The Victron Cyrix-ct is a microprocessor-controlled battery combiner built for 12V and 24V systems carrying up to 230A continuous current. It automatically links battery banks when one is being charged and separates them once charging stops, keeping the starter or primary battery protected from discharge. It suits marine, vehicle and off-grid setups where two battery banks need managing without manual switching.

Key features

• System voltage, 12V and 24V DC, detected automatically with no manual configuration.
• Current rating, 230A continuous.
• Control logic, microprocessor-controlled, connecting batteries when voltage rises above a set threshold and disconnecting when it falls.
• Solid-state construction, no moving parts, avoiding the mechanical wear of solenoid-based combiners.
• Weight, 0.3 kg, suited to confined installation spaces.
• Charge source compatibility, works with alternators, solar charge controllers and shore power chargers, since it responds to voltage rather than source type.

How it works

The Cyrix-ct monitors battery voltage continuously. When voltage on either bank reaches 13.7V on a 12V system, or 27.4V on a 24V system, the unit connects the two banks in parallel so both take charge. Once voltage falls below the disconnect threshold, the banks separate again. This stops a depleted auxiliary bank from pulling down the starter battery, a common fault in dual-battery wiring.

Unlike diode-based isolators, the Cyrix-ct introduces no voltage drop between alternator and batteries, so batteries receive full charge voltage. That matters for AGM and lithium batteries, which need accurate charge voltages to reach full capacity. The ct designation refers to a common positive terminal arrangement, which fits most standard dual-battery wiring layouts.

A load detection algorithm adds a short delay before connecting if a sudden load causes a voltage rise that could resemble a charging event, reducing false triggering in real installations.

Applications

Used in motorhome and campervan dual-battery systems to keep the starter battery isolated from the leisure bank, in marine installations sharing charge between engine start and house banks, in off-grid and 4x4 expedition builds, in commercial vehicle auxiliary power systems, and in solar off-grid setups pairing a starter battery with a house bank charged by a solar controller.

Installation notes

Fit by a competent electrician or auto-electrical engineer familiar with dual-battery systems. Both battery connections need correct fusing before installation, and cable sizing must suit the 230A continuous rating. The unit is not suitable for 48V systems. For lithium batteries, check that the Cyrix-ct charge voltage thresholds match the battery management system before wiring it in.

What's in the box

• 1 x Victron Cyrix-ct 12/24V 230A intelligent battery combiner