Victron energy VE.Bus BMS Manual page 4

3.2 AC Detector Li-ion software assistant for MultiPlus and Quattro (not needed for MultiPlus-II models)
The AC Detector is a small add-on that can be built in a MultiPlus or Quattro when used together with a LiFePO₄ battery and a
VE.Bus BMS. Every VE.Bus BMS is delivered with one AC Detector.
The purpose of the AC Detector is to restart the MultiPlus or Quattro when AC supply becomes available, in case it has been
switched off by the BMS due to low cell voltage.
Without the AC Detector the MultiPlus or Quattro would remain off and therefore would not start recharging the battery after shut
down due to low battery voltage.
The AC detector needs the Li-ion software assistant or the Self-consumption Hub-2 v3 assistant to operate as
intended.
Inverters (DC to AC only) with VE.Bus can be connected directly to the MultiPlus/Quattro input of the BMS, no AC Detector or
assistant needed.
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 in order 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: please 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 Battery Protect will disconnect the load when:
input voltage (= battery voltage) has decreased below a preset value, or when
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the remote on/off terminal is pulled low. The VE.Bus BMS can be used to control the remote on/off terminal
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Contrary to a Cyrix or contactor, a BatteryProtect can start a load with a large input capacitor such as an inverter or a
DC-DC converter.
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.
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