Victron Cyrix-Li-ct 12/24V-120A Battery Combiner
 Victron Cyrix-Li-ct 12/24V-120A Battery Combiner
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Victron Cyrix-Li-ct 12/24V-120A Battery Combiner


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Victron Cyrix Li-ct Battery Combiner 12/24V-120A

The functionality of the Cyrix-Li-ct is analogous to the Cyrix-ct. The Cyrix-Li-ct will parallel connect a lead acid starter battery and a LiFePO4 battery:

  • if the Charge Disconnect output of the VE.Bus BMS is high, and
  • if it senses 13.4V (resp. 26.8V) or more on one of its power terminals.

The Cyrix will disengage immediately:

  • when its control output becomes free floating, signalling cell over voltage or cell over temperature, and/or
  • when battery voltage drops below 13.2V.

Start assist function: a short positive pulse will close the relay for 30 seconds. A built-in transient voltage suppressor will limit the voltage spike that may occur when the Cyrix suddenly disengages due to cell overvoltage or over-temperature.

The LiFePO4 Battery: Preventing cell under voltage, over voltage and over temperature

The first line of protection is cell balancing. All Victron LiFePO4 batteries have integrated cell balancing. The second line of protection consists of:

  • shut down of the load in case of imminent cell under voltage, and
  • shut down or reduction of the charging current in case of imminent cell over voltage, high temperature (>50°C) or low temperature (<0°C).

The VE.Bus BMS is the core of the second protection line. However, not all loads or chargers can be controlled directly by the VE.Bus BMS. In order to shut down such loads or chargers several VE.Bus BMS controllable Cyrix switches are available.

Some battery combiners (also called voltage controlled relay, or split charge relay) will disconnect a battery in case of a short but high amperage load. A battery combiner also may fail to connect a large but discharged battery bank because the DC voltage immediately drops below the disengage value once the batteries are connected. The software of the Cyrix-ct 12/24 does more than simply connect and disconnect based on battery voltage and with a fixed time delay. The Cyrix-ct 12/24 looks at the general trend (voltage increasing or decreasing) and reverses a previous action only if the trend has reversed during a certain period of time. The time delay depends on the voltage deviation from the trend. (For battery Combiners with multiple engage/disengage profiles, please see the Cyrix-i 400).

More Product Features:

Protection Against Overheating:

The Cyrix will disengage in case of excessive contact temperature, and reengage again after it has cooled down.

LED Status Indication (Cyrix 12/24 230 only):

  • LED on: engaged
  • LED 10 s flash: disengaged
  • LED 2 s flash: connecting
  • LED 2 s blink: disconnecting
  • LED 0.25 s blink: alarm (over temperature; voltage > 16 V; both batteries < 10 V; one battery < 2 V) (multiply by two for 24 V)

12/24 V Auto Ranging:

The Cyrix-ct 12/24 automatically detects system voltage.

No Voltage Loss:

Cyrix battery combiners are an excellent replacement for diode isolators. The main feature is that there is virtually no voltage loss so the output voltage of alternators or battery chargers does not need to be increased.

Prioritising the Starter Battery:

In a typical setup, the alternator is directly connected to the starter battery. The accessory battery, and possibly also a bow thruster and other batteries are each connected to the starter battery with Cyrix battery combiners. When a Cyrix senses that the starter battery has reached the connect voltage it will engage, to allow for parallel charging of the other batteries.

Bidirectional Voltage Sensing and Power Supply from Both Batteries:

The Cyrix senses the voltage of both connected batteries. It will therefore also engage if for example the accessory battery is being charged by a battery charger. The Cyrix-ct 12/24 has a dual power supply. It will therefore also close if the voltage on one battery is too low to operate the Cyrix. In order to prevent unexpected operation during installation or when one battery has been disconnected, the Cyrix-ct 12/24 will not close if the voltage on one of the two battery connections is lower than 2 V (12 V battery) or 4 V (24 V battery).

Parallel Connection in Case of Emergency (Start Assist):

The Cyrix can also be engaged with a push button (Cyrix remains engaged for 30 seconds) or a switch to connect batteries in parallel manually. This is especially useful in case of emergency when the starter battery is discharged or damaged.

More about Victron:

Victron Energy has a strong, unrivalled reputation for technical innovation, reliability, and build quality. Their products are widely considered to be a professional choice for independent electric power. Efficiently combining two or more distinct power sources is what they do best. Their products include sinewave inverters, sinewave inverters/chargers, battery chargers, DC/DC converters, transfer switches, battery monitors and more.

Continuous current and breaking capacity at 12V or 24V


Breaking capacity at 48V

n. a.

Control input

The Cyrix engages when the control input is high (appr. Battery voltage) The Cyrix disengages when the control input is left free floating or pulled low

Connect voltage

13.4V < V < 13.7V: 120 s,    13.7V < V < 13.9V: 30 s,    V > 13.9V: 4 s

Disconnect voltage

13.3V < V < 13.2V: 10 s,    V < 13.2V: Immediate

Current consumption when open

<4 mA

Protection category
46 x 46 x 80mm


Please see more details in the 'Data Sheets' tab.


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