Electrical contact resistance

Example

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Use in Lemonergy

Make series/parallel architecture explicit.

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Bolted busbar joint

A busbar connection clamped by a bolt or stud rather than welded, so it can be undone for service. Its resistance depends on keeping the clamping force, which aluminium creep and thermal cycling relax, so designs use conical spring washers, a specified torque and torque marking. A loose joint heats up and is a classic cause of pack hot spots.

Busbar

A rigid copper or aluminium conductor that joins cell terminals into series and parallel groups, and modules into the pack. Its cross-section is sized for current and heating, and its joints — welded or bolted — are a classic source of resistance and failure.

Internal resistance

The resistance a cell presents to current, from its foils, electrolyte, interfaces and the reactions themselves. It converts part of the delivered energy into heat, sets the voltage drop under load, and rises as the cell ages; a large automotive cell has about a milliohm, a small cylindrical cell tens.

Kelvin sensing

Measuring voltage through a separate pair of leads that carry no current, so the drop along current-carrying wires and joints is left out. In a BMS, 100 mA of balancing current through 0.5 Ω of sense wire would add a 50 mV error, so designs either give balancing its own leads or pause balancing while measuring.

Ohm’s law

Voltage across a resistance equals current times that resistance. Applied to a cell it predicts the voltage drop under load from the internal resistance, which is the first-order reason terminal voltage sags.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. Extended Kalman filtering for battery management systems of LiPB-based HEV battery packs: Part 2. Modeling and identification

   Gregory L. Plett · Journal of Power Sources · 2004

   Topic background · Battery charge balance, open-circuit voltage, ohmic loss, polarization dynamics and model identification; parameters require cell-specific data.

2. Getting Started with the BQ76925

   Texas Instruments · 2019

   Topic background · A concrete BMS analog front-end example: cell voltage, current, temperature measurement and MCU integration.