Considerations of Onboard Power Provision

By John Payne, Westerly Conway

Another cruising season drew to a close, and hopefully it had been without electrical incidents; it would make an interesting survey to determine what issues fellow members experienced during last season. Was it the usual battery power and battery charging issues? or faulty wiring or other irritating and disruptive failures?

While battery power consumption has generally reduced with lower power demand in latest generation electronics and lighting, the usual power-hungry culprits are autopilots, refrigeration and inverters.  While some technical developments such as improved high efficiency inverters have eased the strain along with energy efficient LED lighting, I’m sure that future changes will see the wider implementation of 48 volt power systems as a way to improve available power and 48 volt equipment such as windlasses, thrusters and alternators are readily available.  Batteries are still central to the primary DC power system and, whatever the voltage used, it is important to carry out a basic power balance assessment and capacity calculations to assess the power system requirements.  The bottom line on power requirement has risen, requiring increased battery power installed to support it.  The search for a bullet proof and fault tolerant battery bank is as real as ever. 

Planning Pays Off

Good electrical system power planning requires careful attention to detail and there is a logical sequence for determining the various parameters.  A concise and realistic load analysis should be carried out to determine the battery requirements, including consideration of normal operational loads as well as intermittent and parasitic loads. 

Once this has been completed, a suitable battery type can be selected.  There’s quite a range of battery types available:  flooded cell (yes some still choose them); Gel; AGM; Lithium-ion; and Carbon Foam batteries.  Whatever is chosen, it will have to be compatible with the calculated discharge rates.  While capacity uses amp-hour capacity and discharge rates over nominal 20 hours rates, the charging is based on the charge acceptance rates, which requires a suitable alternator rating and smart charging regulator.

In addition, factoring in solar, wind and water charging systems is important. Questions of potential failure modes and the provision of system redundancy within the power system design are also essential, although rarely considered.  This may then lead to: the installation of dual alternator charging systems; the separation of starting and charging systems from the default engine manufacturers integrated design; the provision of backup power supplies; and splitting loads into dual circuits.  Every electric system should have a “Plan B” built into the design and that doesn’t have to be an oil lamp!  More detail on charging systems and alternative energy systems is the preserve of future articles.

About Batteries

The flooded cell lead acid battery has always filled the house and starting roles and this position is under siege from technology newcomers such as Lithium-ion, Lead Carbon, Carbon Foam and so on. The battery decision making process depends on the load types, such as start or house power, and for deep cycle batteries it is about discharge rates, charge acceptance rates, projected cycle life and for start batteries it is their high cranking current ability.  In most cruising yacht applications inefficient charging is a major cause of shortened life and performance and fast charge smart regulator systems are essential if the full capacity is to be realized. 

Lithium-ion based battery technology is revolutionizing the mobile power market as a result of the rapid advances in the electric vehicle space.  They are a viable alternative to lead acid, AGM and Gel batteries.  There are many advantages that include minimal power loss when discharging to near 100% of capacity (although that isn’t currently recommended) and nearly the entire battery capacity is available unlike lead acid chemistry batteries.  Lithium batteries possess a very high energy and power density.  Other advantages include much lighter weights and they have approximately 500% greater cycling capability than a standard AGM battery.  The drawbacks are that they are not generally suitable for engine starting.  In late 2022 Mercury Marine approved the use of one battery for use for starting outboard engines.  This was the RELiON Model RB100-HP.  This is a LiFePO4 battery with a minimum cranking amp rating of 800A with a peak acceptance charge of 165A. Many engine makers advise that using a Lithium-ion battery that is not approved will void the warranty.  Like all batteries, they do not tolerate rough mistreatment very well.  So, absolutely do not short circuit one, do not overcharge them or subject them to reverse polarity and do not damage or fracture the casing. 

Lithium Batteries

One of the frequent cautionary notes is that Lithium-ion batteries have a flammable electrolyte and are at risk of what is known as thermal runaway. 

In certain situations, a Lithium-ion battery can suffer very rapid internal heating and once this exothermic reaction is initiated, and it is hard to extinguish or contain.  The initial cause of thermal runaway is an internal short circuit. Another is very fast charging and discharging which generates excessive heat.  Overcharging is also a primary cause, and so only use charging systems, and fast charge regulators that are specifically designed for use with Lithium-ion batteries, not all are.  This is one of the reasons that a Battery Management System should be installed at all times.  

Battery Management System (BMS)

The BMS monitors and shuts off when it detects either high or low voltage limits, high and low temperature limit and lastly when current charge limits are exceeded, both charging and discharging.  The BMS should monitor these parameters at cell level.   Only install batteries that are from manufacturers with cell level BMS monitoring systems installed.  There are equipment manufacturers that specify only selected Lithium-ion battery makes and models.  Andersen compact deck winches are one of them.  They only accept Super B, Mastervolt and Victron Energy (MG Energy Systems) batteries.  These batteries have undergone compatibility testing and have integral protection to prevent battery, motor and systems damage. 

Absorbed Glass Mat (AGM) Batteries 

AGM batteries like Gel cells are classed as Valve Regulated Lead Acid (VRLA) batteries The electrolyte is held within a very fine microporous (boron-silicate) glass matting that is inserted between the plates, which absorbs and immobilizes the acid while still allowing rapid plate and acid interaction.  Another term used for AGM batteries is starved electrolyte batteries, and this is because the glass matting is only 95% soaked in electrolyte.  In a normal lead-acid battery, water loss will occur when it is electrically broken down into oxygen and hydrogen near the end of charging.  The operational principle is called the recombinant gas absorbed electrolyte, as the generated gases recombine within the battery and significantly reduce hydrogen emissions. 

They emit less than 2% hydrogen gas during severe overcharge. This recombination process reduces water loss by over 98% in comparison to flooded cell batteries, so the elimination of maintenance is obvious.  The recombination process is different to a gel cell and takes place within the separator in a molecular state, with the cells being sealed and the relief valves provide a safe positive pressure during charging.  There are variations to traditional flat plate manufacturing techniques, and the Optima® AGM batteries have a spiral cell, and dual plate construction. Another important claimed feature is a greater shock and vibration resistance than gel cell or flooded batteries.  Charging of AGM cells have few limitations, and no special charge settings are required to smart fast charge regulators.  The batteries have a very low internal resistance and during heavy charge and discharge there are no heating effects.  As they have a high charge acceptance rate, they can be bulk charged at very high currents, typically by a factor of 5 over flooded cells, and a factor of 10 over gel batteries.  They also allow 30% deeper discharges and recharge 20% faster than gel batteries and good recovery performance from full discharge conditions. 

Lead Carbon Batteries

The Lead Carbon AGM battery is also worth consideration and I have recently installed Lead Carbon AGM batteries on my Conway so I will be watching the overall performance closely.  Replacing the active material of the negative plate with a lead carbon composite that reduces sulfation and improves the charge acceptance of the negative plate. 

The advantages of lead carbon are deceased sulfation when partially discharged.  They have a lower charging voltage which results in increased efficiency and reduced positive plate corrosion. The overall benefit is increased cycle life.  The chemistry is interesting and these battery types employ a standard lead positive electrode and a supercapacitor negative electrode. 

Theoretically, the lead carbon battery has an unlimited discharge and fast charge rate.  This innovative and complex technology comprises Activated Carbon and Nano Carbon (Graphene) to optimize the electrochemical reaction between the electrolyte and active electrode material and prevents sulfation.  Carbon has very good conductivity and capacitance characteristics.  This combination of asymmetric supercapacitors and lead acid cell processes results in significantly enhanced performance due to low internal resistance and energy conduction. 

And finally:

If your season cruise has resulted in the need to replace or upgrade your batteries, you may wish to use the opportunity to consider options for replacement.  Firstly, carry out an energy audit, then you can plan upgrades to ensure that your next season cruise energy requirements will be properly met.

Biographical Details

John Payne cruises a Westerly Conway 36 foot ketch.  He is author of The Marine Electrical & Electronics Bible (4th Edition pending) and currently works as a consultant Marine Electrical Engineer in the commercial shipping and offshore oil industry.