CDU4C-FC High Capacity Fast Charging Model Railway Capacitor Discharge Unit

About the Product

The BLOCKsignalling CDU4C-FC is a high-capacity fast-charging capacitor discharge unit (CDU) for model railway points motors, designed for large layouts, multiple points and demanding point-motor installations. It provides a powerful, short-duration current pulse for reliable operation of solenoid point motors while helping protect the motors, switches and layout power supply.

The CDU stores electrical energy in its capacitors and releases it as a high-current pulse when a point switch is operated. This provides strong, positive movement of the point motor without requiring the layout power supply itself to deliver the full switching current.

Because the high-current pulse has finished before the switch contacts open, electrical arcing across the contacts is greatly reduced. If a switch is accidentally held in the operated position, the CDU limits the subsequent current through the point motor, helping protect its coils from overheating and damage.

The fast-charging design recharges in a fraction of a second, making the CDU4C-FC particularly suitable where several points need to be operated in quick succession. This rapid charging is achieved without requiring a larger power supply.

Key Features

• High-capacity fast-charging capacitor discharge unit for model railway points motors.
• Provides a high-current pulse for strong and reliable point operation.
• Designed for large layouts and multiple point operation.
• Suitable where point motors are located some distance from the controller.
• Helps protect point motors from overheating and burn-out.
• Reduces electrical arcing and damage to switch contacts.
• Helps prevent voltage fluctuations elsewhere on the layout.
• Recharges in a fraction of a second for rapid successive point operation.
• Suitable for operating multiple points when the layout wiring and power supply are appropriate.
• Built-in Discharged and Ready LED indicators.
• Connection for an optional remote Ready LED on a control panel.
• Compatible with conventional twin-solenoid model railway point motors.
• Accepts either AC or DC power supplies.
  

Fast Charging

Conventional capacitor discharge units can take around a second to recharge after operating a point. The CDU4C-FC uses a fast-charging circuit that allows it to recharge in a fraction of a second, which is particularly useful when several points need to be switched rapidly or in succession.

This makes the CDU4C-FC particularly suitable for large model railway layouts, complex pointwork and applications where several point motors may need to operate together.

The fast-charging system achieves its rapid recovery without requiring a larger power supply.

LED Status Indicators

Two built-in LEDs provide a clear indication of the CDU's operating state:

• Yellow Discharged LED: Illuminates while the CDU is discharged and remains illuminated while the point switch is operated.
• Red Ready LED: Illuminates when charging is complete and the capacitors have charged to over 15V.

These indicators make it easy to confirm that the power supply is connected correctly and that sufficient charge is available for point operation.

The CDU4C-FC also provides terminals for an optional remote Ready LED, allowing the charged status to be displayed on a model railway control panel. A suitable series resistor is already incorporated into the CDU for this connection.

Wiring

The CDU is connected between the layout power supply and the point operating switch. The negative CDU output is normally connected to the common connection of the point motor, with the remaining point-motor connections operated through the point switch.

The optional remote Ready LED can also be connected to provide a convenient indication on the control panel when the CDU is fully charged.

Power Requirements

• AC input: 12V to 24V AC.
• DC input: 15V to 35V DC.
• Recommended power supply current: 1A.
• DC input polarity: Not polarity sensitive.
• Typical high-current wiring: Approximately 1.5mm² (16 AWG / 18 SWG) where appropriate.

The CDU can be powered from a suitable dedicated supply or a compatible auxiliary output on a model railway controller. A 16V AC auxiliary output is a common option. Suitable DC supplies can also be used and, when using DC, the input does not need to be connected with a particular polarity.

For fast-charge operation, a 1A power supply is required. Adequately sized wiring is also important because point motors require high current during operation, particularly when several points are operated together or are located some distance from the CDU.

Point Motor Compatibility

The CDU4C-FC is intended for conventional twin-solenoid model railway point motors operated by short electrical pulses.

The manual specifically covers Hornby and Peco point motors. For Hornby point motors the common wire is normally black, while for Peco point motors the common wire is normally green.

Passing-contact switches can also be used. The manual discusses both Hornby R044 and Peco PL-26 passing-contact switches. When using a Hornby R044, it may be necessary to pause briefly around the centre position to allow the CDU to recharge as the lever is moved.

Which CDU Do I Need?

For compact layouts where only one or two points need to operate at the same time, the CDU1C-FC Fast Charging Capacitor Discharge Unit will normally be sufficient.

For larger layouts where several points may need to operate simultaneously or where point motors are further from the controller, the CDU2C-FC Fast Charging Capacitor Discharge Unit provides greater storage capacity.

The CDU4C-FC Fast Charging Capacitor Discharge Unit provides the highest storage capacity in the range, making it the best choice for large layouts, demanding point-motor installations and maximum capacity for future expansion.

The CDU4C-FC Fast Charging Capacitor Discharge Unit with Ready LED is also available, supplied with a remote LED for mounting on your control panel to indicate when the CDU is fully charged.

Documentation & Support

For full installation instructions, wiring diagrams and troubleshooting guidance, please refer to the product instruction manual:

Product Instruction Manual