Overview
The M40FA640A is an Automatic Voltage Regulator (AVR) that maintains the generator output voltage within precise limits by controlling the exciter field current. It continuously samples the generator output voltage and adjusts excitation to compensate for load changes, engine speed variations, and temperature drift.
Key Features
- 6A Continuous Output — 63VDC max for large alternators
- ±1% Regulation — Stable voltage under varying loads
- Self-Excited Shunt — Reliable excitation control
- 190-264VAC Sensing — Wide input range
- Large Alternator Ready — Higher current than M16FA655A
Technical Specifications
| Parameter | Value |
|---|---|
| Type | Self-excited shunt AVR |
| Sensing Input | 190-264VAC, 1-phase |
| Output Voltage | Max 63VDC |
| Output Current | Continuous 6A |
| Regulation Accuracy | <±1% |
| Frequency | 50/60 Hz |
| Excitation Type | Self-excited shunt |
| Application | Maralli large brushless alternators |
Compatibility
Marelli MJ/MK series brushless generators 160-400kW.
Why Choose ZenixPower
- Tight Voltage Regulation — <±1% RMS regulation ensures stable generator output under 0-100% load transients
- Fast Response — Sub-0.5 second recovery time prevents voltage dips during motor starting and load switching
- Dual Excitation Compatibility — Self-excited shunt or PMG-powered configurations clearly labeled for correct selection
- Built-in Protections — Under-frequency roll-off, over-excitation limiting, and soft-start ramp as standard
- Drop-In Replacement — Terminal layout and mounting dimensions match STAMFORD, Leroy-Somer, Marathon, and Mecc Alte OEM AVRs
- Pre-Calibrated — Each AVR ships with factory-default potentiometer settings for immediate plug-and-play operation
Specification Comparison
Compatible Generators Marelli MJ/MK series brushless generators. These are OEM-spec AVRs for Italian-designed Marelli alternators widely used in European generator sets.
| Parameter | M16FA655A | M40FA640A |
| Output Current | 4A continuous | 6A continuous |
| Output Voltage | Max 63VDC | Max 63VDC |
| Regulation | ±1% | ±1% |
| Generator Power Range | Up to 160kW | 160-400kW |
| Excitation Type | Self-excited shunt | Self-excited shunt |
| UF Protection | Yes | Yes |
| Price | $60-100 | $80-150 |
Selection Advice
These two models are the Marelli MJ/MK series’ only AVR options — the selection is entirely determined by generator power. Under 160kW, the M16FA655A is the correct choice; 160-400kW requires the M40FA640A’s higher 6A output.
Key compatibility note: Marelli AVRs use a proprietary terminal layout and connector pinout that is NOT interchangeable with Stamford, Leroy Somer, or Basler AVRs. Even if the electrical specs appear similar, the physical connector will not fit. Always verify the generator nameplate shows “Marelli” or “MJ/MK series” before ordering. Using a non-Marelli AVR on a Marelli alternator risks terminal mismatch, incorrect voltage sensing, and potential field winding damage.
For generators above 400kW, Marelli uses a different AVR series entirely — contact the manufacturer for the correct model. These two models do not scale beyond 400kW.
