- Charge batteries correctly & prevent premature wear and tear -
In order to maintain battery performance and prevent premature deterioration, care must be taken to ensure that batteries are always properly charged. A standard alternator alone is not able to fully recharge cyclically used batteries (consumer batteries, which are usually discharged up to 50%). In order to do this, shore power chargers are used. We stock a wide range of high-quality chargers from leading manufacturers such as VICTRON, STERLING, QUICK, MASTERVOLT, DOMETIC (formerly WAECO), CTEK, BLUESEA and more.
Until recently, a rule of thumb was that the required charging current should correspond to 10% of the installed battery capacity. However, this rule no longer applies, as it does not take into account the fact that during the charging process in the harbour, active power consumers are still connected to the DC on-board power supply. For example, if there are two 100 Ah batteries, a 20 A charger would be required. Assuming that heating, laptop, refrigerator, television or a few halogen lights are used during charging, these also consume part of the charging current. In this case, not much remains of the 20 amps and the battery will only charge slightly. With this in mind, a charger output of 20-25% of the battery capacity is needed. This ensures that batteries are fully charged overnight and ready for the next trip.
Modern yachts are equipped with a large number of electrical consumers. For this reason, particular attention should be paid to energy supply on board. In harbours and marinas with very long 230 volt supply lines and where many consumers are connected, very often the voltage drops to below 200 volts on the last sockets on the last jetty. For chargers with conventional transformer technology this is a disadvantage, as any drop in charge voltage/charge current prevents reasonable charging. Modern switching power supply technology guarantees optimal charging, features small housing dimensions and is light in weight. These modern battery chargers for boats operate with high-frequency switch-mode power supply technology and have compact ferrite core transformers. This makes them significantly smaller and lighter than devices with older transformer technology. They are designed to tolerate voltage and frequency fluctuations when connected to the mains and can therefore also be used with a 230 V generator away from the harbour.
Our tip: If you're sailing "across the pond", make sure that the charger is suitable for international use, i.e. for mains voltages and frequencies around 115 V and 60 Hz.
Maintenance-free lead-acid and lithium type batteries are best charged by means of multi-stage constant current/constant voltage (CC/CV) characteristics, also known as IU characteristics.
Example IuoU characteristic curve: I = constant current, U = constant voltage, the "o" indicates that there is a voltage change in the characteristic curve.
Thanks to sophisticated control technology, further functions are included in a multi-stage characteristic curve, such as soft start, trickle charge, desulphation, etc..
Different types of batteries (maintainable or sealed lead acid, GEL, AGM or LiFePO4) require different voltages and charging times for optimal charging. High quality chargers can be configured to be compatible with the most common battery types. In this case, meaning lead acid, GEL, AGM or lithium characteristics. The IU charging procedure is the same, but the device then works with manufacturer-set voltage and time parameters for the respective battery type. For some devices, these parameters can be changed manually with coding switches (DIP switches) or with software as required.
Main charging phase / bulk phase
A battery charger supplies a constant current (its nominal current) in the main charging phase (bulk phase) and charges the battery up to 70-80%. When empty, the battery has low resistance and can absorb a lot of current. While it is being charged, internal resistance rises continuously and the rate at which the battery is able to absorb charging current is reduced. This leads to a current decrease and voltage rise until the final permissible charging voltage is reached.
If a battery type can be configured or is set on the charger, the level of the final charge voltage is automatically set. This is determined in such a way that no strong gassing can occur in the battery. It is important to set the battery type correctly, because gassing releases hydrogen and oxygen (= explosive oxyhydrogen gas), which in maintenance-free and sealed batteries leads to gas overpressure, which is released from the battery via safety valves. These batteries cannot be topped up with water, as is well known, which results in a loss of performance and premature deterioration!
Constant voltage phase / absorption phase / equalising charge
Once the final charge voltage has been reached, the battery charger switches to the constant voltage phase (absorption phase, equalisation charge) and fully charges the battery at a constant voltage and a low, continuously decreasing current.
The constant voltage phase (equalising charge, absorption phase) is very important because it brings the individual cells of the battery to the same charge level (balancing) and ensures that the battery remains efficient. This requires a certain amount of time, which is automatically set by the charger when selecting the type of battery. This is done either via an integrated timer and/or by means of voltage and current values.
Trickle charge / float phase / trickle phase
At the end of the equalising charge, the device goes into trickle charge (float or trickle phase). It provides a lower, constant voltage. The level of this voltage is also automatically set by the charger when the battery type is selected.
If the float charge voltage is too high, excess oxygen and unwanted corrosion within the battery can lead to irreversible damage and premature failure.
The use of chargers with very low output current in combination with high battery capacities is not recommended, as they are not suitable for recharging cyclically used batteries (consumer batteries) quickly and fully. These devices are suitable for recharging starter batteries or small battery capacities and they can be used for maintaining batteries in winter storage. With trickle charging, the voltage is slightly higher than the open circuit voltage of a charged battery. Only a very small current goes into the battery, which prevents self-discharge.
During charging, a battery charger also functions as a DC power supply unit and provides power to consumers in the vehicle electrical system. Consequently, consumption current reduces the charging current. If consumers require more than the charger's nominal current, the battery provides the required difference and is discharged. When the consumers are switched off, it is automatically recharged. Longer charging times result from this and the battery may not be fully charged by the time it is next used. There is a risk of sulphation and loss of performance. (Sulphation can be reduced with a NOVITEC Megapulse)
Charging technology without temperature compensation requires batteries to be at room temperature when charging, i.e. 20-25°C. The charging voltage is based on this value. Charging a battery is an electrochemical process. Reaction rates of chemical processes increase at higher temperatures and are faster - at a temperature increase of 10°C (10 Kelvin) two to three times as fast. This means that very hot batteries, despite having the correct set charging characteristic, can gas during charging and are not optimally charged at cold temperatures.
High-quality battery chargers have a temperature sensor which is either affixed to the battery housing or screwed to a pole terminal. Such a temperature-compensated charger would reduce the charging voltage for a 50°C warm battery in the engine compartment by up to 0.75 V. Temperature-compensated charging is therefore an important factor in maintaining the performance of the batteries.
Battery chargers with 1 charging output
These devices are for charging a battery (bank). If the charger with one output can supply sufficient current, it is possible to charge other batteries of the same type (e.g. all batteries being AGM) using a charging relay or a low-loss charging current distributor. Simple isolating diodes are unsuitable for this purpose due to their typical voltage losses and do not allow reliable charging. If different types of batteries are to be charged (e.g. AGM and GEL), we recommend the use of a DC-DC charging converter or a battery to battery charger instead of a separating diode or a low-loss charging current distributor.
Battery chargers with 2 or 3 charging outputs
Devices with 2 or 3 charge outputs are suitable for simultaneous charging of several batteries of the same type, for example AGM starter battery, AGM consumer battery and AGM winch battery.
All charge outputs have only one common MINUS connection. This reduces installation effort, as the MINUS poles of all batteries are usually connected together on board.
Depending on the manufacturer and type, the charging current (depending on the battery charge level) is distributed to the individual outputs. Larger chargers often have a powerful main charging output for the consumer battery and other outputs with limited charging current for starter, bow thruster or winch batteries.
All outputs of these chargers are galvanically isolated from each other and have their own PLUS and MINUS connection cables, so they do not have a common MINUS connection!
Each output can supply max. 50% of the total charging current. These units are usually waterproof and release their operating heat to the environment through the housing only. For this reason, they are only available with low nominal current. Depending on the type and manner of installation, 12 or 24 V batteries can be charged.
Most battery chargers with several outputs are suitable for charging different types of batteries. However, it is not possible to select different battery characteristics for the individual outputs. If you have different batteries on board and want to charge them in the best possible way, you should consider using several shore power chargers or DC-DC charging converters or battery to battery chargers (B2B).
If you want to increase battery capacity on board, you should check whether the capacity of the existing charger is sufficient. If not, there is no need to replace the existing charger straight away. You can connect a second charger in parallel.
Battery chargers with one charging output or with a low charging current are often already provided with battery connection leads. For powerful devices with several charging outputs, the battery connection cables must be chosen according to requirements. Manufacturers often provide recommendations on the required cable cross section. These recommendations should be observed, so that the charging voltage reaches the battery without loss and in full. On request we can supply you with professionally manufactured connection cables with solid ring cable lugs. To do this, we need the screw/bolt diameters of the components to which the cables are to be connected (battery pole terminals, fuse holders, master switch, selector switch, etc.).
According to installation regulations, a circuit must be fused at a distance of 20 cm from the power source. In a charging circuit, the battery is considered to be the energy source. This can be done with a safety fuse or with an automatic circuit breaker. This should be installed as close as possible to the battery so that any short circuit on the charging cables does not lead to overheating or, in the worst case, to fire. If the required fuse value is not specified in the installation/operating instructions of the charger, the fuse value used should be 5 A above the maximum charge current. The following must considered: fuse rating and cable cross-section must match each other! For example, an existing 150 A main fuse on the battery is not suitable for protecting the PLUS and MINUS cables of a 40 A charger 3 metres away from the battery from overheating.
It is wrong to assume that a discharged consumer battery can be fully recharged with the alternator alone! Normally the Lima only generates a charging voltage of approx. 14 volts. Charging is done according to a simple W characteristic curve. Line and terminal losses, in the worst case even a loss-causing isolating diode, reduce the charging voltage so that it is significantly lower on the battery. With a W characteristic curve, the level of the charging current is only determined by the internal resistance of the battery. A discharged battery has low resistance and initially absorbs a lot of current. However, internal resistance increases immediately and continuously during charging, so that the charging current rapidly decreases sharply. This is not enough for a reliable full charge.
In this case, battery charging can be optimised by means of an additional high performance regulator, alternator-to-battery charger and/or solar or wind generators. All these chargers work with multi-stage IU characteristics.