Basic concepts

For Battery Management Systems

back to top Cell sensing methods comparison: wired vs. distributed

Wired Distributed
Description N+1 tap wires are connected to N cells. A cell board is mounted on each cell.
General
  • Simple to understand: one box, wires.
  • Few electronic assemblies
  • Lots of wires
  • Safer: no high voltage wires in battery
  • Few cables
  • Lots of electronics
Costs
  • Total initial BMS cost is similar
    • Cheaper electronics: fewer assemblies
    • More expensive wiring: lots of wires
    • Cost of thermistors, beyond just a couple, escalates rapidly
    • If there's a connector on the tap voltage wires, labor cost is high
  • Total repair cost is similar
    • Parts cost is higher: entire BMS is replaced
    • Labor cost is lower: BMS is easy to access
  • Total initial BMS cost is similar
    • More expensive electronics: more assemblies
    • Cheaper wiring: few cables
    • No additional cost for temperature measurement
    • If there's a connector on the cables, labor cost is low
  • Total repair cost is similar
    • Parts cost is lower: single cell board or module is replaced
    • Labor cost is higher: access to cell boards is harder
Measurement accuracy
  • Inherently more immune to AC noise: filters in slave
  • DC errors: current in tap wires, resistance of bus bars
  • Inherently more immune to DC errors: voltage is measured directly, at both cell terminals
  • Careful design required for AC noise immunity
Temperature measurement
  • Limited temperature information: few thermistors
  • Complete temperature information: one thermistor per cell
Volume, weight
  • Larger master
  • Space required for lots of wires
  • Practically no space required for voltage tap terminals
  • Smaller master
  • Little space required for few cables
  • Little space required for cell boards
Reliability
  • Reverse or peak cell voltage beyond a certain duration will damage entire slave
  • Open connection within a bank will damage entire slave (no damage if open is between banks)
  • Inherently ESD proof
  • If there's a connector on the tap voltage wires, lots of terminations may result in more failures
  • Cell voltage tap wires may be exposed to some mechanical stress during installation; vibration during use not an issue
  • Sealed slave is environmentally water-proof; connectors are not
  • Reverse or peak cell voltage, even of short duration, will damage only one cell board
  • Open connection within a bank will damage only one cell board (no damage if open is between banks)
  • Some ESD sensitivity
  • If there's a connector on the cables, few terminations may result in fewer failures
  • Cell boards may be exposed to some mechanical stress during installation, vibration during use
  • Sealed cell boards and slaves are environmentally water-proof; connectors are not

 

 

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Cell sensing
 
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