Unique Products for Your Boat
  • CMI-HD125-ER - 125A 3.15" Saddle Mount, 1" Foot or 2" Foot Heavy Duty Marine Alternator

    $579.99 $499.99


    We Do Not Ship Alternators Internationally

    IMPORTANT:  All CMI Alternators are custom built and may require a short lead time. If you are unsure about fitment or compatibility please use the "Contact Us" tab at the top of this page.

    The CMI-HD125-ER

    Ample Power recently closed its doors leaving many of its alternator customers without a direct replacement option. We have had many requests for Ample Power replacement alternators so the CMI-HD125-ER has been re-introduced and heavily tweaked in the process. The CMI-HD125-ER an exact replacement for the Ample Power small frame alternators, such as the 4023-S, and it's available in a Yanmar 3.15" saddle mount, 2" foot or 1" Motorola style foot mount (please specify mount type when ordering).

    Never settling when it comes to performance Compass Marine Inc. has taken the Ample Power small frame platform to a whole new level of quality. Ample Power used 200V 50A diodes, we are using 400V 75A diodes. This means the alternator runs considerably cooler. Ample Power used a mid grade magnet wire we are using the finest magnet wire available and it has a higher temp tolerance rating. 

    The CMI-HD125-ER is the best and most heavy duty small-frame alternator we build. The CMI-HD125-ER saves you over $250.00 when compared to 120A Balmar 6-Series. The Balmar 6-Series is an excellent small frame alternator, but not all boaters have this in the budget.

    Serpentine Pulley Kit Compatibility:

    A major benefit to the CMI-HD125-ER is that it can be used with AltMount serpentine kits with minimal to almost no alignment during set up. See image above with a CMI-HD125-ER installed with an AltMount serpentine kit on a Yanmar 4JH3-HTE.

    External Regulators:

    We can package this alternator with either a Balmar MC-614H or ARS-5H regulator. We strongly recommend setting the Belt Manager feature to level three or four when setting up the regulator. It's also mandatory that an alternator temp sensor be used. Compass Marine Inc. will never make the lofty (bogus) claims Ample Power made about these alternators being constant duty. We choose not to mislead our customers. No small frame alternator we know if is constant duty no matter how much a manufacturer tries to mislead you.

    CMI-HD125-ER Specifications:

    The CMI-HD125-ER comes standard with tachometer output (stator tap) for diesels that run the tachometer sense off the alternator. Not all engines drive the tachometer from the alternator, but most Westerbeke and Universal engines do and many Yanmar engines do as well.


    • Intended to fit many diesel engines that use a 1" foot, 2" foot or Yanmar 3.15" Saddle Mount
    • 125A cold rated, 106A hot rated with excellent high idle performance.
    • Hand wound stator (wound in the USA) of 14GA extreme duty magnet wire = higher temperature tolerance.
    • Precision machined rotor and slip rings for greater contact at all RPM.
    • High performance 400V 75A rectifier diodes.
    • Directional (Clockwise) or Unidirectional Fan
    • Billet Machined Steel Pulley - 2.6" Diameter X 1/2" or 3/8" 10mm Belt Will Also accept an AltMount J10
    • Brushes are high copper content, not run of the mill cheap carbon brushes.
    • High copper brushes yield superior conductivity and considerably longer brush life.
    • Ready to accept an external regulator. We recommend only Balmar or the WakeSpeed WS500 regulators.
    • OPTIONAL - Isolated ground for steel or aluminum boats or for using a shunt in the negative path.
    • Hand wound stators and rotors and Made in America.
    • USCG Certified - Gas or Diesel Engines
    • 5/16" B+ Stud
    • 5/16" X 18 B- Bolt
    • 5/16" X 18 Adjuster Ear Tapping
    • 10mm Foot Mount Hole