REC Q BMS Wiring and Logic

This is our fifth version of the BMS Wiring and Logic design. It reflects our reroute of the Wakespeed 500 'Engine Run' signal through the Cerbo 'Relay1' to allow us to set a state of charge (SOC) range for alternator charging. We generally limit alternator charging to 95% SOC and below.

This schematic captures the full system upstream of the positive and negative bus. Greyed-out sections and connections represent design, but not fully implemented portions of the design.

Operation

System SECURED

With the Egis XD 500 switch open, all power is secured to the system with the exception of the REC Q BMS which derives power from its cell connections. This is mode is for long term storage and maintenance.

Manual ON

REC Q BMS is always powered, Internal relay is normally closed*. When the Blue Sea 2155 Remote Control Switch (RS) is closed (PIN 2 connected to PIN 3), Vbat is applied through the RS, through the internal relay, to REC PRE-CHARGE BMS+ Input. REC PRE-CHARGE Applies VBat via 66 ohm internal resistor to the load side of the Tyco EV200HAANA (Main Contactor) via System+ connection for a preset delay. After the preset delay, REC PRE-CHARGE energizes the Main Contactor control inputs causing it to close. After one second, application of power via System+ is removed and all power flows to the system via the Main Contactor.

Note, REC PRE-CHARGE manual states:

At system start up the REC Q BMS activates the charging procedure by powering the pre-charge unit. The pre-charge unit closes the power circuit through its internal relay (RELAY ON). The inrush current flows entirely through the precharge 66 Ω internal resistor. After set delay the transient current should be decrease to a safe value. The pre-charge energizes the contactor coil through open collector circuit and after 1 second opens the internal relay (RELAY OFF). All of the system current now passes through the contactor. Normal system operation is achieved.

Manual OFF

When the RS is opened, Vbat is removed from the REC PRE-CHARGE BMS+ input. The REC PRE-CHARGE will float its Contactor- output (it powers the Main Contactor coil via an open collector configuration) which deenergizes the Main Contactor coil and opens the Main Contactor.

Protective OFF

When the REC Q internal relay is opened, Vbat is removed from the REC PRE-CHARGE BMS+ input. The REC PRE-CHARGE will float its Contactor- output (it powers the Main Contactor coil via an open collector configuration) which deenergizes the Main Contactor coil and opens the Main Contactor.

The following events result in the REC Q Internal Relay opening:

• Cell Voltage High (cell over voltage switch-off + hysteresis
• Cell Voltage Low (cell under voltage protection switch-off + hysteresis)
• Cell Temp High (cell over temp switch-off + hysteresis)
• Number of cells or BMS address is not set properly
• Temperature sensor error (connection problem)
• Cell Short Circuit or BMS measurement error
• Main Relay is in short circuit
• Current measurement disabled or > 2x shunt max current
• Wrong Cell Chemistry Selected
• Cell balancing or measurement failure
• BMS internal communication failure

Note: The internal relay is NOT opened under Temperature Low (under temperature charging disable + hysteresis) conditions. As discussed below, we will use charger enable signal to provide secondary protection of low temperature charging under loss of CAN conditions.

Protections

Primary Over Voltage Protection

This is accomplished by CANBUS communication of the Charge Current Limit and Charge Voltage Limit from the BMS to the Wakespeed and the Victron Cerbo (that coordinates charging from the MPPT and Multiplus). From the Victron Cerbo manual:

If a CAN-bus BMS is connected and the BMS requests a maximum charge current that is different from the user-configurable setting, the lower of the two will be used.

From the REC-Q BMS manual:

When the highest cell reaches the End of charge CHAR voltage setting, charging current starts to ramp down to 1.1 A x Number of Inverter/Charger Devices SISN until the last cell rises near the End of Charge Voltage CHAR (CC/CV). At that point the Maximum charging voltage allowed is set to Number of cells x (End of Charge Voltage per cell CHAR– Maximum Cell Float Voltage Coefficient CFVC x End of charge hysteresis per cell). End of Charge SOC hysteresis SOCH and End of charge cell voltage hysteresis CHIS is set to prevent unwanted switching. SOC is calibrated to 100 % and Power LED lights ON 100 % Charge optocoupler is turned off.

Secondary Over Voltage Protection

This is accomplished by removal of CHARGE ENABLE signal by the BMS, which is provided separately to the Wakespeed, the MPPT, and the Multiplus and does not rely on CANBUS communication.

Tertiary Over Voltage Protection

This is accomplished by opening the Main Contactor by the BMS via its internal relay. It does not rely on any signals to any charge devices.

Primary Under Voltage Protection

This is accomplished by CANBUS communication between the BMS and the Victron Cerbo (that coordinates/inhibits discharging by the Multiplus). From the Victron Cerbo manual:

Multis and Quattros will shut down when the max discharge current is zero. They will automatically start again as soon as either AC mains returns or when the BMS increases the max discharge current again.

From the REC-Q BMS manual:

When the lowest cell open circuit voltage is discharged bellow the set threshold CLOW maximum discharging current starts to decrease down to 0.02 C (5 % of Capacity in A). After decreasing down, maximum allowed discharging current is set to 0 A. SOC is reset to 3 % and Discharging SOC hysteresis is set to 5 %.

Note:

• "max discharge current" == "discharge current limit" == "maximum allowed discharging current"
• CLOW == "cell under-voltage discharge protection"

For DC loads there is no Under Voltage Primary Protection. We will explore means to implement a cutoff for these later.

Secondary Under Voltage Protection

This is accomplished by opening the Main Contactor by the BMS via its internal relay. It does not rely on any signals to any load devices.

Primary Low Temperature Protection

This is accomplished by CANBUS communication between the BMS to the Wakespeed and the Victron Cerbo (that coordinates/inhibits charging from the MPPT and Multiplus). From the REC-Q BMS manual:

Charging current is limited to 30% of the maximum charging current, but more than 5 A near both ends of temperature (Max cell temperature TMAX and Min temperature for charging TMIN).

Secondary Low Temp Protection

This is accomplished by removal of CHARGE ENABLE signal by the BMS, which is provided separately to the Wakespeed, the MPPT, and the Multiplus and does not rely on CANBUS communication.

Tertiary Low Temperature Protection (Wakespeed Only)

The Wakespeed has its independent battery temperature sense that can be used to limit low temperature charging with programmable set points. Importantly, it will override any outside direction based on its own sensor. This signal does not rely on CANBUS communication or any signals from other components.

CANBUS Distribution

The REC BMS CANBUS output is connected to the Cerbo VE.CANBUS port 1. The Cerbo VE. CANBUS port 2 is connected to the Wakespeed CANBUS port 1. A 120 Ohm terminator is plugged into the Wakespeed CANBUS port 2. The other end of the CANBUS is terminated by the REC BMS.

The Wakespeed also includes a DUETCH connector terminated CANBUS connection as part of the Van Wiring Harness. We use this CANBUS connection to drive our Logging PI which can be used to record and decode CANBUS data.

CHARGE ENABLE Signal Distribution

The design for distributing the CHARGE ENABLE signal must account for the limits of the BMS hardware and charging source hardware related to this signal.

• The BMS CHARGE ENABLE Optocoupler has a collector-to-emitter voltage rating of 62.5V and a collector current rating of 15mA.
• The MPPT has a REMOTE ON-OFF 'H' and 'L' inputs. The 'L' input will source about 5V (and has a short circuit protection resistor). The 'L' input will sink about 80uA when the 'L' input is directly shorted to it.
• The Multplus has AUX '+' and '-' terminals. The '+' terminal is connected to an internal voltage sensor with an internal 5V source applied through a 10KOhm pullup resistor. The '-' terminal will thus sink about 500uA when the '+' terminal is directly shorted to it.
• The Wakespeed FEATURE-IN input will sink about 3mA when full VBatt is applied to it.

Based on these limits, we elected to use these ICStation 12V optocoupler boards.

These boards use an 817 optocoupler with maximum input-side LED current of 50mA and maximum output collector current and collector-emitter voltage of 50mA and 80V.

We apply VBatt to the CHARGE ENABLE input on the REC BMS. The CHARGE ENABLE output drives the four optocoupler boards in series. With the 1KOhm resistors in series with each input-side LED, placing three boards in series will limit the input-side LED current to ~9.6mA satisfying the limits of the 817 optocouplers and the BMS CHARGE ENABLE optocoupler.

The outputs are wired depending on the equipment each is driving but in all cases the limits of the 817 optocouplers and the charge equipment being driven are met.

This is our design for distributing the BMS CHARGE ENABLE signal to the charging sources.

The gritty details for the CHARGE ENABLE characteristics and settings are available by expanding the summaries below: