Victron Energy - 12/24V - Cyrix-ct Intelligent Battery Combiner Kit 12/24V-120A VSR

Victron Cyrix-ct 120A Intelligent Battery Combiner Kit: Reliable Dual-Battery Management for 12V and 24V Systems

Advanced Voltage-Sensitive Relay for Automatic Battery Isolation and Parallel Charging

The Victron Cyrix-ct 120A is a microprocessor-controlled bidirectional voltage sensitive relay (VSR) designed to intelligently manage multiple battery banks in vehicles, boats, and off-grid installations. This kit includes the relay, heavy-duty cables, and terminals, providing a complete solution for adding a second or third battery without modifying factory wiring. The Cyrix-ct automatically parallels the starter and auxiliary batteries when a charging source is present and isolates them when charging stops, ensuring the starting battery is always protected from deep discharge.

Unlike basic voltage-sensing relays, the Cyrix-ct employs intelligent battery monitoring to prevent rapid cycling. Its software analyses voltage trends over time, not just instantaneous thresholds, so it only switches when a genuine change in charge state is detected. This eliminates unnecessary relay chatter and extends the life of both the relay and connected batteries. The unit is auto-ranging for 12V and 24V DC systems, making it versatile for cars, trucks, motorhomes, marine vessels, and solar setups.

Key Features of the Cyrix-ct 120A Combiner

• 120 A continuous current rating with 180 A cranking assist for 5 seconds, suitable for alternators up to 150 A
• Bidirectional operation – engages when either battery bank receives charge, from an alternator, shore charger, or solar controller
• Trend-based switching logic prevents false triggering and relay cycling, improving reliability in fluctuating voltage conditions
• Emergency start assist – a momentary switch can be wired to the dedicated terminal to parallel batteries for 30 seconds, aiding engine cranking if the starter battery is low
• Low power consumption – draws less than 4 mA when open, minimising drain on the batteries when the engine is off
• IP54 protection – resistant to dust and water splashes, suitable for engine bays and exposed marine environments
• Compact design – 46 x 46 x 80 mm footprint allows installation in tight spaces

Complete Installation Kit with Premium Cables

This kit includes everything needed for a professional installation. The supplied cables are sized for the 120 A rating, with a 6-metre red 10 mm² power cable for the main run and a 0.5-metre black 10 mm² ground cable. A pre-assembled control cable with an M8 lug and 6.3 mm fast-on terminal simplifies the start assist wiring. Copper lugs with insulation sleeves (two M8 and four M6) and cable ties are provided to ensure secure, tidy connections. No cutting into factory wiring is required, preserving vehicle warranties and reducing installation time.

Why Choose the Victron Cyrix-ct Over Standard Relays?

Conventional VSRs often rely on simple voltage thresholds with fixed time delays, which can lead to nuisance switching when loads cause temporary voltage dips. The Cyrix-ct’s intelligent algorithm evaluates the voltage trend over a period, reversing a connection only if the trend has genuinely reversed. This is particularly beneficial in systems with variable loads, such as fridges or inverters, where voltage can fluctuate without indicating a change in charge state. The result is stable, predictable battery management that reduces wear on contacts and prevents unintended discharge of the starter battery.

Additionally, the bidirectional design means the relay will close not only when the engine is running but also when a mains charger or solar regulator is connected to the auxiliary bank. This allows all batteries to benefit from any charging source, maximising energy utilisation and simplifying system design.

Applications

• 4WD and camping vehicles – keep the cranking battery isolated while running accessories from a deep-cycle auxiliary battery
• Marine installations – automatically combine battery banks during shore power charging or alternator operation, with emergency parallel for engine starting
• Caravans and motorhomes – charge house batteries from the vehicle alternator while driving, and from solar when parked
• Commercial vehicles – manage multiple battery banks in trucks, buses, and emergency vehicles with high alternator outputs
• Off-grid solar systems – use as a battery combiner to share charge between banks without complex wiring

Installation Considerations

The Cyrix-ct requires a common negative reference between all batteries, which is standard in most 12V and 24V vehicle and marine systems. The relay should be mounted close to the batteries, with the included cables cut to length as needed. Fusing is recommended on all positive connections (not included) to protect against short circuits. The start assist terminal can be connected to a momentary push-button switch on the dashboard for convenient emergency starting.

With its robust construction, intelligent control, and comprehensive kit contents, the Victron Cyrix-ct 120A provides a reliable and long-lasting solution for dual-battery management. Whether you are building a touring setup, upgrading a marine electrical system, or adding redundancy to an off-grid power installation, this combiner delivers consistent performance and peace of mind.

Equip your vehicle or vessel with the Victron Cyrix-ct 120A Intelligent Battery Combiner Kit today and ensure your batteries are always charged and ready, without the risk of a flat starter battery.

Specifications