Electrical system on a yacht: practical advice

It is impossible to imagine modern yachts without a whole set of electrical appliances: refrigerators, navigation devices, boilers, radios, chargers for various devices... The list of devices that operate on electricity is growing every year. Even the most ascetic yachtsmen today admit that they cannot do without the necessary minimum of electrical appliances on board. Therefore, managing your electrical network is not only about safety, but also about saving money. 

In this article we will turn to Mike Morgan's excellent material, which was recently published on the Yachting Monthly website, and will try to understand the basics of electrical systems and their maintenance using his example.

Preamble

Mike Morgan is a yachtsman who has long since moved to live on a yacht with his wife Debbie. They spend nine months a year in the waters of the Mediterranean. As Mike himself notes, their yacht is anchored most of the time. However, unlike many yachtsmen, Morgan's boat stops in remote places and anchorages. The Morgans avoid docks and marinas and, as Mike notes, the yacht rarely charges from the shore. 

A word about the boat: The Morgans cruise on a 2021 Bavaria C57 called Spirit. All of Mike's calculations apply to boats of similar dimensions, namely:

• length – 16.73 m;
• width – 5.28 m;
• draft – 2.52.

It should be noted that the advice given in this material should be effective for yachts of any size. The main thing is the general principle of construction and control of the electrical system. Each boat is a unique mechanism that works according to its own rules. 

Just to be clear, before making any changes to your boat, you should consult with a qualified professional to assess the actual need for modification. 

Lithium and lead batteries

The Spirit's electrical system is based on a bank of lithium batteries. When choosing the battery type, Mike reasoned as follows: despite being more stable, lead batteries have a lower charge and are heavier. At the same time, lithium batteries, although more flammable, with proper care will provide the yacht with more electricity than lead batteries. 

Lead-acid batteries can last for years, but many yachtsmen do not accept their use as the main batteries on board. There are many reasons for this, and we will talk about them in the text, but we will make a remark: there is no 100% correct option for using lithium and lead batteries. The main thing is to comply with their operational requirements (you will also find information about these requirements below).

Nowadays, there is an alternative to lithium and lead batteries. Lithium-ferrum-polymer or lithium-iron-phosphate batteries have now corrected the problems of their older lithium "brothers" (not as flammable) and, like lead batteries, can serve for a long time. However, the main disadvantage of LFP batteries is their cost. 

Battery operation

The amount of available electricity directly depends on the capacity of the installed batteries. The capacity of a regular battery is measured in ampere-hours, that is, the total number of amperes that the battery can deliver in one hour. In simple terms, if you have a battery with a capacity of 100 Ah, it will last for one hour of operation with a current of 100 A or for 100 hours with a current of 1 A. But this is in theory. In practice, things are a little different.

The performance characteristics of different types of batteries vary. For example, lithium batteries can easily withstand a full discharge-charge cycle. Lead-acid batteries should not be discharged below 50 percent, because their capacity gradually decreases due to too low a charge level. 

Visualization of the maximum discharge depth of lead-acid and lithium-ion batteries. The normal operational discharge depth of lead batteries is 30-40%, then they enter the deep discharge stage. For lithium-ion, the operational discharge depth is 80-90% of the total capacity.

This is the peculiarity of lead batteries - their actual capacity is about half of the theoretical capacity declared by the manufacturer. Therefore, if we start from the example above, a lead battery with a capacity of 100 Ah will only be able to work for 50 hours at a current of 1 A before it needs to be recharged. This does not mean that the remaining 50 Ah will not be available, but if you try not to discharge the battery below 50%, then the working capacity is 50 Ah without deep discharge.

With these considerations in mind, Mike replaced the standard 240 Ah lead-acid batteries with 800 Ah lithium batteries. As a result, the four lithium batteries weighed less than the single lead-acid battery in the old kit.

Operational problems

It would seem that this is happiness! Look at this fantastic difference in capacity - 240 Ah for lead and 800 Ah for a bank on lithium batteries. Almost a fourfold gap! However, there are some nuances here too. 

It is not without reason that not all yachtsmen prefer lithium batteries. The characteristics of this type of battery include increased sensitivity to operating conditions and the need to use a battery management system to ensure safety. 

However, contrary to fears, modern lithium batteries, with proper care and operation, usually have a longer service life compared to lead-acid batteries. Lithium batteries can withstand a greater number of charge-discharge cycles, while maintaining high performance. Yes, lead batteries must be constantly charged, but their stability in operation has been tested by more than one generation of yachtsmen. Many yachtsmen combine battery types, using them for different tasks. 

In addition, lead batteries are often used as starting and traction batteries. Lead-acid batteries are better at handling high momentary loads (engine start) and constant loads (engine or steering column operation). Lithium batteries, due to their high energy density and stable voltage, are better suited for powering lighting, electronics, and other onboard systems that require constant load.

What does a lead-acid battery look like inside?

It is also important to note that Mike did not provide clear data on the final capacity of his battery bank in the article, so we relied solely on the description of the installed equipment. 

To prevent lithium batteries from catching fire, Mike recommends using a battery management system (BMS). Because of the complexity of installing such a system, it is best to entrust it to a professional. Such a system is used for centralized control of batteries, it notifies about their charge level, has several emergency operation scenarios. A battery management system also allows for easier diagnostics of the battery condition.

Power supplies

Installing batteries of the required capacity is not a problem. But they need to be charged somehow! The easiest option is to head to the nearest marina and connect to the shore power grid. A standard production boat of medium dimensions is usually equipped with a charger (adapter) for 60 A batteries. 

In addition to the shoreline, you can charge the batteries from the engine. Modern boats are often equipped with engines that can operate in alternating current generator mode. Some boats have both an engine and an alternator. The strength of the current generated depends on the power and dimensions of the engine. 

Mike gives the following example. His yacht's engine is capable of producing 60 A of current, meaning the batteries will receive a 60 A charge in one hour. If you, like Mike, have 800 Ah lithium batteries and they are charged to 50%, then it will take about 7 hours to charge to 100% percent. The calculation is as follows: 50% capacity (400 Ah) should be divided by the power of the charging source (60 A) to get the charging time (6.6 hours). Important: the calculations given in the article are approximate and do not take into account many factors. Take them as calculations for the system in ideal conditions.

In order not to abuse the use of the internal combustion engine (Mike is an environmentalist), it was decided to install solar panels. Due to the large width of the boat, there was room for four large solar panels with a capacity of 400 W. Potentially, these batteries can produce more, but everything depends on the strength of sunlight.

Principles of battery charging

The noise of the engine during electricity generation will not be to anyone's liking. In addition, thoughtlessly using the engine to charge the battery means significantly reducing its service life. The engine, like any mechanism, has its own strength threshold, reaching which will have a very negative effect on its performance. 

However, there are situations when the marina is too far away, the weather is cloudy, and the batteries are about to run out. In this case, you will have to use the engine for charging. Mike describes his system as follows: he replaced the standard adapter (battery charger) with 60 A and installed a 120 A, which accelerated the charging process. For AC devices, Mike installed a 3 kW inverter. And although it is still possible to charge from the engine, Morgan decided to additionally purchase a generator.

A standard electricity generation scheme: batteries (center) receive electricity from a generator (top left), from engine generation (bottom left), or from the shoreline.

Please note that Mike changed the adapter based on the features of his equipment. If you decide to purchase a more powerful adapter, make sure that the batteries and electrical system of the yacht can safely handle this power.

The choice fell on Paguro 9000. The specific brand does not matter, pay attention to the output power. Mike's generator is capable of producing up to 9 kW, which, according to him, covers all needs with ease. During operation, the generator powers both the AC electrical system and battery charging.

Again, using the engine as an electricity generator to charge the batteries is possible, but this will increase fuel consumption and wear of engine parts. This option is best used in situations where other ways to recharge the batteries are simply not available. 

Natural sources 

Renewable energy sources are a universal way to charge onboard equipment. One problem is that they are not as constant as generators or engines. However, in most cases, natural energy is available anywhere on the planet, which makes it easier to extract. 

Some yachtsmen combine approaches. We haven't seen the underwater part yet...

As mentioned earlier, Mike installed four solar panels of 400 watts each. The potential output was 1600 watts at 12 volts, or about 130 amps. MPPT controllers are used to monitor the batteries. These maximum power point monitors can be used to check if the batteries are getting enough charge while the panels are running.

Another great way to get "free" electricity is hydro generation. Modern saildrives and dedicated hydro generation units have become much more efficient in the last couple of years. In theory, up to 300 Ah can be generated in one day of sailing at 7-8 knots.

What to consider when choosing batteries, solar panels and generators

The key to setting up and using your onboard electrical system is to keep track of all the devices on board, specifying their exact consumption and required power. And this is a much more complex process than it might seem at first glance. You need to clearly establish not only the power of the devices, but also the amount of time the device is used. 

The first step is to measure "zero consumption." This is how much your boat uses in standby mode, such as when it's at anchor or in a marina. Mike found that his boat uses about 200 Ah per day in standby mode, with three refrigerators, a freezer, and interior lighting running all the time. 

Next, you should measure the amount of energy consumed while running and when parked, but using different devices. This way, you can make a schedule for charging batteries from solar panels or a generator - you will know what and when from the equipment on board is used and when you can recharge the batteries without harming your ears or sleep.

At the same time, teapots, coffee makers, hair dryers, microwaves and other joys of civilization may consume a decent amount of electricity, but they do not do so on a permanent basis. Such devices can generally be excluded from the list of consumers, but should be kept in mind when drawing up charging schedules.

However, special attention should be paid to devices such as washing machines, boilers, freezers, refrigerators, heaters and air conditioners. These devices consume large amounts of energy and can be used for long periods of time, putting a strain on the boat's electrical system. 

Energy-consuming devices are the most serious consumers, so their operating schedule must be strictly regulated. It is better not to run the air conditioner at all when powered by batteries - it "eats" the charge too much. Leave cooling until a marina with a shore power line or until the generator is turned on.

Battery update

If you don't have enough power and capacity for your batteries, you can improve the situation. Mike offers two options:

• complete replacement of the battery pack with a new one;
• installation of additional batteries.

The first option is easier and simpler, but more expensive. Installing new batteries can cost a pretty penny, but the batteries should not have any serious problems in operation. The second option is a little more complicated, since for the correct operation of an existing battery bank, the additional battery must be of the same type, capacity and even age. 

All external wiring should be neatly laid and organized. This will allow for faster repairs or maintenance in the future.

In the second case, there may be a problem with battery compatibility. If the new battery is significantly "younger" than the old ones, it will have better performance, which may lead to an uneven load on the batteries in the bank. In addition, there may be problems with finding the ideal candidate for capacity increase or replacement - it is advisable to install batteries from one manufacturer, and the desired battery may simply be discontinued.

Battery Monitoring

Modern batteries are often equipped with a whole set of monitoring tools – right up to SMS notifications about the state of charge. If the batteries are quite old, various systems are designed to simplify monitoring. Such “smart monitors” can be supplied both as a full-fledged solution and in the form of small devices that will be connected to the battery terminals and monitor the battery condition.

And although today's electrical requirements are an order of magnitude higher than in the past, modern batteries, accumulators and monitoring systems allow you to assess the state of the electrical system quite accurately. Keep an eye on your instruments and their readings, update your batteries in a timely manner and do not leave them without charging for too long, and pay close attention to the wiring on board - and there will be no problems with electricity on board your boat.

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24.08.2024