Boating NZ : FREE TO READ February 2014
W hich is the most reliable health indicator of your boat’s electrical system? A volt meter or an amp meter? Should you have both? Well, unless you’ve an intimate knowledge of electricity, you might consider swapping both for a battery monitoring system. Most yachts and launches with 12-volt DC systems have at least one volt meter, typically indicating the status of the start battery. Some have a second, dedicated volt meter for the house batteries or, occasionally, a meter that can measure both – you toggle between start and house batteries. But what does a volt meter actually tell you? We put that question to Simon Jennings, managing director of HMB Marine Electrical in Auckland’s Half Moon Bay. “Superficially, two things,” Jennings says. “First, with the engine running, it’s an easy, visual cue to confirm that the alternator is charging the batteries. If the alternator’s working properly the volt meter should read up to 14.4 volts. If it’s reading around 12 volts or lower, chances are that there’s a problem with the charging system. “Second, it’s a simple – though often misleading – indicator of the health of the battery. A fully-charged battery, in good condition and without any load, reflects about 12.6- 12.7 volts. Anything lower should be cause for concern.” Few boat owners, he stresses, understand the significance of even small variations in a volt meter reading. “A battery showing 12.4 volts on the meter is down to about 75% of its capacity – at 12.1 volts it’s only about 50%. If it drops below 12 volts it will struggle to turn over the engine. Anything below 11.5 volts PRACTICAL BOATING LAWRENCE SCHÄFFLER 44 If you know what Watt is what, you might be happy with conventional ways of keeping track of your batteries' charge. Or, you may consider a battery monitoring system. METER Matters Volt and amp meters are useful tools but they don't tell the whole story. BEP Marine's DCSM 600, right, can display data such as amps, volts and amp-hours 44 Boating New Zealand February 2014 PBoating_volt metres_Feb14.indd 44 21/01/2014 4:34:30 p.m.
FREE TO READ March 2014