Are marine batteries ready for a revolution? – American Boat and Yacht Council developer

New technologies are enhancing the electrical propulsion capabilities of ships, but marine batteries standards and charging infrastructure are still developing.

12v Marine Batteries

Electrification has become an increasingly popular buzzword in the international maritime industry, particularly over the past four to five years. Of note, the recreational marine industry is witnessing the development of lithium marine batteries, electrical propulsion, and charging infrastructure. The electrification revolution of onboard power and propulsion systems can largely be attributed to advancements in battery technology. While batteries have been improved since the first lead-acid battery was produced in 1859, there were still limitations with this technology. Lithium batteries address many of these issues; these batteries are often better suited for larger loads and provide more available energy. They also have longer lifespans and higher energy densities. The majority of lithium marine batteries installed on boats use lithium iron phosphate (LiFePO4 or LFP) as the cathode material. LFP has very high thermal stability as a cathode material, which means that these batteries are much safer than cobalt-based lithium batteries.

Using high-quality batteries is crucial. The market is saturated with lithium marine batteries of unknown quality, and many boat owners may opt for lower-priced products. If inferior batteries are used, even the best systems will fail.

However, proper installation and system design are crucial for the safety and performance of a vessel’s electrical system. In response to industry guidance requirements for the installation of these batteries, the American Boat and Yacht Council released a Technical Information Report (TE-13), which will be replaced this year by the updated standard E-13, titled Lithium Batteries. While the E-13 standard does not include any testing requirements, it refers to industry-recognized IEC and UL testing standards that marine battery or battery manufacturers are required to follow. Aside from the chemistry aspect, one of the most important terms when discussing lithium batteries is the safe operating range, which is a set of operating parameters specified by the battery manufacturer. These parameters include high and low voltage limits, charge and discharge current limits, charge and discharge temperature limits, and so on.

To ensure that the battery operates within these limits, each battery (or battery module) should have a Battery Management System (BMS). The BMS is an electronic circuit used to protect lithium marine batteries from dangerous situations such as overcharging, over-discharging, high-temperature charging/discharging, and low-temperature charging/discharging. If the BMS detects any of these situations, it will disconnect the battery from the charging source or load.

The main goal of the American Boat and Yacht Council (ABYC) and the related technical committees established with the E-13 standard is to ensure the safe installation and operation of battery systems without imposing restrictions on the development of technology. Therefore, although most lithium marine batteries are lithium-iron-phosphate batteries, the document does not limit installers to one cathode chemistry.

In 1897, German scientist Wilhelm Peukert proposed an approximate law for the capacity variation of rechargeable batteries at different discharge rates. As the discharge rate increases, the available capacity of the battery decreases. Compared to lead-acid batteries, lithium-ion batteries are much less affected by Peukert’s law. They can handle high discharge currents without losing too much available energy.

This characteristic becomes very convenient when we start considering electric propulsion. The motor used for propulsion is a high current load, and Peukert’s law and low energy density are limiting factors for traditional lead-acid batteries in propulsion scenarios. The development of energy-dense lithium-ion marine batteries that can be deeply discharged at high currents without losing capacity has broken the barriers that electric boats have experienced in the past.

Because of this, electric propulsion is no longer restricted to low-speed boats with traction motors. We are now seeing large yachts and high-speed boats using electric engines. Some electric propulsion systems operate at very high voltages, so proper installation is essential. In 2018, ABYC developed the standard E-30 “Electric Propulsion System”, which addresses the design, construction, and installation of AC (>300 VAC but <1000 VAC) and DC (>60 VDC but <1000 VDC) electrical systems on board ships. High voltage systems have unique safety requirements. For example, the standard requires the disabling of emergency shutdowns of propulsion systems, insulation fault monitors, battery voltage and temperature monitoring, isolation of electrical systems, simultaneous opening of positive and negative disconnect switches, etc.

Most of the major shipbuilders and propulsion equipment manufacturers are researching and developing new electrical products. We can see new developments in some technologies, of which charging is an example. The combined charging system is an open, universal, and standard solution for quickly charging large battery packs in cars as well as electric boats. However, only a few European marinas now have fast-charging posts, as the installation of these requires an upgrade of the marina’s electrical system.

Most vessels have access to shore power outlets and can charge their batteries using onboard chargers, but not as quickly as CSS. As a result, some ship owners may decide to go off the grid and use solar panels, fuel cells, or conventional generators to generate electricity. This is a dynamic and emerging market for yachts and we will see new products in the near future. Shore power demands of the electrical revolution are not limited to propulsion systems and lithium marine batteries, marine electrical systems are becoming more and more complex as customers’ demand for more power continues to grow.

Large inverters are becoming the norm, not only on large yachts but also on smaller ones. For example, many ship owners want to be able to use air conditioning without having to run noisy generators, or they do not have enough space on their ships to install generators. A solution we often see on boats and caravans is a large lithium-ion battery pack combined with an inverter and a high output alternator for fast battery charging.

ABYC Standard A-31, Battery Chargers, and Inverters deals with the design, construction, and installation of battery chargers, power inverters, and inverters/chargers. The standard includes topics such as installation, earthing requirements, and marking, as well as everything a marine technician needs to know to ensure the safe installation and operation of this part of the electrical system.

The higher demand for robust shipboard power requires more sophisticated AC shore power systems. Particularly on larger ships or commercial vessels, we may see more AC shore power converters, often with electrical isolation, frequency conversion and voltage conversion occurring between the shore socket and the ship’s electrical system. It is not hard to see the complexity of electrical systems on ships and the application of new technologies.

ABYC provides technical information to the maritime industry through the development of safety standards to ensure the safe implementation of all these new technologies. We are fortunate to have a group of industry professionals who volunteer to work on the project’s technical committees and sub-committees to help develop technical standards and ensure that we are always able to respond to recent trends.