Victron smallBMS with Pre-Alarm: Setup & Wiring

Key Takeaways

• The smallBMS with pre-alarm provides cost-effective, solid-state battery management for Victron Lithium Battery Smart installations.
• Broad supply voltage range: Operating voltage (Vbat) 8 - 70Vdc.
• Requires branch power protection: Recommended fuse size 0.3A - 2.5A, dependent on devices connected to Load disconnect and pre-alarm output.
• Minimal quiescent battery drain: Current consumption, remote on 2.2mA (excluding Load and Charge disconnect output current).
• Ultra-low deep discharge standby: Current consumption, low cell voltage 1.2mA and Current consumption, remote off 1.2mA.
• Heavy-duty DC load control port: Load disconnect output Normally high (Vbat - 0.1V) Source current limit: 1A (not short circuit protected).
• Precision charger control port: Charge disconnect output Normally high (Vbat - 0.1V) Source current limit: 10mA (short circuit protected).
• Early warning alarm port: Pre-alarm output Normally free floating (low) In case of alarm: output voltage Vbat -0.1V Max output current: 1A (not short circuit protected).
• Broad environmental rating: Operating temperature range -20°C to +50°C (0 - 120°F).

Solid-State Safety Architecture & BTV Daisy-Chaining

The smallBMS interfaces with the internal cell balancing and temperature sensors of Victron Lithium Battery Smart modules. When any cell drops below voltage limits or temperature exceeds safe charging thresholds, the smallBMS commands external disconnect devices to protect the cells.

The Victron smallBMS with Pre-Alarm operates as a compact solid-state BMS controller across an 8 - 70Vdc operating window (Supply Fusing: 0.3A - 2.5A | Quiescent Current: 2.2mA Active / 1.2mA):

• Battery BTV Cables: Daisy-Chain In/Out, Cell Voltage Sense, Temperature Sense, Cell Imbalance Test.
• Control Outputs: Load Disc (1A), Chg Disc (10mA), Pre-Alarm (1A), Remote L / H Pins.
• Environmental: -20 to +50°C, IP20 Enclosure, Compact Size, Reliable HW.

Installation Rules & Control Wiring

1. Power Supply Wire: Connect battery positive to the smallBMS positive terminal with an inline fuse per Recommended fuse size 0.3A - 2.5A, dependent on devices connected to Load disconnect and pre-alarm output across the Operating voltage (Vbat) 8 - 70Vdc window.
2. BTV Sensor Loops: Connect the M8 3-pole cables from the Lithium Smart battery bank directly to the smallBMS BTV input connectors.
3. Low Standby Loss: Consumes negligible energy: Current consumption, remote on 2.2mA (excluding Load and Charge disconnect output current), reducing to Current consumption, low cell voltage 1.2mA and Current consumption, remote off 1.2mA.

Output Signalling & Pre-Alarm Logic

The smallBMS manages power flow through three distinct solid-state output terminals:

• Load Disconnect Port: The Load disconnect output Normally high (Vbat - 0.1V) Source current limit: 1A (not short circuit protected) directly drives the remote on/off pins of Smart BatteryProtect switches, power relay coils, or inverter remote terminals.
• Charge Disconnect Port: The Charge disconnect output Normally high (Vbat - 0.1V) Source current limit: 10mA (short circuit protected) drives the remote on/off terminals of solar MPPTs or AC chargers.
• Pre-Alarm Output: The Pre-alarm output Normally free floating (low) In case of alarm: output voltage Vbat -0.1V Max output current: 1A (not short circuit protected) activates approximately 0.1V before low-voltage disconnect, alerting operators before loads are cut.
• Thermal Capabilities: Designed for reliable performance across Operating temperature range -20°C to +50°C (0 - 120°F).

Technical Specifications & Control Port Summary