Balmar 120A Spindle Mount Alternator, K6 Pulley

The Balmar 621 Series 120A Spindle Mount Alternator has a K6 pulley and isolated-ground construction, for 1-inch or 2-inch single-foot mounts.

Isolated ground is the construction detail worth understanding, and it changes how the charging current returns. A conventionally grounded alternator sends its return through the engine block and the boat's bonding. Isolating it keeps that current in a dedicated cable, which stops stray current corrosion and keeps noise out of the electronics.

The 1-inch mount suits Westerbeke, Lehman, Hino and Pathfinder engines; the 2-inch Delco-style covers Volvo Penta, John Deere, Perkins and MerCruiser. Both are single-foot arrangements rather than the dual-foot saddle mounts used elsewhere in the range.

This is the alternator alone rather than a kit, so a regulator and temperature sensors are needed alongside it. The K6 six-groove serpentine pulley has to match the belt already on the engine. Explore more marine alternators.

• Isolated ground keeps return current in its own cable
• It stops stray current corrosion and electronic noise
• 1-inch and 2-inch are both single-foot mounts
• Alternator alone: regulator and sensors separate