Boat Electrics 101

Basic Electric Troubleshooting

Problems in electrical systems can almost always be traced to one of four causes: 

• resistance in connections
• breaks in conductors
• short circuits in conductors
• the failure of components or devices 

Troubleshooting typically consists of using voltage, resistance and current measurements to detect unwanted resistance, or a break in a conductor, or a short-circuit. If none of these conditions exist the circuit is most likely OK, in which case the device has probably failed. 

The task of troubleshooting is to use a logical process to find the resistance, interruption, or short circuit, or to determine which device has failed. 

In this lesson, we will describe techniques that will, in most cases, quite quickly enable a problem, together with its location, to be identified, even if the problem is hidden behind paneling or in a conduit.

Basic Tools

A key tool is the eye. A visual inspection often reveals that a connection is corroded, a conductor broken, or a module has failed due to mechanical damage. Sometimes the nose comes into play. For example, burned motor windings have a distinctive smell, as do overcharged wet-cell (flooded) batteries that are venting sulfuric acid. And then there is touch: warmth or heat is a sure sign of excessive resistance. However, it is important to be careful here – sometimes resistive connections can become hot enough to cause instant burns, and of cours,e live AC components can kill you! Ideally, you will have an infrared thermometer or thermal camera to check for heat.

All too often, conductors and connection points are not accessible and thus evade visual inspection. And you can’t tell from looking at the outside of a device whether something internal has failed. If you jump to premature conclusions about why something has failed, you are just as likely to make the problem worse as you are to fix it. The fastest and safest approach is to narrow down and isolate the fault with methodical testing and measurement. This is what we will do in this module using a multimeter as our principal tool.

Multimeters

Given the prevalence of electrical system problems on boats, a multimeter is, in our opinion, the single most useful tool to have on board, so long as you know how to use it. We hope at the end of this lesson, you will have the necessary knowledge to track down most problems. But first, we must decide what features we want in our multimeter and how much we are willing to pay for it.

Traditional multimeters are analog devices (with a swinging arm). If you have one of these, you should consider replacing it with a digital meter. 

No Cheap Meters!

You should avoid cheap meters for two reasons. First, you want a robust housing; experience has shown that the meter is likely to have to survive tough encounters with floorboards or bilges. Second, you absolutely want built-in safety features that will prevent meter damage and potential personal injury if you accidentally use the meter incorrectly. For example, resistance (ohms) measurements require a circuit or device to be isolated from its power source (see below). If voltage or current is present, a cheap meter may be destroyed. At best, a fuse will blow.

Higher-quality meters will protect themselves. Somewhere on the meter, you want to see it stamped, at a minimum, 'CAT II', and preferably 'CAT III 600 V'. A higher quality meter will likely also be stamped 'CAT IV 300 V'. There should also be a UL, CSA, and/or CE mark to indicate it has been tested to a recognized standard.

A meter with separate AC & DC switch positions, which we recommend