3. Installation

3.1. Important warning

Warning

Lithium batteries are expensive and can be damaged due to over-discharge or overcharge.

The shutdown by the BMS due to low cell voltage should always be used as a last resort to be safe at all times. We recommend not letting it get that far and instead either switching off the system automatically after a defined state of charge via the BMS discharge floor limit so that there is always sufficient reserve capacity in the battery or using the BMS remote on/off port as a system on/off switch.

Damage due to over-discharge can occur if small loads (such as alarm systems, relays, standby currents 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; for example, a residual current of just 10mA can damage a 200Ah battery if the system is left discharged for more than 8 days.

If a low cell voltage disconnect has occurred, immediate action (recharge the battery) is required.

3.2. Things to consider

3.2.1. Controlling DC loads via Load disconnect

To prevent deep discharge, DC loads must be switched off or disconnected when there is a risk of cell undervoltage. The Load disconnect output of the smallBMS NG can be used for this purpose.

The Load disconnect output is normally high (equal to battery voltage) and switches to a free-floating (open-circuit) state in case of imminent cell undervoltage.
DC loads with a remote on/off terminal that activates when pulled high (to battery plus) and deactivates when left free-floating can be controlled directly via the Load disconnect output. See [→Appendix A] for a list of Victron productswith 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, a Inverting remote on-off cable can be used. See Appendix A.

3.2.2. Controlling DC loads with a BatteryProtect

The smallBMS NG can control the remote on/off terminal of a BatteryProtect to manage load disconnection.

A BatteryProtect will disconnect the load when:

The input voltage (battery voltage) falls below a preset threshold (adjustable in BatteryProtect), or when
The remote on/off terminal is pulled low.

3.2.3. Controlling a battery charger via Charge disconnect

Battery chargers must interrupt charging in case of imminent cell overvoltage or low/high cell temperature. The Charge disconnect output of the smallBMS NG can be used for this purpose.

The Charge disconnect output is normally high (equal to battery voltage) and switches to an open-circuit state when cell overvoltage or temperature issues occur.
Chargers with a remote on/off terminal that activates when pulled high (to battery plus) and deactivates when left free-floating can be directly controlled by the Charge disconnect output. See Appendix A for a list of Victron products with this behavior.
Alternatively, a Cyrix-Li-Charge can be used. This unidirectional battery combiner sits between the charger and battery, engaging only when a charge voltage is detected. Its control terminal connects to the Charge disconnect outputof the smallBMS NG.

3.2.4. 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.
Be sure to read and follow the installation instructions in the Lithium NG battery manual.

3.3. System examples

3.3.1. smallBMS NG with SmartSolar Charger and a BatteryProtect for DC loads

The below system example shows a small DC off-grid system. The main components are:

The Charge disconnect output controls a SmartSolar Charger via a VE.Direct non-inverting remote on/off cable (not necessary with larger MPPTs with a remote on/off port). The solar charger will stop charging in the event of low/high temperature or cell overvoltage.

DC loads are controlled via a Smart BatteryProtect. Its remote H input connects to the Load disconnect output of the smallBMS NG. In the event of a low cell voltage, the Load disconnect output and, as a result, the remote H input of the Smart BatteryProtect becomes free-floating and disconnects the DC load to prevent further battery discharge.

A remote on/off switch wired between the battery positive busbar and the remote H input of the smallBMS NG can be used to switch DC loads and chargers off. Additionally, a main switch can be used to isolate the positive busbar from the battery.

3.3.2. smallBMS NG with Cyrix-Li-ct as a battery combiner

The below system example shows a small DC system in an RV or Boat. The main components are:

The Charge disconnect output of the smallBMS NG controls the BMS charge disconnect input of the Cyrix-Li-ct (pin 85). In the event of low/high temperature or cell overvoltage, the Cyrix-Li-ct will stop charging the lithium battery.

DC loads are controlled via a Smart BatteryProtect. Its remote H input connects to the Load disconnect output of the smallBMS NG. In the event of a low cell voltage, the Load disconnect output and, as a result, the remote H input of the Smart BatteryProtect becomes free-floating and disconnects the DC load to prevent further battery discharge.

A remote on/off switch wired between the battery positive busbar and the remote H input of the smallBMS NG can be used to switch DC loads and chargers off. Additionally, a Main switch can be used to isolate the positive busbar from the battery.

3.3.3. smallBMS NG with Inverter VE.Direct

The below system example shows a small DC system. for example, in a Camper. The main components are:

The Charge disconnect output of the smallBMS NG controls a SmartSolar Charger via a VE.Direct non-inverting remote on/off cable (not necessary with larger MPPTs with a remote on/off port). The solar charger will stop charging in the event of low/high temperature or cell overvoltage.

An Inverter VE.Direct 12/375 allows powering domestic equipment. Its remote H input connects to the Load disconnect output of the smallBMS NG. In the event of a low cell voltage, the Load disconnect output and, as a result, the remote H input of the inverter becomes free-floating and disconnects the inverter to prevent further battery discharge.