CDU4C-FC Fast Charging Model Railway Capacitor Discharge Unit with Ready LED

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. This version is supplied with an additional remote Ready LED for mounting on a control panel, providing a convenient visual indication when the CDU is fully charged.

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.
• Supplied with a remote Ready LED for control panel mounting.
• 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.
• 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 LEDs built into the CDU provide a clear indication of its 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.

This version is also supplied with an additional remote Ready LED, which can be mounted on your layout control panel. The remote LED illuminates with the Ready LED on the CDU, allowing you to see when the unit is fully charged without needing to view the CDU itself.

A suitable series resistor for the remote LED connection is already incorporated into the CDU, so an additional resistor is not required.

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 supplied remote Ready LED connects to the dedicated terminals on the CDU and can be mounted in your control panel to provide a convenient indication 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 instructions specifically cover 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, including Hornby R044 and Peco PL-26 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.

If you do not require the additional control panel LED, the CDU4C-FC Fast Charging Capacitor Discharge Unit is also available without the remote Ready LED included.

Documentation & Support

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

Product Instruction Manual