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Battery charging and maintenance FAQS CruzPro Ltd.
207 Whau Valley Road
Whangarei 0112
New Zealand
Tel: 64-9-459-1922

Internet: http://www.cruzpro.com
Voltage monitor

3 Bank Voltage monitor

3 Bank Amp-Hour monitor

Amp-Hour monitor

Charge Controllers

Alternator Controller

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Simple Battery Maintenance and Proper Charging Extends Battery Life

Many boat owners replace their lead-acid batteries every couple of seasons because they unknowingly kill them. Improper charging must rank as the number one cause of early battery death. With the right kind of battery, properly charged, you could get ten years of use. The 8 deep cycle golf cart batteries in my boat have been performing since mid 1992 and were slowly replaced in 2000 and 2001. A little knowledge of how batteries work and how to charge them will not only save you money but can also prevent those embarrassing calls for help when you can't start your engine.

Practical lead-acid batteries consist of lead/lead-dioxide plates submerged in sulfuric acid. A single cell produces about 2 volts and a 12 volt battery contains six cells. When discharging, a chemical reaction transforms lead dioxide to lead sulfate. Lead sulfate is an insulator - meaning current can't flow well through it and the battery voltage drops. A lead-acid battery will also slowly self-discharge converting lead-dioxide to lead sulfate. When you recharge a lead-acid battery the lead sulfate is converted back to lead dioxide and the voltage goes back up. A 12 volt battery will read about 12.7 VDC when charged and is flat when the voltage drops to about 10.7 VDC. These numbers change a little depending upon temperature, acid strength and how recently it has been used or charged.

When a battery is left in the discharged state, the lead sulfate slowly hardens and it becomes more difficult to charge and discharges more quickly. This in turn causes more lead-sulfate to form and the problem gets worse until the battery becomes useless. So the first tip to longer battery life is to fully charge the battery and to keep it charged. My brother put his new launch away for the winter and both batteries had to be replaced at considerable expense the following spring. He learned the hard way to keep the battery fully charged at all times.

A second reason for early battery death is deep discharges. The service life of most batteries is severely shortened if discharged below 50% of capacity. Some car-type start batteries can be destroyed by discharging them completely only three or four times! To prevent deep discharges you must match battery size to the expected load or re-charge more often. If you regularly discharge your batteries more than 10% of capacity, purchasing deep cycle batteries will pay for itself very quickly.

Battery capacity (amps times hours - or amp-hours) is basically determined by weight. The heavier the battery, the more capacity it has. Car batteries are designed to provide a lot of amps very quickly for starting the motor. This is accomplished by building in many thin porous plates, thereby increasing the surface area. This allows the battery to supply a large amount of current, but only for a very short amount of time. The sulfates soon reduce the effective surface area limiting the battery's ability to deliver more current. In a car this is not a problem because the alternator quickly recharges the battery In boats (especially yachts) it is more important for a battery to be able to supply a smaller amount of current for a long period of time in order to run refrigerators, anchor lights, auto-pilots, etc. For this application a deep cycle battery with its thick plates is clearly superior.

Proper and timely charging dissolves the soft sulfates and keeps them from hardening into sulphur insulators. Unfortunately car-type 13.8 VDC fixed voltage regulators do not charge batteries very effectively. To completely dissolve the lead-sulfates your lead-acid battery should occasionally be "equalized" or charged to about 16 VDC. Clearly a fixed 13.8 VDC regulator will not allow your battery to charge to this voltage. After you have fully charged your battery, the voltage of the charging source needs to be reduced below 13.8 VDC to prevent overcharging and the resultant loss of electrolyte due to gassing. A car type voltage regulator is a trade-off between manufacturing costs and battery life. Since car manufacturer's don't have to pay for battery replacement, there is little incentive to spend money on better regulators. This is why multi-step marine chargers are so important to proper battery charging and battery life. They will recharge your battery more quickly, requiring less engine run time, and simultaneously prevent overcharging of your battery on long trips. They usually charge your lead-acid battery to 14.4 VDC, delivering the bulk of the charge quickly. By now your battery is about 60-70% charged. Multi-step chargers then keep the voltage constant at 14.4 VDC and allow the battery to charge to about 90-95% of capacity. Switching to a lower voltage float mode then safely charges the battery to it's maximum capacity.

Even multi-step chargers don't dissolve all the sulfates and it is recommended that you "equalize" your batteries about once a month by limiting the current of your charge source to 4-5% of battery capacity and charging to 16 VDC or for four hours, whichever occurs first. A word of warning - some equipment is not rated for 16 VDC and can be damaged at this voltage - be sure to disconnect such equipment first. Also, at voltages above 14.4 volts, lead acid batteries will gas vigorously generating large amounts of potentially explosive hydrogen and oxygen. Ventilate your battery compartment and keep ignition sources away. Gel batteries should not be charged to 14.4 VDC or equalized to 16 VDC and most smart-type multi-step chargers will have a separate setting for gel batteries.

It is also important to keep the water level topped up at all times and never let it drop below the level of the plates. Use of distilled water is highly recommended as regular tap water may contain harmful chemicals and minerals that can shorten battery life.

A number of CruzPro products can help you maintain longer battery life. The V55 and V60 Battery Voltage Monitors can warn you if battery voltage drops too low or rises above a safe level. The CC-10, CC-20, CC-30 and CC-35 Charge Controllers can be used with solar panels or "dumb" low-cost car battery chargers to safely charge wet or gel type batteries. The SAR-20 Smart Alternator Controller can be used to optimize your shipboard charging of wet and gel batteries quickly and "equalize" your wet batteries safely. The VAH-60, VAH-65 and VAH110 amp-hour monitors will keep track of the amount of charge remaining in your batteries, just like a fuel gauge tells you how much fuel remains in your tank.

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