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Pulley Selection Guide

Alternator Pulley Selection Guide

The standard diameter pulley for Balmar alternators is 2.7″. While all Balmar high-output marine alternators are rated for much higher speeds, the ideal sustained operating range is 4000-4500 RPM.

Divide your crankshaft pulley diameter by the alternator pulley diameter to get the speed ratio. Multiply this by the engine’s cruising RPM to get the alternator RPM.

For Example:

  • Engine crankshaft pulley diameter: 5.0″
  • Alternator pulley diameter: 2.7″
  • Engine cruising RPM: 2400

5.0″ ÷ 2.7″ = 1.85 (Speed Ratio)
1.85 x 2400 RPM = 4440 RPM (Alternator)

If your engine is typically run at low speeds, or if it has a small crankshaft pulley, select a smaller alternator pulley.

CAUTION: Use of an undersized pulley may cause the alternator to exceed its RPM rating when the engine is run at wide-open throttle (WOT). Use the formula above to determine the alternator RPM at max engine speed.

Note: Certain marine engine applications have specific pulley requirements, and other pulleys are available. We have attempted to make the selection as easy as possible for you, and the selections provided will fit most engine applications. However, if you have questions, please contact us.