Inverter Battery And Boat Negative Bus: Safe To Connect?

The question of whether an inverter battery should be connected to a boat's negative bus is a complex one and depends on a variety of factors, including the type of boat, the electrical system design, and safety considerations.

In some cases, it may be advisable to connect the inverter battery to the negative bus, especially if the boat has a dedicated grounding system in place. This can help ensure a stable electrical connection and reduce the risk of electrical issues.

However, in other cases, it may be recommended to keep the inverter battery separate from the boat's negative bus. This is particularly true for boats with aluminium hulls, as connecting the electrical system to the hull can lead to corrosion and other issues.

It is important to consult with a qualified marine electrician to determine the best approach for a specific boat and its electrical system. They can assess the unique characteristics of the boat and provide guidance on safe and effective wiring practices.

Additionally, it is worth noting that different regions may have varying standards and practices for boat electrical systems, so it is essential to be aware of local regulations and guidelines.

The impact of wiring batteries in series

Wiring batteries in series has a number of impacts on a boat's electrical system. Firstly, it increases the overall voltage of the circuit, which can be useful when powering devices that require higher voltages, such as electric motors in boats. This higher voltage also results in a lower system current, meaning thinner wiring can be used and there is less voltage drop in the system.

Additionally, connecting batteries in series can improve the system's overall efficiency by distributing the load across multiple batteries, reducing stress on individual batteries. This configuration also increases the system's ability to store energy, which is beneficial when powering devices for extended periods in remote areas with limited power sources.

However, there are also some drawbacks to wiring batteries in series. If one battery in the series is weaker than the others, it can become overcharged or undercharged, reducing its lifespan and negatively impacting overall system performance. An external device, such as a battery equalizer, is usually required to balance the charge and discharge across the batteries.

Connecting batteries in series can also reduce their lifespan as they may not discharge evenly, leading to premature failure. If one battery in the series fails, it can cause the entire system to fail, which can be problematic in situations where reliable power is critical.

Furthermore, wiring batteries in series requires additional wiring and components, increasing the complexity of the system and making installation and maintenance more difficult. It is important to ensure that all batteries in a series configuration have the same voltage and capacity ratings to avoid problems that may damage the batteries.

In summary, wiring batteries in series can provide benefits such as increased voltage and improved efficiency, but it also comes with drawbacks related to complexity, reliability, and battery lifespan. The impact of wiring batteries in series depends on the specific needs of the devices being powered and the overall design of the electrical system.

The importance of battery switches

Battery switches are an essential component of a boat's electrical system, providing control over the flow of electricity between the battery and the rest of the boat's systems. They are especially important for boats with multiple batteries, allowing the user to switch between them and prevent one battery from draining another.

The Different Types of Battery Switches

There are three main types of battery switches: the ON-OFF switch, the 1-2-BOTH switch, and the ON-OFF-COMBINE switch. Each type has its own advantages and disadvantages, and the right switch for a boat depends on the specific needs and complexity of its electrical system.

ON-OFF Switch

The ON-OFF switch is the simplest type, with just a single pole that can be connected or disconnected from the battery. It is easy to use and affordable but offers limited functionality and may not be suitable for larger boats or those with multiple batteries.

1-2-BOTH Switch

The 1-2-BOTH switch offers more flexibility, allowing the user to choose between two batteries or combine their power. It provides improved battery management and is suitable for emergency situations but is more complex and costly than the ON-OFF switch.

ON-OFF-COMBINE Switch

The ON-OFF-COMBINE switch is the most advanced type, offering greater control, flexibility, and safety. It allows the user to isolate one battery in an emergency and simplifies operation when used with an Automatic Control Relay (ACR). However, it is also more complex and costly than the other types.

Best Practices for Battery Switch Usage

To optimise energy management and ensure the seamless operation of electrical systems, it is important to adopt best practices for battery switch usage. For boats with an OFF-1-2-ALL switch, a strategic approach is recommended:

• When starting the engine, set the switch to position 1 (start battery).
• While motoring, switch to position 1 to recharge the start battery for around 20 minutes.
• Shift to position 2 to recharge the house bank for the remainder of the journey.

Automatic Battery Management Solutions

Advancements in marine technology have led to the development of automatic battery management systems, such as the Blue Sea Systems' "Automatic Charging Relay" (ACR) or their "Add-A-Battery" system. These systems eliminate the hassle of manual battery management by automatically managing the dual-circuit switch positions, ensuring batteries are charged and ready without user intervention.

Understanding AFD (Alternator Field Disconnect) for Safety

In boats without a battery isolator, the alternator's output is typically connected to the load side of the battery selector switch. This allows the user to select the bank they wish to charge, but it can also lead to a voltage spike if the battery switch is accidentally turned to the "OFF" position while the engine is running. This spike can damage the alternator's diodes and voltage regulator.

To mitigate this risk, an AFD (Alternator Field Disconnect) switch is used. It disconnects power to the alternator's field windings when the battery connection is broken, preventing the damaging voltage spike. Boats equipped with a battery isolator, on the other hand, maintain a constant connection between the alternator and the batteries, eliminating the need for an AFD switch.

How to prevent corrosion

Corrosion is a constant threat to boats, especially those exposed to saltwater. To prevent corrosion, you can take the following steps:

Wash and Rinse

After every trip, wash your boat with soap and freshwater, paying special attention to metal components such as railings, hinges, and rod holders. Use a rag or soft-bristled brush for this task.

Next, rinse the boat's engine with freshwater for at least five minutes to eliminate any saltwater remnants from the cooling system.

Keep it Protected

If your boat is stored in a slip, keep the outboard engine or I/O lower unit tilted to the highest position to avoid constant exposure to saltwater. Always cover your boat when not in use, and consider investing in custom-made covers for a perfect fit.

Lubricate

Lubrication ensures smooth movement and protects against rust and water intrusion. Apply marine grease to the fittings on your outboard steering tilt tube and engine trim mechanism. For sterndrive boats, lubricate the gimbal bearing and engine coupler.

Apply a light coat of moisture-displacing lubricant to all moving metal parts, including latches, hinges, linkages, bow rollers, and trailer winch rollers.

Protect Your Engine and Fuel System

Use a top-quality marine fuel additive to stabilize the fuel during storage, and store your boat with a full tank of fuel (95% or more). Regularly inspect the fuel lines, fittings, hose clamps, inline fuel filters, and water-separating fuel filters, replacing or cleaning any parts that appear dirty or damaged to prevent engine and fuel system damage.

Check Your Power Systems

Battery terminals and connections are prone to corrosion, which can cause ignition or power supply issues. Regularly inspect your battery posts and terminals, cleaning them with a wire brush if necessary. Reattach the terminals tightly and apply battery terminal spray or white dielectric grease to prevent future corrosion.

Additionally, inspect battery cables for any signs of damage, such as cuts or nicks in the insulation, and replace any damaged cables.

Inspect Sacrificial Anodes

Sacrificial anodes, often called "zincs," are designed to protect aluminum components from galvanic corrosion. These are usually located on the gearcase, transom bracket, or trim rams of a Mercury outboard or MerCruiser sterndrive.

Inspect these anodes frequently, especially if you operate your boat in saltwater. Mercury recommends replacing the anodes when about half of the anode has been lost to corrosion.

Other Tips

• Keep your boat and engine shining with a spotless shine product to remove water spots from fiberglass, metal, plastic, and rubber surfaces.
• Use a corrosion-resistant coating like Mercury Corrosion Guard Engine Protect on sterndrive and inboard engine blocks and under-cowl areas of outboard engines.
• Avoid using your boat's hull as a conductor for your electrical system. Ensure that the negative pole of the lighting system is wired directly to the battery.
• If you have an aluminum boat, ensure that all equipment, including engines, generators, alternators, and navigation equipment, is unearthed and that the negative pole of the battery is connected to the hull at a single central point only.
• If you are concerned about corrosion but still want to ensure a proper earthing system, consider installing an isolation transformer to block the connection between different metals and prevent electrolytic corrosion.

By following these steps and staying vigilant, you can keep your boat in top shape and enjoy your time on the water without worrying about corrosion.

The role of a galvanic isolator

A galvanic isolator is a critical piece of equipment in the fight against corrosion. It is a modern solution to protect your boat from corrosion, specifically galvanic corrosion, which occurs when different metals are submerged near each other and naturally create a battery effect with their own small currents between them.

Corrosion can destroy propellers, thru-hull fittings, and any other submerged metal on the outside or inside of a boat. Corroded metal is typically below the waterline, so problems can develop before they are noticed. Galvanic isolators are inexpensive, simple to install, and can extend sacrificial anode service life.

The galvanic isolator is installed in the green grounding conductor in your shore power system. It works by introducing a low DC voltage drop in that conductor, effectively isolating your boat from your neighbours on the dock.

It is important to use fail-safe galvanic isolators. Older galvanic isolators and non-fail-safe isolators typically disconnect the AC ground when they fail, removing the AC safety protection. A fail-safe galvanic isolator is slightly more expensive but will maintain the grounding connection even if something goes wrong.

The American Boat & Yacht Council (ABYC) has strict guidelines for galvanic isolators. They must be rated for system amperage, hard-wired into the system, and meet design specifications to ensure they can never inadvertently open-circuit, eliminating the safety ground.

If your boat is plugged into shore power on a regular basis, you need a galvanic isolator installed in your shore power system.

The difference between positive and negative battery switching

When it comes to battery switching, there are two methods: positive switching and negative switching. Functionally, it makes no difference which method is used. However, from a safety perspective, it is always recommended to switch the line that is not connected to the earth or chassis. This reduces the risk of short circuits.

Positive switching involves placing the switch in the positive leg of the circuit. This is typically done when the negative side of the battery is tied to the earth/safety ground or frame ground of a vehicle. It is also recommended to place the fuse near the positive terminal of the battery so that if the fuse blows, the entire circuit will be dead.

On the other hand, negative switching involves placing the switch in the negative leg of the circuit. This method is preferred by some for safety reasons. In the event of a crash, the exposed terminals on the back of the disconnect switch could contact metal and cause a short circuit or even a fire. Since the negative side of the circuit is already grounded to metal, this risk is mitigated.

It is important to note that the switch should always be connected to the live wire to ensure that when it is turned off, no current flows through the appliance. Connecting the switch to the neutral wire would result in the circuit remaining on even when turned off.

In the context of boats, it is generally recommended to isolate the electrical system from the boat's hull. This is especially important for aluminium boats to prevent any impact on the surrounding fish. All grounds should go to the negative side of the battery or to a central grounding block connected to the negative terminal. Additionally, each circuit should have both a positive and negative wire returning to the battery.

Frequently asked questions