Battery Chargers

How does a marine battery charger work?

 The principle of maritme battery charger operation is quite simple. The alternating voltage is applied to the transformer, which reduces it to a level close to the battery’s voltage. The rectifier then converts the voltage to a constant one, the filter reduces the pulsation, and the regulator supports the voltage at the specified level. There are many ways to combine these components in a single device. Do you want to know what marine chargers are and when to use them? Then…

A small boat charger.

The charger is connected to the service battery. As soon as the voltage on it increases, the relay closes and connects the start-up storage battery to charge. On the water, the charge goes in the opposite direction. One switch opens the two circuits (starting and service circuits) and combines them, if it is necessary. After the engine is switched off, the relay is unlocked and prevents battery collision.

For an open boat with one additional battery, a hermetically sealed charger with one or two exits is suitable. It is installed anywhere on a boat without worrying that water or strong vibration will take it out of standing. The charging mode is fully automatic, and there are no settings or adjustments. Once the charge is complete, the device lowers the voltage to 13.3 V and can remain connected to the battery for as long as necessary.

Boat motor batteries charger.

The main and auxiliary motors typically have two or three batteries, one of which has a voltage of 24 or 36 V and the other two 12 V. From the on-board 220 V, all accumulators are charged with one device with multiple outputs. However, this option is not the most optimal in terms of cost or quality of charge. Instead of one, it is more convenient to use two chargers – one AC-DC (110/220-12 V)  and one DC-DC (12-24 or 12-36 V). Together they allow charging of all batteries from both the shore network and the boat engine generator. In this case, batteries can be of different types – liquid acid and helium or liquid acid and LiFePO4, etc.

Most chargers for motorboats have a single charge voltage of 14.4 V. It is suitable for helium and hermetically sealed batteries with liquid electrolytes. However, it does not comply with the recommendations of manufacturers of liquid acid, some AGM and calcium batteries. They require 14.6-15.1 V.

Low voltage is a common cause of low charge. Due to incomplete charge, lead sulfate formed in battery plates during discharge hardens over time and forms large crystals that are difficult to convert back into active material. This process, known as sulfate, reduces battery capacity and kills it slowly.

There are several causes of sulfate, but two of them are directly related to the incorrect charge voltage:

1). The battery is regularly under-charged, and part of the active material of the plates is permanently unlocked.

2). Inside thick plates or plates with dense active material, chemical reactions do not occur sufficiently intensively.

The higher the charge voltage, the more energy the battery receives and saves.

Chargers for the big boats.

For sailing and motor yachts, the level of protection of the charger is of little importance. Vessels of this class usually have a common negative tire, are equipped with connectors to connect to the shore electrical grid, and often use an additional generator and inverter. The DC electrical system on most of them is 12 or 24 V, but some voltages can be 36 or 48 V.

Typically, chargers are installed in the engine compartment of the motorboat. The water-tightness of the device is not decisive. It must be powerful, light has a remote control, and can quickly charge several groups of batteries.

Very often, large boats are equipped with two or three groups of batteries. The total capacity of batteries may vary depending on the length of the boat and the number of customers on board but generally ranges from 300 to 400Ah and above. Batteries of this size require a powerful charger. Choosing the correct one, it is necessary to answer the following questions:

  • Which electrical equipment is used when the boat is at the dock?
  • What current does the vessel consume when the lights are entirely switched on, and the electrical equipment is in operation?
  • What is the voltage in the on-board electrical system – 12, 24, 36 V, etc.?
  • Is there an inverter? If so, what is its power?
  • How many batteries are installed, and what is the capacity of each battery?

Suppose the electrical system operates at 12 V. The parking lot is lit by ten lamps, each of which consumes 1 A current. In addition to the lamps, a radio station, satellite television and a refrigerator are permanently switched on. The capacity of the battery is 100 Ah.

In this case, the current consumed is about 20 A. A minimum of 10 A is also required for charging the battery. This means that a charger with an output current of 30 A is suitable. It can be Blue Smart IP22 Charger 12/30 or Mastervolt ChargeMaster 35 Amp, 12V.
Characteristics of chargers for large boats:
  • Low energy consumption. Most of the time, the electrical system operates on batteries that serve as a buffer between consumers and the charger. Charging only activates when the battery voltage falls below a given level
  • The temperature sensor and operating modes for each storage battery make it possible to select a precise charging algorithm for any battery. As a result, expensive batteries are charged more, properly serviced and serve longer
  • Several chargers may be installed in parallel. This makes it easy to increase the charge current and storage capacity of batteries
  • Two operating modes – storage battery charging and power supply. Onboard charging equipment will operate even if no batteries are available
  • Remote Control Panel. The charger can be controlled even if installed in a hard-to-reach location
  • Voltage pulsations at output 2-3%, safe for electronics and batteries

On a big boat, it’s better to install a more powerful charger.

How to choose a charger?

First of all, before buying a charger, you have to choose the level of protection against water and dust. Environmental resistance is characterized by a protection class developed by the International Electrotechnical Commission to classify electrical casings. The Ingress Protection (IP) rating is convenient to use when choosing a charger. The digits following the letters of the IP in this classification correspond to the levels of leak proofness, which varies from zero to complete protection against dust and water.

For example, IP65 means that the device is protected from the ingress of heavy dust for 2-8 hours and the action of water jets. But some of the water can get inside the hull.

The next step is to adjust the power based on the desired charging time.

For boats and yachts, which spend most of the week onshore or in dock and are permanently connected to the AC network, charging time is of no decisive importance. The charger’s capacity is then selected to be equal to 10% of the capacity of the accumulators. This is sufficient to charge batteries for 8-10 hours.

However, if the boat is used daily, the duration of the charge is significant. Several factors affect the charging time:

  • Battery efficiency. Liquid acid batteries have an efficiency of about 80%. This means that they have to pass 120 Ah to get 100 at discharge during the charging period. Gel, AGM, and lithium batteries have an efficiency of 85-90%, while energy loss and charging time are less.
  • Charging current. The higher it is, the shorter the charging time. For liquid electrolyte batteries, manufacturers recommend a current of 10-20% of the capacity for gels up to 25%. The highest permissible current for AGM batteries is 30-50% C20. Lithium batteries charge up to 100% of capacity.

The approximately charging time of the battery can be calculated by:

T = Co/(Ai-Ab)*eff + Tabs

Т – the duration of the charge

Tabs – the duration of the second charge phase

Ai – the current of the charger

Аb – the current consumed by the connected equipment

Co – the storage capacity of the battery that needs to be restored

eff – battery efficiency. 1.1 for AGM, 1.15 for gel, and 1.2 for liquid acid

The duration of the second charging stage depends on the degree of the battery discharge, which varies between charging device models and ranges from thirty minutes to four hours.

If batteries need to be charged quickly:

  • Use AGM batteries. They allow the highest charge current among lead-acid batteries
  • Try to operate within 50-85% of battery capacity. In this case, you will recover the vessel within a little more than an hour with the right charger.
  • Increase capacity of batteries. This will keep the batteries free of charge above 50%, allow the use of high current and further reduce recharge time.
  • Charge up to 100% once a month

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