Alpha 12/90 III

Delivery includes Alpha Pro III charge regulator. 

  • Fast & complete charging of starter and service batteries.
  • Power supply for all consumers.
  • 12 V and 24 V versions.
  • 75 A to 150 A charge current.
  • Standard delivered with Alpha Pro III charge regulator for an optimal performance and longer-lasting batteries.

Using a Battery Mate or battery isolator in conjunction with an Alpha alternator makes it possible to easily charge two or three separate battery sets simultaneously.

TIP: A second alternator on the main engine, combined with a larger battery bank and inverter, could be an alternative for a generator.

For all engine types

Alpha alternators are equipped with several fixations for customised alternator brackets, available from your installer or engine supplier. Some engine brands come with Mastervolt alternator brackets as an option.

Fast charging, even at a stationary rpm

Standard alternators only supply the specified capacity at a high rpm. The Mastervolt Alpha alternator is specifically designed for powerful charging, even with a low engine rpm. 

Multigroove pulley

The 12/130 and 24/75 models are also available with a multigroove pulley.

Performs above 40 °C

Forced cooling by fan operation of the pulley provides a lot of power in higher temperatures, especially close to the engine.

Product code: 48612090
download pdf


General specifications
Charge regulation an Alpha Pro III regulator comes standard with all models
Total charge current 90 A
Cable length regulator/alternator 1.5 metre, oil resistant connection cable - delivered as standard
Belt section 2xA
Isolated operation yes
Rotational direction 2
Mounting five to six, six o’clock & five past six
Dimensions see ‘Downloads’ for drawings
Weight 5.5 kg
12.1 lb
Technical specifications
Charge voltage Absorption 14.25 V
Charge voltage Float 13.25 V
Nominal diameter pulley 73 mm
2.9 inch



Alpha 12/90 III

Charge characteristics for Mastervolt alternators models Alpha 12/90, 12/130, 24/75, 24/95C, 24/110...


Drawings (dimensions)

Dimensions Mastervolt Alternator model 12/90 (zipped DWG, PDF and EPS file)


Drawings (installation)

Installation drawing Mastervolt Alternator model 12/90 (zipped PDF and EPS file)


Drawings (installation)

Installation drawing Mastervolt Alternator model 12/90 with DC-distribution (zipped PDF and EPS file)


Installation manuals

Alpha 12/90 III

Appendix Alpha Pro Alternator (English)


User manuals

Alpha 12/90 III

User's manual Alpha Alternator and Alpha Pro regulator (English)


Product notifications

Alpha 12/90 III

Mastervolt alternators & brackets



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