Woodward 5501-381

Model Series

Woodward 5500 Series Digital Load Controllers

Related models in the 5500 series include:

• Woodward 5501-001 — Base 5501 single-channel load controller
• Woodward 5501-101 — 5501 with speed droop and load sharing
• Woodward 5501-201 — 5501 with dual load input and synchronization
• Woodward 5501-381 — 5501 with programmable load ramp, fuel limiting, and advanced protection (this model)
• Woodward 5505 — Five-channel load controller for large genset installations
• Woodward 5550 — Dual-channel load controller with integrated governor
• Woodward 5466 — Next-generation EasyGen-3500 controller (successor platform)
• Woodward 505E — Legacy analog speed controller (replaced by 5448/5501 series)

Manufacturer

Woodward, Inc.
Hexatronic Group AB
Address: 1000 East Drake Road, Fort Collins, CO 80525, USA
Parent Company: Hexatronic Group AB, Drottninggatan 89, 111 60 Stockholm, Sweden

Technical Specifications

Functional Features

• Single-channel precise load control — maintains generator load at a user-defined setpoint with ±0.5% accuracy using a closed-loop PID algorithm
• Automatic load sharing — when multiple 5501 controllers operate in parallel, each unit automatically adjusts its fuel output to share total load equally within ±1% without requiring a master controller
• Programmable speed droop — adjustable from 0% (isochronous) to 10%, enabling stable parallel operation of generators with different ratings
• Load ramp control — programmable acceleration and deceleration ramps from 0.1%/s to 50%/s for controlled load changes during startup, shutdown, and load transfer
• Fuel limiting — hard and soft fuel limit functions protect the engine from overfueling during sudden load rejection or synchronization events
• Engine protection suite — includes overspeed trip, underspeed trip, overtemperature trip, low oil pressure trip, high exhaust temperature trip, reverse power trip, and loss of load trip with fully configurable setpoints
• Synchronization support — voltage matching, frequency matching, and phase angle matching for automatic paralleling with bus or other generators
• Remote monitoring and control — RS-485 Modbus RTU and RS-232 interfaces enable full remote access to load setpoint, actual load, fuel position, speed, and all alarm/trip status
• Event logging — internal non-volatile EEPROM stores the last 512 events with millisecond timestamps for post-incident analysis
• Load transducer calibration — built-in two-point calibration routine for 4 to 20 mA load inputs with automatic sensor fault detection (open circuit, short circuit, out-of-range)
• Governor override — load controller output can be overridden by an external speed governor signal for seamless speed-to-load transfer during mode switching

Performance Parameters

Material Composition

Structural Characteristics

• Form Factor: DIN rail or panel-mountable controller with integrated front panel interface, compatible with standard 35 mm DIN rail (EN 60715)
• Front Panel Layout:
  • 20 × 2 character LCD display — shows load percentage, speed, fuel position, droop setting, mode, and alarm status
  • 5 × push-button navigation keys — menu navigation, up/down, enter, escape, mode select
  • 2 × rotary potentiometers — load setpoint and speed droop adjustment (10-turn, sealed)
  • 8 × LED indicators — power, run, alarm, trip, sync, communication, load share active, fault
  • 2 × mini-DIN connectors — RS-485 and RS-232 communication ports
  • 1 × DB-25 connector — analog I/O and digital I/O breakout
  • 1 × USB Type-B connector (optional) — firmware update and configuration download
• Rear Panel:
  • 2 × 6-pin terminal blocks — speed input (MPU or PMG)
  • 1 × 8-pin terminal block — load input (4 to 20 mA, ×2 channels)
  • 1 × 8-pin terminal block — fuel servo output (4 to 20 mA)
  • 2 × 6-pin terminal blocks — digital inputs (×16 channels total)
  • 2 × 8-pin terminal blocks — relay outputs (×6 channels total)
  • 1 × 4-pin terminal block — 24 VDC power input
  • 1 × 6-pin terminal block — RTD inputs (Pt100, ×2 channels)
• Internal Layout:
  • Main processor board — mounted vertically on the left side, 6-layer PCB with isolated analog and digital ground planes
  • Power supply module — isolated DC-DC converter (24 VDC to 5 VDC, 3.3 VDC, ±12 VDC), mounted on the right side
  • Analog I/O board — removable plug-in module with 16-bit ADC and 12-bit DAC, shielded compartment
  • Digital I/O board — removable plug-in module with opto-isolated inputs and transistor/relay outputs
  • Communication module — removable RS-485/RS-232/Ethernet board with galvanic isolation
  • Backup battery — CR2032 lithium coin cell for real-time clock and event log retention during power loss

Working Principle

1. Load Sensing: The load transducer (4 to 20 mA current loop) connected to the controller’s load input provides a real-time signal proportional to the actual electrical load on the generator. The internal 16-bit ADC samples this signal at 10 ms intervals
2. Speed Sensing: The MPU (Magnetic Pickup Unit) or PMG provides engine speed frequency to the controller. The speed signal is conditioned through a Schmitt trigger and frequency-to-voltage converter
3. Error Calculation: The measured load is compared against the load setpoint (entered via front panel potentiometer or remote Modbus command). The difference is the load error signal
4. PID Control: A digital Proportional-Integral-Derivative (PID) controller with auto-tune capability processes the load error and generates a fuel demand signal (4 to 20 mA) proportional to the required fuel flow change
5. Droop Compensation: The controller calculates a droop correction factor based on the configured droop percentage and current speed deviation. This factor is added to the load setpoint to create the effective speed reference, ensuring stable parallel operation
6. Fuel Servo Actuation: The 4 to 20 mA fuel demand signal drives the fuel control valve servo motor, which adjusts the fuel rack position to increase or decrease fuel flow
7. Load Sharing (Parallel Mode): In parallel configurations, each 5501 controller communicates load data via RS-485 Modbus RTU. Each unit compares its own load against the average load of all units and adjusts its fuel output to achieve equal sharing within ±1%
8. Load Ramping: During startup, shutdown, or load transfer, the controller ramps the load setpoint at the programmed rate (e.g., 1%/s to 50%/s) to prevent sudden fuel changes that cause mechanical stress
9. Protection Monitoring: The controller continuously monitors all protection inputs. If any parameter (overspeed, underspeed, overtemp, low oil pressure, high exhaust temp, reverse power, loss of load) exceeds its trip setpoint, the controller immediately commands a fuel cut via relay output and sends a trip alarm via Modbus
10. Event Recording: Every state change, alarm, trip, and operator action is timestamped and stored in non-volatile EEPROM for post-event analysis. The log retains the last 512 events

Advantages and Highlights

• Single-channel precision load control — dedicated load management without the complexity and cost of multi-channel controllers for single-generator applications
• Automatic load sharing — achieves ±1% load balance among parallel generators without a master controller, using peer-to-peer RS-485 communication
• Programmable speed droop 0% to 10% — fully configurable for isochronous or droop operation, enabling seamless parallel operation of generators with different kVA ratings
• Load ramp control — smooth acceleration and deceleration ramps protect the engine and generator from thermal and mechanical shock during load transitions
• SIL 2 safety rating — with optional safety I/O module, the controller meets IEC 61508 SIL 2 for safety-critical load management applications
• Event logging with 512 entries — comprehensive post-event diagnostic capability eliminates guesswork in fault analysis
• Wide operating temperature -20°C to +60°C — suitable for outdoor installations in arctic, desert, and tropical environments without climate control
• Drop-in replacement for legacy analog load controllers — identical footprint and wiring compatibility with Woodward analog load control systems simplifies migration
• Field-upgradeable firmware — software updates performed via RS-232, RS-485, or USB without removing the controller from the panel
• Modbus RTU standard protocol — seamless integration with any SCADA, DCS, PLC, or HMI system without proprietary gateway hardware
• IP54 front panel rating — dust and splash-proof front panel suitable for harsh industrial environments
• 15-year product lifecycle guarantee — Woodward guarantees minimum 15-year availability for the 5501 series

Applicable Industries

Installation Requirements

• Installation must be performed by qualified electrical technicians trained in Woodward controller wiring and VDE/NEC standards
• The controller must be mounted on a vertical DIN rail (35 mm, EN 60715) or panel-mounted using the four corner mounting holes with M4 screws
• Power supply wiring: Connect 24 VDC (18–32 VDC) to the rear panel terminal block with minimum 14 AWG copper wire. Do not exceed 32 VDC under any condition
• Speed input wiring (MPU): Connect magnetic pickup output to the rear panel speed terminals using shielded twisted pair cable. Shield ground must connect to chassis ground at one end only (controller end)
• Speed input wiring (PMG): Connect PMG output (A+, A−, B+, B−) using shielded twisted pair cable. Shield ground connects to chassis ground at one end only
• Load input wiring: Connect 4 to 20 mA load transducer output using shielded twisted pair cable. The transducer loop resistance must not exceed 750 Ω
• Fuel servo wiring: Connect the 4 to 20 mA fuel output to the fuel servo motor using shielded cable. The servo motor impedance must be 250 Ω to 750 Ω
• Grounding: The controller chassis must be connected to equipment ground with a wire size no smaller than 10 AWG copper. Ground resistance must be < 5 Ω
• Ambient temperature: Ensure the installation location maintains temperature within -20°C to +60°C. Do not install in direct sunlight or near heat sources exceeding 70°C
• Ventilation: Provide minimum 10 cm (4 inches) clearance above and below the controller for natural convection cooling. Do not stack controllers directly on top of each other
• Cable routing: Keep signal cables (speed, load, analog I/O) separated from power cables by a minimum of 15 cm (6 inches) to prevent electromagnetic interference
• RS-485 wiring: Use shielded twisted pair cable (120 Ω characteristic impedance) with termination resistors (120 Ω) at both ends of the bus for installations exceeding 10 meters
• After installation: Perform a full functional test using the front panel menu to verify load sensing, fuel output, droop setting, protection functions, and communication before energizing the engine

Usage Precautions

• Do not exceed 32 VDC on the power input — overvoltage permanently damages the internal isolated DC-DC converter
• Do not connect MPU input when the engine is rotating above 120% speed — overfrequency input damages the speed measurement circuitry
• Do not short the 4 to 20 mA fuel output — a short circuit causes the fuel servo to drive to full stroke, resulting in engine overspeed and potential catastrophic failure
• Do not disconnect the speed signal while the engine is running — loss of speed signal causes the controller to trip on underspeed protection within 2 seconds
• Do not modify the firmware without Woodward authorization — unofficial firmware changes void the certification, warranty, and SIL rating
• Do not operate the controller in environments with corrosive gases (H₂S, Cl₂, SO₂) without an NEMA 4X enclosure — corrosion degrades terminal contacts and PCB traces within months
• Do not cover the front panel ventilation slots — blocked airflow causes internal temperature to exceed the +60°C limit, leading to thermal shutdown and potential component damage
• Do not use the relay outputs to switch inductive loads exceeding 5 A without a snubber circuit (RC 100 Ω / 0.1 μF) — inductive kickback damages the relay contacts and causes EMI
• Calibrate the load transducer input annually — load transducer output drifts over time, affecting load control accuracy beyond the ±0.5% specification
• Replace the CR2032 backup battery every 3 years — battery failure causes loss of real-time clock and event log timestamps during power outages
• Do not exceed the maximum of 16 digital inputs and 12 digital outputs — overloading the I/O bus causes communication errors and unreliable operation
• Recalibrate the speed input (MPU/PMG) after any mechanical disturbance — vibration or shock can shift the air gap, affecting speed measurement accuracy
• Store spare units in a dry environment at 5% to 85% RH, temperature 10°C to 35°C — moisture ingress causes PCB corrosion and conformal coating delamination
• Replace the controller at end of lifecycle (15 years from manufacture date) — component obsolescence, capacitor aging, and solder joint fatigue degrade long-term reliability beyond this period

Part Number Decoding

Document Reference

• Manufacturer: Woodward, Inc., 1000 East Drake Road, Fort Collins, CO 80525, USA
• Parent Company: Hexatronic Group AB, Drottninggatan 89, 111 60 Stockholm, Sweden
• Technical Manual: Woodward Publication 82701 (5501 Controller Installation and Operation Manual)
• Application Guide: Woodward Publication 82702 (5501 Load Sharing Configuration Guide)
• Applicable Standards: ISO 8528-5, ISO 8528-9, IEC 60034, IEEE 1547, NFPA 85, IEC 61508, IEC 61000-6-2, IEC 61000-6-4, DNV GL (marine)
• Communication Protocol: Modbus RTU, Slave Address configurable (default 1), Baud Rate 9600–115200 bps
• Replacement Part Numbers:
  • 5501-001 — Base load control (no ramp, no fuel limit)
  • 5501-101 — Load control with speed droop
  • 5501-201 — Dual load input with synchronization
  • 5505-001 — Five-channel load controller (for large installations)
  • 5466-001 — Next-generation EasyGen-3500 controller (recommended successor)
• SIL Rating: SIL 2 per IEC 61508 (with Woodward safety I/O module 5501-SIL)
• Firmware Version: Field-upgradeable, current version: 4.1.x (verify at time of installation)