Note the drawings dimensions for each case.  Measure your alternator and the space available.  We must have the following information for us to select the proper pulley and cooling fan. 

1. Type foot 1”, 2”, or Japanese saddle mount
2. Belt width at widest point
3. Engine Crank shaft pulley diameter
4. Alternator pulley diameter
5. Direction of alternator rotation, looking at the pulley
6. RPM of engine while under way
7. Some alternators may need a new tensioning bracket

The engine crankshaft pulley is usually 5 to 8 inches in diameter.  For optimum performance we will size the alternator pulley so the alternator attains proper output for your application.  The smallest pulley provides the highest alternator rpm, but the belt wears faster.  If the alternator is the only charging source, we recommend at least a 2.6 inch alternator pulley.  As a back up, a smaller pulley is all right. 

Small fram alternators are 31% efficient and require 6.5 horsepower at full output while large frames are 45% efficient and use 8 HP.  Small engines can drive high output alternators, but may stall while charging a low battery and propelling the boat at the same time.  A switch installed by the engine gauges to stop charging can solve this problem. 

With a wind generator and/or other alternate energy charging equipment, the alternator makes a good back up charging source. 

Choosing the right amp rating.  For liquid electrolyte batteries choose an alternator 25-40% of the total AH in the house batteries.  For gel cells use 50% of the house battery capacity and for Lifeline absorbed glass matt batteries use 100%. 

Wiring Caution.  Don’t forget to replace your positive and negative alternator with the proper size wire for the new higher charging amps and wire length.  Call us, we’ll help you choose the correct size and supply it. 

For N type alternators refers to where the regulator is installed in the field coil.  Ninety five per cent of today’s alternators are P type as are EEI alternators.  Almost all 3 step regulators are P type, however, we can supply N type alternators and regulators.  Call us for information. 

Monitoring Alternator output.  An ammeter capable of reading 100 to 200 amps using an external shunt will be required.  Most digitial system monitors and analog ammeters using shunts can be used.  We carry all the digital AH monitors and can help you select the correct one for your boat.  Our AM-5, 0-150 amp ammeter with shunt is a good less expensive choice. 

V belts.  All belts are not created equal.  Buy good belts locally like a Gates Tri-power or Dayco Topco.  For dual pulleys buy matched sets.  Always carry spare belts.