REV7K-4A High Power 15V DC Model Railway Autoreverser - Hornby™ HM7000 Compatible

About the Product

The BLOCKsignalling REV7K-4A is a high-power 15V DC model railway autoreverser for Hornby™ HM7000, reversing loops, wyes, turntables and other reversing sections. It provides fast automatic polarity switching for layouts using a constant 15V DC track supply.

When a train crosses into an isolated section where the rail polarity does not match the adjoining track, the REV7K-4A detects the resulting polarity mismatch and automatically reverses the polarity of the isolated section. This happens in a fraction of a second, preventing the short circuit from shutting down the layout and allowing the train to continue through the reversing section.

The REV7K-4A uses a fully solid-state design with no relays or moving parts. This provides extremely fast switching and avoids mechanical relay wear. No programming or adjustments are required - once correctly wired, the module operates automatically whenever a polarity mismatch is detected.

Key Features

• Automatically detects track polarity mismatches and reverses the isolated section.
• Suitable for reversing loops, figure-of-eight layouts, wyes and turntables.
• Designed for constant 15V DC model railway layouts.
• Compatible with Hornby™ HM7000 when using a 15V DC track supply and Bluetooth locomotive control.
• Solid-state electronic design with no relays or moving parts.
• Ultra-fast polarity restoration in less than 25ms.
• Detection time of up to 10µs.
• Microprocessor controlled for fast and reliable operation.
• No programming or adjustments required.
• High-power design suitable for layouts using larger power supplies.
• LED indicators show input polarity, output polarity, reversing state and fault conditions.
• Automatic LOCKOUT protection for persistent track short circuits.
• Reverse-polarity protected input.
• Designed to minimise interruptions to sound-equipped locomotives.
  

Ultra-Fast Solid-State Operation

The REV7K-4A uses solid-state electronics rather than mechanical relays, allowing it to react extremely quickly when a polarity mismatch occurs.

The module can detect a polarity mismatch in up to 10µs, with a maximum trip time of 250µs and polarity restoration completed within 25ms.

Because the interruption to track power is so brief, sound-equipped locomotives will generally experience only a very short interruption. In many cases, a stay-alive may not be required simply to maintain continuous sound while crossing the reversing section.

Hornby HM7000 Compatibility

The REV7K-4A is designed for layouts where the track is supplied with a constant 15V DC supply, including Hornby™ HM7000 layouts where compatible locomotive decoders are controlled using Bluetooth and the HM7000 App.

It is not suitable when HM7000 locomotives are being powered from a DCC command station. Connecting DCC to the REV7K-4A may damage the module.

For DCC layouts, use the REV1 DCC Autoreverser.

For layouts requiring compatibility with variable DC, DCC or 15V DC, use the REV2 Universal Autoreverser.

Automatic Short-Circuit Protection

The REV7K-4A continuously monitors the isolated reversing section for polarity mismatches and short circuits.

Normally, a detected mismatch is corrected simply by reversing the output polarity. If changing the polarity does not remove the short circuit – for example, because a locomotive has derailed – the module automatically switches off its output to protect itself and the layout.

The red LOCKOUT LED illuminates to indicate the fault. After approximately five seconds, the REV7K-4A attempts to restore power. If the short circuit remains, the output is switched off again and the process repeats until the fault has been removed.

LED Status & Diagnostics

A comprehensive set of on-board LEDs provides information about the operating state of the autoreverser.

The indicators show:

• Input polarity
• Output polarity
• Normal or inverted output state
• Internal power supply status
• Detection of a short circuit
• LOCKOUT status if a persistent short circuit cannot be cleared

These indicators make it easier to confirm correct operation and diagnose wiring or track problems.

Typical Applications

The REV7K-4A can be used anywhere an isolated section of a 15V DC model railway needs its rail polarity automatically matched to the adjoining track.

Reversing Loops

The REV7K-4A can automatically control the polarity of an isolated reversing loop, allowing a train to enter and leave the loop without causing a short circuit.

The reversing loop must be isolated from the adjoining track using rail breaks as shown in the diagram below. When the train reaches a boundary where the rail polarity does not match, the REV7K-4A automatically switches the polarity of the loop so the train can continue onto the main layout.

Figure-of-Eight Layouts

An isolated section can be installed where the track arrangement creates opposing rail polarities. The autoreverser automatically switches this section as required, allowing trains to travel continuously around the figure-of-eight.

Turntables

The turntable bridge track can be isolated from the approach tracks and powered through the REV7K-4A. The module then automatically corrects the bridge track polarity when required as a locomotive enters or leaves the turntable.

Wye Layouts

A wye creates a point where opposing rail polarities would otherwise connect and cause a permanent short circuit. By powering an isolated section through the REV7K-4A, its polarity can be automatically changed as the train enters and leaves the section.

Additional Wiring Diagrams

Detailed wiring diagrams for figure-of-eight layouts, turntables and wyes are included in the REV7K-4A instruction manual.

Isolated Track Section

The section of track connected to the REV7K-4A output must be completely isolated from the adjoining track.

For reliable operation, the isolated reversing section should also be at least as long as the longest train that will use it. This prevents a train from bridging both boundaries of the reversing section at the same time.

Electrical Requirements

• Track Supply: Fixed 15V DC
• Designed Operating Input Range: 15V to 18V DC
• Recommended Power Supply Rating: 1A to 8A
• Maximum Continuous Output Current Before Tripping: 1A
• Typical Trip Current: 1.5A
• Input Protection: Reverse-polarity protected
• Variable DC: Not suitable
• DCC Track Power: Not suitable
• Approximate Module Dimensions: 40mm × 40mm × 15mm
• Mounting Holes: 3mm diameter

The REV7K-4A has an internal current limit of approximately 1.5A, so using a higher-capacity power supply does not increase the current delivered through the module beyond its designed limit.

Wiring Diagram

The REV7K-4A is connected between the 15V DC track supply and the completely isolated section of track requiring automatic polarity reversal.

Documentation & Support

For full installation instructions, application-specific wiring diagrams, LED indications and troubleshooting information, please download the latest REV7K-4A instruction manual:

Product Instruction Manual