How to select batteries for your boat?
In order to start the engine of your boat, marine starter batteries generate a current of 500 – 1000 amperes for 5-10 seconds. This is achieved by installing a large number of thin plates inside the batteries, which provide the maximum contact surface with the electrolyte. However, this design does not allow deep discharge of the battery, so starter batteries are not suitable for working with electric motors, pumps and powerful marine electronics.
If a single battery is used to start the gasoline engine and connect electrical equipment on the boat, choose a starting and traction battery. It can withstand a discharge of 10 amperes for 7 hours and has a starting current of 500 amperes and higher. Starting and traction batteries are often marked with DP symbols – dual purpose.
Batteries of any type are capable of starting the engine – gel, AGM or liquid electrolyte. But for sufficiently powerful gasoline and diesel engines, it is preferable to use AGM batteries.
What characteristics are important when choosing batteries?
Motor manufacturers in the documentation indicate the minimum recommended battery characteristics for their products – capacity in ampere hours (Ah) and cold cranking current (CCA) or reserve capacity (RC @ 25) and marine starting current (MCA).
When buying a battery, check that the battery you have chosen has both parameters not lower than the recommended ones. Using a battery with a lower capacity puts additional stress on the electrical system of the yacht or boat and may damage it.
Battery capacity C20 – characterizes the current that the battery can provide for 20 hours until the voltage at the terminals drops to 10.5 Volts. The higher the capacity, the longer the battery can power the devices connected to it.
Reserve capacity RC @ 25 – time in minutes for which the battery will be discharged with a current of 25 A at a temperature of 27 degrees Celsius to a voltage of 10.5 Volts.
Marine starting current MCA – the current that a new, fully charged battery provides for 30 seconds at a temperature of 0 degrees Celsius. In this case, the battery cell voltage does not fall below 1.2 Volts.
Cold Cranking Current CCA – is the same as MCA but at -18 degrees Celsius.
How to properly organize battery charging on your boat.
Service batteries on a boat or yacht are designed to power on-board equipment. In addition to the service group, the vessel can be equipped with batteries for a bow thruster, an electric boat motor or an anchor winch. Considering that each group of traction batteries can have different voltages, capacities and chemical composition, the correct organization of charging these different batteries becomes a daunting task.
The solution consists of several steps.
Firstly, choose a charger that has sufficient power, has profiles for charging the main types of traction batteries and is equipped with two or three outputs.
Secondly, a decoupling device is selected for charging several battery groups from the main engine generator. It can be either a relay or a battery divider of the corresponding rating.
Special devices to help you use your batteries more efficiently.
Autonomous swimming is impossible without monitoring the condition of the batteries. In the simplest case, a voltmeter is used, however, devices that combine a voltmeter, ammeter and ampere-hour meter and other parameters in one case are much more informative and more accurate. The battery control monitor can be designed to work with one group, or to control several charging sources and batteries.
If traction batteries supply powerful consumers, for example, an inverter, they must be protected from deep discharge. Special devices designed for this disconnect the load as soon as the battery voltage drops below 11.5-12.0 volts. Protection devices are also installed when a single battery is used both for starting the engine and for powering on-board equipment.
During the movement, the traction batteries are charged from the generator of the propulsion engine of the boat or yacht. However, due to the engine generator features, the charging of traction batteries takes too long and leads to increased fuel consumption and additional wear if the engine is started on purpose to charge the batteries. Special devices increase the charging efficiency of the generator, and additional charging sources such as solar panels recharge the batteries while the engine is not running.
So, let’s summarize.
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