undersized electrical systems, resulting in problems that drain both your patience and pocketbook: dead batteries, long charging times, and more. A quick fix may alleviate the problem for the short term, but if the system remains unbalanced, problems will continue to plague it. To balance your boat's electrical system you need to:

• determine your power requirements
• provide adequate power storage capacity
• provide the proper charging capacity
• set voltage regulation levels to keep the system in balance.

First, calculate your daily (24-hour) average power consumption for all of the electrical loads you place on your system. List all of the appliances and their amp draws. If amps are not listed on the appliance, you can figure amps with the following formula:

amps = watts

               volts

Next, estimate the normal daily usage for each in hours, so that you have a list of appliances and their daily draw in amp-hours (Ah). Now total them all up. You should have something that looks like the chart at right.

What Size Battery Do You Need?

Let's assume your daily power consumption totals 100 Ah. A 100-Ah battery won't do it. Why? Because battery capacity is determined in part by the intervals between battery charges, and the discharge level. A 100-Ah battery would meet your daily energy requirements, but would have no reserve, and a battery should never be fully discharged. It must be able to store and deliver the full 100 Ah between charges.

Automotive batteries are made for starting engines, with the quick release of a big burst of power. They discharge only about five percent, and are immediately recharged by the alternator. They cannot handle the repeated deep discharges typical of marine use or the constant pounding they receive at sea. Conventional wet (liquid electrolyte) batteries or deep-cycle gel cells are best at withstanding the deep discharges, recharging abuse, and the physical pounding of the marine environment. Look for batteries with the greatest number of life cycles at 50% discharge, and do not mix gel cell and lead acid batteries-use one or the other.

You will double the life of your battery if you don't discharge it below 50% capacity. Consider also that batteries recharge rapidly only up to around 70-80% of capacity. If you don't want to spend a lot of time recharging that last 30%, plan on using only about 30% of the battery's full capacity; i.e., the capacity between the 50% you're discharging down to, and the 80% you recharge to. Add in another 20% to account for the fact that no battery operates at 100% over its full life, giving yourself a little power in reserve.

Given all this you will need a 400-Ah battery to meet your 100-Ah daily energy habit. In general, a battery rated at four times your daily usage will be adequate.

Engine Starting Batteries

Do yourself a favor by reserving an adequately sized, fully charged battery solely dedicated to starting your engine. A deep-cycle battery can be used for this purpose, as long as it provides enough cold-cranking amps (the measure of how many amps the battery will supply to the starter motor for 30 seconds continuous at 0¡F). Then use a separate bank of deep-cycle "house" batteries to supply the rest of the boat's electrical needs.

Or, you can use two banks of deep-cycle batteries, each with enough cold-cranking amps to start the engine. Parallel the two banks with a dual-purpose battery isolation/selector switch for tough engine starts and then alternate between the two banks for "house" use.

Battery Charging

If you don't replace what you use, your batteries will eventually go dead, no matter how much battery capacity you have on your boat.

The rate at which you can recharge your batteries depends on a number of factors, including how much you discharged them, the temperature, the alternator's power (in amps) and its output (in volts).

Most boats charge their batteries with an engine-driven alternator. If your engine running time is minimal, you want to charge as quickly as possible, without damaging the battery. Battery damage begins when the internal temperature becomes too high, causing it to gas and heat up. If it feels warm to the touch, it's getting too hot. The voltage regulator, which tapers off the charge to prevent overheating, may be defective or improperly adjusted.

Alternators are rated in amps; the rating refers to the maximum output at a certain temperature and rotation speed. You will need about 120% of the energy you used to restore it. Take into account any other power-draining loads you might be adding to the system as you are recharging, such as refrigeration. If you install an oversized alternator, you can recharge efficiently while at anchor, with the engine at idle and the alternator operating below its rated speed and output. In general, charging capability should be approximately one third of battery capacity, plus any additional loads mentioned.

The speed of your alternator's rotation is a function of engine r.p.m.'s and pulley size. Once you have determined the maximum alternator output you require, add 25% so you won't have to operate it at full bore to achieve the required results. Now check how many alternator r.p.m.'s it takes to reach that output. Then figure the minimum engine r.p.m.'s at which you will be charging. You need a pulley ratio that gives you maximum required output at your minimum engine speed. Make sure that if you punch your engine up to 3,000 r.p.m.'s, thereby increasing your alternator speed to 12,000, you are not exceeding maximum safe alternator speed.

Voltage Regulation

The voltage regulator maintains voltage at a certain level by matching alternator output with the load and the charge level of the battery. Voltage drops when a load is placed on the power system, or when the battery discharges. The regulator then increases the amperage output of the alternator until the voltage level is restored, and then tapers output to a level that will sustain that voltage.

You should have a regulator that is external, field adjustable, so that you can tailor the settings to your specific power needs and charging patterns. If your engine running time is minimal, you may need a high setting, like 14.4 volts, to get the fast charge you need without damaging your batteries. If you run your engine for extended periods, 13.8 volts may be adequate. Multi-stage regulators, as well as multi-stage chargers, are highly recommended for gel cell battery applications.

If you own a small boat and you only need battery power at dockside intermittently for things like lights and bilge pumps, a high-frequency switcher battery charger may work best for you. It varies its charge to keep your battery at a constant 13.4 volts. The ones we carry are fully automatic and have multiple charging capabilities.

Live-aboards and larger boats with many 12-volt accessories usually have ferro-resonant chargers that put out 12 volts continuously to keep up with constant power demands. Ours are fully automatic, self-regulating, and ruggedly built to give many years of dependable service. Experts agree, however, that the best way to replace the energy you consume from your boat's batteries is through a controlled, multi-stage charging process. Both conventional lead-acid (flooded) batteries and gel cells will charge faster and last longer if they are charged in distinct phases that take into account their chemical and physical properties. The voltage levels required are both very precise and temperature dependent. The acceptance and float voltages for wet cells at 40¡ and at 90¡ vary by one volt. The recommended four-stage charging process works as follows:

1. Bulk Stage: This first stage provides a constant amperage bulk charge of 25-40% of the battery's capacity in amp hours (Ah), up to about 14.4 volts (14.2 for gel cells). This bulk charge will restore about 75% of the battery's total capacity. Smart chargers take less time because they deliver constant-current (amperage) output during the initial bulk stage. Conventional chargers taper off amperage output throughout the charging cycle until 14.2 to 14.4 volts (upon which they switch off entirely.

2. Absorption Stage: To prevent driving up the voltage beyond what the battery can safely accept, the remaining 25% capacity is restored at a gradually decreasing amperage rate, while maintaining the battery at 14.2- 14.4 volts acquired at the end of the bulk stage. The reduced amperage output gives the battery time to absorb this last 25% of energy without damaging the plates. The battery is considered nearly fully charged.

3. Float Stage: To maintain battery capacity, the charge amperage decreases to 2-4% of the battery's amp-hour capacity while maintaining a constant voltage output of 13.2 to 13.6 volts, which is enough to meet ongoing DC power demands and avoid overcharging.

4. Equalization Stage: This conditioning phase is essential for obtaining the maximum life expectancy from wet-cell batteries. To achieve this, a small constant current is applied until the battery reaches 16 volts. This dissolves the hardened lead sulfate crystals on the battery plates and prolongs battery life.

How Do You Know When You're Fully Charged?

To save engine running time, many boaters charge their batteries to only 80-85% of capacity. But you can maintain a better, balanced energy system aboard your boat and prolong battery life by installing an amp-hour meter or percentage meter. The meter will tell you how much battery capacity you have discharged. If you follow the experts' advice and never discharge below 50% of capacity, the amp-hour meter will let you know when it's time to begin charging. When the battery is fully charged, the amp-hour meter will read "0." Your charging time will be more efficient, and you'll rest assured you have enough power to start your engine.

An amp-hour meter will also let you monitor your charging so you can decide how much time you want to spend in the absorption phase to gain the battery capacity you need. A good rule of thumb for achieving adequate, but less than full charge in a reasonable amount of time is to bring your battery quickly through the bulk stage to the absorption phase, and then let the amperage decline to about 10% of your battery capacity; i.e., charge a 200-Ah battery until it accepts about 20 amps at 14.4 volts (14.2 for gel cells.) If you don't usually recharge to full capacity, remember to top off your batteries to full charge periodically to prolong their life, and to "zero", or reset, your amp-hour meter when your battery is fully charged.

Note that gel, AGM, or any sealed battery will typically have bulk and float rates different from those for the more common wet-cell lead-acid battery. All chargers must be adjusted to the appropriate output level to avoid overcharging. Consult battery and charger manufacturers to ensure compatibility.

Although wet-cell batteries will benefit as well as multi-stage "smart" chargers (and multi-stage regulators) are highly recommended. Never use a charger intended for wet-cell batteries on sealed batteries.

There's nothing quite like a boat for testing an electrical circuit to its limits! At the best of times the cables and terminals must put up with a combination of the omnipresent salt atmosphere and vibration (the United States Coast Guard requires fuel tanks to be tested at up to 25 G's); at the worst of times these cables may be totally submerged in bilge water, or dripping with engine oil, or cooked at high temperatures. All too often, salt infiltrates terminals and wicks up conductors, causing corrosion and electrical resistance; vibration causes copper conductors to work harder and fracture; and oil and high temperatures degrade insulating properties, leading to short circuits. As electrical efficiency declines, equipment fails, and in worst cases fires are started.

It makes no sense to install high-quality, marine-rated electrical and electronic equipment on boats without at the same time using high quality, marine-rated cables and terminals to power the equipment. In the marine environment, "high-quality, marine-rated" is determined by the following:

• Tinned conductors, in which every strand of a cable is individually tinned to minimize corrosion.
• Multi-stranded conductors, which use what is known as Type 3 stranding to maximize flexibility and minimize the potential for work hardening and fracture.
• Heavy-duty, moisture- and oil-resistant, high-heat rated PVC insulation.
• Tin-plated, annealed copper terminals with a rugged nylon insulator designed to be double crimped so as to relieve vibration-induced stresses at the crimp;.
• Heavy-wall, glue-lined, heat-shrink tubing to seal connectors against salt intrusion.
• Ancor cables, terminals, and heat-shrink tubing, which we stock, are built to meet these demanding standards. Properly installed, they will ensure the integrity of electrical circuits for many, many years to come.

Cable Sizing

Proper installation is primarily a matter of sizing a cable to match its tasks, using the correct tools to attach terminals, and providing adequate overcurrent protection for fuses and circuit breakers.

Cable sizing is simple enough. It is a function of the length of a cable (measuring from the power source to the appliance and back), and the current (amperage) that will flow through it. This can be found by checking the label on the appliance in the circuit, or the specifications sheet for the appliance. The longer the cable, or the higher the amperage, the bigger the cable must be to avoid unacceptable voltage losses.

For 12-volt circuits, the relationship between cable length, current flow, and cable size is given in the two tables below. Note that Table 1 presupposes a 3% voltage loss in the cable, while Table 2 presupposes a 10% voltage loss. What this means is that when the circuit is fully loaded (i.e. operating at rated amperage), the voltage at the appliance will be 3% or 10% below that at the battery. For example, if the battery is at 12.6 volts, the appliance will be seeing 12.2 volts (3% loss), or 11.34 volts (10% loss).

The cable sizing tables are used by running across the top row until the column with the relevant amperage is found, and then moving down the left-hand column until the row with the relevant distance is reached. The number in the body of the table at the intersection of this row and column is the wire size (in something known as the American Wire Gauge); the lower the number, the bigger the cable! Use this wire size (gauge) to find the correct product in our catalog.

Many appliances (notably lights) will run fine with a 10% voltage loss, but others are particularly sensitive to such losses (notably charging circuits, and some electric motors). In general, given the harsh realities of the marine environment, it's better to use the 3% volt drop table when sizing cables, rather than the 10% table. There's never a performance penalty if a cable is marginally oversized; there is always a performance penalty (and possibly a safety hazard) if it's undersized. ABYC and the United States Coast Guard require a 3% drop for circuits involving the safety of the vessel or it's passengers.

The ground (negative) cable is as much a part of a circuit as the positive cable; it must be sized the same. In general, each appliance should be supplied from the distribution panel with its own positive and negative cables, although lighting circuits sometimes use common supply and ground cables to feed a number of lights (in which case the supply cables must be sized for the total load of all the lights).

Terminals and Tools

Terminals need to be matched to their cables. A 16-gauge cable needs a 16-gauge terminal. However, the same-sized terminals are sometimes used for more than one cable size. Red terminals fit 22 to 18 gauge cables, blue terminals 16 to 14 gauge cables, and yellow terminals 12 to 10 gauge cables. In larger sizes, each cable has matching terminals.

The terminals are the weak link in an electrical circuit. If installed incorrectly, they're likely to create power-robbing resistance. Since resistance causes heat, fires can result from improperly installed terminals. Crimp-on terminals have gained universal acceptance in marine wiring, but to work effectively they must be put on with the proper tools. For marine electrical work you need a wire stripper (rather than a pocket knife, which is likely to nick the copper strands in the conductor), and a decent crimping tool. The crimper needs to be matched to the terminal size being crimped, and should preferably make a double crimp, once on the conductor and once to grip the insulation for strain and fatigue relief.

For the ultimate in terminal protection and longevity following crimping, a connection can be protected with a length of glue-lined, heat-shrink tubing. Properly applied, this will make the connection watertight; the connection should last the life of the boat.

Overcurrent Protection

Overcurrent protection is a frequently misunderstood subject. Its need arises from the fact that if a short circuit develops in onboard wiring, high current flows occur, generating heat and causing cables to melt down. If the short is a serious one (a "dead short"), cables can burst into flames, setting fire to the boat and its surroundings. Electrical fires are among the most common fires onboard.

Fuses and circuit breakers, which collectively are known as overcurrent protection devices, are the primary defense against electrical fires. To be effective, they must meet two conditions: they must be properly sized for their circuit, and they must be placed as close as possible to the electrical source for the circuit.

Sizing is a function of the cable sizes in the circuit, not the amperage draw of the appliance in the circuit. A fuse or circuit breaker is sized to protect the smallest wire in its circuit. The current-carrying capability (ampacity) of this wire is determined by referring to Table 3, and then a fuse or circuit breaker is chosen with a rating no higher than this (it can be lower). If there is not an exact match between cable ampacity and available fuse or circuit breaker ratings, an overcurrent device with a rating of up to 150% of the ampacity of the cable can be used, but that's the limit.

There are two columns in the ampacity table-one for use outside engine spaces, and one for use inside engine spaces. The reason for this is that engine rooms are usually hot. Even before a circuit is turned on, a cable is warm. In these conditions it takes less current flow to bring the cable to a dangerous temperature than it does in a colder environment; hence, the de- rating in high ambient temperatures. If any part of a circuit runs through engine room spaces, the lower ampacity rating is used to determine the proper overcurrent protection for that circuit.

To be effective, overcurrent protection devices must be installed as close as possible to the source of power for a circuit. In fact, the ABYC recommends that circuits be fused within 7" of their connection to a power source. There are some exceptions to this recommendation, notably cranking circuits (these require no protection at all), circuits that are connected directly to a battery post (in which case the 7" is extended to 72"), and cables which are housed in a sheath (in which case the 7" is extended to 40"), but in general the point needs to be made: every circuit should be provided with a properly sized overcurrent protection device at the circuit's connection to a power source. If you've got a bunch of cables hot-wired to your batteries with no overcurrent protection, not only are these circuits not recommended, but you're also inviting a fire!

Circuit breakers and fuses are available for anything from a fraction of an amp up to 800 amps. We also carry a wide array of fuse blocks and distribution panels for mounting these fuses and circuit breakers. We urge you to take advantage of them and provide the proper overcurrent protection for your boat.

Miscellaneous

Other important points to bear in mind when wiring boats:

• All circuits should be as high as possible with no connections in bilge water or damp areas.
• Use twisted-pair conductors for any wiring within three feet of a compass.
• You should never tap into existing circuits when installing new equipment; run a properly-sized new duplex cable (positive and negative conductors in a common sheath) from the distribution panel (or a source of power) to the appliance.
• All conductors should be labeled at both ends, and you should keep an updated wiring plan on board, to aid in future troubleshooting.
• Each circuit should have an independent ground cable, and all the ground cables should eventually be tied back to a common ground point which is grounded to the battery negative; if devastating stray current is to be avoided, this is the only point at which the grounds should be interconnected.
• Unless in a conduit, cables should be supported at least every 18".
• Although black is often used for DC negative, it is also used for the live wire in AC circuits. That means there is potential for dangerous confusion. Instead, you should use yellow for DC negative wherever possible.
• High-quality coax cable is critical to the effective functioning of radios; use only fully-tinned, 96% braid coax, and ensure that all connectors and terminals are properly installed.
• DC and AC wiring should be kept separate; if they have to be run in the same bundle, one or the other should be in a sheath to maintain separation and ensure safety.
• Be sure to isolate the batteries before working on the DC system, and, for safety's sake, shut off all potential AC power sources (the shorepower cord,an onboard AC generator, or an inverter).

Crimping Facts

Fine stranded cables, those with a large quantity of small-diameter strands, improve a crimped joint's performance. Finer strands more readily fill the inside contour of a terminal as it is crimped. This even distribution of strands allows imposed loads to be distributed more evenly. Air pockets or voids in a crimped joint with coarse stranding increase resistance and temperature which in turn can lead to a faster rate of corrosion.

When selecting the correct terminal, make sure the terminal's wire range is compatible with the actual wire size. Make certain the terminals and wire strands are free of oxidation and corrosion. This will insure a positive connection.

While crimping, an adequate amount of pressure must be applied so that oxides that build up on the inside of the terminal barrel are broken down. Unless good metal-to-metal contact occurs, resistance can build up on the terminal.

Our thanks to Ancor for this information.

If your idea of getting away from it all is taking it all with you, onboard AC power is a must. With the use of a 120vAC power source you can operate your microwave, TV, hair dryer, or any other appliance that you'd rather not do without.

120vAC power is available three ways: as shorepower, or through the use of a generator or inverter. Your choice of which to use will depend on your power requirements. Assuming you don't want to stay tethered to the dock, let's compare generators (gensets) to inverters. Gensets produce large quantities of continuous power, and are ideal for running air conditioners, refrigeration, and other high-load, long-duration applications. They will also charge the ship's batteries while providing all your power needs. However, gensets are engines and require periodic maintenance. And although modern technology has rendered the generator's old smoky, noisy, monolithic stereotype obsolete, gensets do vibrate, require a fuel supply and exhaust system which consume space, and aren't all that quiet. If your needs are simpler-or at least more intermittent-an inverter might be the tool of choice. Compared to gensets, inverters provide an economical, maintenance-free, and relatively compact source of AC power. Because of their solid state circuitry, inverters no longer use mechanical vibrators and are therefore quiet and non-intrusive. Although the inverter produces a modified sine wave that's less pure than the true sine wave of a genset, the power from most of today's inverters is "clean" enough to run even very sensitive electronics, including computers.

Whether an inverter, genset, or a combination of both is the best solution for you requires an honest accounting of your power needs and an understanding of how these AC sources work.

How Inverters Work

Inverters work somewhat like battery chargers in reverse: they convert 12vDC power from a battery, through modern circuitry and a step-up transformer, into 120vAC current. The ship's batteries are the inverter's fuel tank, and by nature, inverters are real gas guzzlers. You can only draw upon the juice left in the tank without recharging, which is why the inverter's optimal application is handling lighter, intermittent loads. Since the inverter places such a huge drain on the batteries, it is strongly recommended that you have a separate, dedicated engine starting battery. You wouldn't want to sacrifice your engine starting for the sake of a cold drink.

Because inverters and battery chargers can share certain electrical components, many units are available with both these capabilities. Of course, you need to be drawing power from an alternate source (either shorepower or a genset) to charge the inverter's batteries. Most of today's inverter/chargers are "smart"; that is, they contain an AC sensing circuit that will switch the inverter to charge mode when in the presence of an alternate power source. They can also safeguard and prolong the life of your batteries. While charging, the inverter/charger will monitor the batteries' level of charge, backing off the power when it senses the batteries are nearing full capacity. Since overcharging is the leading cause of failure among batteries, this is an important feature to consider.

Choosing an Inverter

To select the appropriate inverter, determine your maximum requirements at any given time. This refers to the wattage drawn by each appliance, the duration that it is used, and the number of appliances you want to operate simultaneously. The examples in the chart below will help you estimate your "energy bill" for certain appliances. Use this chart as a guide-the most accurate way to total up the watts is to check the data plate on the appliance itself. This is especially important for items like hair dryers, which can vary in wattage from 500-1,500 watts, depending on the model. Keep in mind too, that some equipment, like blenders and power tools, will draw a power surge for a few seconds when they are first switched on. Modern inverters will generally accommodate these surge loads, as long as you don't switch everything on at the count of three.

To determine the maximum power you require, and the size inverter you need, make a list of all the equipment you will run simultaneously, and the amount of time it will be in use. Then simply use the chart to fill in the wattage and battery amps you'll require.

*Refrigeration as shown is calculated using a 1Ú3 duty cycle. Run time numbers represent total amp hours used @ 12vDC based on various continuous run times.

The total wattage you will be drawing at any given time will be 3,200 watts, so you'll require a 3,200-watt inverter. What about your vacuum cleaner, waffle iron, or anything else not listed on the chart? Again, check the appliance's data plate; it will tell you number of watts the item draws. If the plate states the power in amps, convert to watts using this simple formula:

Volts x Amps = Watts

Choosing Batteries

Your boat won't go far without fuel, and the same is true of inverters and batteries. The type and size batteries you use are critical to the proper operation of the inverter. An engine starting battery is designed with numerous thin plates, providing a high surface area needed to produce the short, powerful energy burst to start the engine. Inverters, however, are constantly discharging and recharging their batteries, demanding a different battery configuration. Deep-cycle batteries contain thick plates designed specifically for this type of load. To determine the size and number of batteries you'll need, let's look again at the chart. This time, we'll be adding up the amps for each appliance: in our example, the sum is 397 amp hours. We still want that waffle iron-what does it cost in battery power? You can determine the amp hours drawn by any appliance by using this formula (always round up):

AC watts x 1.1 x Hours of Use 12

Example: For a 13" TV: 50 watts x 1.1 x 2 hours= 9 amp hours 12

Notice (by rounding up) the formula answer is the same as that given in the chart! If the data plate lists AC amps rather than watts, no problem, just use a different formula:

AC Amps x 10 x 1.1 x Hours of Use= Amp hours

In the earlier example, we figured that you needed 397 amps to meet your power requirements. So, simply check the chart below to determine the type and number of batteries you need to reach a capacity of 397 amps, right? Well, almost. Nothing's perfect, and batteries are no exception. Batteries enjoy a subtropical 77¡, and hotter or colder conditions can reduce their efficiency by 20-50%. So instead of selecting batteries having a 397-amp capacity, play it safe and look for 50% more amps, in this case, a total of 595.5.

One more wrinkle: when figuring the amp hours you need, don't forget that your AC appliances aren't the only items your battery has to handle. There are DC appliances to consider-including 12vDC lights, electric head, pressure pumps, etc., so take a hard, thorough look at what you're running.

Just as you monitor your fuel gauge, you must be aware of the status of your batteries. Methods of checking the battery's juice level can range from using an inexpensive hydrometer, to purchasing one of the excellent monitoring systems offered by inverter manufacturers. Some of the features available include low battery and overload warnings and the number of amp hours consumed, displayed on a remote panel.

Only a complete accounting of your power needs will determine the source of AC power that's best for you. Whether the answer is a genset, an inverter, or a combination of both, the technology is available to make you feel like you never left home.

Inverter/chargers have revolutionized the way sailors and powerboaters think about AC appliances afloat.

The latest crop of solid state high-output inverter/battery chargers offers boaters two valuable energy transforming features. In their inverter mode, these compact units change 12vDC battery bank current into 120vAC current that can run anything from power tools to a microwave oven. Just how much load can be placed on such a surrogate power plant, and how long it can supply such demands, depends upon the size of the inverter and the capacity of the battery bank that it's connected to. The larger your AC appetite, the bigger the inverter and the more hefty the battery bank should be. The best news is how efficient these units are at transforming DC to AC energy-very little current is actually consumed by the inverter itself in the conversion process.

In its second role, the unit becomes a battery charger, and modern three-stage current regulation provides fast, complete, safe charging. Naturally there must be a source of AC current to power the unit, but this can either be a shorepower cable or the "genset" aboard your own boat. Like any electrical system, it's important to be sure that all components are equivalently matched for the job at hand. For example, a large inverter may have a high enough continuous duty power rating to handle an air conditioning unit, however there are very few boats with battery banks that can cope with such prolonged 12vDC demand. Most inverter users prefer using the unit in a less continuous manner, providing power for microwave ovens, entertainment systems, and a wide array of household tools and appliances.

It's important to keep the safety issues of 120vAC in mind. An extension cord and a power drill can be a lethal combination if it inadvertently falls over the side when a swimmer is nearby. This isn't just a trait of inverter-produced current, it's a fact of life for all forms of higher voltage electrical current whether it's born in an onboard generator, or the electrons march down a thick yellow shorepower cord. With an inverter, however, AC power can be on tap with neither the grumble of an engine nor the proximity of a shore-side outlet. This means that the entire crew needs to be aware of the on-tap convenience as well as safety issues involved.

Before picking out the right size inverter for your needs, look at the usage level of AC power you desire and the amp-hour capacity of your ship's bank of batteries. There's no free lunch, so the stingier you can be with your AC requirements, the easier it will be on your batteries and wallet. We like the idea of a simple energy audit, a simple 24-hour estimate or calculation of the amp-hours you use on an average away-from-the-dock day. Products like Heart Interface's Link battery monitors can automatically give you such numbers, or you can do it the hard way and watch amp meter readings as you isolate what each light, pump, instrument, etc. uses in amps, and then factor in how much time it will be used during the average 24-hour period. These meters also display how much discharge time is left in the batteries based upon the load at any given moment.

Ballpark accuracy is OK, but more precise information is even better. The objective of this exercise is to ascertain if there's enough unused current left in the batteries at the end of the 24 period to satisfy your AC needs. If you find yourself electrically tapped-out, the addition of an inverter may mean that you will have to charge batteries longer, more often, and/or add more storage capacity, in order to add silent AC comfort to life away from the dock.

Keep in mind the fickle nature of the 12vDC energy stored chemically in the ship's batteries. One of the most important facts of battery life is that the higher the discharge rate (measured in amperes) the less your energy reserve will be. The relationship between current draw and battery capacity is non-linear, so while battery statistics look great when a small current drains big batteries, when there's 35 amps of lights, radar, refrigeration, instruments, autopilot, etc. already in place, and somebody hits the microwave button and the inverter kicks in, the power curve will drop precipitously. A good rule of thumb to remember: every amp of AC drawn from the inverter requires 11 amps of DC from the batteries.

Batteries don't like long-term heavy lifting, it's kind of like filling saddle bags with lead-it can be a real test for a big horse and definitely life-threatening to a tired pony. If your ship's battery bank doesn't stack up as a big palomino, beware of long term big AC demands. Running the engine and capitalizing on a high-output alternator can be a means of coping with large peak loads. Those with AC refrigeration and an AC watermaker may want to power up these units when the engine is running and the bulk phase of battery charging has been completed. This power management scheme makes better use of extra alternator capacity. Heart Interface's Link 2007R system offers alternator regulation that automatically copes with efficient current regulation and also regulates their inverter/charger.

Installing an Inverter

As one of our weekend projects, we installed Heart Interface's Freedom Marine 25-12 inverter on a 1987 Egg Harbor 35 at Bob Campbell's Marine Electric Systems in Maryland. We chose this 2,500 watt inverter/charger because of its versatility both as a source of a substantial amount of alternating current as well as for the punch it packs as a 130-amp battery charger. In addition to its continuous rating, it also produces an impressive maximum output. A variety of controllers can be used to add even more versatility to the charging equation. For example, when connected to Heart Interface's Link 2007R control module, battery condition can be closely monitored. The controller can display how many amp-hours have been used, and the percent of capacity that remains in the battery bank. It can even display how long it will be before recharging is needed. Not only does this controller interface with the Freedom 25-12 but it also acts as a voltage regulator and current limiter for a high-output alternator, and can monitor and control the charging of more than one battery bank. It's an optional purchase, but its versatility and ability to enhance charging efficiency make it a worthwhile investment.

Installation

In order to balance both sides of the energy equation, the installation aboard our test boat included the new Freedom Marine inverter/charger as well as an upgrade to the ship's battery bank. One of the refinements found on the unit's handy front panel is the ability to select the type of battery charging profile that's best for either lead acid, gel, or AGM batteries. There's also a battery temperature sensing function, easy-to-read LEDs, and a low voltage cut out that further protect both the charger/inverter and the batteries it's connected to.

Do-it-yourselfers as well as the pros should follow ABYC wiring standards. The well outlined step-by-step procedures listed in the installation manual provided by Heart Interface are clear and profile an efficient installation. It's important to recognize, however, that only the engine's starter and perhaps the anchor windlass have a bigger hunger for DC current, so if the unit is to be located any distance from the battery bank that provides it power, hefty cables must be used. Be sure to provide a circuit breaker of high enough amperage or install a fuse as far up stream as possible.

In the installation aboard the Egg Harbor, we opted for a dry, well-ventilated area outside the engine room to securely bulkhead mount the Freedom 25-12. The heavy-gauge battery cables were fastened with screwed-in-place wire ties and extra care was given to eliminate any sources of chafe. The AC output leads were routed to the ship's AC breaker panel and the self-stick safety alerts were put on all appropriate breakers, reminding users that AC current may be present even when the engine is not running.

To handle the increased DC demand, we upgraded the ship's battery bank with the addition of four deep cycle golf cart Seaworthy by Exide batteries. These heavy batteries were placed low in the bilge between the two engines, and the Blue Sea Systems battery boxes that held them were securely fastened to the hull. Easy access allows for regular checks of the electrolyte, and there's enough air space to provide adequate ventilation. It would have been nice to place the batteries away from the high heat of the engine room, but as with boats and life in general, a few compromises have to be made.

The main input/output cables of the Freedom Marine 25-12 were connected to the golf cart batteries for inverting and charging while the exclusive "Echo-Charge" outputs were connected to two engine start batteries.

The Freedom 25-12 inverter/charger added a big step forward to comfort, convenience, and functionality aboard our generator-equipped powerboat. Now AC is available with the engine off, allowing us to better enjoy quiet evenings in our favorite anchorages. The ice maker and refrigeration compressor run without the grumble of the genset and in addition to eliminating the noise, we make more efficient use of the energy we produce on board.

\There are several sizes of deep-cycle and lead acid batteries commonly used in inverter applications. Most are rated in amp hours. The amp-hour rating is usually relative to a 20-hour discharge cycle. Therefore, a 100-amp hour battery will provide 5 amps for 20 hours. If the rate of discharge is higher, the battery will not deliver its full rating.

Unless you run your generator all the time, your shorepower connections are the electrical lifeline for your boat while it's at the dock. Using and maintaining your shorepower cords and connectors properly extends their life.

Safety Guidelines

Part of understanding your boat's electrical system includes following some basic safety guidelines when working with alternating current (AC) marine electrical equipment and wiring.

1. Be sure that the boat's shorepower cord set is disconnected and that the auxiliary generator is turned off.

2. Be sure the area in which you are working is dry and will remain dry when your work is completed.

3. Keep all electrical wiring as high as practical above bilge water accumulation levels and a safe distance from exhaust and fuel systems.

The Basics of Your Boat's Circuitry

Regardless of whether your boat is a runabout, sailboat, or power cruiser, the principles of a boat's AC electrical system are the same. In the simplest terms, electricity is transmitted from a shoreside power source to your boat through a shore cord that connects to the boat at an AC electrical inlet. In small boats with a basic system, the shore connection is a three conductor, 15-amp, vinyl-covered cord. The 15-amp shore cord is little more than a marine grade 125-volt extension cord usually supplying a battery charger and having no branch circuits.

Many midsize boats use a 30-amp, 125-volt electrical system. The 30-amp shore cord and matching shorepower inlet are fitted with threaded rings providing a watertight connection from the power source to the boat. From the shorepower inlet, 30-amp conductors lead to the boat's AC panel board, from which power is distributed through the boat by wiring systems called branch circuits. Some larger boats use a 50-amp, 125-volt system.

In both the 30-amp and 50-amp systems, the shore cord contains three conductors-the black conductor is ungrounded or "hot" and carries 125-volts of electricity; the white conductor is the grounded conductor or neutral, and the green conductor is the ground.

In still larger yachts, a 50-amp, 125/250-volt system is employed which has a shore cord containing four conductors-the white neutral conductor, the green grounding conductor, and red and black ungrounded conductors each carrying 125-volts. In this system, the two 125-volt conductors can be combined to provide 250-volts necessary for large appliances like ranges and clothes dryers. The 50-amp 125-volt system is different than the 50-amp 125/250-volt system. The plugs and connectors from one system will not fit into the other system. To find out what you have in your boat, read the electrical rating on the face of the inlet.

Nomenclature

Understanding the proper terms for electrical products is necessary to discuss your shorepower system. Following are commonly used terms.

Shorepower Inlet

The electrical "connector" that is mounted on the boat. Power goes into the inlet. The inlet has male blades similar to a plug.

Connector

A connector is the device at the end of a shorepower cord set which makes the electrical connection to the inlet. Although any device making an electrical connection may be called a "connector," technically the connector is the device on the end of the flexible cord that has recessed (female) contacts. A connector delivers power. The contacts are recessed so a person cannot touch the live parts and get a shock.

Plug

A plug is the device at the end of a shorepower cord set which makes the electrical connection to a receptacle. The plug receives power, and its blades, or prongs, are typically exposed.

Shorepower Cord Set

A shorepower cord set is a flexible cord with a locking plug on one end and a locking connector on the other. A cord set must never have plugs on both ends, because if one end is energized, the blades on the other end will become live.

Receptacle

The receptacle is the device on the dock that supplies the power to the shore power cord set. Like the connector, its contacts are recessed (female) so that the live parts cannot be touched.

Adapter

Adapters consist of a plug and connector electrically connected together. The plug and the connector are different configurations to adapt from one current rating to another. There are also "Y" adapters so that when the adapter is plugged into a receptacle, or connector, it splits the power to two different inlets, or cordsets.

It is important for your boating safety and enjoyment that you understand your boat's AC electrical system. For a thorough guide, order MARINCO's "Boater's Guide to AC Electrical Systems." It's free! (Item 226047)

Information provided courtesy of Marinco.