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Tech Tip #28: Selecting and Installing A High Output Alternator

Helpful guide on selecting and installing your alternator

Replacing a standard output 35-55 amp diesel alternator on a Perkins or other marine diesel with a significantly higher output alternator is one of the easier and more cost-effective upgrades an engine owner can make. This Foley Tech Tip discusses the various considerations in choosing an alternator and provides a simple installation guide for the Foley Hy-Output Series.

Choosing the Alternator

Once the decision has been made to upgrade the charging system, there are a few installation considerations. These include case size, location of regulator (internal or external), number of drive pulleys required, provision for a tach, maximum output and cost. We have developed a high output alternator that addresses these concerns and offers significant savings and ease of installation.

The Foley Hy-Output 105 a alternator is a single wire, negative ground 12 volt alternator. It has a 105 amp stator and a compatible high amp rotor. The diodes are heavy duty and the voltage regulator is an internal, attached, self-exciting, solid state device. As soon as the alternator starts to turn, current is formed and the regulator turns on. Stop the turning and it shuts itself off. The case is a standard GM Delco case and the unit comes with a single drive pulley. An additional crankshaft pulley will have to be purchased only if this is going to be a second alternator as opposed to an upgrade of the original unit.

Installing the Alternator

Installing a Foley Hy-Output Alternator is very simple and requires no real tech skills. You’ll need a few simple hand tools (combination wrenches, pliers, wire crimper and cutter and a couple of large screwdrivers – to serve as pry bars), some WD40, and a roll of #8 wire.

To get started, disconnect the positive cable form the battery to shut off the electrical system, then disconnect the wires from the old alternator to the ground, starter, and tach. Remove the old alternator by loosening the mounting bolts. If necessary, use a block of wood (rather than a hammer) as a persuader, one of the screw drivers, and WD40. Install the Foley alternator on the old brackets, cutting with a hacksaw if required. Fasten a length of #8 wire to the battery terminal on the back of the alternator and run to the starter solenoid and on to the positive battery terminal (you can use the existing wire if this alternator is going to be a replacement). If you have an electric tach, there is a terminal for it on the back. Tape up any old alternator wires and you’re done.

Finally for those who do choose a double pulley alternator, we have auxiliary crankshaft pulleys for the Perkins 4108 engine under Foley part number AUXPULLEY 4108 (see Tech Tip #38 Foley Pulley to the Rescue for Perkins 4107/108’s)  for more information on this pulley. If you would like more information on alternators, we encourage you to consult the Balmar installation manual provided on their web site. Please call or email us with any questions.

We welcome your feedback on this Tech Tip.  We believe tech support matters and publish these Tech Tips to advance the knowledge base on the industrial and marine diesel field.

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