Skip to end of metadata
Go to start of metadata

You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 7 Next »

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

  • Carrier should provide isolated power to the AFEs, ideally at a voltage already equal to one of the required rails to minimize external components. 5V is much easier to provide than 51V, and can be done with something like this J0505N-1WR3.

    • This is to satisfy regulations section 8.6.A.4 requiring that no loads be connected to the main pack before the primary fuse and relays. Currently the AFEs are being powered off the voltage taps from the main pack. While we have done this in the past and have not been called out for it, we wish to avoid complications at scrutineering.

    • Given that there are 4 outputs, we can probably get rid of the iso 3V3 regulator that is currently for the current sense interface too and drop down the 5 to 3v3 for that with an LDO or buck

  • Should add voltage monitoring for the aux battery

    • Passive protection for the aux battery is required to be in the battery enclosure as per regs section 8.4. This is a dumb rule but the fix is low effort so we will make the change.

 Old

  • Replace inrush current limiting (ICL) circuit with the one on UV cutoff.

    • Simpler, cheaper

  • Reduce number of fans?

  • High voltage interlock loop?

    • Requires changes to all other HV boards (MCI, DC-DC, solar)

  • No labels