Mahle Alternator 12V 100A MG309

The MAHLE Alternator MG309 is a new 12V, 100A unit supplied with a belt pulley and internal regulator. It is listed as a single-leg alternator with a 51mm mount leg thickness, 86.0 mounting points diameter, and 50.8 mounting bores distance, so the physical mounting arrangement should be checked carefully before purchase.

This alternator is described as dust-proof with insulated ground, and it uses a single A-section belt with a 70mm pulley outside diameter. The alternator charge current is 100A, which makes the electrical rating clear for systems that need the same output and the same 12V operating requirement.

The listed part number is MG309 and the brand is MAHLE. Fitment data supplied for this unit includes PRINCESS P42 and a number of VOLVO MARINE/PENTA applications, but those applications should still be confirmed against the exact part number, mounting layout, and belt setup on the existing unit.

A one-year warranty is listed, and the alternator is supplied as each new unit rather than a remanufactured part. Packaging dimensions are 24.8 long, 18.60 wide, and 17.50 high, which can matter if the part is being shipped to a workshop, marina, or freight depot.

Key Features

• 12V alternator with 100A charge current
• New unit supplied each
• Internal regulator
• Single-leg alternator mount
• Supplied with belt pulley
• Dust-proof and insulated ground

Specifications

• Brand: MAHLE
• Part No.: MG309
• Type: Alternator
• Voltage: 12V
• Power Rating: 100A
• Alternator Charge Current: 100A
• Regulator Type: Internal
• New / Reman.: New

Known application references supplied

• PRINCESS P42
• PRINCESS P42 1980
• VOLVO MARINE/PENTA 2001
• VOLVO MARINE/PENTA 2001 1991
• VOLVO MARINE/PENTA 2002T
• VOLVO MARINE/PENTA 2002T 1983
• VOLVO MARINE/PENTA 2003
• VOLVO MARINE/PENTA 2003 1983

Application and Buying Notes

For a correct replacement, compare the part number MG309 first, then check the alternator mount layout and belt arrangement on the existing unit. This one is a single-leg alternator with a 51mm mount leg thickness, 86.0 mounting points diameter, and 50.8 mounting bores distance, so matching the physical fixings matters as much as the electrical rating.

The unit is rated at 12V and 100A, with an internal regulator and a single A-section pulley. If the vehicle or marine engine uses a different voltage, pulley section, belt count, or regulator arrangement, it should not be assumed to be a direct swap without checking the installed part.

The supplied fitment references include PRINCESS P42 and several VOLVO MARINE/PENTA applications, which are useful starting points only. Exact compatibility still depends on engine variant, model year, mounting dimensions, and whether the current alternator matches the same MG309 configuration.

Because this alternator is listed as dust-proof and insulated ground, it may suit environments where protection and tidy electrical isolation are important. Even so, the practical check is always the same: confirm the part number, the pulley size of 70mm outside diameter, and the 21.3 distance from pulley to alternator before ordering.

If you are replacing a marine alternator, pay close attention to the mounting bores, adjusting hole diameter, and pivot hole diameter, both listed at 11.5. Those figures help determine whether the alternator will physically line up with the existing bracket and belt path without modification.

Before supply, the safest approach is to confirm the original unit details against the listed part number, voltage, output rating, mounting arrangement, and pulley configuration. That checking process is standard practice in the parts trade because visually similar units can still differ in service-critical ways.

For workshop, fleet, and equipment applications, accurate identification of part number MG309 helps avoid unnecessary freight, additional labour, and vehicle or machine downtime. Where the application is not straightforward, the original unit, OEM reference, or workshop records should be used as the primary confirmation point.

Relevant published details for this unit include Type ALTERNATOR, Unit of Measure EACH, Warranty One Year, Mount Leg Thickness 51mm, Power Rating (Amp) 100, Pulley Section A, Suits Unit Make Mahle, Note Dust-proof. Insulated ground, New / Reman. New, Pulleys with belt pulley.

Additional published details for cross-checking include Mounting points diameter 86.0, Distance from pulley to the alternator 21.3, Packaging width 18.60, Net Weight 5361, Product Group 1 ROTATING ELECTRICAL, Part No. MG309, Brand MAHLE, Description Mahle Alternator 12V 100A, Adjusting Hole Diameter 11.5, Pivot Hole Diameter 11.5.

Mahle Alternator 12V 100A. Part number MG309 should be checked first. Listed voltage is 12. Listed output rating is 100. These details form the core reference points used by parts interpreters when confirming the correct replacement.

Mount style is Single Leg. Regulator type is Internal. Pulley configuration is A. Those physical and electrical details should line up with the original unit before the replacement is approved for fitment.

For part number MG309, the normal identification sequence is part number, electrical rating, mounting arrangement, connector or terminal style, and pulley or drive details. Using those checkpoints helps confirm that the listed unit matches the service requirement rather than only looking similar.

For a alternator in workshop, fleet, trade, agricultural, or construction service, the listed voltage 12 and output 100 should be checked carefully. Incorrect selection can affect installation time, return freight, and equipment availability.

Compatibility note: Confirm compatibility using the MG309 part number, the 12V 100A rating, the single-leg mount dimensions, and the listed application references before purchase. Do not rely on model names alone, as the fit can vary with engine version, year, mounting arrangement, and pulley setup.

FAQ

What is the part number for this alternator?

The listed part number is MG309.

Is this alternator new or remanufactured?

It is listed as new, not remanufactured.

What electrical rating does it have?

It is a 12V alternator with a 100A charge current and 100A power rating.

Does it have an internal regulator?

Yes. The regulator type is listed as internal.

What pulley setup is supplied?

It is supplied with a belt pulley, with an A-section pulley and a 70mm outside diameter. It uses one belt.

What fitment references are supplied?

Supplied fitment references include PRINCESS P42 and multiple VOLVO MARINE/PENTA applications, including 2001, 2002T, 2003, 2003R, AD31B, and AQ100 references.