In last month’s issue, we explored the differences between external and internal battery management systems. This month, we’ll look at lithium-battery installation requirements to ensure that the new system will be safe. Proper charging systems, wiring, alternator controls and fusing are all essential to avoid catastrophic failures.
The first crucial step is to consult your insurance company regarding any specific requirements before starting the installation. While many providers permit lithium battery systems on board, some require installation by a certified marine professional.
Are Lithium Batteries Safe?
Lithium batteries, especially the lithium iron phosphate (LiFePO4) variants that are common in the boating industry, are inherently safe when integrated into a well-designed system. The American Boat & Yacht Council recently released its latest standard, E-13, which outlines the requirements for installing a lithium battery system aboard a boat.
Lithium batteries contain significantly less flammable material compared to conventional fuel or propane tanks. In developing the ABYC standards, experts conducted rigorous “torture tests,” subjecting the lithium batteries to unapproved uses and extreme conditions. The only scenario that caused smoke was two nails being driven into the battery’s side.
Also, traditional lead-acid batteries have their own safety risks. Overcharging them can release hydrogen sulfide gas, which is highly corrosive, flammable and poisonous. Overcharged lead-acid batteries have also been known to explode, spreading corrosive battery acid throughout a boat.
A well-designed lithium system can offer enhanced safety features, superior performance and greater cost efficiency.
Lithium Bank Size
In planning a lithium battery installation, it’s important to determine the required battery bank size. This task involves conducting an onboard energy usage audit, which approximates the overall amperage needs based on the equipment power requirements and time used. It’s advisable to assess power usage when the boat is underway and, separately, when it’s at anchor. These values can differ significantly.
Energy usage audit templates are available online. You can use the one at www.seaandlandyachtworks.com/boat-power-usage-audit.
Lithium Battery Location
Next, determine the mounting location. Look at the battery’s IP rating. This indicates its waterproof capabilities, as well as heating or ventilation requirements that the manufacturer mandates. While many internal lithium batteries are rated to IP67 standards, many high-quality external BMS systems are not. They require additional environmental protections for proper and safe operation.
Another crucial factor is temperature management. Most lithium batteries have a Goldilocks principle, with optimized operating temperatures between 32 and 80 degrees Fahrenheit. Be sure that lithium batteries are not placed in an engine room, or in any compartment prone to temperatures above this range. While lithium batteries can withstand conditions outside of this range in storage mode, choosing an inappropriate mounting location only invites problems.
Unlike lead-acid batteries, lithium batteries don’t need to be mounted in a battery box, because they lack internal battery acid. However, they must be secured more robustly to prevent excessive movement and vibration. In short, special attention should be given to securing lithium batteries.
Wiring Requirements
Even if the lithium batteries are advertised as “drop-in” replacements, the typical wiring setup of an original lead-acid battery bank is not suitable for lithium batteries. There are differences in fusing, cable size and wiring configuration.
Improper fusing is a common problem in professional and DIY installations. A thorough understanding of ABYC standards E-13 and E-11 is essential to ensure that a lithium system is adequately protected. This is especially necessary regarding ampere interrupting current. AIC measures a fuse’s ability to stop a short circuit. Lithium batteries, because of their low internal resistance, can deliver extremely high amperage if shorted. A fuse that lacks the appropriate AIC rating could fail from plasma arcing. Preventing this situation means using a class T fuse on the output to meet the 20,000 AIC requirement.
Additional fusing may be necessary for larger lithium systems to meet E-13 specifications. As a measure of additional safety, protect each battery individually with an MRBF-style fuse before the batteries are paralleled together on a bus bar.
A bus bar system ensures redundancy if a battery is disabled, and guarantees equal charging and discharging of all batteries. To achieve this, all battery cables, positive and negative sides, must be of equal length to account for the low internal resistance.
The cables between each battery and the bus bar should be sized according to the maximum rated amperage output of each battery. Additionally, wires leading from the bank should comply with E-11 standards, which dictate sizing based on allowable voltage drop and conductor length. All positive wires on the boat, except for the starting circuit, must be fused per ABYC standards, and the fuse size should match the wire size.
Last, it is vital to include a battery disconnect switch that is sized for the maximum amperage used on board, to cut power quickly in case of an emergency.
Charging Systems
It’s also essential to pay close attention to all charging sources connected to the lithium system. Each charging source must have a lithium charging profile and be programmable to match the specific charging parameters that the battery manufacturer provides. This applies to all charging sources, including solar controllers and inverter/chargers.
One critical parameter to consider, especially for smaller lithium systems, is the battery’s C rating. The C rating indicates how quickly a battery can be charged and discharged. A rating of 1C means the battery can be fully charged and discharged within one hour, while a 2C rating means this process can occur in 30 minutes.
It’s important to match the charging output to the battery’s C rating, as many marine batteries are rated at 0.3C.
Alternator Options
Special attention should be given to the boat’s alternator charging system. Neglecting to implement the appropriate measures can result in catastrophic alternator failure.
The first and simplest option is suitable for smaller, less-complicated lithium retrofits that don’t rely on high-output alternators. This setup typically involves an originally installed alternator that’s directly connected to a lead-acid start battery. The lithium bank is then charged via a DC/DC converter, which ensures the correct charging profile based on the state of charge.
However, it has the drawback of being less efficient in charging the lithium bank. The problems are the internal resistance of the lead-acid battery and the amperage limitations of the DC/DC converter.
The second option, although more expensive, is generally better for high-capacity systems that require greater charging capacity. This method uses an external alternator regulator to control the field winding voltage of the alternator, providing the proper charging parameters directly to the lithium battery bank.
This setup often employs a high-output alternator, typically ranging from 100 to 275 amps, and has the potential of eliminating the need for an onboard generator.
The control strategy for this system depends on whether an internal or external lithium system is used. External systems allow for direct control of the alternator regulator, signaling it to shut down charging output if the batteries are fully charged or in an alarm state. Internal batteries rely more on charging settings to control the alternator.
Using an alternator protection module, such as the Balmar APM, is crucial in case the internal system disables charging. Without this device, alternator diodes can fail if the batteries reach a full state of charge and the system disables the charging input.
System Commissioning
Upon completing a lithium battery installation, system commissioning is a crucial step. This process typically involves a thorough inspection, ensuring that all cables and connections are properly tightened and torqued, and that all charging settings are correctly implemented.
Before assembling the battery bank, be sure to fully balance all the batteries. This can be achieved using a remote charger prior to installation, or by isolating and charging each battery individually after installation.
It is generally recommended to bring all batteries to a 100 percent charge, though some manufacturers allow for a maximum voltage difference of 0.3V.
If you’re planning to undertake this conversion yourself, it’s crucial to ensure that all system requirements are thoroughly met to guarantee safety and reliability. Several companies, including mine, offer guidance and custom electrical schematics to ensure that specific electrical needs and safety standards are upheld.
Mike Garretson owns Sea & Land Yacht Works in Wakefield, Rhode Island. This article was originally published in the September 2024 issue.
