Boating NZ : FREE TO READ April 2014
42 Boating New Zealand April 2014 An inexpensive multimeter can beat difficult-to-trace electrical gremlins that steal your power. PRACTICAL BOATING LAWRENCE SCHÄFFLER 42 MULTIMETER TROUBLESHOOTING witha F or the average DIYer, the chief benefit of a multimeter is basic sleuth work: a logical process of elimination to find the probable cause of a problem. If you don’t already have a multimeter on board, it’s worth investing in a digital model. A decent digital multimeter retails for well under $100. Multimeters are designed to test three units of electricity: ohms, ie, resistance; volts, ie, potential energy; and amps, ie, current – for DC and AC power. Depending on which of the three units you’re checking, the multimeter’s two leads – red and black – are plugged into the instrument’s appropriate sockets. The choice is easy because the black lead always plugs into the black socket, usually marked COM for common. The red lead plugs into one of two red sockets – one for testing voltage and resistance, typically marked VΩmA; the other, for current/amps (A). The selection dial on the multimeter may seem confusing as it offers multiple options for the range of the units – ie, amps, milliamps, volts, millivolts in DC and AC. A good reason to invest in a modern digital meter is that it will be an auto-ranging model. You use the dial to select which units you want to test, but won’t have to worry about choosing the appropriate scale – it does so automatically. The most basic multimeter test, says Glenn Powell, a marine electrician at Westhaven’s World Power Electrical, is a continuity check – a simple yes/no test that uses the meter’s resistance setting; ie, ohms – Ω, to see if a wire, light, fuse or circuit can conduct electricity. “Any break in a circuit stops the flow of electricity,” Powell says. “Common breaks are blown fuses, corroded wires or loose connections. But you want to find which of these is faulty. If, for example, a navigation light isn’t working, a series of continuity tests will quickly establish whether the break is the bulb’s filament, or perhaps because of poor contact between the bulb and its socket usually caused by corrosion, or an actual break in the wiring.” NOTE REGULAR_PB_Mulitimeters_April14.indd 42 18/03/2014 5:18:23 p.m.
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