Overview
The SX440 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
- PMG Powered — Independent excitation source for superior voltage stability
- High Output — 120VDC maximum for demanding excitation requirements
- 3-Phase PMG Input — 140-220VAC, 3-phase, 3-wire, 3A per phase
- Dual Frequency — 50/60 Hz nominal sensing for global compatibility
- Soft Start Ramping — Smooth generator voltage buildup
- Under-Frequency Protection — Automatic voltage reduction during low speed
Technical Specifications
| Parameter | Value |
|---|---|
| Sensing Input | 190-264VAC, 1-phase, 2-wire |
| Sensing Frequency | 50-60 Hz nominal |
| PMG Power Input | 140-220VAC, 3-phase, 3-wire, 3A/phase, 100-120Hz |
| Output Voltage | Max 120VDC |
| Output Current | Continuous 4A, Intermittent 6A for 10s |
| Regulation Accuracy | <±1% (with 4% engine governing) |
| Excitation Type | PMG-powered |
| Soft Start | Yes |
| UF Protection | Yes |
Compatibility
- Stamford Brushless Alternators with PMG Excitation
- Compatible with: Part.: SX440
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 BC/UC 50-200kW, generator sets equipped with PMG exciter.
Competitors SX460 (no PMG), SX421 (latest SX series upgrade).
| Parameter | SX440 | SX460 | SX421 |
| Excitation Input | PMG or self-excited | Self-excited only | PMG or self-excited (dual-mode) |
| Output Current | 4A | 4A | 4A |
| Regulation | ±1% | ±1% | ±1% |
| PMG Voltage Protection | Yes (PMG won’t lose magnetization during short circuit) | N/A | Yes |
| Interface Compatibility | SX440 dedicated terminals | SX460 terminals | Backward compatible with SX460/SX440 |
| Price | $40-60 | $25-45 | $45-65 |
Selection Advice The key differentiator is PMG (Permanent Magnet Generator) support. If the alternator has a small PMG exciter mounted on the rear, an AVR with PMG input such as the SX440 or SX421 is required. PMG excitation provides output voltage independent of load and maintains excitation current during short circuits for protection relay operation. Generators without PMG can use the SX460. The SX421 is the latest SX series upgrade with dual-mode design (supports both self-excited and PMG), and is backward compatible with SX460/SX440 wiring, making it suitable for legacy upgrades without rewiring.
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