Battery knowledge · Modules, packs and battery management
Electrical contact resistance
The extra resistance where two conductors touch, because current passes only through microscopic contact spots and any oxide film on them. It falls with contact force and good plating and rises with corrosion and fretting. At 300 A a joint of 50 µΩ dissipates 4.5 W, enough to overheat a poorly cooled connection.
- Also called
- contact resistance, joint resistance, constriction resistance
- Unit
- Ω
- Relationship
- P = I²·R_contact
Example
Find heating at a joint
An illustrative 0.5 mΩ joint carrying 100 A dissipates 5 W. Even a small contact resistance matters at high current; its actual temperature rise depends on the local thermal path.
Explore the graph
Double the current and ohmic heating increases fourfold.
At 5 A: 0.5 W. At 10 A: 2 W.
P_heat = I²R
Illustrative model. Resistance is constant; reversible entropic heat and other losses are excluded.
Use in Lemonergy
Lemonergy Studio blocks
Cell contact residual monitor worked example
Filters cell/group voltage residuals against their median and qualifies persistent differences. Residuals are not a unique contact-fault diagnosis.
Blocks to use
- Cell contact residual monitor
Forms measured-minus-predicted voltage residuals, subtracts their channel median, filters the differences and qualifies consecutive threshold crossings when current is large enough.
Inputs & settings
- Use the parameter values in the block reference.
- Bundled example verified on the production release of 28 October 2026.
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Review the block inputs, units and model limits.
- Open the Studio example and run its bundled model.
- Compare the output channels with the numerical checks; change one input and run again.
Example. Use the defaults below with Measured cell/group voltages = [3.64, 3.66, 3.66] V, Predicted healthy voltages = [3.66, 3.66, 3.66] V, Signed current = 2 A, Enable = 1 true / false. At 0 s, Filtered differential residual is [0, 0, 0] V. Additional checks are listed below.
Observe. Inspect the outputs and numerical checks on the block reference page.
Requires at least three channels. Contact loss, parameter mismatch and sensor bias can produce the same symptom; this is not a unique fault diagnosis. The example verifies numerical behavior for synthetic parameters. Cell characterization and validation for an intended use are separate tasks.
Open Studio example →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.
- 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.
- 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.