AC current must alternate between two points making a circuit.

Coming from the power source is the “hot” wire, which normally has black insulation, and returning is the neutral or “grounded” conductor, which is white. “Neutral” carries the same current as the hot wire. As long as the current remains in this closed circuit there is no danger, but if it should escape (a “fault” or “short circuit”), it will attempt to go directly to ground.

Most modern AC circuits have a green third wire, which is a “grounding” wire. It is connected to the third prong of the common three-prong plugs; it parallels the white wire and it connects to neutral at the power source. It’s supposed to ground the circuit when a short occurs.

In a household system the third wire works well as long as three-prong plugs are used and the grounding wire is intact. (Note: it won’t protect you if you touch the hot and neutral wires at the same time.) Household electrical systems are grounded through a metal rod driven into the earth under or next to the building. Between that rod and the people in the house are many layers of wood, concrete and other electrically insulating materials.

In a boatyard, where workers may be standing or crawling on wet ground, there is a potential for electrocution. When a boat is floating, the water is the ground and any metal that has an electrical path to it, including the hull of a metal boat or the engine of a glass or wood boat via the shaft, becomes a path to the ground. Touching any of these items and a hot wire at the same time can send current through the body.

When an alternator produces AC voltage, the voltage switches polarity over time, but does so in a very particular manner. When graphed over time, the "wave" traced by this voltage of alternating polarity from an alternator takes on a distinct shape, known as a sine wave: Figure below

Graph of AC voltage over time (the sine wave).

In the voltage plot from an electromechanical alternator, the change from one polarity to the other is a smooth one, the voltage level changing most rapidly at the zero ("crossover") point and most slowly at its peak. If we were to graph the trigonometric function of "sine" over a horizontal range of 0 to 360 degrees, we would find the exact same pattern as in Table below.

The reason why an electromechanical alternator outputs sine-wave AC is due to the physics of its operation. The voltage produced by the stationary coils by the motion of the rotating magnet is proportional to the rate at which the magnetic flux is changing perpendicular to the coils (Faraday's Law of Electromagnetic Induction). That rate is greatest when the magnet poles are closest to the coils, and least when the magnet poles are furthest away from the coils. Mathematically, the rate of magnetic flux change due to a rotating magnet follows that of a sine function, so the voltage produced by the coils follows that same function.

If we were to follow the changing voltage produced by a coil in an alternator from any point on the sine wave graph to that point when the wave shape begins to repeat itself, we would have marked exactly one cycle of that wave. This is most easily shown by spanning the distance between identical peaks, but may be measured between any corresponding points on the graph. The degree marks on the horizontal axis of the graph represent the domain of the trigonometric sine function, and also the angular position of our simple two-pole alternator shaft as it rotates: Figure below

Alternator voltage as function of shaft position (time).

Since the horizontal axis of this graph can mark the passage of time as well as shaft position in degrees, the dimension marked for one cycle is often measured in a unit of time, most often seconds or fractions of a second. When expressed as a measurement, this is often called the period of a wave. The period of a wave in degrees is always 360, but the amount of time one period occupies depends on the rate voltage oscillates back and forth.

A more popular measure for describing the alternating rate of an AC voltage or current wave than period is the rate of that back-and-forth oscillation. This is called frequency. The modern unit for frequency is the Hertz (abbreviated Hz), which represents the number of wave cycles completed during one second of time. In the United States of America, the standard power-line frequency is 60 Hz, meaning that the AC voltage oscillates at a rate of 60 complete back-and-forth cycles every second. In Europe, where the power system frequency is 50 Hz, the AC voltage only completes 50 cycles every second. A radio station transmitter broadcasting at a frequency of 100 MHz generates an AC voltage oscillating at a rate of 100 million cycles every second.

Prior to the canonization of the Hertz unit, frequency was simply expressed as "cycles per second." Older meters and electronic equipment often bore frequency units of "CPS" (Cycles Per Second) instead of Hz. Many people believe the change from self-explanatory units like CPS to Hertz constitutes a step backward in clarity. A similar change occurred when the unit of "Celsius" replaced that of "Centigrade" for metric temperature measurement. The name Centigrade was based on a 100-count ("Centi-") scale ("-grade") representing the melting and boiling points of H₂O, respectively. The name Celsius, on the other hand, gives no hint as to the unit's origin or meaning.

Period and frequency are mathematical reciprocals of one another. That is to say, if a wave has a period of 10 seconds, its frequency will be 0.1 Hz, or 1/10 of a cycle per second:

An instrument called an oscilloscope, Figure below, is used to display a changing voltage over time on a graphical screen. You may be familiar with the appearance of an ECG or EKG (electrocardiograph) machine, used by physicians to graph the oscillations of a patient's heart over time. The ECG is a special-purpose oscilloscope expressly designed for medical use. General-purpose oscilloscopes have the ability to display voltage from virtually any voltage source, plotted as a graph with time as the independent variable. The relationship between period and frequency is very useful to know when displaying an AC voltage or current waveform on an oscilloscope screen. By measuring the period of the wave on the horizontal axis of the oscilloscope screen and reciprocating that time value (in seconds), you can determine the frequency in Hertz.

Time period of sinewave is shown on oscilloscope.

Voltage and current are by no means the only physical variables subject to variation over time. Much more common to our everyday experience is sound, which is nothing more than the alternating compression and decompression (pressure waves) of air molecules, interpreted by our ears as a physical sensation. Because alternating current is a wave phenomenon, it shares many of the properties of other wave phenomena, like sound. For this reason, sound (especially structured music) provides an excellent analogy for relating AC concepts.

In musical terms, frequency is equivalent to pitch. Low-pitch notes such as those produced by a tuba or bassoon consist of air molecule vibrations that are relatively slow (low frequency). High-pitch notes such as those produced by a flute or whistle consist of the same type of vibrations in the air, only vibrating at a much faster rate (higher frequency). Figure below is a table showing the actual frequencies for a range of common musical notes.

The frequency in Hertz (Hz) is shown for various musical notes.

Astute observers will notice that all notes on the table bearing the same letter designation are related by a frequency ratio of 2:1. For example, the first frequency shown (designated with the letter "A") is 220 Hz. The next highest "A" note has a frequency of 440 Hz -- exactly twice as many sound wave cycles per second. The same 2:1 ratio holds true for the first A sharp (233.08 Hz) and the next A sharp (466.16 Hz), and for all note pairs found in the table.

Audibly, two notes whose frequencies are exactly double each other sound remarkably similar. This similarity in sound is musically recognized, the shortest span on a musical scale separating such note pairs being called an octave. Following this rule, the next highest "A" note (one octave above 440 Hz) will be 880 Hz, the next lowest "A" (one octave below 220 Hz) will be 110 Hz. A view of a piano keyboard helps to put this scale into perspective: Figure below

An octave is shown on a musical keyboard.

As you can see, one octave is equal to seven white keys' worth of distance on a piano keyboard. The familiar musical mnemonic (doe-ray-mee-fah-so-lah-tee) -- yes, the same pattern immortalized in the whimsical Rodgers and Hammerstein song sung in The Sound of Music -- covers one octave from C to C.

While electromechanical alternators and many other physical phenomena naturally produce sine waves, this is not the only kind of alternating wave in existence. Other "waveforms" of AC are commonly produced within electronic circuitry. Here are but a few sample waveforms and their common designations in figure below

Some common waveshapes (waveforms).

These waveforms are by no means the only kinds of waveforms in existence. They're simply a few that are common enough to have been given distinct names. Even in circuits that are supposed to manifest "pure" sine, square, triangle, or sawtooth voltage/current waveforms, the real-life result is often a distorted version of the intended waveshape. Some waveforms are so complex that they defy classification as a particular "type" (including waveforms associated with many kinds of musical instruments). Generally speaking, any waveshape bearing close resemblance to a perfect sine wave is termed sinusoidal, anything different being labeled as non-sinusoidal. Being that the waveform of an AC voltage or current is crucial to its impact in a circuit, we need to be aware of the fact that AC waves come in a variety of shapes.

• AC produced by an electromechanical alternator follows the graphical shape of a sine wave.
• One cycle of a wave is one complete evolution of its shape until the point that it is ready to repeat itself.
• The period of a wave is the amount of time it takes to complete one cycle.
• Frequency is the number of complete cycles that a wave completes in a given amount of time. Usually measured in Hertz (Hz), 1 Hz being equal to one complete wave cycle per second.
• Frequency = 1/(period in seconds)

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Anderson Connectors or Anderson Plugs as they are more commonly known, are designed for connecting large cables used in high current applications.

Each plug is a mirror of the other and are simple to assemble, There is no Male & Female. One simply connects into another of the same amperage. The plugs push together to form a very solid and reliable connection.

A common application in marine would be in the wiring that distributes AC power.

From the Anderson Power Products website:

Anderson Power Products is an industry leader in the manufacture of high current, quick-disconnect power connectors and provides a variety of interconnect solutions for the material handling, telecommunications, medical, power electronics and other industries. Our connectors are available from 10 to 700 amp maximum ratings for use through 600 Volts continuous, AC or DC operation. We are well known for our ability to develop creative solutions for our customers’ power interconnect requirements. We are flexible and will make modifications to standard products or develop complete custom solutions to satisfy particular customers’ needs. APP provides a complete engineered interconnect solution for all types of power distribution needs.

Most students of electricity begin their study with what is known as direct current (DC), which is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other.

As useful and as easy to understand as DC is, it is not the only "kind" of electricity in use. Certain sources of electricity (most notably, rotary electro-mechanical generators) naturally produce voltages alternating in polarity, reversing positive and negative over time. Either as a voltage switching polarity or as a current switching direction back and forth, this "kind" of electricity is known as Alternating Current (AC): Figure below

Direct vs alternating current

Whereas the familiar battery symbol is used as a generic symbol for any DC voltage source, the circle with the wavy line inside is the generic symbol for any AC voltage source.

One might wonder why anyone would bother with such a thing as AC. It is true that in some cases AC holds no practical advantage over DC. In applications where electricity is used to dissipate energy in the form of heat, the polarity or direction of current is irrelevant, so long as there is enough voltage and current to the load to produce the desired heat (power dissipation). However, with AC it is possible to build electric generators, motors and power distribution systems that are far more efficient than DC, and so we find AC used predominately across the world in high power applications. To explain the details of why this is so, a bit of background knowledge about AC is necessary.

If a machine is constructed to rotate a magnetic field around a set of stationary wire coils with the turning of a shaft, AC voltage will be produced across the wire coils as that shaft is rotated, in accordance with Faraday's Law of electromagnetic induction. This is the basic operating principle of an AC generator, also known as an alternator: Figure below

Alternator operation

Notice how the polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit. The faster the alternator's shaft is turned, the faster the magnet will spin, resulting in an alternating voltage and current that switches directions more often in a given amount of time.

While DC generators work on the same general principle of electromagnetic induction, their construction is not as simple as their AC counterparts. With a DC generator, the coil of wire is mounted in the shaft where the magnet is on the AC alternator, and electrical connections are made to this spinning coil via stationary carbon "brushes" contacting copper strips on the rotating shaft. All this is necessary to switch the coil's changing output polarity to the external circuit so the external circuit sees a constant polarity: Figure below

DC generator operation

The generator shown above will produce two pulses of voltage per revolution of the shaft, both pulses in the same direction (polarity). In order for a DC generator to produce constant voltage, rather than brief pulses of voltage once every 1/2 revolution, there are multiple sets of coils making intermittent contact with the brushes. The diagram shown above is a bit more simplified than what you would see in real life.

The problems involved with making and breaking electrical contact with a moving coil should be obvious (sparking and heat), especially if the shaft of the generator is revolving at high speed. If the atmosphere surrounding the machine contains flammable or explosive vapors, the practical problems of spark-producing brush contacts are even greater. An AC generator (alternator) does not require brushes and commutators to work, and so is immune to these problems experienced by DC generators.

The benefits of AC over DC with regard to generator design is also reflected in electric motors. While DC motors require the use of brushes to make electrical contact with moving coils of wire, AC motors do not. In fact, AC and DC motor designs are very similar to their generator counterparts (identical for the sake of this tutorial), the AC motor being dependent upon the reversing magnetic field produced by alternating current through its stationary coils of wire to rotate the rotating magnet around on its shaft, and the DC motor being dependent on the brush contacts making and breaking connections to reverse current through the rotating coil every 1/2 rotation (180 degrees).

So we know that AC generators and AC motors tend to be simpler than DC generators and DC motors. This relative simplicity translates into greater reliability and lower cost of manufacture. But what else is AC good for? Surely there must be more to it than design details of generators and motors! Indeed there is. There is an effect of electromagnetism known as mutual induction, whereby two or more coils of wire placed so that the changing magnetic field created by one induces a voltage in the other. If we have two mutually inductive coils and we energize one coil with AC, we will create an AC voltage in the other coil. When used as such, this device is known as a transformer: Figure below

Transformer "transforms" AC voltage and current.

The fundamental significance of a transformer is its ability to step voltage up or down from the powered coil to the unpowered coil. The AC voltage induced in the unpowered ("secondary") coil is equal to the AC voltage across the powered ("primary") coil multiplied by the ratio of secondary coil turns to primary coil turns. If the secondary coil is powering a load, the current through the secondary coil is just the opposite: primary coil current multiplied by the ratio of primary to secondary turns. This relationship has a very close mechanical analogy, using torque and speed to represent voltage and current, respectively: Figure below

Speed multiplication gear train steps torque down and speed up. Step-down transformer steps voltage down and current up.

If the winding ratio is reversed so that the primary coil has less turns than the secondary coil, the transformer "steps up" the voltage from the source level to a higher level at the load: Figure below

Speed reduction gear train steps torque up and speed down. Step-up transformer steps voltage up and current down.

The transformer's ability to step AC voltage up or down with ease gives AC an advantage unmatched by DC in the realm of power distribution in figure below. When transmitting electrical power over long distances, it is far more efficient to do so with stepped-up voltages and stepped-down currents (smaller-diameter wire with less resistive power losses), then step the voltage back down and the current back up for industry, business, or consumer use use.

Transformers enable efficient long distance high voltage transmission of electric energy.

Transformer technology has made long-range electric power distribution practical. Without the ability to efficiently step voltage up and down, it would be cost-prohibitive to construct power systems for anything but close-range (within a few miles at most) use.

As useful as transformers are, they only work with AC, not DC. Because the phenomenon of mutual inductance relies on changing magnetic fields, and direct current (DC) can only produce steady magnetic fields, transformers simply will not work with direct current. Of course, direct current may be interrupted (pulsed) through the primary winding of a transformer to create a changing magnetic field (as is done in automotive ignition systems to produce high-voltage spark plug power from a low-voltage DC battery), but pulsed DC is not that different from AC. Perhaps more than any other reason, this is why AC finds such widespread application in power systems.

• DC stands for "Direct Current," meaning voltage or current that maintains constant polarity or direction, respectively, over time.
• AC stands for "Alternating Current," meaning voltage or current that changes polarity or direction, respectively, over time.
• AC electromechanical generators, known as alternators, are of simpler construction than DC electromechanical generators.
• AC and DC motor design follows respective generator design principles very closely.
• A transformer is a pair of mutually-inductive coils used to convey AC power from one coil to the other. Often, the number of turns in each coil is set to create a voltage increase or decrease from the powered (primary) coil to the unpowered (secondary) coil.
• Secondary voltage = Primary voltage (secondary turns / primary turns)
• Secondary current = Primary current (primary turns / secondary turns)

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Working inside a boat up on blocks is essentially the same as one in the water, if it is grounded through its three-wire power cord. If the vessel is not grounded and a fault develops in the hot lead, workers outside the boat on wet ground or contacting metal ladders or stands are in danger.

Extension cords, especially the household two-prong type, increase the risk; wearing rubber boots and rubber gloves can reduce the risk somewhat. Using an AC on the exterior of a floating boat is courting disaster. If a power drill or sander gets splashed or falls overboard, seawater will conduct current from the hot wire to the case, making the tool hot. If the grounding wire is not effective, any path to the sea via wet decks or a metal conductor makes the worker part of the circuit. Divers and swimmers in the water are susceptible to electrical shock, especially if there is a direct short such as would occur if a live power cord drops into the water.

Even a relatively low-voltage fault can establish an electrical field around the boat, which could cause a current flow through a swimmer’s body causing fibrillation. Current leakage into the water can also paralyze muscles and cause drowning with no visible evidence of electrocution.

The electrons of different types of atoms have different degrees of freedom to move around. With some types of materials, such as metals, the outermost electrons in the atoms are so loosely bound that they chaotically move in the space between the atoms of that material by nothing more than the influence of room-temperature heat energy. Because these virtually unbound electrons are free to leave their respective atoms and float around in the space between adjacent atoms, they are often called free electrons.

In other types of materials such as glass, the atoms' electrons have very little freedom to move around. While external forces such as physical rubbing can force some of these electrons to leave their respective atoms and transfer to the atoms of another material, they do not move between atoms within that material very easily.

This relative mobility of electrons within a material is known as electric conductivity. Conductivity is determined by the types of atoms in a material (the number of protons in each atom's nucleus, determining its chemical identity) and how the atoms are linked together with one another. Materials with high electron mobility (many free electrons) are called conductors, while materials with low electron mobility (few or no free electrons) are called insulators.

Here are a few common examples of conductors and insulators:

• silver
• copper
• gold
• aluminum
• iron
• steel
• brass
• bronze
• mercury
• graphite
• dirty water
• concrete

• glass
• rubber
• oil
• asphalt
• fiberglass
• porcelain
• ceramic
• quartz
• (dry) cotton
• (dry) paper
• (dry) wood
• plastic
• air
• diamond
• pure water

It must be understood that not all conductive materials have the same level of conductivity, and not all insulators are equally resistant to electron motion. Electrical conductivity is analogous to the transparency of certain materials to light: materials that easily "conduct" light are called "transparent," while those that don't are called "opaque." However, not all transparent materials are equally conductive to light. Window glass is better than most plastics, and certainly better than "clear" fiberglass. So it is with electrical conductors, some being better than others.

For instance, silver is the best conductor in the "conductors" list, offering easier passage for electrons than any other material cited. Dirty water and concrete are also listed as conductors, but these materials are substantially less conductive than any metal.

Physical dimension also impacts conductivity. For instance, if we take two strips of the same conductive material -- one thin and the other thick -- the thick strip will prove to be a better conductor than the thin for the same length. If we take another pair of strips -- this time both with the same thickness but one shorter than the other -- the shorter one will offer easier passage to electrons than the long one. This is analogous to water flow in a pipe: a fat pipe offers easier passage than a skinny pipe, and a short pipe is easier for water to move through than a long pipe, all other dimensions being equal.

It should also be understood that some materials experience changes in their electrical properties under different conditions. Glass, for instance, is a very good insulator at room temperature, but becomes a conductor when heated to a very high temperature. Gases such as air, normally insulating materials, also become conductive if heated to very high temperatures. Most metals become poorer conductors when heated, and better conductors when cooled. Many conductive materials become perfectly conductive (this is called superconductivity) at extremely low temperatures.

While the normal motion of "free" electrons in a conductor is random, with no particular direction or speed, electrons can be influenced to move in a coordinated fashion through a conductive material. This uniform motion of electrons is what we call electricity, or electric current. To be more precise, it could be called dynamic electricity in contrast to static electricity, which is an unmoving accumulation of electric charge. Just like water flowing through the emptiness of a pipe, electrons are able to move within the empty space within and between the atoms of a conductor. The conductor may appear to be solid to our eyes, but any material composed of atoms is mostly empty space! The liquid-flow analogy is so fitting that the motion of electrons through a conductor is often referred to as a "flow."

A noteworthy observation may be made here. As each electron moves uniformly through a conductor, it pushes on the one ahead of it, such that all the electrons move together as a group. The starting and stopping of electron flow through the length of a conductive path is virtually instantaneous from one end of a conductor to the other, even though the motion of each electron may be very slow. An approximate analogy is that of a tube filled end-to-end with marbles:

The tube is full of marbles, just as a conductor is full of free electrons ready to be moved by an outside influence. If a single marble is suddenly inserted into this full tube on the left-hand side, another marble will immediately try to exit the tube on the right. Even though each marble only traveled a short distance, the transfer of motion through the tube is virtually instantaneous from the left end to the right end, no matter how long the tube is. With electricity, the overall effect from one end of a conductor to the other happens at the speed of light: a swift 186,000 miles per second!!! Each individual electron, though, travels through the conductor at a much slower pace.

If we want electrons to flow in a certain direction to a certain place, we must provide the proper path for them to move, just as a plumber must install piping to get water to flow where he or she wants it to flow. To facilitate this, wires are made of highly conductive metals such as copper or aluminum in a wide variety of sizes.

Remember that electrons can flow only when they have the opportunity to move in the space between the atoms of a material. This means that there can be electric current only where there exists a continuous path of conductive material providing a conduit for electrons to travel through. In the marble analogy, marbles can flow into the left-hand side of the tube (and, consequently, through the tube) if and only if the tube is open on the right-hand side for marbles to flow out. If the tube is blocked on the right-hand side, the marbles will just "pile up" inside the tube, and marble "flow" will not occur. The same holds true for electric current: the continuous flow of electrons requires there be an unbroken path to permit that flow. Let's look at a diagram to illustrate how this works:

A thin, solid line (as shown above) is the conventional symbol for a continuous piece of wire. Since the wire is made of a conductive material, such as copper, its constituent atoms have many free electrons which can easily move through the wire. However, there will never be a continuous or uniform flow of electrons within this wire unless they have a place to come from and a place to go. Let's add an hypothetical electron "Source" and "Destination:"

Now, with the Electron Source pushing new electrons into the wire on the left-hand side, electron flow through the wire can occur (as indicated by the arrows pointing from left to right). However, the flow will be interrupted if the conductive path formed by the wire is broken:

Since air is an insulating material, and an air gap separates the two pieces of wire, the once-continuous path has now been broken, and electrons cannot flow from Source to Destination. This is like cutting a water pipe in two and capping off the broken ends of the pipe: water can't flow if there's no exit out of the pipe. In electrical terms, we had a condition of electrical continuity when the wire was in one piece, and now that continuity is broken with the wire cut and separated.

If we were to take another piece of wire leading to the Destination and simply make physical contact with the wire leading to the Source, we would once again have a continuous path for electrons to flow. The two dots in the diagram indicate physical (metal-to-metal) contact between the wire pieces:

Now, we have continuity from the Source, to the newly-made connection, down, to the right, and up to the Destination. This is analogous to putting a "tee" fitting in one of the capped-off pipes and directing water through a new segment of pipe to its destination. Please take note that the broken segment of wire on the right hand side has no electrons flowing through it, because it is no longer part of a complete path from Source to Destination.

It is interesting to note that no "wear" occurs within wires due to this electric current, unlike water-carrying pipes which are eventually corroded and worn by prolonged flows. Electrons do encounter some degree of friction as they move, however, and this friction can generate heat in a conductor. This is a topic we'll explore in much greater detail later.

• In conductive materials, the outer electrons in each atom can easily come or go, and are called free electrons.
• In insulating materials, the outer electrons are not so free to move.
• All metals are electrically conductive.
• Dynamic electricity, or electric current, is the uniform motion of electrons through a conductor. Static electricity is an unmoving, accumulated charge formed by either an excess or deficiency of electrons in an object.
• For electrons to flow continuously (indefinitely) through a conductor, there must be a complete, unbroken path for them to move both into and out of that conductor.

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Disclaimer

Modern cruising vessels have high electrical demands, where refrigeration, radar, laptop computers and even plasma TVs are the norm. Keeping batteries charged is a challenge, and fitting a second alternator, says Scott Fratcher, is an easy solution

Alternator II

More charge needs either a bigger alternator, or better yet, a second alternator which adds significantly more potential to the boat than only increasing the amperage of the original alternator.

The math is easy. Imagine a typical diesel with a 55 amp alternator. If the alternator is removed and replaced with a 100 amp model, we gain 45 amps. If you add a second 130 amp alternator to the original 55 amp system, you instantly send a battery-boosting 185 amps into the electrical system.

Higher charging also increases the vessel’s safety margin. Single alternators may fail due to overwork – the constant heavy load to recharge the boat’s electrical demand takes its toll. This could lead to discharged batteries, with all electrical systems shut down. I’ve encountered many boaties who’ve spent an uncomfortable night in the shipping lanes alternating the last of the battery power between radar and navigation lights…

Many consider the decision to fit a second alternator a no-brainer. The only question is: how do you install one easily? This article discusses a technique to mount a second alternator on almost any inboard engine. And it’s worth noting that the process can be used to belt drive more than just an alternator – a hydraulic pump, dewatering bilge pump or anything else you might need to turn are also possibilities.

SIX STEPS TO ALTERNATOR II

1. Design and planning
2. Mounting a second front pulley
3. Making a base plate
4. Building a bracket from the base plate
5. Installing a belt tensioning device
6. Bolting in the alternator

DESIGN AND PLANNING
Start the design process by taking an alternator in hand and holding it next to the engine with the pulleys aligned.

There should be 12 possible positions: starboard low, starboard high, port low, port high, and above or below the drive pulley.

Face the alternator aft and you have six more possible locations – for a total of 12.

Hold the alternator in all 12 positions. Pick the best two or three positions and compare the possibilities. Choose a mounting position with the alternator as close to the engine as possible. Look for access, wire runs, mounting bolt holes in the engine and cooling air.

MOUNTING A SECOND PULLEY
We need to spin the second alternator from a second drive pulley at the front of the engine. Your engine may already have one, but usually you’ll have to add one, bolting it to the front of your existing engine pulley.

First, choose a pulley size. For a typical 30 to 75hp engine with maximum rpm of around 3600, a good drive pulley diameter is about 175mm.

I’ve experimented with larger pulleys (up to 230mm) but it’s not effective as most engines begin to hunt at low rpm. Conversely, if the pulley diameter is less than 150mm I often have to run the engine up to 1200rpm to get a good charge.

If in doubt, duplicating the original pulley size is usually a good bet.

There are two easy methods to fit a spare pulley to the front of an engine:

1. Have a machine shop make the new pulley; or,
2. Modify an existing pulley.

METHOD 1
A machine shop makes the new pulley, the simplest but most expensive option.

The machine shop will need the bolt pattern and centering ring measurements from the existing drive pulley on your engine. If you can take the measurements from the manual, the machine shop should have an easy job. If you have to take the measurements yourself, use digital calipers. Be sure to scrape away any old paint so your measurement is metal to metal.

Note: If the alternator is to produce more than 80amps, you should use a dual belt drive. You’re pushing the limit with a single belt – it will often slip, leaving gobs of black, sticky dust in your engineroom.

METHOD 2
Buy an “off-the-shelf” pulley at your local hardware store and have a machine shop make a new centering ring that fits your engine. You can even use an old car’s sheetmetal “stamped” pulley. The machine shop will combine the pulley onto a centering ring and you’re ready to install.

This option has the advantage of knowing the pulley face angles are going to be correct and smooth. It does not take much angle error, a nick or lathe marks left in the pulley face to make the belt begin to “dust”. Belt dusting is the major problem in building a dual alternator system. Twist, misalignment, rough surfaces, and drawing too much load all add to the amount of the belt dust. Commercial pulleys help solve this issue.

MAKING THE BASE PLATE
The base plate is a steel plate that gets bolted to the engine, and it becomes the base which holds the soon-to-be fabricated alternator bracket. The bracket is typically welded to the base plate.

Look for flat areas on the side of the engine block near where you want to mount your alternator. You want the plate to cover a minimum of three bolt holes – five or six is better.

Cut a piece of steel to cover the bolt holes. Using 6mm plate is the minimum – 8mm is better. Test fit the piece of steel over the area of the engine block. If it all fits and covers the bolt holes, you’re ready to start marking and drilling the holes.

Marking where the holes are to be drilled can be challenging, especially if the plate is in a difficult to reach location. Here’s an easy trick – it’s what I call the “sneak and tap” approach, and involves using a sharpened bolt screwed into each of the engine bolt holes (one at a time) to serve as a “reverse punch”.

Leave just enough bolt thread (the sharpened point) showing so you can use a pair of pliers to remove the bolt. Lay the base plate in the exact final location. Now for the tricky part – strike the steel plate with a single sharp blow from a hammer directly over the punch. Once marked you are ready to drill the hole.

Remove the bolt/punch and shift it to a new hole. Fasten the base plate (with a bolt through the newly-drilled hole) in position. Another sharp tap, remove the plate and drill the new hole. Repeat this process until all holes are drilled. This method is fast and easy and leaves no sloppy holes. If you make the base plate perfect, the rest of the job becomes much easier.

BUILDING A BRACKET
The bracket is the metal frame that holds the alternator, allowing it to pivot for tensioning the belt. I like to use a 50mm piece of 6mm flat bar. Cut two ears and weld them on the flat bar at a 90º angle (see photo).You should now have a base plate and bracket all made up. They may need to be connected with a strut (depending on the position of the alternator) to get the two pulleys in alignment. It’s usually the simplest to weld the plate, strut and bracket together.

ALIGNMENT
To find the correct alignment for the alternator, lay a wooden dowel rod in the drive pulley of the engine. Let the rod find its natural centre. You can now simply lift the rod up and down to show where an exact straight line to the slave pulley will fall. Reverse the procedure until the slave pulley is pointed directly at the drive pulley.

Remove all parts and tack the strut into position.

Replace and see if it all fits. If it does it’s time to weld it up and paint. Use this dowel rod method anytime you want an easy check of belt alignment.

MAKING A BELT-TENSIONER
Turnbuckle tension arms are an easy solution for making an alternator adjusting arm, and you only need simple tools – a hacksaw, welder and a drill. If you were making a conventional car-type tensioning arm, you’d have to cut an arc in the flat bar with an oxy-acetylene torch. Many boaties fit this turnbuckle swing arm to their existing alternator just to solve adjustment problems.

Begin with a half-inch or larger open barrel turnbuckle, and remove the studs from the barrel.

Cut the centre out of the barrel, leaving leavening 120 to 150mm of turnbuckle barrel.

Weld the barrel back together. Put the studs back in place and cut them to the length you worked out for the project at hand. Weld a flat plate to the end of each stud, drill a hole in the plates and mount to the engine.

STOP ENGINE BEFORE TURNING “OFF”
Ever notice what battery switches have printed on their faces? We all know not to disconnect the batteries while the engine is running, but what would happen if we did?

An alternator diode would fail – and that’s not good.

The reason is buried in Ohm’s Law which lays out the relationship between volts, amps, and watts. An alternator’s total power output is measured in watts. A typical high-output alternator might be charging 100amps at 14V – 100 x 14 = 1400 watts. If we had a 24-volt system, the alternator would be producing 50amps at 28 volts to make 1400 watts.

So, when we have an alternator producing 1400 watts and someone turns off the battery switch, the 1400 watts is already in the pipeline, so to speak. But the load (or current or amp draw) just dropped to zero because of disconnection to the battery.

Ohm’s Law tells us 1400 watts divided by zero (our new amp load) equals infinity. In other words, the voltage inside the alternator will climb toward infinity till it finds an escape route (the path of least resistance). That’s the shortest path to ground and typically, that’s the thin film inside a diode. Pop! The diode shorts.

Quickly switching the batteries back on might save the situation, but usually the damage is done. The boat owner may see the output of the alternator suddenly drop by a third. A typical complaint from boaties is: “My 100amp alternator is now producing 66 amps on the meter.”

This is because the alternator stator is really three-phase, and has three separate windings combining to produce 100amps. Since only the diode was ruined, each phase of the stator is still producing 33amps. If all three phases of the alternator are still producing 33amps each, why is the boat’s electrical meter only showing 66amps?

The “lost” 33amps are still being produced, but they’re not being rectified because that is the diode’s job. And un-rectified means alternating current (AC) is entering your DC system.

This is bad. At the same time that we are charging at 14 volts DC, we are also sending a battery-destroying AC “charge” into the boat’s electrical system. And because the boat’s electrical charge meter does not read AC, the owner has no clue something has gone wrong.

Those 33 AC amps are destroying the boat’s battery bank, electrical boards, and maybe even the hull zincs.

DIODE TEST
To check whether your alternator has a shorted diode you can clamp the positive alternator output lead with an AC/DC “clamp amp” meter. Switch the meter to DC amp and read the charge rate. Switch the meter to AC and we should see three or four amps.

A reading half of the DC charge rate indicates a bad diode. For example, if we were to see 66amps DC and 33amps AC, this would tell the technician it’s time to pull the alternator and change the diode pack.

Although not as accurate, we might also take a high-quality digital volt meter and measure voltage at the back of the alternator. We should see around 14 volts, but switch to AC and we should see around seven volts. Reading 14 volts AC could also indicate a faulty diode.

Adapted from Scott Fratcher’s How To Make Money With Boats, available at www.yachtwork.com

AUTO TENSIONING ARM
An automatic tensioning arm is another easy solution for a DIY installed alternator.

You can buy a “rasta” or LoveJoy arm for automatic belt tensioning from a good bearing supply house. Check out http://www.lovejoy-inc.com/

The device costs about $100. Simply mount the roller inside the unloaded belt between the drive pulley and alternator. In the photo above, the pulleys turn clockwise. Adjust the tension and ignore it for the life of the belt.

The second advantage of using a “rasta” or LoveJoy tensioning arm is the alternator does not have to rotate away from the engine to adjust the belt. This may mean a lot if you have a tight space to work in. You simply mount the alternator as close to the engine as you can manage and let the tensioning arm take up the belt slack.

AUTHOR PROFILE
Scott Fratcher has designed and installed more than 100 dual alternator systems. More photos can be found at www.yachtwork.com

Mr. Fratcher’s highly regarded books include

• How to Make Money with Boats
• Metal Boat Repair and Maintenance
• How to Buy Your Cruising Boat Now
• Earthrace – First Time Around

Mr. Fratcher also has an excellent website that is highly recommended to all easyacdc.com readers. Please be sure to visit Team Yachtwork and thank him for his thoughtful generosity.

A GFCI, or ground fault circuit interrupter, is an inexpensive (~$20 each), switch-like device that continuously monitors current in the hot and neutral conductors. When the GFCI detects an imbalance between the two, as would occur if there were a short to ground, it instantly trips the circuit.

A single GFCI can protect persons throughout the boat if it is located on the main AC feed, but because boats usually have various small current leaks, the unit may trip frequently with no indication of the source of the fault. It may be more practical to install one GFCI on each of the circuits to wet locations, such as head, galley, engine room, and weather deck.

GFCIs are extremely sensitive and can be tripped by “steam” or dense moisture in the air such as from cooking or showering, so they should be mounted in dry locations. On gas-powered boats, GFCIs must be ignition protected, or located in areas where fumes cannot collect. GFCIs should be checked at least monthly.

When the boat is afloat, inverters and gensets are grounded to the water via the engine and shaft, which act like the metal rod driven into the ground under your house.

The risk aboard a boat comes from a short that bypasses the grounding system and finds an alternative route to the sea. Standing in bilge water or touching a metal object like rudder stock or engine block, while contacting a hot wire, could make you the conductor if there is no functional grounding wire.

Marine electrical shore power presents a different set of potential problems. The shore power circuit is grounded at the dock junction box through the shore power cord and receptacle. Faulty installation, reversed polarity, defective or damaged cord or boat receptacle can create a situation that could be hazardous to persons or contribute to stray current corrosion damage to the boat.

By Terry Johnson , University of Alaska Sea Grant, Marine Advisory Program

We all live safely with alternating current (AC) electricity in the home. But with the same voltage, the marine AC system is potentially more dangerous because the boat and the people who work on it are surrounded by water.

A person who becomes part of the pathway between a hot wire and the sea can experience severe shock. Forget the blinding flash and the smoking flesh. It doesn’t take a lot of juice to kill a person. Remember, what makes the heart tick is a faint electrical impulse generated within the muscle itself. It takes only a very small amount of current through the chest to disrupt the heart rhythm, causing fatal fluttering of the heart muscle called fibrillation.

A critical factor is where the current passes through the body. Touching hot and neutral leads with one hand can give you a jolt and maybe even a burn, but won’t kill you. But grabbing a hot lead with one hand and a neutral with the other, or the lead with one hand while standing in water, can send the current through the chest.

One effect that electrical current has on the body is to make muscles contract, so a person getting a shock may be unable to release the item that’s carrying the current. The body isn’t a perfect conductor of electricity, but passing through the chest it takes only 0.05 amp to kill. That’s barely enough to light a small bulb, and an amount which easily can pass through a human body that becomes a conduit between a hot AC wire and ground.

No one intentionally grabs a hot wire, but things happen. Two-prong plugs get put into sockets backwards (a condition known as reverse polarity). Circuitry chafes or cracks, exposing bare wire. Wiring inside a power tool breaks and contacts the metal case. Pick up with one hand an electric drill that has a loose wire inside, while bracing against the engine block with the other hand, and you could be the next industrial fatality.