{ "node": { "id": "term:contact-resistance", "type": "Term", "label": "Electrical contact resistance", "properties": { "id": "contact-resistance", "name": "Electrical contact resistance", "aka": [ "contact resistance", "joint resistance", "constriction resistance" ], "section": "topic-pack", "definition": "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.", "formula": "P = I²·R_contact", "unit": "Ω", "related": [ "bolted-busbar-joint", "busbar", "internal-resistance", "ohms-law", "kelvin-sensing" ], "example": { "title": "Find heating at a joint", "text": "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." }, "url": "https://lemonergy.com/learn/glossary/contact-resistance/", "mentions": [] } }, "edges": [ { "id": "edge:4980", "source": "term:contact-resistance", "target": "topic:topic-pack", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:4981", "source": "term:contact-resistance", "target": "term:bolted-busbar-joint", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4982", "source": "term:contact-resistance", "target": "term:busbar", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4983", "source": "term:contact-resistance", "target": "term:internal-resistance", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4984", "source": "term:contact-resistance", "target": "term:ohms-law", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4985", "source": "term:contact-resistance", "target": "term:kelvin-sensing", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4986", "source": "term:contact-resistance", "target": "visual:heat", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-pack", "type": "Topic", "label": "Modules, packs and battery management", "properties": { "id": "topic-pack", "name": "Modules, packs and battery management", "lede": "From a single cell to a working battery system, and the electronics that keep it safe.", "context": "Make series/parallel architecture explicit.", "example": "Twelve 3.6 V, 5 Ah cells in 6s2p give 21.6 V, 10 Ah and 216 Wh nominally before other restrictions.", "lesson_url": "https://lemonergy.com/learn/fundamentals/cell-architecture/", "lesson_label": "Open cell architecture" } }, { "id": "term:bolted-busbar-joint", "type": "Term", "label": "Bolted busbar joint", "properties": { "id": "bolted-busbar-joint", "name": "Bolted busbar joint", "aka": [ "bolted joint", "screwed busbar connection" ], "section": "topic-pack", "definition": "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.", "related": [ "busbar", "contact-resistance", "terminal", "remanufacturing", "laser-welding" ], "url": "https://lemonergy.com/learn/glossary/bolted-busbar-joint/", "mentions": [] } }, { "id": "term:busbar", "type": "Term", "label": "Busbar", "properties": { "id": "busbar", "name": "Busbar", "section": "topic-pack", "definition": "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.", "related": [ "series-parallel", "terminal", "laser-welding", "internal-resistance", "wire-bonding" ], "url": "https://lemonergy.com/learn/glossary/busbar/", "mentions": [] } }, { "id": "term:internal-resistance", "type": "Term", "label": "Internal resistance", "properties": { "id": "internal-resistance", "name": "Internal resistance", "abbr": "IR", "aka": [ "DC resistance", "DCIR" ], "section": "topic-units", "definition": "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.", "unit": "mΩ", "related": [ "ohms-law", "ir-drop", "impedance-rise", "dcir", "area-specific-resistance", "resistance-capacity-product" ], "lesson": "fundamentals/battery-basics/#datasheet", "url": "https://lemonergy.com/learn/glossary/internal-resistance/", "mentions": [ "electrolyte", "cylindrical-cell" ] } }, { "id": "term:ohms-law", "type": "Term", "label": "Ohm’s law", "properties": { "id": "ohms-law", "name": "Ohm’s law", "section": "topic-units", "definition": "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.", "formula": "V = I × R", "related": [ "internal-resistance", "ir-drop", "ohm", "kirchhoffs-laws" ], "example": { "title": "Convert a resistance into a voltage drop", "text": "A 10 A current through a 20 mΩ resistance produces 0.2 V of voltage drop. Use 0.020 Ω in V = IR; inserting the number 20 without converting milliohms would be wrong." }, "url": "https://lemonergy.com/learn/glossary/ohms-law/", "mentions": [ "voltage" ] } }, { "id": "term:kelvin-sensing", "type": "Term", "label": "Kelvin sensing", "properties": { "id": "kelvin-sensing", "name": "Kelvin sensing", "aka": [ "four-wire sensing", "four-terminal sensing", "4-wire measurement", "separate sense and balancing leads" ], "section": "topic-data", "definition": "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.", "related": [ "voltage-sense", "cell-balancing", "current-sensor", "contact-resistance", "dcir", "thermoelectric-error" ], "url": "https://lemonergy.com/learn/glossary/kelvin-sensing/", "mentions": [ "bms" ] } }, { "id": "visual:heat", "type": "Visual", "label": "Current and resistive heating", "properties": { "title": "Current and resistive heating", "summary": "Double the current and ohmic heating increases fourfold.", "readout": "At 5 A: 0.5 W. At 10 A: 2 W.", "formula": "P_heat = I²R", "note": "Resistance is constant; reversible entropic heat and other losses are excluded.", "software": { "status": "reference", "label": "Reference concept", "body": "P = I²R is the ohmic contribution. The product Charge session can also use a lumped thermal model; the native Studio battery does not calculate temperature evolution.", "href": "https://design.lemonergy.com/" }, "html": "
Ohmic heating
Ohmic heatingCurrent magnitude (A) versus Heat rate (W). I²R. Interpretation follows the graphs.0025410615820Current magnitude (A)Heat rate (W)
I²R
" } } ] }