Victron smallBMS with pre-alarm

The Victron SmallBMS with Pre-Alarm (BMS400100000) is a compact, low-cost, all-in-one Battery Management System designed for use with Victron Lithium Battery Smart (LiFePO₄) batteries in 12V, 24V, and 48V systems. A simple and affordable alternative to the VE.Bus BMS V2, it provides the same core cell-level protection with three independent control outputs — Load Disconnect, Charge Disconnect, and Pre-Alarm — in a slim matt-black ABS enclosure that requires no configuration and occupies minimal installation space.

The SmallBMS monitors each connected Lithium Battery Smart cell via M8 BMS cables and automatically disconnects loads or chargers when cell voltage or temperature moves outside safe operating limits. The Load Disconnect output goes free floating in the event of imminent cell undervoltage, disabling inverters, DC-DC converters, and BatteryProtect units. The Charge Disconnect output goes free floating in the event of cell overvoltage or high/low cell temperature, disabling chargers and Cyrix combiners. The Pre-Alarm output goes high at least 30 seconds before a Load Disconnect event — providing advance warning via an external relay, buzzer, or LED to alert users before a full system shutdown occurs.

A Remote On/Off terminal allows the system operator to manually switch both outputs off simultaneously — disabling all connected loads and chargers — via a simple switch or contact closure. Both the Load Disconnect and Charge Disconnect outputs behave identically to those of the VE.Bus BMS V2, allowing the same remote on/off cables (non-inverting and inverting) to be used for compatible connected devices.

Important note: the SmallBMS does not include a VE.Bus interface and is therefore not compatible with Victron MultiPlus or Quattro inverter/chargers. For systems requiring VE.Bus integration, the VE.Bus BMS V2 is the correct product. The SmallBMS supports up to 20 Lithium Battery Smart batteries per system — up to 84 kWh at 12V and 102 kWh at 24V/48V.

Features

Load Disconnect Output — Prevents Battery Over-Discharge

The Load Disconnect output is normally high (Vbat – 0.1V) and becomes free floating in the event of imminent cell undervoltage — disabling inverters, DC-DC converters, BatteryProtect units, and other loads connected to the output. Maximum source current is 1A, capable of driving a high-current relay or contactor for higher-current load switching.

Pre-Alarm Output — 30-Second Advance Warning

The Pre-Alarm output is normally free floating and goes high (Vbat – 0.1V, max 1A) when cell undervoltage is imminent — triggering at least 30 seconds before the Load Disconnect output disables. This allows an external relay, DC buzzer, or LED to alert the user in time to take action before a full load disconnect occurs.

Charge Disconnect Output — Prevents Cell Overcharge and Temperature Damage

The Charge Disconnect output is normally high and goes free floating in the event of cell overvoltage or high/low cell temperature — disabling connected chargers, Cyrix-Li-Charge combiners, and Cyrix-Li-ct battery combiners to prevent damage to the lithium battery bank under adverse conditions.

Remote On/Off Terminal

Both Load and Charge Disconnect outputs can be manually controlled via the Remote On/Off terminal — supporting four wiring modes including switch to battery minus (Remote L) and switch to battery plus (Remote H) — for flexible manual system control in addition to automatic BMS protection.

Simple Alternative to VE.Bus BMS V2 — Without VE.Bus Interface

The SmallBMS replaces the VE.Bus BMS V2 in systems that do not include VE.Bus MultiPlus or Quattro inverter/chargers. It provides the same Load Disconnect, Charge Disconnect, and Pre-Alarm outputs at a lower cost and in a significantly more compact enclosure — making it ideal for smaller DC-only systems in RV, marine, and off-grid applications.

Supports Up to 20 Lithium Battery Smart Batteries

A maximum of 20 Victron Lithium Battery Smart batteries can be connected to a single SmallBMS in series, parallel, or series/parallel configurations — supporting system voltages of 12V, 24V, or 48V with a maximum energy storage of 84 kWh in a 12V system and up to 102 kWh in a 24V or 48V system.

Two LED Status Indicators

A blue LED confirms that the Load Disconnect output is high and cell voltage is above the undervoltage threshold. A red LED indicates that the Charge Disconnect output has gone free floating due to high/low cell temperature or cell overvoltage — providing clear at-a-glance BMS status without any app or display required.

Compact Matt-Black ABS Enclosure — IP20

The slim 106 × 42 × 23 mm matt-black ABS enclosure occupies minimal panel or cabinet space and is rated IP20 for indoor installation. Operating across a temperature range of −20°C to +50°C, it is suitable for battery compartments, electrical panels, and enclosures in marine, RV, and off-grid installations.

Specifications

Datasheets and Manuals

Datasheet

Product Manual