Victron Cyrix-Li-CT 120A Battery Combiner

The Victron Energy Cyrix-Li-ct 120A is a microprocessor-controlled intelligent battery combiner purpose-built for systems combining a lead-acid starter battery with a Victron LiFePO4 service battery. Available in 12/24V and 24/48V variants, it automatically connects the two battery banks in parallel to allow the alternator or shore charger to charge both batteries simultaneously — then disconnects them immediately when the VE.Bus BMS signals a cell overvoltage or overtemperature alarm, protecting the lithium cells from damage caused by uncontrolled charge current.

Unlike conventional voltage-sensitive relays that connect and disconnect based solely on battery terminal voltage, the Cyrix-Li-ct adds a BMS control input that makes its engage and disengage logic lithium-aware. The relay will only engage when the VE.Bus BMS Charge Disconnect output is high — indicating that charging is permitted — and one of its power terminals senses 13.4V or more (26.8V for 24V systems). When the BMS signals a cell overvoltage or overtemperature event by pulling the Charge Disconnect output free floating, the Cyrix-Li-ct disengages immediately — protecting the lithium cells rather than waiting for the standard voltage-based disconnect threshold.

A built-in transient voltage suppressor limits the voltage spike that can occur when the Cyrix-Li-ct suddenly disengages under load — an important protection feature in systems where the alternator field collapses rapidly when the combiner opens. An emergency start assist function is also included: a short negative pulse on the start assist terminal closes the relay for 30 seconds, allowing the lead-acid starter battery to be boosted from the LiFePO4 service battery in an emergency without any permanent parallel connection.

With a maximum continuous and breaking current of 120A at 12V or 24V, a current consumption when open of less than 4mA, and an IP54-rated enclosure measuring just 46 x 46 x 80mm and weighing 110g, the Cyrix-Li-ct is a compact, low-power solution for alternator charge management in marine, RV, and vehicle lithium battery systems. Certified to automotive ECE R10-6 and EN/IEC 60335-1 safety standards.

Features

Lithium-Aware BMS Control Input

The Cyrix-Li-ct only engages when the VE.Bus BMS Charge Disconnect output is high — confirming that charging is safe for the lithium cells. When the BMS signals a cell overvoltage or overtemperature event by pulling the output free floating, the Cyrix-Li-ct disengages immediately, protecting the LiFePO4 cells from uncontrolled alternator charge current without delay.

Voltage-Based Engage Logic with Intelligent Delay

The relay engages when one of its power terminals senses 13.4V or more (26.8V for 24V systems), with a time delay that reduces progressively as voltage increases — from 120 seconds at moderate charge voltage, to 30 seconds at higher voltage, to 4 seconds above 13.9V. This prevents nuisance engagement during brief voltage transients while responding quickly at sustained alternator output voltage.

Immediate Disengage on Alarm or Low Voltage

The Cyrix-Li-ct disengages immediately when either the BMS Charge Disconnect output goes free floating or battery voltage drops below 13.2V (26.4V for 24V systems), with a secondary 10-second delayed disconnect between 13.2V and 13.3V. This prevents the lead-acid starter battery from discharging the lithium service battery under low-load conditions.

Built-In Transient Voltage Suppressor

A built-in transient voltage suppressor clamps the voltage spike that occurs when the relay suddenly disengages under alternator load — protecting connected electronics, the alternator, and the lithium battery BMS from voltage transients that can exceed safe levels when a high-current relay opens abruptly in an inductive circuit.

Emergency Start Assist Function

A short negative pulse on the start assist terminal forces the relay closed for 30 seconds, allowing the LiFePO4 service battery to boost a depleted lead-acid starter battery in an emergency — without any permanent parallel connection between the two banks and without overriding the normal BMS protection logic during regular operation.

Ultra-Low Standby Current — Under 4mA

With a current consumption of less than 4mA when open, the Cyrix-Li-ct draws negligible standby power from the battery bank during periods when the relay is disengaged — making it suitable for permanent installation in systems where minimising parasitic drain during extended lay-up or storage is important.

Compact IP54-Rated Enclosure

The IP54-rated enclosure — measuring just 46 x 46 x 80mm and weighing only 110g — is dust-protected and splash-resistant, making the Cyrix-Li-ct suitable for installation in exposed locations in engine bays, bilges, and vehicle battery compartments without requiring an additional enclosure or protection cover.

12/24V and 24/48V Variants Available

Available in two voltage variants — 12/24V-120A (CYR010120412) for 12V and 24V lithium systems, and 24/48V-120A for 24V and 48V systems — the Cyrix-Li-ct covers the most common vehicle and marine dual-voltage system configurations with a single compact and proven relay design.

Specifications

Datasheets and Manuals

Datasheet