The Blue View - Finding DC Electrical Faults

Note: This blog is the condensed version of the article I wrote for Good Old Boat magazine in the June 2016 issue. For the complete version, visit their website at www.GoodOldBoat.com.

Introduction

The electrical wiring on the typical boat has a tough life. The combination of salt, water, copper wire and electricity inevitably leads to poor connections, faulty circuits and corrosion. With a little time and persistence, some basic tools and a plan of attack, it is usually not that difficult to ferret out and correct those pesky electrical problems.

Test Equipment

Some electrical problems can be found just by observation - a green, corroded terminal or a broken wire, for example, are usually easy to spot. Most electrical faults, however, will require at least a basic inventory of test equipment. The following is a list of test equipment ranging from the most basic to the more specialized.

Test Lamp

This is the most basic fault-finding tool. Connect one wire to ground and the probe tip to the circuit being tested, and if the bulb lights, there is a voltage present. A test lamp is a quick and easy tool to use and will help find blown fuses, broken wires or defective breakers. They typically cost a few dollars, or you can make your own by soldering wires to a bulb or bulb socket. If you buy one, make sure the test lamp is intended for DC circuits – most test lamps sold at hardware stores are designed for household AC circuits and won't light up when connected to 12 or 24 VDC.

Inexpensive Multimeters

For a few dollars more, typically between $10 and $35, you can purchase a basic multimeter, and no boat should be without one. A multimeter allows you not only to determine whether a voltage is present, but to quantify it as well, e.g. is the voltage at the positive power terminal of that flaky VHF 10.5 volts or 12.5 volts? It will also measure DC currents up to about 10 amps, and make resistance measurements.

High End Multimeters

The next step up is a multimeter with a DC current clamp. An inexpensive multimeter can measure small DC currents, but the multimeter must be in series with the circuit to do so. For example, if you want to measure the amount of current your refrigerator compressor is drawing, you must remove one of the power wires, then connect one lead of the meter to the wire and the other lead to the terminal. If the current is more than 10 amps, the internal fuse of the meter will blow. To measure the same current using a multimeter with a current clamp, all that is necessary is to clamp the current probes over one of the power wires and set the meter to measure DC current. The current clamp is very easy to use and will typically measure currents exceeding 400 amps – more than adequate for the circuits on a typical boat. The price for a multimeter with a DC current clamp ranges from about $40 to $250

Jumper Wires

I keep a cache of jumper wires of various lengths, each terminated with alligator clips. The shortest is about 6” long, while the longest is about 30'.

Finding and Correcting Faults

A basic DC circuit aboard a boat is shown in Figure 1. A wire leads from the battery's positive terminal, through some sort of circuit protection device, like a fuse or breaker, through a switch, and then on to the load, whether it be a lamp or a windlass. A return wire is used to complete the circuit from the load back to the negative distribution terminal, and then to the negative terminal of the battery.

In a normal circuit in good condition, when the circuit breaker is turned on and the switch is closed, current flows to the load and the lamp lights up.

If the lamp doesn't light or the windlass doesn't turn, I have a number of steps that I follow to determine the cause of the problem. Before diving in, however, I first think about any clues. Was something recently changed? A new circuit added or modified? Do some parts of the circuit work while others don't. I remember more than one instance where I modified a circuit to add some new gear and in the process, inadvertently disconnected something else. Often the newly introduced problem didn't become apparent until weeks later.

Next, I do a check for obvious problems. Is the breaker on? Are there any fuses in the circuit, and if so, are they blown? Are any of the connections corroded or questionable? Do the terminal blocks and splices look good?

If I haven't discovered the problem by now, I get out my trusty multimeter and jumper wires, and start checking voltages. A very likely place for the fault to occur is in the load itself … the bilge pump has pumped its last drop of water, the LED light has emitted its last photon or the windlass has hoisted its last foot of chain. I set the multimeter to DC volts and to the appropriate range. Once all the switches and breakers in the circuit are in the “On” position, I measure the voltage across the load as shown in Figure 2. If I measure a voltage close to the battery voltage, then the problem lies in the load.

If the problem lies elsewhere, I methodically work my way through the circuit until I find it. Figure 3 illustrates the same DC circuit with several test points added. My plan of attack is to check the voltage at each point until I find the fault.

Using jumpers as necessary, I attach the negative lead of the multimeter to the negative distribution terminal, (if your boat doesn't have one, connect the negative lead directly to the negative terminal of the house battery) and starting with Point A, check each voltage in the circuit. If I see a voltage close to the battery voltage at Point A, but not Point B, I know there is a problem with the breaker. If I see the correct voltage at Point B, but not Point C, I know the fault lies in the wiring between the breaker and the switch. I continue working my way through the circuit until I find the problem. The only point I shouldn't see a voltage is at Point G. If there is a voltage there, I know there is a break in the return wire.

Additional Tips

In a perfect world, the fault would be readily apparent. The switch is defective and there is no voltage at Point D, for example, or there is a voltage at Point D and not Point E, indicating a broken wire between the two. Many times, however, the problem is more difficult to figure out. Here are some additional tips that might help.

• There are many times when I can't access a particular point to measure the voltage. I sometimes use sewing needles to pierce the wire to make contact with the conductor, then connect it to the multimeter with a jumper wire. When I'm done making the measurement, I use silicone caulk to seal the hole.
• Many times a problem won't be apparent unless there is a substantial current flowing through the circuit. A windlass, for example, has a very high current draw. If the breaker or foot switch has dirty contacts, voltage measurements taken while the windlass is idle may all appear normal. The same measurements taken while the the windlass is energized may show a large difference in voltage. The same is true for any device with a large current draw – a refrigerator compressor, starter motor, autopilot drive, etc. Make sure you make the voltage measurements while the load device is energized. This may require the assistance of a helper on occasion.
• I don't look for just the presence or absence of a voltage. If I see 12.45 VDC at one point, and only 11.20VDC at the next, I know there is a significant voltage drop between the two points. The usual culprits are corroded terminals or wires, or dirty switch contacts. If it is a new installation, another possibility is that the conductors that are too small.

Good hunting!

The Blue View - How to Make a Rope Rug

A few years ago I did a blog on making a nautical rope rug, or in sailor's parlance, an ocean plaitt mat. As I was making my 50^th or so mat a couple of weeks ago, Marcie suggested doing it again as a video. It seemed like a good idea, so here is the video version.

The Blue View - Bilge Pumps

Nine of Cups has four bilge pumps in place – one electric pump with a 3700 GPH (gallon per hour) capacity, one electric with a 500 GPH capacity and two hand operated 3600 GPH pumps. And if all else fails, we have several buckets aboard. Discounting the buckets, if both electric pumps were running and Marcie and I were giving it our all at the pumps, we should, in theory, be able to pump more than 11,000 GPH, or almost 200 gallons per minute! That should handle just about anything, right?

If you've followed our blogs over the years, you may remember a few that talked about bailing water from Nine of Cups. I can recall three occasions when we were at sea and taking on water – a most distressing situation. The leaks turned out to be relatively small and easily repaired, but what was more distressing was that the combined output from three of the four bilge pumps would barely keep up with even those small leaks (Marcie was hand pumping while I tracked down the source of the leak). Had we suffered some serious hull damage, all four of the pumps would not have even come close to handling the water ingress. The best we could have hoped for was that our pumps would buy us enough time to fix the problem, get help, run Cups aground on a beach somewhere – or, sigh, get the life raft deployed and loaded.

On the other hand, our bilge pumps are adequate for routine water ingress, minor emergencies and pumping out all the collected water once the emergency has been handled. Here are my thoughts on a reasonable bilge pump system.

• Small Automatic Pump. We have a small pump (500 GPH) with an automatic switch located in the lowest part of the bilge. This pump takes care of routine water ingress. We almost always take on some water during rainstorms or from waves over the bow or into the cockpit during rough weather. A small capacity pump is desirable for this application. When a bilge pump runs, it has to pump water out of the bottom of the bilge to a height above the waterline of the boat. When the pump shuts off, all the water in the hose will eventually run back down through the pump and back into the bilge; the bigger the pump, the bigger the hose, and the more water that will make its way back into the bilge. Thus, a smaller pump with 3/4” diameter hose is preferable. It is controlled via a switch on the breaker panel and an automatic switch – see below for a discussion on automated switches.
• Large Capacity Electric Pump. We have a large capacity (3700 GPH) electric pump located next to the small pump. It is not automatic, and is turned on via a switch on our breaker panel. This pump is used in emergencies or when more than the usual amount of water has made its way into the bilge. For example, when it's time to clean the bilge, we first use oil absorbent pads to collect any fuel or oil, then turn off both pumps and pour several gallons of fresh water mixed with an acceptable bilge cleaner into the bilge and let it set a day or so, allowing it to slosh around. Next we turn on both pumps, quickly pumping the cleaner out and cleaning the hoses at the same time.
• Hand Operated Pump #1. This hand operated pump is permanently mounted below the cabin sole and while primarily intended for emergencies, is used more frequently than you might think. On passages, we usually turn off the automatic pump and use the hand operated pump once or twice a day to determine whether we are taking on more than the usual amount of water. By counting and tracking the number of pumps required each morning to empty the bilge, the early signs of a pending problem, like a leaking fitting, can be identified before it becomes an emergency.
• Hand Operated Pump #2. This pump is attached to the underside of one of the cabin sole hatches, along with 15' (4.5m) of hose. In an emergency, the hose can be fed down into the bilge and the pump taken up into to cockpit and operated there.
• Automatic Switch. I have tried a multitude of automatic bilge switches, most of which didn't work reliably. The mechanical float switches would sometimes stick, or would run the pump dry while on a heel. The automatic bilge pumps have a tendency to cycle on and off frequently as the water is pumped out of the bilge, then drains back down into the bilge from the hose. (See the further discussion below regarding non-return check valves in the discharge hose).I do like a few of the electronic sensors that detect water level by measuring the capacitance between two sensor pads. The capacitance will be different depending on whether there is air, water or fuel between the sensors, and since it can detect the difference between oil/fuel and water, the switch has been programmed to turn the pump on only when water is present. Since oil and fuel float on water, the switch will then turn the pump on only until all or most of the water is pumped out, and turn the pump off before any oil or fuel gets pumped overboard. The switch I use is the Water Witch Model 101*. One of its features is that it keeps the pump switched on for several seconds after the level of the water drops below the sensor. If the switch is mounted above the bilge pump, the pump will continue running until the water level drops well below the sensor height, so when the water left in the hose drains back into the bilge, the water level will still be well below the sensor, preventing it from cycling on and off.

• Check Valves. A non-return check valve will prevent the water in the hose from draining back into the bilge. The ABYC allows the use of a check valve in the discharge hose of an automated bilge pump for just this purpose - to prevent the pump from cycling on and off. I'm not a big fan of check valves in bilge discharge lines. Since the bilge water often has debris in it, the check valve often becomes fouled, causing it to leak and rendering it useless.
• Operational Feedback. Having some sort of feedback to let me know the automatic bilge pump is running is important. We have an indicator light on the alarm panel that illuminates when the pump is running. On my wish list is the addition of a cycle counter – a device that keeps track of how many times and for how long the bilge pump has turned on. An increase in the amount of time the automatic bilge pump has come on may well be an indicator of a problem that is simple to fix now, but which could be catastrophic if allowed to get worse.

• High Water Alarm. We have a water activated switch located well above the normal level of water in the bilge. If the water ever rises to the level of the switch, it sets off audible and visual alarms both below deck and in the cockpit. I use a different model Water Witch switch for this application – the Model 10, which is identical to the Model 101 but without the shut-off delay. We installed it after our passage from Easter Island to Ecuador when we began taking on water and were blissfully unaware of the problem until the floorboards were almost awash with water.

So that, in a nutshell, is our bilge pump system.

BTW, I want to thank our JALF blog reader, Tony in California, for suggesting this blog. I thought I had covered the topic long ago, but neither Tony nor I could find an older Blue View on the subject. So, thanks Tony.

This is a link to the Water Witch bilge switch on Amazon. If you buy anything from Amazon using this link, it costs you no more, but we make a tiny percentage on your purchases.