If you have ever turned your boat key to hear that dreaded "click, click" you know how a dead battery can ruin your day. If your batteries are not charged sufficiently, you are destined to have a frustrating and possibly unsafe outing. While most boaters know to purchase high-quality marine batteries, some are less informed when it comes to selecting the right kind of battery charger.
There have been considerable advancements in charging technology over the last few years. Gone are the days of using that old, bulky portable unit made for the family car. Modern onboard marine-battery chargers now available from manufacturers like Guest and Minn Kota are designed for specific boating situations and applications. Yet, chargers made for marine use can differ in technology and construction.
Portable vs. Onboard Units
Due to differing boat designs and boater requirements, it makes sense to invest a little extra time in selecting a charger to suit your particular needs. How do you know what type of battery charger is right for you? First off, you’ll need to choose between a permanently installed onboard charger and a portable unit. In certain cases, portable chargers (typically ferro-resonant, constant voltage units) may fit the bill, especially in situations where outboard engines and batteries are constantly removed from a smaller boat, or when charging batteries on several boats is required.
For most trailer boaters, however, onboard chargers can provide several important benefits. Although onboard models are more expensive than portables (prices start at $100 and range up to $495), onboard chargers provide a definite time advantage, allowing boaters to charge all of the boats batteries at the same time, instead of individually. Onboard chargers are also more convenient than portables, because they are constantly hooked up. There’s no need to crawl into the bilge compartment to hook up your boat’s batteries for recharging.
Perhaps most important, onboard chargers are almost always more technologically advanced units, providing multi-stage switching to manage and maintain a boat’s batteries during the charging process.
Linear vs. Multi-Stage
Most onboard battery chargers are either linear chargers or the electronic switching variety. However, many manufacturers are moving away from linear chargers because, by nature, these units ten to negatively affect battery life and performance. With the typical linear charger, once the battery becomes fully charged, the unit shuts off. It does not begin charging again until the battery drops below 90 percent capacity. Because linear chargers "cycle" the batteries in this manner - as opposed to "maintaining" the charge - such units tend to reduce battery life. What’s more, some linear models are often set at voltages that are too high for maintaining batteries. This results in overcharging, a process that can boil the electrolytes dry in lead acid batteries and harm gel cell batteries as well.
Onboard chargers offered by Guest, on the other hand, incorporate electronic multi-stage technology. Manufacturers such as Minn Kota and DuraCharge make onboard chargers that are actually linear transformer models, however, these units are electronically controlled to provide the same effect as a multi-stage charger. Both of these types of "smart" chargers take better care of batteries than do pure linear chargers.
All of the smart units on the market charge a boat’s batteries in different phases. By controlling the charging output in various steps, this technology significantly reduces charge time and also allows for the "float," or maintenance charging capabilities of each unit.
In multiple battery applications, the needs of invidual batteries vary widely. The "cranking" (or starting) battery, replenished by the alternator, requires a different kind of charging than a depleted deep-cycle battery. Sue Delelys, technical support manager at Meridian, Connecticut-based Guest, points out that Guest’s three-stage electronic switching technology provides a separate charger for cranking batteries within the same housing as the deep-cycle charger.
"Each Charge Pro three-stage onboard charger has an independent cranking charger that tops off and maintains the starting battery, while also supplying the house/trolling motor batteries with full output," explains Delelys. "Once the unit fully charges your boat’s batteries, it automatically drops to a maintenance mode that holds the batteries at a 95 to 100 percent charge. This eliminates the cycling or potential overcharging associated with linear chargers."
Overcoming Voltage Drops
Because linear chargers rely tremendously on AC line input, drops in AC voltage (typically due to long extension cords or finger docks with high power consumption) can cause a longer than anticipated battery charge time. In such situations, you can go to sleep at night thinking your batteries will be fully charged in the morning, only to wake up and find your cells only partially charged. For example, a reduction in 120 volts to 100 volts can cause a 10-amp linear charger to put out only 3 amps. According to Delelys, high-frequency-switching power supplies do not rely on AC line voltage, so this kind of situation doesn’t present a problem. "Multi-stage switching chargers will simply pull more power if needed," she said. "If AC line voltage drops to 100 volts from 120 volts, for instance, a 10-amp multi-stage charger will still provide over 9 amps, so recovery time is not affected." In addition, "battery friendly" multi-stage chargers can be left on indefinitely during off-season storage to maintain full charge without harming the battery in any way. This is a real advantage.
Choosing Your Charger
So let’s say you’ve decided to purchase a multi-stage electronic switching battery charger for greater efficiency, convenience and overall performance. How do you choose the right model to meet your specific needs? First, consider the type of boat you have and how you plan to use it. Just because two boats are the same size, doesn’t mean that their batteries and charging requirements will be the same. Chances are your battery charging needs will be different if you own a bass boat as opposed to a small cruiser.
First off, boaters should consider how many batteries will be used and the capacity (the amp hour or group number). This information will determine whether your boat will require a one-, two-, or three-output battery charger.
Another major factor is charging time - the time you can allow for your batteries to recharge. If you are a "weekend warrior," you may have the luxury of waiting 10 to 12 hours for a full charge. If so, a lower amperage multi-stage three-output charger - with 3-amps output for cranking and two 5-amp outputs for trolling batteries - will work. A tournament fisherman or guide, on the other hand, may need to be back up to full power within just a few hours. In such cases, a more powerful unit, such as a 3-output charger offering 10 amps from each output, would be the best way to go.
Additionally, you should consider the number of engines on your boat. If you have one engine, you’ll only need a charger with a single starting-battery output. Twin-engine applications, however, call for a charger with dual starting-battery outputs.
DC at the Dock
It’s also important to think about what your DC usage will be while your boat is connected to shore power. Do you use a lot of lights? Do you have a DC-only refrigerator? How about a high-power stereo system? If yours is a fishing boat, consider the accessories you’ll be using, such as bait tanks, marine electronics and other power-drawing devices. All of these variables come into play when selecting the ideal battery charger.
Most onboard chargers offered by various manufacturers are extremely durable. However, not all are "potted." This means that the unit is fully encapsulated in thermal epoxy to protect against shock, moisture and corrosion. Manufacturers offering "potted" units feel that this design is better able to withstand the pounding boats take, as well as the harsh marine environment. On the other hand, manufacturers of chargers that are not fully encapsulated contend that their more "open" design allows for easy access if servicing is required, which is not the case when it comes to potted units.
Will It Fit?
Boaters should also be aware of the amount of space needed for an onboard charger. Most of the onboard models are designed to be compact and lightweight. For example, the smallest model from Guest measures 6 3/8 inches long by 3 ½ inches wide, and weighs just four pounds. Mounting holes on most chargers are typically pre-drilled, making installation an easy task. The length of the cables that come with onboard chargers are generally 4 to 6 feet. In the event longer cords are needed, most manufacturers offer extension kits. Exactly where you mount an onboard charger depends not only upon the size of the model, but also on the way the unit is constructed. To minimize the length of the charging leads, it’s best to mount the charger close to the batteries. Some chargers may need to be shielded from the elements. If the charger is not potted, it should be mounted in an enclosed area that is not exposed to water.
Any charger you purchase should meet U.S. Coast Guard requirements for spark protection. Since such chargers are specially designed to prevent sparks, they can be safely mounted below decks or in engine compartments.
Delelys also notes that because all batteries are designed to accept certain maximum voltages, be sure the charger you buy is set properly according to these limits. "Before any of Guest’s batteries leave the factory, we ensure they are set not to exceed the voltage levels acceptable for most batteries currently available," she explains.
All factors considered, selecting an advanced, high-quality battery charger designed to fit the specific requirements of your boat will make life easier for you and your batteries.
Some Information on Inverters
Many of the same manufacturers that offer battery chargers, such as Xantrex and Vector, make power inverters and combination inverter/charger units as well. Marine inverters transform battery (DC) power to household (AC) power, so you can use various home appliances and equipment offshore, without the vibration, noise and fumes of a generator. Available in different sizes ranging from 150 watt models to large 4,000 watt units, inverters present a quiet, environmentally friendly option for mariners that use devices and appliances out on the water.
While battery chargers convert AC current into DC voltage for your batteries, the function of inverters is just the opposite. Inverters convert low voltage DC current into higher voltage AC power for running appliances and other loads. Combination "charger/inverter" units provide these two functions in a single unit, offering a space and cost-saving option for boaters that require both.
Although some smaller inverters are portable, most of the larger versions need to be hard wired. Some models feature an AC transfer switch that allows shore power to be transferred through the inverter to the loads when it is available. When AC power is not available, the inverter is capable of producing its own AC power from the batteries. This provides for a seamless transition from shore power to ship’s power. Without a transfer switch, the inverter-powered devices need to be separate from the shore power devices. Because of the high currents, larger inverters need to be located adjacent to onboard battery banks and have larger cables.
Types of Inverters
There are essentially two types of inverters - True sine wave units and Modified sine wave models. True sine wave units supply premium power, similar to the power you receive at home from your utility company. Modified sine wave inverters, which produce a "square wave" with characteristics that can change with the applied load, offer several performance and cost advantages.
Whether you select a true sine wave or modified sine wave inverter, really depends upon the specific devices you’ll be running and your planned usage. Whereas some products, such as laser printers, variable speed motors and digital clocks, function properly only with true sine wave power, others can accept the voltage fluctuations of a modified sine wave unit. Generally speaking, true sine wave inverters allow for easier starting and cooler running for most appliances. Modified sine wave inverters, on the other hand, are a more cost-efficient option for mobile AC power.
What Size Inverter Do I Need?
Since inverters are offered in a variety of sizes, how do you know what model is right for your boat? First, consider the devices you’ll be running and how much wattage will be needed to run them (consult the owner’s manuals for each). Also make sure that the "surge rating" of the inverter you are considering meets the requirements of the specific appliances you’ll be using. It’s also important that you match your inverter with an appropriately sized battery to ensure optimum performance.