The high amp alternator is much the same as any other, just bigger. The rectifier part of any alternator comprises a bridge or network of six diodes, and these are interconnected between the positive and negative plates. Two power diodes are connected in each phase, this means that one diode is connected to the positive side, and one to the negative side. These diode plates also serve as heat sinks to help dissipate the heat generated from the power conversion process within the diode. The positive sinusoidal half waves pass through the positive side diodes and the negative half waves pass through the negative diodes. This rectifies the three generated AC phase voltages into the DC output for charging. Two diodes are used on each winding to provide full wave rectification. The rectifier diodes also prevent the battery discharging through the 3-phase winding as the diodes are polarized in the reverse direction.
You can opt for installing a much higher output alternator however if the output is within the 70-90 amp output range the best solution is often the use of one of the many regulators designed to maximise the output and optimise charging. Larger output alternators often require multiple drive belts and pulleys and this costs more in engineering and economic terms. But that may be worth the cost.
The exciter or pre-excitation diodes are a network of three low power diodes which rectify each AC phase and then give a single DC output for the warning light function. The exciter diodes are necessary as the residual magnetism of the stator core is generally too low when engine is operating at relatively low revolutions during starting and idle to initiate the self-excitation that is required to build up the magnetic field. This condition only occurs when the alternator voltage exceeds the voltage drop across the two diodes. Current will then flow through the alternator warning light, then through the excitation winding then back through the voltage regulator to ground. This current then pre-excites the alternator. The warning lamp also functions as a resistor and provides pre-excitation current, which generates a field in the rotor. The power rating of the lamp is quite important and 2 - 5 watts is typical. As many have found out the alternator will often not operate when the lamp fails and this is due to the residual voltage or magnetism has dissipated. When the lamps are undersized you will see that characteristic need to "rev" the engine to get the alternator to "kick" in.
The traditional voltage regulator is designed to recharge a partially discharged battery in a relatively short period and also to supply the onboard electrical power in the vehicle. To achieve the efficiencies we require on a boat we have to look at improving the power availability of the alternator. The best way to do this is by using one the many “fast charge” voltage regulators on the market. These often “intelligent” regulators tend to be multi stage, step charge or programmed cycle devices that have either automatic or user settable charge settings.
Alternators and regulators are inextricably linked to the battery sizes along with the battery types, and matching of charging characteristics is important. The use of any fast charge regulator must consider the whole system and not simply be used in isolation as a cure for charging problems. Most multi-step regulators have similar operating principles. The first charging step is the Bulk charge phase, and this is where voltage rises steadily up to approximately 14.2 - 14.4 volts, and maximum current output occurs up until approximately 80% charge level. Many fast charge regulators allow this to be set to suit the battery type and it is different for AGM, Gel or flooded cell batteries. The second charging step is the Absorption or Acceptance phase and this is where the charging voltage is maintained at a constant level and the charge current slowly reduces. The third and final step is the Float charge phase where voltage reduces to approximately 13.8 volts and maintains a float charge to the battery, and this stage suits most boats where long motoring periods are being used.
Some cycle regulators repeat this so that the battery is brought up to full charge and follows the optimum charge curve as a battery can only accept charge current at a finite rate. One of the Balmar regulator range has a microprocessor-controlled regulator and also has several user selectable multi-voltage variable-charge time programs that suits six battery types. The basic principle is the use of an automatic absorption time program. Some regulators also incorporate battery temperature compensation sensors and alternator temperature sensors for improved accuracy. Some of these smart regulators also have an equalization function that is also a user adjustable feature. The function enables the application of an equalization current until battery voltage reaches 16.2 volts. Other regulators generally follow similar principles that are variations on step charging techniques.
The smart fast charge voltage regulator is only effective in upgrading the charging performance of an alternator when all parts of the charging system are considered. If the battery bank is too large for the alternator capacity the smart regulator may simply stress and overheat the alternator causing early failure. The charging source must be capable of meeting the expected maximum charge current demands. The factor of speed range also needs to be considered and getting the right pulley ratio is a factor to consider. In many cases under rated cables and terminations are also become a problem as the circuits are designed on some systems to carry less than the rated maximum output of the alternator. High Amp Alternator information and boat charging systems.