Victron Energy smallBMS with Pre-Alarm

1. General Description

A simple and low cost alternative to the VE.Bus BMS. The smallBMS can replace the VE.Bus BMS in several applications. It is however not suitable for use with VE.Bus MultiPlus and Quattro inverter/chargers as it has no VE.Bus interface. The smallBMS is intended for use with Victron Smart LiFePo4 batteries with M8 circular connectors. The smallBMS has three outputs, similar to the VE.Bus.BMS.

Load Disconnect output

The Load output is normally high and becomes free floating in case of imminent cell under voltage (default 2.8V/cell, adjustable between 2.6V and 2.8V per cell). Maximum current: 1A. The Load output is not short-circuit protected. The Load output can be used to control: A high current relay or contactor; or the remote on/off input of a BatteryProtect, inverter, or DC-DC converter or other loads (a non-inverting or inverting on/off cable may be required).

Pre-alarm output

The pre-alarm output is normally free floating and becomes high in case of imminent cell under voltage (default 3.1V/cell, adjustable between 2.85V and 3.15V per cell). Maximum current: 1A (not short circuit protected). The minimum delay between pre-alarm and load disconnect is 30 seconds.

Charge disconnect output

The Charger output is normally high and becomes free floating in case of imminent cell over voltage or over temperature. Maximum current: 10mA. The Charger output is not suitable to power an inductive load such as a relay coil. The Charger output can be used to control: The remote on/off of a charger; a Cyrix-Li-Charge relay; or a Cyrix-Li-ct Battery Combiner.

System on/off input

The system on/off input controls both outputs. When off, both outputs will be free floating so that loads and chargers are turned off. The system 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.

LED indicators

• Load ON (blue): Load output high (cell voltage > 2.8V, adjustable on the battery).
• Temp or OVP (red): Charger output free floating (due to cell over temperature (>50°C), cell under temperature (<5°C) or cell over voltage).

2. Safety Instructions

Installation must strictly follow national safety regulations regarding enclosure, installation, creepage, clearance, casualty, markings, and segregation requirements of the end-use application. Installation must be performed by qualified and trained installers only. Switch off the system and check for hazardous voltages before altering any connection.

1. Do not open the Lithium Ion Battery.
2. Do not discharge a new Lithium Ion Battery before it has been fully charged first.
3. Charge only within the specified limits.
4. Do not mount the Lithium Ion Battery upside down.
5. Check if the Li-Ion battery has been damaged during transport.

3. Things to Consider

3.1 Important Warning

Li-ion batteries are expensive and can be damaged due to over discharge or over charge. Damage due to over discharge can occur if small loads (such as alarm systems, relays, standby current of certain loads, back current drain of battery chargers or charge regulators) slowly discharge the battery when the system is not in use. In case of any doubt about possible residual current draw, isolate the battery by opening the battery switch, pulling the battery fuse(s), or disconnecting the battery plus when the system is not in use.

A residual discharge current is especially dangerous if the system has been discharged completely and a low cell voltage shutdown has occurred. After shutdown due to low cell voltage, a capacity reserve of approximately 1Ah per 100Ah battery capacity is left in the battery. The battery will be damaged if the remaining capacity reserve is drawn from the battery. A residual current of 10mA for example may damage a 200Ah battery if the system is left in discharged state during more than 8 days.

3.3 DC loads with remote on/off terminals

DC loads must be switched off or disconnected in case of imminent cell under voltage. The Load Disconnect output of the VE.Bus BMS can be used for this purpose. The Load Disconnect is normally high (equal to battery voltage) and becomes free floating (= open circuit) in case of imminent cell under voltage (no internal pull down to limit residual current consumption in case of low cell voltage). DC loads with a remote on-off terminal that switches the load on when the terminal is pulled high (to battery plus) and switches it off when the terminal is left free floating can be controlled directly with the Load Disconnect output. See appendix for a list of Victron products with this behavior. For DC loads with a remote on/off terminal that switches the load on when the terminal is pulled low (to battery minus) and switches it off when the terminal is left free floating, the Inverting remote on-off cable can be used. See appendix.

Note: check the residual current of the load when in off state. After low cell voltage shutdown, a capacity reserve of approximately 1Ah per 100Ah battery capacity is left in the battery. A residual current of 10mA, for example, may damage a 200Ah battery if the system is left in discharged state during more than 8 days.

3.4 DC load: disconnecting the load with a BatteryProtect

A BatteryProtect will disconnect the load when: input voltage (= battery voltage) has decreased below a preset value, or when the remote on/off terminal is pulled low. The smallBMS can be used to control the remote on/off terminal.

3.5 Charging the LiFePO4 battery with a battery charger

Battery charging must be reduced or stopped in case of imminent cell over voltage or over temperature. The Charge Disconnect output of the VE.Bus BMS can be used for this purpose. The Charge Disconnect is normally high (equal to battery voltage) and switches to open circuit state in case of imminent cell over voltage. Battery chargers with a remote on-off terminal that activates the charger when the terminal is pulled high (to battery plus) and deactivates when the terminal is left free floating can be controlled directly with the Charge Disconnect output. See appendix for a list of Victron products with this behavior. Battery chargers with a remote terminal that activates the charger when the terminal is pulled low (to battery minus) and deactivates when the terminal is left free floating, the Inverting remote on-off cable can be used. See appendix. Alternatively, a Cyrix-Li-Charge can be used: The Cyrix-Li-Charge is a unidirectional combiner that inserts in between a battery charger and the LiFePO4 battery. It will engage only when charge voltage from a battery charger is present on its charge-side terminal. A control terminal connects to the Charge Disconnect of the BMS.

3.6 Charging the LiFePO4 battery with an alternator

See figure 6. The Cyrix-Li-ct is recommended for this application. The microprocessor controlled Cyrix-Li-ct includes a timer and voltage trend detection. This will prevent frequent switching due to a system voltage drop when connecting to a discharged battery.

3.7 Battery

In case of several batteries in parallel and/or series configuration, the two M8 circular connector cord sets of each battery should be connected in series (daisy chained). Connect the two remaining cords to the BMS.

4. System Examples

Figure 1: Application example for a DC off-grid system, with on/off switch between L and battery negative

This diagram illustrates a DC off-grid system setup. It shows a smallBMS connected to a lithium battery. A BatteryProtect is included, along with DC loads. An on/off switch is connected between the 'L' terminal of the smallBMS and the battery's negative terminal. The system also features an MPPT charge controller and solar panels.

Figure 2: Application example for a vehicle or boat, with on/off switch between L and battery negative

This diagram depicts an application for a vehicle or boat. It shows a smallBMS connected to a lithium battery. Components include a BatteryProtect, DC loads, an alternator/battery charger, and a DC buzzer. An on/off switch is wired between the 'L' terminal of the smallBMS and the battery's negative terminal. The setup also incorporates an MPPT charge controller, solar panels, and a BMV712 smart monitor.

Figure 3: Application example for a vehicle or boat, with on/off switch between H and L

This diagram illustrates an application for a vehicle or boat. It features a smallBMS connected to a 24V lithium battery bank. The system includes an MPPT charge controller, solar panels, a BMV712 smart monitor, and a Phoenix Inverter. An on/off switch is shown connected between the 'H' and 'L' terminals of the smallBMS.

Figure 4: Solar application with two MPPT 150/85 CAN-bus

This diagram shows a solar application utilizing two MPPT 150/85 CAN-bus units. It includes a Color Control GX, a Phoenix Inverter, a BMV Battery monitor, and a 48V Lithium battery bank, all managed by a smallBMS. The diagram highlights that the MPPT 150/85 CAN-bus has a remote on/off port that can be controlled directly by the VE.Bus BMS.

5. Specifications

Appendix

1. Loads which can be controlled directly by the Load Disconnect output of the BMS

Inverters: All Phoenix inverters VE.Direct. Connect to the left hand terminal of the 2 pole connector for Phoenix 12/800; 24/800; 48/800. Connect to the right hand terminal of the 2 pole connector for Phoenix 12/1200; 24/1200; 48/1200.

DC-DC converters: All Tr type DC-DC converters with remote on/off connector, and Orion 12/24-20; 24/12-25; 24/12-40; 24/12-70. Connect to terminal H of the 2 pole connector.

BatteryProtect and Smart BatteryProtect: Connect to the right hand terminal respectively to terminal H of the 2 pole connector.

Cyrix -Li-Load: Connect to the control input.

2. Loads for which an inverting remote on-off cable is needed (article number ASS030550100)

Phoenix 12/180; 24/180; 12/.250; 24/350. All Phoenix VE.Bus inverters rated at 3kVA and more (see fig 4).

3. Solar charge controllers which can be controlled directly by the Charge Disconnect output

BlueSolar MPPT 150/70 and 150/80 CAN-bus: Connect to the left hand terminal of the 2 pole connector (B+).

SmartSolar MPPT 150/45 and higher, Smart Solar MPPT 250/60 and higher: Connect to the right hand terminal (marked + or H) of the 2 pole connector.

4. Solar charge controllers for which a VE.Direct non inverting remote on-off cable is needed (article number ASS030550310)

All BlueSolar models, except the two CAN-bus models BlueSolar MPPT 150/70 and 150/80 CAN-bus. SmartSolar MPPT up to 150/35.

5. Battery Chargers

For Skylla TG battery chargers, a non-inverting remote on-off cable is needed (article number ASS030550200).

For Skylla-i battery chargers, a Skylla-i remote on-off cable is needed (article number ASS030550400).

Other battery chargers: Use a Cyrix-Li-Charge.