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Assessing your boat-electrics and battery charging risk

RISK ASSESSMENT FOR CHARGING SYSTEMS

This article is about boat-electrics and battery charging and this is based my presentation to the ARC Rally Seminar for cruising yachts doing the transatlantic crossing rally. This information is also based on the contents contained within the Motorboat Electrical and Electronics Manual. Over the past few years, apart from cruising yacht and motorboat electrical systems, I have been actively involved in many new large commercial ship and oil rig systems, and as I write I am Commissioning manager for BP Thunderhorse, the worlds largest floating oil production and drilling rig. Before we commission a new offshore installation we carry out what is called a Failure Mode and Effects Analysis (FMEA), and then perform extensive testing and trials to prove and verify the conclusions. After a few lectures on boat-electrics and many emails from people and continually seeing the same mistakes I decided that the same principles could easily be adapted to boat-electrics on smaller vessels, in particular cruising yachts and power boats. This exercise isn't as difficult as the name suggests, and it essentially entails the analysis of the boat-electrics starting and battery charging systems, as both are critical to propulsion or electrical power generation. The primary function of the exercise is the analysis of the systems and identification of any single point failures. In simple terms this means looking at what can happen in a worst-case situation for all main boat-electrics systems. It is a fact that in most cruising yachts, trawler yachts and motorboats there is virtually no redundancy on any critical boat-electrics systems. It is necessary to first identify all of the points that upon failure will also fail the entire system, these are called single point failures for obvious reasons, and then devise suitable methods and strategies to improve boat-electrics reliability and provide some redundancy. West Marine- America's Favorite Boating Supply Source

It is important when assessing the failure risks in any boat-electrics system to consider the following factors and statistics:

1. A failure in the battery charging system means no charging of batteries and therefore an eventual loss of all electrical power, and possibly propulsion engine starting, loss of communications, navigation instruments etc.

2. A failure in the engine starting system means no propulsion and no charging of batteries, and eventual loss of all electrical power.

3. Approximately 80% of all boat-electrics system circuit failures are due to faulty or failed electrical connections.

4. Approximately 70% of boat-electrics equipment and machinery failures are attributable to poor or improper maintenance or installation. In general most people look at the charging system in terms of a series of discrete components. A charging system must not be viewed as a collection of components, but as an entire electrical power supply system, the boat power station or onboard electricity utility. The typical charging system comprises a considerable number of elements and these are summarized.

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THE CHARGING SYSTEM

Make a simple drawing of your boat-electrics systems. It is a good idea to trace out each circuit on your boat, and draw in each component and mark each connection on it. As a minimum the average boat-electrics system will have 4 main positive circuit connections, 4 main negative circuit connections, 4 control circuit connections, 2 changeover switch contacts, a meter shunt, the alternator, the regulator and the batteries.

1. The alternator (which includes several integral components such as the brushes, brush holders, sliprings, bearings, diodes and stator windings)

2. The regulator, (which may be integral or separate)

3. The DC positive circuit, (which includes the connections at the alternator and battery, and the changeover switch or isolation switch)

4. The DC negative circuit, (which includes the connections at the alternator and battery, the cable back to the battery, and the meter shunt if fitted). In addition the engine block also becomes part of the negative circuit, along with alternator bracket, holding bolts etc.).

5. The batteries. The math of this simple analysis is that on an average boat-electrics system there are an average total of 14 connection points plus the alternator, regulator and battery that can directly impact on the starting system, plus the human element, the �boat owner�. Each point represents a single point failure with subsequent total system failure, with no apparent redundancy. For this exercise wind, water and solar panels are considered extra or supplementary boat-electrics battery charging sources, as are diesel generators with AC battery chargers. These however can be factored into the redundancy provisions. The operational factors also must be considered, the human factor in particular. If a battery changeover switch is opened or fails during operation, the alternator can be destroyed, and it is more common than one might think on battery charging systems.

THE ENGINE STARTING SYSTEM

A starting system must also be viewed as not simply a collection of series connected components, but as a system. The typical boat-electrics starting system comprises the following elements

1. The DC positive circuit, (which includes connections at the battery, the isolator or changeover switch, the solenoid connection, and solenoid contacts, the starter motor (which includes several components such as brushes, brush gear, commutator, bearings, windings).

2. The DC negative circuit, (which includes connections at the battery, engine block, the cable back to the battery, the engine block, and the meter shunt if fitted).

3. The engine control system (from panel and includes key switch, stop and start buttons, wiring harness, connectors, fuses etc.).

4. The preheating system (which includes the heating elements or glow plugs, and the connections, relays and connectors).

5. The engine starting battery.

The math of this analysis is that there are also a total of around 14 connection points plus the solenoid coil, the starter motor, the battery, the key switch that can directly impact on the starting system and prevent the system functioning. Each point represents a single point failure with subsequent total system failure, with no apparent redundancy. If a person persists with turning over an engine that will not start they may also burn the starter motor out. There are other less common boat-electrics scenarios. West Marine- America's Favorite Boating Supply Source

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ELECTRICAL SYSTEMS REDUNDANCY

The key to minimizing failure or mitigating the effects of failure in any boat-electrics system is the provision of redundancy. Redundancy in simple terms is having backup systems as part of the design, so that on one system failing the other will provide the charging or starting. In the average single engine boat, normal systems design and installation rarely incorporates any redundancy on charging, power or starting systems. In most commercial shipping, this is a basic premise in all systems design. There are several methods for improving redundancy and the following are the easiest and most economical to carry out. While not easy on some yachts there are some measures that can be implemented. This includes carrying appropriate spares, it is quite astounding how few people carry spare alternator or starter motor, a cheap investment I would have thought.

WHAT ABOUT ALTERNATIVE CHARGING SOURCES?

1. An engine powered DC generator. Compact units are available which are small diesel powered alternators

2. An AC generator with mains powered battery charger. The on board generator with a battery charger offers the best battery charging source, however its relatively expensive and has space and weight constraints limiting it to larger yachts

3. A combination of wind, solar and water powered charging systems. They are supplementary only as they depend on environmental factors, if the sun doesn't shine and the wind doesn't blow then no charging is possible

WHAT ELECTRICAL SYSTEM MODIFICATIONS CAN I MAKE?

There are several relatively low cost modifications that can be carried out on the battery charging system to provide some measure of redundancy and increased reliability:

Installing a second alternator

Install a second alternator on the engine, and this will generally require the addition of a second pulley. Some boats have very tight engine spaces and this may be difficult. The second alternator is for the house battery charging circuit, with the existing alternator being used just for charging the start battery. Each alternator will have a separate positive circuit without any switches or other devices in it. This will eliminate changeover switch problems on alternators that commonly destroy the alternator rectifier diodes, and just as importantly reduces electrical connections to just 2. It also eliminates the accidental (human error) switch operation under load, or switch contact failures, which are both very common. Each alternator will have a separate negative circuit cable running back to the respective battery from the alternator. This provides separation from the starter motor to battery negative, with the main starter negative serving as a backup. This also reduces circuit connections to just 2. It also takes the engine block out of the circuit, and generally reduces voltage drop in the circuit. There is anecdotal evidence that current flow though a bearing also results in reduced engine bearing life.

Separate the Charging System.

Separate the battery charging system from the starting circuit, in the long term this will considerably reduce problems and increase reliability. This process entails the deletion of battery selection changeover switches, and the installation of a separate charging circuit, which may include charge splitting diodes or relays. An emergency crossover switch between battery banks can be installed, however this does not affect the circuit during operations.

Install Separate Negative Cables

Install a separate negative conductor of at least 15mm� (6 AWG) from each alternator case or negative terminal directly back to the corresponding battery negative. This bypasses the engine block and all the cumulative resistances of mountings and brackets. This offers a good low resistance path and reduces stray currents through the block, which can cause pitting of bearings. It also eliminates a single point failure of the main negative connection to the engine block, which if it comes loose, off or fails the spike also blows the alternator diodes as well as causing serious charging efficiency losses.

Replace the Positive Cable.

Most installed positive cables are too small, especially if a fast charge regulator is installed. The cable size should generally be doubled over existing sizes. Ideally install a minimum of 15mm� (6 AWG) cable size. I usually take the alternator maximum rating and add 25 - 35% as a rule of thumb. A common problem is that besides having a maximum current going through it with fast charge devices connected or when heavily discharged batteries are recharged, the heat of the engine compartment also de-rates the current capacity of the cable. In most cases a significant voltage drop develops across the cable under full output conditions. This also should ensure that cable connections are also properly rated for the maximum current, a common failure point is undersized terminals causing high resistance and hot spots. This drops charging efficiency and can lead to major failure. When a main positive cable connection fails the spike usually blows the diodes in the alternator.

The Starting Circuit.

Relocate and connect the main negative cable as close as possible to the starter motor. This maintains 2 connections but takes the engine block out of the circuit, and generally reduces charging circuit voltage drop in the battery charging circuit. These commonly vibrate loose and are rarely checked and tightened. In most cases a new negative cable will be required.

HOW DOES MAINTENANCE FIT INTO YOUR BOAT-ELECTRICS PICTURE?

There are a variety of boat-electrics maintenance philosophies used in commercial and offshore-based rigs and ships. The traditional and most accepted is the Planned Maintenance System (PMS). This is based on maintenance tasks based on time intervals, either set periods or operational hours, and is still a useful basis for maintaining equipment. In most cases the only planned maintenance undertaken is engine oil changes based on running hours. The previous FMEA exercise allows the implementation of what is called Risk Based Maintenance and Inspection. We have evaluated all the areas most critical to boat operation, so the maintenance strategy should be centered on this. For example we know that the main failure causes in boat-electrics are poor connections so routinely checking and tightening them reduces the failure rate. As a start point perform the recommended maintenance on all critical equipment and systems.

STARTER MOTORS

Starter motors have relatively low failure rates, as actual operating hours are also relatively low in comparison to motor vehicle applications. Boat-electrics failures are usually dependent on operational frequency with seized bearings, or stuck brush-gear being the major failure causes. Regular operation reduces failures, so running the engine regularly has positive advantages. In addition this will generate heat, which assists in displacing moisture within the windings. Starter motors should be cleaned or overhauled on a regular basis, ideally not exceeding two years. I usually take it off, take it to my favorite automotive electrician, and back in the same day. If your boat has not had the starter out in years then a service is a good precaution before you head off.

ALTERNATORS

Alternators have quite a low failure rate, as actual operating hours are also relatively low. Failures are generally caused by diode failures, or overheating, in particular with fast charge regulators and oversized battery banks. Alternators should be cleaned and overhauled on a regular basis, ideally not exceeding two years. Consider a higher output rated alternator to reduce overloading and heating. Again it is cheaper to take it to an automotive electrician and have it overhauled before you set out.

BATTERIES

IN boat-electrics the batteries generally have the highest failure rate of all components. This is not failure in the true sense but due to either inadequate charging with resultant sulfation, lost capacity and failure, or flattening of the battery with subsequent damage. In most cases this is due to poor systems design or human factors. The second highest baot-electrics failure cause is inadequate inspection and topping up of electrolytes, with resultant plate damage. Consider different batteries such as AGM types with lower failure rates, improved charging characteristics and elimination of the human and maintenance factor. A consequence of the tragic Sydney � Hobart yacht race is a coroners recommendation for installing only sealed batteries. All these are good reasons to upgrade and improve overall boat-electrics systems reliability.

WIRING CONNECTIONS

The greatest cause of failure is boat-electrics is that of connection or termination failure. All connections on alternators, starters, engine blocks, batteries should be check tightened every six months, it is an easy task and results in fewer intermittent and complete failures. It is as not as onerous as it seems, and will pay dividends. Remember to switch all power off before you start the exercise.

SPARE PARTS

It is rare to see a boat with a spare starter motor, or alternator and these should be a prerequisite on an extended ocean voyage. Whilst some boats may carry spare bearings, diode plates and brush-gear the task does require skills and tools and it is quicker to change out the entire alternator. Invest in a spare starter motor and alternator, it is a small price to pay in the overall scheme of things.

SUMMARY OF BOAT-ELECTRICS SYSTEM IMPROVEMENTS and ADVANTAGES

After carrying out our FMEA and a systems assessment, and implementing some modifications, just how much further ahead are we. The most salient point is that there is now a significant reduction in single point failures. With two separate charging circuits there is full charging system redundancy and there are now significantly reduced connections in both the positive and negative circuits, the negative having a backup with the starter motor negative. In a typical system using a changeover switch arrangement there is a reduction of up to 75% in possible failure points. In addition, the person has been designed out of the system as the possibility for accidental switching off the changeover switch is removed. There is a significant improvement in charging efficiency, with a gain of up to or exceeding 0.5 VDC due to lower circuit resistance in both the positive and negative circuit. This reduces alternator loads, and can shorten charging time, reduce charge current and extend alternator life by imposing less stress. The starting system is more efficient with the negative at the starter reducing voltage drops, lowering current, reducing run time, and improving starting times, which also reduces stress on the motor. Coupled with carrying a spare starter motor/solenoid, there is a reasonable chance of being operational within an hour. Separation of the start and battery charging systems eliminates the many problems of voltage surges and transients. There are now two redundant power systems, each one being capable of powering the vessel, and any single failure of one system will not affect the other. The alternator negatives provide some redundancy to the main starter negative. As critical equipment has been evaluated and appropriate maintenance strategies implemented, the average time between failures is also extended.

The question remains, �How great is your battery charging system risk? And how are you going to reduce it?�