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Multihull sailors need adequate charging sources to routinely replenish the battery power they use, and the proper controls for those charging sources to protect and extend the life of their battery banks on board. In this two-part column we'll review the charging controls on the market and their operation.
Each charging source you install on your boat must have some sort of charging control to limit or shut off the current once the batteries are full. Alternators and other charging sources are designed strictly to provide power, a given amount for the conditions they operate under. If no electrical "brain" in the form of an automatic charge control is in the system, and the operator doesn't manually intervene, charging sources will supply power indefinitely (as operating conditions allow)
Automatic Vs. Manual Charge Controls
Charge control can be achieved automatically, manually, or some combination of the two. Since automatic controls are generally reliable and modestly priced, boaters usually choose them over manual controls.
Alternator controls are almost always automatic, although I can think of two devices for alternators where both automatic and manual control is available. The first is an adjustable 2- or 3-stage control for a high-output alternator. The control functions automatically, but the user can tweak the voltage setpoint to allow for different motoring patterns—a higher setpoint for occasional motoring and a lower setpoint for more frequent motoring. The second device, for many years marketed under the name Auto-Mac, allows the user to dial up the charging current even after the standard voltage regulator determines that it's time to limit the current. The Auto-Mac, originally intended to over-ride the voltage regulator on a standard alternator, is less popular now that high-output alternators and fully automatic 3-stage controls have come down in price.
Alternator controls are almost always automatic. Some liveaboard boaters choose to manually control the output from a renewable charger, at least initially, in an effort to save money or maintain simplicity in the system. Manually stopping the rotor of a wind or water generator or switching off the output of a solar panel is relatively easy and can be effective, but failure to do when the batteries are full can be an expensive mistake. And without an automatic controller you won't be able to keep your batteries charged if you have to leave your boat for an extended period of time.
Charge Controls for Alternators
Charge controls for alternators are commonly known as voltage regulators, although I feel that name is a bit dated, especially for multi-stage controls designed to achieve high performance. An alternator control does indeed regulate output using some voltage setpoint—or multiple setpoints if a multi-stage control is used—as a reference, but it is the amount of current that is being regulated to prevent battery overcharge.
For a given RPM, the output of an alternator is regulated simply by reducing or increasing the level of what is know as the "field current", or the small amount of DC current needed to create electro-magnetism inside the alternator. The smaller the amount of current passing through the field current windings, the weaker the magnetic field and the less electricity produced by the alternator. Instead of handling the full output current, as do controls for permanent magnet electrical generating devices such as wind and water generators, an alternator control handles only the field current, which varies from 0 to 6 amps for a standard alternator and 0 to 10 amps for a high-output alternator. This is why charge controls for alternators are typically not suitable to handle the output of renewable chargers, and why you need a seperate charge control for each unit in a dual alternator installation.
There are 3 main battery charging cycles to consider when you have a relatively high output charging source: bulk, absorption and float. Standard 2-stage voltage regulators allow for the bulk cycle and essentially an indefinite absorption cycle (they don't drop to a lower float level). Battery protection is achieved through a reduced voltage setpoint, which to some degree compromises the performance of the charging source. 2-stage controls work fine for most powerboat applications, using a lower voltage setpoint, and for sailors who motor infrequently, using a higher voltage setpoint, but 3-stage controls offer a higher level of performance and battery protection to sailors and even power boaters who spend time at anchor and want to minimize engine-running time just for charging batteries.
2-stage controls are typically installed inside the alternator, and thus the voltage setpoint is not adjustable. This type is the most common and least desirable. Externally mounted, adjustable controls are preferable since the voltage setpoint can be adjusted to meet individual needs. 3-stage controls are best since they automatically provide a good balance between performance charging and battery protection.
There are several good alternator controls on the market, including the Ample Power "Next Step Regulator", the Heart Interface "incharge" control, and Balmar's new "Max-Charge" control. The Next Step and Max-Charge models have advanced functions and sophistication. For example, the Max Charge has everything you could ask for in a high-performance alternator control. It has all the usual features, including 3-stage operation, optional temperature compensation, a battery equalization feature, and monitoring functions, but it offers much more. This versatile control also has:
In the last issue we covered charge controls for alternators. In Part II we'll examine controls for other charging sources, including battery chargers and inverter-chargers, as well as solar-, wind- and water-powered generators.
Charge Controls for Battery Chargers and Inverter-Chargers
Battery chargers, and inverter-chargers in the charging mode, usually have an internal charge control circuit; on some models the voltage setpoints are adjustable. High-performance models take the batteries through a 3-stage charging cycle and automatically shut off when the batteries are full. Less sophisticated "trickle-charge" models reduce charging current to a low but constant trickle charge that can spell disaster for batteries when the charger is plugged into dockside power and left unattended. If there is no electrical load to moderate battery voltage, the voltage can rise to unacceptable limits and destroy your batteries.
If you are in the market for a battery charger, make sure to purchase one with 3-stage operation. An inverter-charger may make the most sense if you presently or in the near future wish to operate household appliances on board.
Charge Controls for Renewables: Solar, Wind & Water Generators
The output from solar, wind- and water-powered generators is typically fed to individual charge controls for each source, although there are some multi-source controllers on the market that can handle charging current from any renewable power source up to the control's maximum current limit. If the idea of a single controller intrigues you, your aim should be to find one that has the capacity to handle your present as well as your future needs. For instance, a multi-source control rated at 30 amps may be able to handle a 20-amp wind generator and two 60-watt solar panels, but if you decide to add more solar panels at a later date a second controller will be needed.
3-stage charging is less of a concern for renewable chargers. Unlike high-output charging sources, their current output is usually low compared to the size of the battery bank. This means that almost all of the charging power is converted to stored power in the batteries, reducing the need for what we call an absorption cycle. When the voltage setpoint of what would be considered the bulk charging cycle is reached, the batteries will be nearly full. When the voltage setpoint is reached most renewable charger controls simply disconnect the circuit until the voltage falls to some preset level, then reconnect again. This on-off action continues until the batteries are completely filled.
A relatively new feature on charge controllers is something called pulse width modulation (PWM), which automatically varies the duration of the charging pulse to optimize charging efficiency. Many of the new renewable charge controls have PWM circuitry.
Charge Control Features & Options
Battery Type Selection
Most alternator and battery charger controls allow the operator to select which type of batteries they are using, either gel or wet. Changing the battery type selector switch on the control changes the bulk voltage setpoint, which is usually 14.1 or 14.2 for gel batteries and 14.4 for wet batteries. Solar, wind and water controls typically use the lower of these two values and are therefore suitable for use with either type of battery. The slight difference in voltage (and therefore charging performance) isn't a problem with renewable chargers, since by the time the voltage setpoint is reached the batteries are very nearly full, and there is no concern about how long an engine is running.
An important optional feature found on many controls for high output charging sources is temperature compensation. All charging controls base their operation on battery voltage and its relationship to state of charge. The relationship between battery voltage and state of charge, however, changes with battery temperature. In fact the difference can be rather dramatic when the batteries are very warm or very cold. A temperature compensation circuit in an alternator or battery charger control ensures that the various charging cycles begin and end when they are supposed to, and that the batteries aren't routinely under- or over-charged.
Controls with temperature compensation come with a temperature sensor that adheres to one battery in the bank. A low-voltage wire links the sensor to the the charge control. Locating the sensor on a battery in the middle of the bank will give best accuracy.
As with multi-stage charging, temperature compensation is less of an issue with renewable charge controls since the current levels are usually low relative to battery capacity. Even so, if this option is available for a solar, wind or water controller, I recommend you opt for it.
Equalization Cycle Feature
Some alternator and battery charger controls allow you to equalize wet batteries. They do this by temporarily, under controlled conditions with low charging current, allowing battery voltage to rise until the batteries are gassing vigorously to remove sulphate deposits on the battery plates. The operator should always monitor conditions during an equalization cycle, and keep in mind that gassing means the release of hydrogen gas. Proper ventilation and the elimination of any possibility of sparks or open flames is essential. Under no circumstances should you attempt to equalize gel batteries—they don't need it and a potentially dangerous condition will result from applying high voltage to a gel battery.
Many charge controls incorporate monitoring functions so you can see what is happening as the batteries are charged.Some have basic LED lights that indicate if there is power to the control, if conditions are right for charging (on solar, wind & water controls), which charging cycle is in process (bulk, absorption, float), and basic battery state of charge information. Other controls display charging amperage with either analog or digital displays.
Low Voltage Disconnect
Some small to modest capacity solar charge controllers have provisions for a Low Voltage Disconnect (LVD) circuit for the house loads (up to the unit's rated current capacity). This feature protects the batteries from over-discharge by disconnecting the appliance loads when battery voltage drops to a preset level. LVD circuits are independent of the charge control circuit, but similar enough to make them compatible when mounted in a single control device.
|Kevin Jeffrey is a long-time multihull sailor, independent energy consultant, author and book publisher. He is the author of Independent Energy Guide, a valuable resource for cruising mutihull sailors, and is the publisher of Adventuring With Children by Nan Jeffrey and the first three editions of the Sailor's Multihull Guide.|
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