• StandardProducts
• Lithiumate
• Service
• Troubleshooting
• Banks
• Missing
• Noise

In the presence of electrical noise, some cells or banks stop reporting

There are two approaches to handle noise susceptibility:

• Reduce the level of noise at the source
• Reduce the sensitivity to the noise

It is beyond the scope of this troubleshooting guide to deal with noise reduction at the source. Instead, we will focus of how to minimize the effect of noise on the BMS.

Typical ways in which noise disturbs the BMS are:

• Communication harness shielding
  • The communication harness between the BMS controller and the banks is not shielded
    • Both section of the harness must be shielded: the one to the negative end cell board, and the one to the positive end cell board
    • At most 1 inch (2.5 cm) of wire can be unshielded at the ends of the communication harness
  • The communication harness' shield is not connected
    • The shield must be connected only in one spot: at the 5-pin connector on the BMS controller
  • The communication harness' shield is connected in more than one place
    • The shield must not be connected to chassis or to other shields
• Noise coupling
  • Inductive coupling: communication wire routing
    • The area enclosed by the communication wire, the B+ wire (red wire in prismatic cell boards) and the power conductor (bus bar, power wire) forms a loop antenna, that picks-up electrical noise
      • Minimize that area by running the communication wire as close as possible to the B+ wire, and the power conductor, to the next cell board
      • Make the power conductor as short as possible: a short bus bar is ideal, a power cable that is more than a few inches in length is totally not appropriate
        • If you cannot make the power conductor short, split the bank into 2 banks at that point
      • Secure the communication wire to the B+ wire and the power conductor, but don't twist them around each other
  • Capacitive coupling
    • Electrically, the battery may be "shaken up and down" by the source or the load, at a frequency of 5 to 50 kHz, and a level that can be as high as 100s of volts
    • As long as the cell boards are allowed to "jump up and down" together with the cells, they are fine
    • Any capacity between a cell board and ground will keep the cell boards from "jumping up and down" together with the cells
    • The idea is to maximize the capacity between the cell board and the cell, and minimize the capacity between the cell board and the chassis ground
    • All that is true not only for the cell board, but also for the communication wire between cell boards
      • A metal case surrounding the battery
        • Face the cell boards so that its components face the cells, and its ground plane side face the metal case
        • Cover a cell board with metal shielding that is electrically connected to the B- of the cell it (make sure it doesn't make electrical contact with the cell board)
        • Use shielded cable in place of the communication wire, with the shielded connected only in one place: the B- pad of the more positive cell board
      • Low voltage wiring routed next to the cell boards (such as the communication harness)
        • Reroute the wiring so that it's away from the cell boards