Friday, December 7, 2012

Maintenance of Marine Batteries


The strength and capacity of a marine battery is defined by its plate size and amperage output. Marine starting batteries, used on larger vessels that have many "house" electrical systems, have high amperage outputs and more plate surface for bursts of energy lasting for five to 15 seconds. Starting batteries are independent of all the other electrical systems on board a craft, including house batteries.

House batteries have thicker but fewer plates than starting batteries, use (DC), or direct current and are designed to supply electricity to on board components such as the windless, stereo, bilge pump, navigational instruments and lighting. Smaller craft use a single dual-purpose deep cell marine battery, designed to start and run all electrical systems. Picking a starting or house battery requires matching the amperage and type of battery to the engine size and number of electrical components on the craft, which is outlined in the owner's manual.

The charging fluids in marine batteries come in three basic types: wet cell, AGM (absorbed glass mat), and gel. Wet cell batteries are filled with a watery charging fluid, which can be inspected from a removal cell cap. These batteries last long and are cheaper than the other types. They need to be vented to dissipate internal pressure and pose the problem of acid spills and deterioration. AGM batteries are sealed, making them maintenance free. They resist shock and vibration better than the wet type, but cost more. They are also heavier and can suffer damage from overcharging. Gel batteries, also maintenance free and resistant to shock damage, have a very low discharge rate, making them the optimum choice for long-period storage. They cost more than the other types, and are more sensitive to recharging techniques, which requires a special gel-type battery charger.

Maintenance on the AGM and gel batteries requires only a visual inspection, to check for outer case damage and clean-tight cable connections. Since they are sealed, a voltmeter is used to measure the standing volts, or charge capacity. A 100% charge will indicate 12.73 volts; a 60% charge will indicate 12.24 volts and a 20% charge will show a reading of 11.66 volts. Wet cell batteries can be checked with a hydrometer in each of the battery cells, or by a voltmeter. A hydrometer will show the specific gravity of the acid fluid by indicating a reading that is produced by a floating ball inside a tube. The scale on the hydrometer tube will show charge rates beginning with low and ranging to full. Wet cell battery fluid must be checked and maintained at least once a month. Distilled water is added to the cell, to bring the level up to 1/8-inch over the top of the plate.

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