Description
Key Technical Specifications
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Model Number: 9905-228
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Manufacturer: Woodward Inc.
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Product Family: 2301A Load Sharing and Speed Control (LSSC)
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Power Supply: 20-40 V DC (Low Voltage Model)
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Power Consumption: ≤15 W nominal
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Actuator Output: 0-200 mA current signal
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Actuation Type: Forward-acting, single actuator
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Speed Sensing: Magnetic Pickup Unit (MPU), 1.0 Vac minimum to 30 Vac maximum
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Speed Sensor Input Impedance: 100-300 Ω
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Speed Ranges (Switch-Selectable): 500-1500 Hz, 1000-3000 Hz, 2000-6000 Hz (standard), 4000-12000 Hz
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Control Modes: Isochronous or Droop (selectable via external switch/relay)
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Load Sharing: Analog load-sharing lines (0-6 Vdc) for multi-unit paralleling
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Operating Temperature: -40 to +85°C (-40 to +185°F)
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Vibration Rating: 4 Gs, 5 to 500 Hz
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Shock Rating: 60 Gs
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Weight: Approximately 1.8 kg (4 lb)
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Enclosure: Sheet-metal chassis with single PCB architecture
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Special Feature: Deceleration ramp (decel ramp) for controlled shutdown
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Start Fuel Limiting: Automatic, adjustable to reduce emissions and engine wear
WOODWARD 9905-020P
Field Application & Problem Solved
In the field, the biggest challenge with multi-generator installations is maintaining stable frequency and equal load distribution across units. When you’ve got two or three gensets paralleled on an isolated bus—common in mining camps, remote power plants, or marine switchboards—without proper load sharing, one unit ends up carrying the bulk while others “motor” or fight each other. That creates thermal stress, fuel inefficiency, and potential reverse power trips. The 9905-228 solves this by providing true isochronous load sharing through analog load-sharing lines that balance kW output proportionally across all units in the system.
You will typically find this controller in power generation applications where reliability trumps complexity—think offshore platform auxiliary generators, drilling rig power plants, hospital backup systems, and industrial cogeneration setups. It’s particularly common on Caterpillar and Waukesha engine packages from the 1980s through early 2000s that shipped with Woodward governing packages. The 9905-228 is the low-voltage, forward-acting variant, meaning it drives the actuator in the standard direction (increasing current increases fuel) and runs on 24V DC battery systems rather than 125V DC station power.
Its core value is maintaining bus frequency within ±0.25% of rated speed while seamlessly transitioning between isochronous mode (isolated bus operation) and droop mode (utility parallel or infinite bus operation). The integrated deceleration ramp is critical for applications where sudden load rejection could cause overspeed—this feature provides a controlled ramp-down rather than an immediate fuel cut. The failed speed sensor protection is another field-saver; if your MPU signal drops out, the control calls for minimum fuel rather than holding last position, preventing runaway conditions. For technicians, the all-front-access potentiometer design means you can tune gain, stability, and droop without pulling the unit from the panel—a significant advantage when you’re working in cramped switchgear rooms.
Installation & Maintenance Pitfalls (Expert Tips)
Verify Your Actuator Direction Before Power-Up
A common rookie mistake is assuming all actuators are forward-acting. The 9905-228 is specifically forward-acting (0-200 mA output where increasing current increases fuel). If you’re retrofitting this onto a reverse-acting actuator setup (like some EGB governor configurations), the engine will slam to minimum fuel when it should be starting. Check your actuator part number and compare against Woodward’s compatibility matrix before applying power. If you smell smoke or hear the actuator rattle against the fuel stop immediately after start, kill power and verify direction.
Load-Sharing Line Terminations Are Critical
The analog load-sharing lines (terminals typically 5-6-7 on the terminal block) must be wired in parallel across all units with proper shielding. I’ve seen installations where the shield was grounded at both ends, creating ground loops that introduced 60 Hz hum into the load-sharing signal. This manifests as erratic kW hunting between units—one genset surging while another sags. Ground the shield at the control end only (terminal 22 or designated ground lug), and keep the load-sharing wiring twisted-pair, separate from high-current power cables.
Droop vs. Isochronous Switch Wiring
The mode selection depends on terminal 14 being connected to terminal 16 (common) for droop, or opened for isochronous. Many field issues stem from improper auxiliary contact wiring from the circuit breaker. If you’re paralleling with the utility, you need droop mode; if you’re on an isolated bus with other Woodward controls, you need isochronous. I’ve seen plants where the breaker auxiliary contact was wired backwards, causing the unit to run isochronous into the grid—resulting in immediate reverse power trips or instability. Verify your breaker contact logic with a multimeter before commissioning.
Speed Sensor Phasing Matters
The MPU input is sensitive to phasing. While the control will typically “run” with reversed leads, you’ll see erratic speed readings and poor stability. If your speed indication jumps around or the control hunts excessively, swap the MPU leads at terminals 9 and 10. Also, ensure your MPU gap is set correctly—typically 0.020 to 0.030 inches for standard magnetic pickups. Too wide a gap gives weak signal; too close risks contact damage from shaft runout.
Decel Ramp Timing for Emergency Shutdowns
The deceleration ramp on the 9905-228 is adjustable, but don’t set it too slow for emergency applications. In a true overspeed emergency, you want fuel shut off immediately, not ramped down over 10 seconds. The decel feature is intended for normal shutdown sequences where you want to avoid thermal shock to turbochargers. If your specification requires emergency overspeed protection, ensure a separate hard-wired fuel shutoff valve is installed outside this control’s authority.
WOODWARD 9905-020P
Technical Deep Dive & Overview
The Woodward 9905-228 is an analog load sharing and speed control module from the 2301A series, representing a mature, field-proven architecture that predates fully digital governor systems. It consists of a single printed circuit board housed in a rugged sheet-metal chassis, with all tuning potentiometers accessible from the front panel—no software interface, no programming cables, no firmware revisions to track.
The control operates as a closed-loop speed regulator with an inner current loop driving a proportional actuator. Speed feedback comes from a magnetic pickup unit sensing gear teeth on the engine flywheel or accessory drive, converted internally from frequency to voltage. This speed signal is compared against a reference (set by front-panel rated speed potentiometer or external trim), with the error amplified and conditioned through gain and stability (reset) networks before output to the actuator driver stage.
The load sharing function operates through an analog current loop between paralleled units. Each 9905-228 measures its generator’s load via CT and PT inputs, generates a proportional 0-6 Vdc signal representing load magnitude, and shares this voltage across the parallel load-sharing lines. The control adjusts its speed reference slightly to equalize these voltages, resulting in proportional kW sharing without master/slave hierarchy. This analog approach is robust against communication failures—if one unit drops offline, the remaining units maintain sharing automatically.
The deceleration ramp circuit on this specific model (indicated by the “decel ramp” suffix in the part number description) provides a controlled fuel reduction rate when transitioning from rated to idle speed or during shutdown sequences. This prevents turbocharger damage from sudden airflow changes and reduces thermal cycling stress on exhaust components. The 20-40V DC power input makes this unit suitable for 24V nominal battery systems common in mobile and marine applications, with internal DC-DC isolation protecting against ground loops and allowing operation during battery transients up to 77V for five minutes without damage.
From a system architecture perspective, the 9905-228 functions as the primary fuel control authority, receiving permissive and mode commands from external switches (idle/rated, raise/lower, droop/isochronous select) and interfacing with accessories like Woodward SPM-A synchronizers for automatic paralleling. It does not provide serial communication or remote diagnostics—tuning requires physical access to the front panel, which is both a limitation and a reliability advantage in harsh environments where network-based controls might fail.
