All about alternators Part 2-outboard engines
With the advent and proliferation of big horsepower outboards, systems on boats that would otherwise not be able to accommodate them are showing up in more and more applications requiring more power. Together with boatbuilders, outboard engine manufacturers are designing and engineering their products to accommodate the extra power needs of these vessels. Today’s outboards are expected to provide onboard electrical energy and charging power for complex power-hungry systems that include air conditioning, refrigerators, ice makers, electric stoves/grills, complex marine electronics arrays, and more. Lithium Iron Phosphate (LiFePO4), commonly called simply “lithium” battery banks typically run all of these systems. For everything to function these powerful batteries need to be regularly charged. Many modern boats are being built without generators onboard which means that outboards and their internal alternators are being called on to charge all of these systems. (See Fathom Technology…Feb, 26.)
Major boat builders are using modern gasoline outboards like the triple 400-hp Mercury engines pictured here powering the Formula 360 Crossover Bowrider. Photo courtesy of Formula Boats and Mercury Marine.
In our first installation on this topic, we covered the use and care of alternators on inboard engines. With this segment, we explore the design and application of outboard engines in today’s high energy market. Large horsepower outboard motors are required to supply the get-up-and-go for owners of larger center consoles, catamaran designs, cruisers, and some sportfishing boats. They are also expected to provide enough energy to drive an array of electronics, live wells, air conditioning, refrigerators, entertainment, and charging systems with inverters. Lithium battery banks controlled by battery management systems store power onboard, in many cases negating the need for a generator, which means alternators in the outboards are the sole charging source.
How an Outboard Engine’s Alternator Works
“Marine alternators typically include features to improve corrosion resistance, operate at a higher voltage setpoint, and incorporate additional ignition-protection measures for the marine environment,” said Nick Nida, Service Product Manager for Mercury Marine. “And just like those on inboard engines, outboard alternators work as a power supply when the motor is running and convert the generated AC to DC via a rectifier which is then regulated down to a level where it can be used to charge batteries and run the electronics aboard.”
On smaller horsepower outboard engines, such as this 40-60-hp Mercury, the alternator is connected to the flywheel by a belt. Photo courtesy of Mercury Marine.
Alternators on both inboard and outboard motors have the same basic components. Power from the engine spins a rotor in the center of the stator’s copper windings creating a magnetic field which produces AC electricity. A set of diodes housed inside the alternator, known as a rectifier, then convert the AC to DC which can be used onboard. A voltage regulator controls the output of the alternator to optimize charging.
While their inner workings are similar the obvious difference between inboard and outboard engines in relation to their alternators is quite clear. With the inboard engine below decks, there is a bit more room for mounting and protection from the saltwater environment, especially with the use of air handler systems, if so equipped, in the engine room. Hanging off the transom, the engine, power head, alternator and other crucial components are more exposed to the water and spray while the engine is in use.
“Whether running a lead-acid or Lithium battery system aboard their boat, there is no change in the alternator’s charge profile,” Nida said. “It is going to use as much of its output current as it can to reach 14.5V at its output terminal. However, it’s the battery that needs to be able to handle running at 14.5V at the alternator’s rated current continuously.” The alternator’s rated output is usually its maximum theoretical output at a specified engine speed. At idle, output may be much lower. “On larger boats with significant electrical loads, careful system design is important to ensure the electrical system can meet demand while keeping the batteries charged. Finding the right balance can be challenging. Alternator output should exceed the anticipated electrical load; otherwise, the batteries will continually lose charge.” added Nida.
Shore power and generator charging may be needed on some vessels that have high loads in order to maintain proper battery charge.
Lithium Batteries Crucial Role
That’s where Lithium batteries such as those from Victron Energy, which are specifically designed and engineered as part of a complete system, play an important part in making sure the downstream relationship between engine, alternator, battery, chargers, including a DC-DC charger, and power sources are in the correct balance.
A Victron Smart Lithium Iron Phosphate battery will provide the correct balance in the system. Photo courtesy of Victron Energy.
One of the more important keys to the system is the Battery Management System (BMS). Victron’s wide selection of BMS’s are dedicated to the company’s batteries and offer fallback safety mechanisms as well as operating as a remote controllable main system switch. It can also monitor the batteries, indicate state of charge percentage, and notify, by means of a pre-alarm signal before a system shut down, of a low cell, among other features. As an added plus, the system is Bluetooth enabled and can be used with the Victron Connect App and will monitor instant readout and key data of the BMS as well as other applications.
The Victron LYNX Smart BMS is a dedicated management system for Victron Lithium Smart batteries. Photo courtesy of Victron Energy.
If you are thinking of retrofitting your outboard powered boat with lithium batteries, and the subsequent components, it would be wise to make sure to employ the services of a qualified American Boating & Yachting Council (ABYC) certified marine electrician with background and expertise in these systems. Should you be in the market for a new boat, your dealer, and engine manufacturer will be able to make sure you are on course to make the right decision.
What Can Go Wrong with an Outboard Alternator
Stator failure is high on the list, and the windings can malfunction for a number of reasons including overheating, insultation breakdown, corrosion or water intrusion, vibration, and excessive electrical loading. Symptoms may include low charging voltage, intermittent charging, or no charging.
Rectifier/regulator failure is another hot spot to take note of and is commonly one of the more failure-prone components It’s demise can be due to many factors including excessive heat, caused by poor cooling or inadequate air flow. Corroded connections, voltage spikes reverse battery connection, short circuits and disconnecting a battery while the engine is running can cause damage. Excessive charging current or prolonged maximum output can also lead to premature malfunction. A breakdown of the rectifier/regulator can produce no charging, or excessive voltage, an AC ripple in the DC system, which can lead to discharged or damaged batteries, and harm to sensitive electronics.
Another place to always check when doing your preventive maintenance inspections is corroded or loose connections. Marine electrical systems are especially vulnerable to battery terminals displaying signs of corrosion, loose engine-ground connections, damaged charging cables, corroded fuse holders, poor crimp connections, and inadequate wire size. If you check the voltage measured at the alternator, it may be normal while voltage at the battery is too low because of the resistance in the cables or connections. In addition, an internal short, a severely discharged condition, or high internal resistance in the battery can cause heat to build up in the stator and regulator. On belt-driven systems, possible faults include loose or slipping belts, a misaligned pulley, or failed bearings, all affecting the output of the alternator.
Sitting on top of the power head of this Mercury V12 600-hp Verado outboard engine, the alternator is not driven by a belt but is connected directly to the flywheel. Photo courtesy of Mercury Marine.
The alternator on larger horsepower outboards use a stator and flywheel magnet system, with stationary copper windings, under the flywheel where the permanent magnets are built in. As the flywheel spins when the engine is in operation, AC electricity is generated. A rectifier/regulator will then convert the AC to DC power and limit the charging voltage with the charging output connected directly to the starting battery. The regulator typically maintains 13.8-14.6 V for 12 V systems and will vary by engine manufacturer and model. This method is suitable for both lead-acid and often lithium batteries. Lithium batteries have very low internal resistance and can accept very high charging current until nearly full, whereas lead-acid naturally limits the charging current as it fills up because its voltage rises along with its internal resistance. The voltage on lithium batteries stays relatively flat during charging meaning faster recharge. However, if an alternator is capable of producing high current, the lithium battery may try to draw nearly all of it for a long time, hence the need for a high-quality BMS to control this.
The use of lithium batteries can affect an engine alternator, as these batteries have a very different charging behavior than their lead-acid battery brethren. First off, they accept high current for longer periods of time and continue to do so until nearly full. Lead-acid batteries gradually reduce charging current as they become full. This means the alternator may operate at near maximum output for much longer when trying to charge a lithium bank. This can cause higher stator and regulator temperatures, leading to premature regulator failure, stator winding breakdown, and reduced alternator life. The alternator may be rated, for example, at 40 A, but that does not necessarily mean it can safely produce 40 A continuously at low engine speed or in a hot, poorly ventilated location like under an outboard cowling.
The BMS on a lithium battery can suddenly disconnect if it detects overvoltage, overtemperature, excessive current, individual cell imbalance, low temperature charging conditions, or a fault condition. If the alternator is running when the BMS disconnects the battery, it may suddenly lose its electrical load, sometimes known as a load dump, and can damage the rectifier/regulator, engine control modules, gauges, fish finders, radios, and other sensitive electronic equipment. It is highly recommended that a compatible alternator be used with a Lithium battery systems. In addition, many boaters are choosing to have a lead-acid battery for starting the engine and a lithium house system for all other power needs.
In wrapping things up on this topic, no system is without its pros and cons, especially with use in the marine environment. While the large horsepower outboards are designed and engineered to supply more power needs aboard, vibration, salt spray, and constant slamming in rough seas can take a toll on the system. Things to look for with your alternator are diminished battery charging, electronics running slow or having trouble holding the screen, and appliances such as live wells, refrigeration, and air conditioning, and others unable to maintain usual levels of operation. Should any of these be present, have your technician check things out and have your alternator rebuilt or replaced if necessary. In addition, have all the components of the downstream system checked as well so you can enjoy your day offshore fishing or out with the family with all the confidence and safety measures in place.
Being precise is essential when discussing alternators on outboard engines and the roles of components like the rectifier/regulator, possible failure modes, and the effects of lithium batteries and their system components, must be taken into consideration. It’s necessary to address issues such as compatibility, charging profiles, temperature management, overvoltage concerns, and current-limiting mechanisms. If any questions on these or any other concerns should arise, always check with your trusted and qualified technician before hitting that starter button or turning the ignition key. Safety comes first before the dock lines come off.
Keeping things electrically sound, from the alternator on down, will keep the power needs aboard in the right balance. Photo courtesy of Formula Boats.
https://www.victronenergy.com/
https://best4boats.com/fathom-technology-on-the-life-proof-boats-45-full-cabin/
ALL ABOUT ALTERNATORS – Part 1: Inboard Engines
Right up there as one of the more important electrical components on a boat, alternators are responsible for keeping the batteries charged and supplying electrical energy to onboard systems. How they work, and what signs to look for when they don’t, should be part of your regular preventive maintenance regimen.
