2. Introduction
2.1. General description
The smallBMS with pre-alarm is an all-in-one Battery Management System (BMS) for Victron Energy Lithium Battery Smart batteries. These batteries are Lithium Iron Phosphate (LiFePO4) batteries and are available in 12.8V or 25.6V in various capacities. They can be connected in series, parallel and series/parallel so that a battery bank can be built for system voltages of 12V, 24V or 48V. The maximum number of batteries in one system is 20, which results in a maximum energy storage of 84kWh in a 12V system and up to 102kWh in a 24V and 48V system.
To reduce required balancing time, we recommend to use as little different batteries in series as possible for the application. 24V systems are best built using 24V batteries. And 48V systems are best built using two 24V batteries in series. While the alternative, four 12V batteries in series, will work, it will require more periodic balancing time.
For more information on these batteries, visit the Lithium Smart Battery product page.
The smallBMS is a simple and inexpensive alternative to the VE.Bus BMS, but does not have a VE.Bus interface and is therefore not suitable for use with VE.Bus MultiPlus and Quattro inverter/chargers.
2.2. Features and functionality
Load Disconnect output
Can be used to control the remote on/off input of a BatteryProtect, Inverters, DC-DC converter or other loads that have remote on/off port functionality.
Normally the Load disconnect output is high and becomes free-floating when cell undervoltage is imminent (default 2.8V, adjustable in battery). Maximum output current: 1A (not short circuit protected).
Note that a non inverting or inverting on/off cable may be required, please consult Appendix A.
Charge disconnect output
The Charge disconnect output can be used to control the remote on/off port of a charger, such as the Phoenix Smart Charger IP43, a Cyrix-Li-Charge relay, a Cyrix-Li-ct Battery Combiner or a BatteryProtect. Note that the Charge disconnect output is not suitable to power an inductive load such as a relay coil.
The output is normally high and becomes free floating in case of imminent cell overvoltage or overtemperature. Maximum current: 10mA
Remote on/off terminal
Both the Load and Charge disconnect output can be controlled remotely via the remote on/off terminal. When off, both outputs will be free floating so that loads and chargers are turned off.
The remote on/off consists of two terminals: Remote L and Remote H. A remote on/off switch or relay contact can be connected between L and H. Alternatively, terminal H can be switched to battery plus, or terminal L can be switched to battery minus.
Note
Note that it is mandatory to install either an on/off switch between L and H of the remote on/off terminal or the wire loop (default) for correct operation. Alternatively, terminal H can be switched to battery plus or terminal L to battery minus.
Pre-alarm output
The pre-alarm output can be used to issue a visible or audible warning when the battery voltage is low and will trip with a minimum delay of 30 seconds before the Load disconnect output is disabled due to cell undervoltage.
Its output may be used to drive a relay, LED or Buzzer. Maximum current: 1A (not short circuit protected)
The pre-alarm output is normally free floating and becomes high in case of imminent cell under voltage (default 3,1V/cell, adjustable in battery).
LED indicators
Load ON (blue): Load disconnect output high (cell voltage >2.8V, adjustable in battery).
Temp or OVP (red): Charge disconnect output free floating (due to cell over temperature (>50°C), cell under temperature (<5°C) or cell over voltage).
2.3. What's in the box
smallBMS