Overview
The MX321 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
- ±1% Voltage Regulation — Stable output under varying load and engine speed conditions
- PMG Excitation Support — Compatible with permanent magnet generator excitation systems
- Selectable Frequency — 50/60 Hz jumper-selectable for global applications
- 6A Intermittent Capacity — Handles short-term excitation surges up to 6A for 10 seconds
- Solid-State Reliability — Thyristor-based control for long service life
- Direct OEM Fit — Drop-in replacement for Stamford MX321 regulators
Technical Specifications
| Parameter | Value |
|---|---|
| Sensing Input | 190-264VAC, 1-phase 2-wire, jumper selectable |
| Frequency | 50/60 Hz (jumper selectable) |
| Output Voltage | Max 90VDC at 207VAC input |
| Output Current | Continuous 4A, Intermittent 6A for 10 seconds |
| Regulation Accuracy | <±1% (with 4% engine governing) |
Compatibility
- Stamford Alternators with PMG Excitation
- Compatible with: Part.: MX321
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 Stamford HC/LC series 200-2000kW, especially power stations requiring parallel operation.
Competitors R438 (Leroy Somer global representative), R450 (Leroy Somer next generation).
| Parameter | MX321 | R438 | R450 |
| Brand | Stamford (UK) | Leroy Somer (France) | Leroy Somer (France) |
| Output Current | 5A cont. | 4A cont. | 6A cont. |
| Regulation | ±0.5% | ±0.5% | ±0.5% |
| Excitation Type | PMG permanent magnet | Self-excited (needs R731) | Self-excited or PMG |
| Parallel Operation | Native support | No | Yes |
| 3-Phase Sensing | Built-in | Needs R731 | Built-in |
| Installation Complexity | Low (integrated) | Medium (needs R731) | Low (integrated) |
| Price | $180-300 | $200-350 + R731 | $220-380 |
Selection Advice The MX321 is Stamford’s high-performance AVR with unique native multi-unit parallel operation support. If the generator needs to parallel with the grid or with other generators, the MX321 is the only choice within the Stamford ecosystem. PMG excitation maintains field current during short circuits for protection relay operation. Compared to R438 — R438 does not support parallel operation, and while it has larger global installed base (single-unit scenarios), parallel scenarios require MX321 or R450. The R450 is the R438 upgrade adding parallel operation and digital calibration — the most direct full-featured MX321 competitor.
