Purpose

BMS Carrier serves as the main logic board for the BMS. It contains interfaces to and controls the current sense and AFE boards, which sense current and monitor/balance cells. In addition, it controls the main relays and pack fans.

Interfaces

AFEs

The AFE interface uses isoSPI, a proprietary LT protocol built for their BMS ICs. The interface must provide isolation between every node, as each AFE is referenced to a different level within the pack and isolation must be maintained between high and low voltage systems for safety. To leverage existing hardware and firmware, MSXV will continue to use isoSPI to interface with the LTC6811.

Current Sense

An isolated I2C interface allows for communication to current sense, while maintaining isolation between high and low voltage systems. An octopolar provides isolation for the incoming “alert” signal from current sense.

Relays

Carrier has individual control over the relays which comprise the main power switch, which are pack neg, pack pos, and solar relay.

Control

Each relay is individually controlled with a low side nfet. This is to allow The relays limit their back EMF to 0, eliminating the need for flyback diodes.

Kill Switch

The sources of the fets for each relay are tied together to the drain of a 4th nfet, controller by the kill switch to provide overriding control over the energizing of the relays.

Fans

Four-wire Noctua PC fans are used for battery cooling. Details of PWM and tachometer operation can be found in Noctua’s whitepaper Noctua_PWM_specifications_white_paper.pdf.

Change Log

Revision 2