Today’s voyaging boat has become a hungry consumer of electricity. Now even nautical charts may blink at us from a silver screen. However modern, all these marvels still depend on a reliable supply of DC electricity. Add the basic systems that keep boats safe and working and it is obvious that today’s sailor better be able to keep those electrons crackling, especially at sea far from shore technicians.
The supply of DC comes from a battery bank that can be recharged by solar panels, wind generators, or the alternators spinning on engines. As numerous devices (inverters in particular) demand large amounts of juice, alternators, which can deliver high output in a short time and are independent of wind or sun, take the lead. Of course, to run an alternator you have to run its engine. So the engine starting system becomes equally important. When the crew goes exploring ashore, the safety of the unattended boat depends on a reliable electrical bilge pump. To be safe at sea at night the boat must display navigational lights. The ability to diagnose ailing lights, switches, fuses, circuit breakers (which combine fuse and switch functions), and supply wires now counts as part of basic seamanship.
A multimeter.To work with electrical circuits you must have a means to measure voltage in volts, amperage (current) in amperes and resistance in ohms (W). A device called a multimeter or VOM will do all three functions. Multimeters can be analog (a moving needle) or digital (numbers). A medium-priced digital meter will measure accurately low voltage and low ohmsan advantage in on-board troubleshooting. To measure amperage over the milliamp level you can use an analog meter or upgrade to an expensive digital meter. Remember that voltage is measured between positive and negative terminals of a source and amperage between the two ends of the positive side. For example: to test a solar panel for current (amps) output you switch the meter to the amps mode (10A range) and connect the red (+) probe to the positive wire of the panel (the supply) and the black (-) to the positive post of a battery (the recipient). To find an unmarked positive wire of the panel (or any other electric source), switch the meter to the voltage mode and connect one probe to each wire. When the analog needle goes off the scale to the left or a minus sign appears on the digital display, you touched the wrong wires. Reverse the probes and the red (+) probe will indicate the positive wire of the panel. You should always perform the above test before wiring DC devices sensitive to reversed polarity such as motors, fluorescent lights, ni-cad battery chargers, computer power converters, etc.
While measuring voltage or amperage you need the DC to flow. However, when it comes to measuring resistance (ohms) you should switch off the power supply to obtain accurate readings and to protect the meter. The ohmmeter mode is often used to check continuity in a circuit. An “O” reading means no resistance and a good electric path. An infinity (·) reading on an analog or “1” (referred to as infinity) on a digital display indicates a break in the circuit. With the multimeter in the high scale of Ohm mode, touch the probes to the opposite ends of a length of wirean intact wire will read “O.” A good fuse will read “O.” A burnt fuse will read infinity. A good circuit breaker or switch will read “O” when in the ON position and infinity in OFF. A good bulb will read “O” between two contacts (DC Bayonet) or the center and the base (SC Bayonet), a burnt bulb will read infinity (·).
A test light. Digital meters are so sensitive that they may read full voltage when, for example, a corroded switch or connection offers too much resistance for a bulb to shine. Instead use a test light that will instantly indicate an obstructed power flow when its bulb fails to light. To make it, wire a spare bulb socket and install a bulb drawing between 1 and 2 amps; for instance, a 15-watt bulb for a 12V DC system and 25-watt for a 24V DC. You will also use the test light in troubleshooting alternators and starter motors.
Electrical equations. Talking about electrical devices and systems becomes meaningful only after you understand the basic relationships within a circuit. In the case of our test light a 15-watt bulb divided by 12V will pull 1.25 ampere. The equation says Amps = Watts/ Volts, which derives from Volt x Amps = Watts. Most electrical devices have the required amp draw and wattage marked on them in addition to the necessary voltage. For unmarked DC devices you can figure the values yourself by using a multimeter. You will easily find the supply voltage and then amps being consumed.
These values will in turn dictate the size of wires, circuit breakers, fuses, and solenoids. Once you know that watts/volts = amps and that volts x amps = watts you are ready to use the multimeter. The wire probes of a multimeter often lack the length to reach remote terminals. Make two pieces of #12 wire, one two feet and one four feet long, ending in alligator clips. Also, buy two alligator clips that can slip tightly over the meter’s probes. This will allow you to leave the meter connected and free your hands for more tasks. After diagnosing and locating a breakdown in a circuit you will have to repair it utilizing crimp-on wire connectors and terminals. The inexpensive all-in-one cutter, stripper and crimper tool tends to cut into the wire when you strip the insulation. Next, it fails to deliver enough pressure to produce a strong connection between the wire and the terminal. Invest in a ratcheting crimper, a separate wire cutter, and an insulation stripper.
Batteries: the source
Ship battery banks typically consist of several individual batteries connected either in parallel or in series. A 12V bank may have two 6V batteries connected in seriesi.e. plus to minusin order to produce 12V. Two 12V batteries in series will deliver 24V. Two batteries are often connected in parallel (i.e., plus to plus and minus to minus, in order to combine the capacity of each batterytwo 120-amp/hr batteries in parallel will make a 240-amp/hr battery bank). Each battery consists of 2V cells connected in series, three to make 6V and six to produce 12V. Inside the battery, lead plates sit in an electrolyte of sulfuric acid and water (flooded lead/acid battery) or in a thick acid goo (gel battery). Depending on construction, size, and maintenance, batteries have a working life from two to five years.
An aging battery sends warning signals before a failure. A battery may read 12V with no load but will drop voltage rapidly when you turn on the lights. Run the battery down to about 11V, take off all loads and a healthy battery should quickly recover to 12V. If it does not, recharge the battery to 14V, turn the charge off, and let the battery settle at 12.8V. Now turn on all lights and watch the voltmeter on the boat’s electrical panela rapidly falling voltage indicates that the battery is no longer able to hold the charge. Also, a weak battery may not recharge to 14V or, if it does, may settle down to only 12V. On a wet battery you can use a hydrometer to compare the specific gravity of the electrolyte in each cell (after recharging). If they differ by more than 0.050, replace that battery soon. Unfortunately you cannot see or test the electrolyte on the sealed lead/acid gel batteries.
The performance of a battery relies on the engine-driven alternator. The faster the engine spins the alternator the higher the output. A proper ratio between the driving pulley of the engine and the pulley of the alternator decides whether the alternator can reach its maximum. This is important because a persistent undercharging will in time weaken a battery. On the other hand, overcharging will ruin a battery very quickly and is usually caused by the failure of the regulator, which keeps the charging current within pre-set limits. The battery housing becoming very warm to the touch and, in the case of wet batteries, the rotten egg smell of the bubbling acid are the warning signs of overcharging. To confirm the bad news, run the engine at fast rpm and watch the voltmeter when the charging begins. For about half an hour the battery voltage should start climbing, peaking between 14V and 15V, and then level at about 14V. If the voltage exceeds 14.8V and remains high, the alternator’s regulator failed replace it. But, because a dying, weak battery in a bank may cheat the regulator into overcharging, you should do the test with one battery at a time. And remember never to disconnect a battery from a running alternatoryou would ruin the regulator transistors and alternator diodes.
When you suspect that an efficient alternator is suddenly failing, switch on several lights, start the engine and increase rpmthe lights should brighten up. When they do not, look for a loose or slipping fan belt on the alternator, a bad ground wire, loose terminals, a bad regulator, a lack of exciting current, or a bad alternator itself. A squeaking noise close to the engine indicates a slipping belt. Slipping causes the belt to heat upcheck by touch after stopping the engine. Some installations use the alternator’s AC for the tachometer. Oscillating tachometer readings may be the first indications of a slipping alternator belt. Worn-out bearings on the alternator pulley may cause inadequate belt tension, so check the pulley for play. Next check that all terminals from the alternator to batteries and the ground are clean and tight. Bear in mind that installing battery-isolation diodes into an existing system will fool the alternator into lowering its outputadjust the regulator if it is possible or re-route the voltage-sensing wire.
Alternators, like most of us, require a jolt to prod them toward hard work. The lack of alternator output may be due to an absence of the excitation current, which should be coming from the start switch via an ignition warning light. This light comes on when cranking the starter and goes out when the alternator begins generating electricity. If the light does not shine when you turn the ignition switch, its bulb or wiring may have failed so no excitation current can reach the alternator. Bypass the ignition light circuit with your test light to see if that is the case. If the light stays on after the engine starts, suspect alternator trouble. To find out, run the engine and connect your test light (as a surrogate excitation source) from the positive battery post to the field terminal (F, FLD) on the alternator if it is type “P,” or to the terminal marked AUX, EXC, D on the type “N” alternator. If it starts charging you will have to work on the excitation circuit. “Type P? Type N? What’s this?” you might cry in despairso read on.
P or N type alternator?
P designates an alternator in which the regulator is wired into the positive side of the field current. On an N alternator the regulator is wired into the negative side. On both types the regulator may be inside or outside the alternator caseon boats the accessible external regulators make repair work much easier. Use your digital multimeter in ohm mode to establish the alternator type. With the engine stopped disconnect the field wire from the alternator, then read the resistance between field terminal and ground. P type will read about 0, and N type will read high ohms.
A bad regulator or a dead alternator?
In order to find out you will bypass the regulator and go directly to the alternator. Detach the field wire from the alternator and set it aside where it cannot touch anything. Clip your voltmeter probes on the plus and minus battery terminals and note the voltage. Next, run your test light between the positive battery post and the field terminal if you have a P alternator. On the N type connect the test light between the field terminal and a good ground like the engine block. Start the engine, run at fast idle, and read the battery voltage. If it increases over the original voltage the alternator works and you have to replace the regulator. In an emergency you can jury-rig regulation by keeping your test light between the plus battery post and field terminal for a P alternator or between field and ground on an N alternator. Monitor the voltmeter so you can adjust the alternator output with the type of bulb you usea higher wattage bulb will increase the output, a smaller wattage bulb will reduce it.
Usually the starter signals its problems by a loud clicking of the solenoidthe system lacks the juice for the job. First look for obstacles in the path between the battery and the starting motor. Crank the starter for a few seconds (never more than 10 seconds at a time or the windings will overheat and possibly develop short circuits) and then run your hand over the cables and terminals. Warm spots will need your attention. Clean the connections to bright metal and try again. Double-check that you have a good, clean ground path. If this fails to improve cranking, check the voltage between the positive lug on the starter and the engine block. If you read 12V, the starter needs replacingprobably a short inside.
If the starter motor tests as not short-circuited there can be trouble in one of the three other elements of a typical starting system: the ignition switch, the relay, and the solenoid. Using the multimeter, test the switch in the “on” position for continuity. If bad, bypass the switch by jumping a wire from a 12V positive source to the positive lug of the relay. If the switch is good, test that the relay delivers 12V when you press the switch down or turn the key. If it does, suspect the main solenoid. You can test the solenoid by the old screwdriver trick. Connect the two heavy terminals on the solenoid with a heavy screwdriver blade. Do not touch the blade to the starter motor housing. There will be a lot of heavy arcing but the motor may turn overthe starter motor is good, the solenoid is bad. If the relay itself failed, you will have to start the engine by the screwdriver short until you get a replacement relay. Note that starter motors are either inertia type or pre-engaged. In the pre-engaged model the solenoid also moves an arm that engages the starter motor to the flywheel of the engine. Using a screwdriver to bypass the solenoid on such a starter will run the motor without engaging the flywheel. Turn the starter switch on to provide the power to the solenoid. Hopefully it will create enough magnetic field for the arm to move even though the contacts inside the solenoid are bad.
Keep her afloat
An electric high-capacity submersible bilge pump that can be turned on automatically by a float or pressure switch in the bilge is a must. Since they are always exposed to bilge water, these automatic switches have limited lives. Buy the more expensive switches and place wire connections above the usual bilge-water level. Spend extra money on adhesive-filled heat-shrink waterproof crimp terminals and large-size tinned marine grade wire. Regularly test by hand that the automatic switch works. Check polarity before you re-wire bilge pumpsa reversed power supply will make the pump run the wrong way! An automatic bilge pump should be wired directly to a battery bank to make it independent of circuit breakers or switches. Use a fuse big enough to carry the high initial current when the pump starts. Position the automatic switch at a higher level than the pump impellerit is better to have a little water in the bilge than a pump that continues to go “on” and “off.”
Navigation lights at deck level tend to suffer corrosion of wire terminals and the contacts inside the fixtures. When a light fails, use the multimeter in resistance (ohm) mode to check the bulb and a test light to check the contacts. Replace or clean as necessary and dab silicone grease on the contacts. When a mast light fails, first use the multimeter or the test light to check the power supply at the foot of the mast and then the switch. Next, turn off the power and use your multimeter in the ohm mode at the lowest value between the positive and negative wires that go up the mast. Any reading above “O” ohms means that the wiring and the bulb are intact. The light failed because of a break between the battery and the mastcircuit breaker, fuse, switch? A definite “O” on a digital multimeter means a short between the wires inside the mast due to broken insulation or a shorted light fixture. An infinity reading indicates a break within the mast circuit, so (with the power off!) connect the two wires at the foot of the mast to make a closed circuit and up the mast you go with the multimeter and a spare bulb. Up there test the old bulb. If bad, replace it, but remember that halogen bulbs must be handled through a soft cloth (bulbs that are scratched or smudged are more likely to shatter explosively). If the bulb is good, test the contacts in the fittingthey should read “O” or low ohms of resistance. An infinity reading may mean corroded connections in the fitting, so clean and/or re-wire the contacts. If you still get infinity reading, there is a break in the wires inside the mast. To trace the bad wire have a helper hold the lower end of one wire against the mast (has to be bare aluminum) and then test for continuity between the mast top and the wire (using its insulation color for identification). Repeat for the other wire. Mark the good wire and replace the bad one.
Masts often carry combination lights that have two bulbs, each to perform a different function (ex., red/green and anchor light). These lights are fed power with a single positive and negative wire. The change of function comes through a double pole, double throw switch, and the diodes in the fixture. Diodes act as one-way valves that let electricity flow only one wayfrom the red to the black probe when you test them. When testing, use the ohm mode or a diode mode installed in digital meters. Manufacturers’ sheets for these fixtures have schematics of the wiring, so keep them.
While working with DC remember that an inverter wired to a battery puts out AC, a current that, apart from always delivering a shock, can kill. Remember to turn inverters off when working with DC circuits.
Tom Zydler and his wife Nancy live aboard their yawl and are working on a cruising guide to the Georgia coast.