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!

Back to Las Vegas

After a wonderful month visiting with Lin, we bid Boston adieu and headed to Las Vegas. David's family lives there and, if you'll remember, we bought a house out there last Spring and we haven't been back since. David's sisters, Mary and Karen, have been keeping the proverbial home fires burning, but it's about time we returned to remember just what we bought.

Lin dropped us (and 4 large duffels, 2 suitcases, a backpack with two laptops and another larger than practical carry-bag) off at Boston's Logan Airport. Departing wasn't quite as traumatic this time. In the past we knew it might be another year or more before we'd see each other again. This time, we're hoping to get back to Boston for a few days in October, so no tears were shed.

Our 2-1/2 hour flight connected at Chicago's Midway Airport, a distant and bedraggled cousin of the glitzy O'Hare Airport. Midway's ill-kept terminal was depressing 20 years ago and it's still depressing. There were signs that said “Excuse the carpeting … we're hoping to replace them this autumn.” I think we saw that same sign in 1996 when we passed through then. We were glad it was only a one-hour layover and a quick plane change. Once on the plane, we settled in for another four hours of flying time and arrived, no worse for wear, but definitely tuckered out, in Las Vegas right on time. Mary was waiting for us with a cart, forewarned of all the luggage that was traveling with us. The heat hit us as soon as we left the terminal … all 109 degrees F of it. We crammed all the luggage and ourselves into her Kia Soul. We were home and unloading by 10:30 pm Pacific time … 1:30 am for us. Quick hellos and hugs and we were off to bed.

Over a couple of days, we've adjusted to the time change. The temps have been well over 100 F since we arrived. “It's a dry heat”, we're told. Quite honestly, 100 F is hot even with low humidity. We're still managing to walk every morning, but it's at a much slower pace. By mid-afternoon, it's literally hot enough to fry eggs on the sidewalk.

The landscape has changed drastically: flat desert compared to hills and trees. Flora is hardy and sparse. Cactus, yucca and sagebrush rule instead of dense evergreens and ferns.

Rather than counting flying fish in the scuppers each morning, we count bunnies (desert cottontails) which seem to be in great numbers. Our highest count to date is 15 … one of which was in our front yard. We see pigeons, doves, starlings and hummingbirds now rather than bluejays, robins and cardinals.

It's a far cry from the sea and definitely different from Boston, but we like the change. We'll be here about a month before heading back to Chesapeake, Virginia where Cups is patiently waiting for us. Desert life makes us appreciate going back to Nine of Cups all the more. Absence does indeed make the heart grow fonder.

Anchors Away

One of our goals when we docked Nine of Cups at the Atlantic Yacht Basin was to raise the waterline. We offloaded hundreds of pounds of stuff destined for yard sales, thrift shops and consignment shops. No, we're not thinking of giving up our life aboard Cups any time soon, but thinning out some of the 16-year accumulation of stuff seemed prudent. Anchors seem to be a passion with David. He's even written a book about anchors. We have had six aboard for several years, and in an effort to thin down the inventory, he decided to part with two of them.

Stored on deck we have a 50 kg Bruce and a 43# Danforth. On the bow roller, we have an 80# Manson Boss which is now our primary anchor. On the aft deck, we have a 10# mushroom anchor for the dinghy. Below decks and under our bunk in the aft cabin, there's a 35# CQR and a 32# aluminum Fortress. It was a heartbreaking decision for the captain … which two would go?

The 50kg (110 lb) Bruce was our primary anchor until we reached Australia. Anchoring along the southern Australia coast is difficult. With hard sand and lots of grass, it was hard for the Bruce to dig in. We replaced it in Port Adelaide with a 80# Manson Boss. The sharp claw of the Boss has been doing a fine job ever since and fits better than the Bruce in the bow roller. David built an anchor chock on deck to store the Bruce, but after hauling it around for the past couple of years and not using it, he felt it was time to retire the old guy.

The CQR was used in the high latitudes as a series anchor with the Bruce, but we've seldom used it in recent years. It go the heave-ho, too.

We loaded both in the SUV and toted them to Lin's house hoping that they'd be sold either via Craigslist or at the yard sale. No luck. As the days in Boston dwindled and the anchors, nestled in pine needles in Lin's backyard, fought off gypsy moth advances, David reluctantly contacted Bud at Newport Nautical Supply, a well-known chandlery and consignment shop in Newport, RI and we made the trek down there with the anchors in Lin's trunk. Needless to say, the car rode much lighter on the return trip.

After offloading the anchors and bidding them adieu, we headed next door to Bishop's 4th Street Diner, a Newport institution and, knowing how much we enjoy diners, a natural place to stop for breakfast. Despite the pleasure of dining, we couldn't help feel a little sad at parting with the anchors. I think we're missing Cups.