High output alternators for cruising and yacht-charter boats

WHAT ARE THE ADVANTAGES?

High output alternators are often touted as a solution to many charging problems, however they must be placed into true perspective. Many falsely believe they are the answer to charging problems, however they are just part of any solution. High output alternators effectively increase available charging capacity, and when a fast charge regulator is used they can offer significant advantages. These advantages however are directly related to the use of larger capacity battery banks, and the use of batteries with high charge acceptance rates such as AGM's and Gel Cells. An additional advantage is the increased current availability for powering windlasses and thrusters which are normally used with the engine running and this significantly improves performance, something cruising yacht owners and Yacht-charter operators should note when considering fleet reliability An added economic advantage is that the extra load will also put more load on the engine and this results in reduced maintenance along with the shorter run times for charging. Again a cost saving for both the average cruising boat owner and the yacht-charter companies, this also increases reliability

STANDARD ALTERNATOR PROBLEMS

In the majority of private cruising and yacht-charter vessels they have standard engine supplied alternators. When used with fast charge regulators they often run at maximum temperatures, at least at the start of the charging cycle. An additional effect is where maximum charging currents are demanded along with onboard electrical loads that exceed the maximum output ratings. The immediate effects are an increase in losses through heat, and on some installations you cannot touch the casing, and this results in a serious reduction in efficiency. This is compounded by poorly ventilated engine compartments so common on many cruising and yacht-charter boats. The real long term problems are the subsequent stressing and degrading of alternator winding insulation values, which leads to premature failures, and the overheating of bearings with degradation of lubrication. Diode failures are also a possibility with the inability of the heat sink to dissipate properly.

High output alternators work much the same as standard units, with some of the parameters modified in the design and construction. The first change is the reduced cut-in speeds, with alternators wound to produce cut-in at much lower speeds. Similarly maximum outputs are available at much lower speeds which more correctly matches normal engine running speeds on boats. Water cooled alternators are not seen on many boats yet, however this is inevitable with the eventual introduction of 42 volt high power alternators. If this becomes a standard fit then both private cruising and Yacht-charter boats will see them

SPECIAL FEATURES

While high output alternators should run cooler manufacturers sensibly use high temperature sealed bearings. Makers such as PowerTap also up-rate diodes to 200 volts to provide some protection against spike damages, and these are mounted on more efficient heatsinks. Cooling is also generally up-rated with improved cooling fans to increase efficiency and reduce losses. As most manufacturers offer isolated ground units, always select this option.

Many cruising yacht owners and Yacht-charter operators could reap real reliability gains by installing an up-rated negative cable direct to this terminal back to the battery will take the engine out of the circuit improving reliability and reduce circuit losses

Double pulleys are essential on high output machines, and belts must be correctly tensioned if good energy transfer is take place. While manufacturers offer models as direct replacements for most alternators, you will have to verify that the additional mechanical sideloads applied by installation of the dual pulleys is acceptable. I have found that some engine manufacturers do not like this citing possible bearing damage, so check up before installing.

SPECIAL CONSIDERATIONS

It is also important to rewire the alternator positive and negative circuits and rate them well above the maximum current ratings. A high output alternator charging into a bank of AGM batteries will result in the cables carrying high current loads, and introducing voltage drop and losing power defeats the whole purpose of the upgrade. It is also important to size the cable connection lugs properly, frequently they are under-rated and run hot causing high circuit resistances, significant voltage drops and again reduce charging efficiency.