Victron Cyrix-ct 120A Intelligent Battery Combiner for Dual Battery Systems

Advanced Voltage Sensing Relay with Trend Detection for Reliable Parallel Charging

The Victron Cyrix-ct 12/24V-120A is a microprocessor-controlled intelligent battery combiner that functions as a bidirectional voltage sensitive relay (VSR). Unlike conventional split charge relays that rely on simple voltage thresholds and fixed time delays, the Cyrix-ct analyses the overall voltage trend to prevent nuisance switching. This ensures your auxiliary battery bank charges reliably from the alternator or mains charger without premature disconnection under heavy loads or reconnection when surface charge dissipates.

Engineered for 12V and 24V automotive and marine electrical systems, the Cyrix-ct auto-detects system voltage and provides a continuous current rating of 120 A, making it suitable for charging large domestic battery banks, bow thruster batteries, and other onboard equipment. Its bidirectional sensing allows the combiner to engage when either battery reaches the connect voltage, so charging sources on either side can parallel the banks automatically.

Intelligent Trend Detection Eliminates Unwanted Cycling

Standard voltage-controlled relays often disconnect a battery when a short, high-current load causes a momentary voltage dip, or fail to connect a deeply discharged bank because the voltage collapses below the disconnect threshold immediately after engagement. The Cyrix-ct’s software monitors the rate and direction of voltage change over time, reversing a previous action only if the trend has genuinely reversed. The time delay adapts based on the deviation from the trend, providing stable operation in demanding conditions.

Key Features

• 120 A continuous current rating with 180 A cranking assist for emergency parallel starts
• 12/24 V auto-ranging detects system voltage automatically, no manual configuration needed
• Bidirectional voltage sensing and dual power supply allows engagement from either battery, even if one is deeply discharged
• Start Assist function via push button or switch provides 30-second emergency parallel connection
• Over-temperature protection disengages the relay if contact temperature becomes excessive, re-engaging after cooling
• Virtually zero voltage drop across the contacts, eliminating the need to increase alternator or charger output voltage
• Prioritises starter battery by connecting auxiliary banks only after the starter reaches the connect voltage
• Compact IP54-rated housing (46 x 46 x 80 mm) withstands dust and water spray in engine bays and marine compartments
• Low power consumption: less than 4 mA when open, 220 mA (12 V) or 120 mA (24 V) when closed
• 13 mm (M6) long stud terminals allow secure connection of multiple heavy-duty cable lugs

Reliable Parallel Charging Without Voltage Loss

Diode-based battery isolators introduce a voltage drop of 0.6–0.7 V, which can prevent full charging unless the alternator or charger is voltage-boosted. The Cyrix-ct uses a high-current relay with negligible contact resistance, so your batteries receive the full charging voltage. This makes it a direct, efficient replacement for diode isolators in 12V dual battery systems and 24V marine setups.

Emergency Start Assist for Peace of Mind

If your starter battery becomes discharged or damaged, the Cyrix-ct can be manually engaged using a momentary push button or switch connected to the Start Assist terminal. The relay remains closed for 30 seconds, allowing you to draw power from the auxiliary bank to crank the engine. This feature is invaluable for remote travel, off-grid work sites, and marine applications where a flat starter battery could leave you stranded.

Designed for Harsh Environments

With an operating temperature range of -40 to +60 °C and an IP54 protection rating, the Cyrix-ct is built to perform in engine compartments, bilges, and exposed vehicle installations. The fully sealed housing resists dust ingress and water spray, while the robust M6 stud terminals accept heavy-gauge cable lugs for secure, low-resistance connections.

Typical Applications

• Charging a second battery in 4WD, caravan, and camper trailer dual battery systems
• Marine installations with separate start and house battery banks
• Bow thruster and windlass battery charging
• Commercial vehicles and agricultural machinery with auxiliary power requirements
• Off-grid solar systems where multiple battery banks need to be combined during charging

Installation and Wiring

The Cyrix-ct features clearly labelled M6 stud terminals for Battery 1 (Terminal 87) and Battery 2 (Terminal 30), plus spade terminals for the negative sensing wire (Terminal 86) and optional Start Assist switch (Terminal 85). A wiring diagram is included in the product images to guide installation. For systems requiring multiple engage/disengage profiles, consider the Victron Cyrix-i 400.

Upgrade Your Dual Battery System with Intelligent Control

Replace unreliable diode isolators and basic voltage-sensing relays with the Victron Cyrix-ct 120A Intelligent Battery Combiner. Its trend-detection logic, bidirectional sensing, and emergency start assist provide dependable parallel charging for your auxiliary batteries. Order today to ensure your onboard power system operates efficiently and reliably, wherever your journey takes you.