A flexible aluminium busbar is a high-current conductor built from many thin aluminium foils or fine wires, with solid contact ends and a flexible middle. It carries hundreds to thousands of amperes while absorbing vibration, thermal expansion and assembly misalignment that would crack a rigid bar. This guide covers the main constructions, conductor alloys, sizing, joints, insulation and installation, so you can specify the right design for EV packs, energy storage, inverters, transformers and switchgear.
Rigid busbars are efficient conductors but they transmit every movement straight into the terminals they connect. Battery modules swell and shrink as they charge, transformers hum, vehicles vibrate and long bus runs expand with temperature. A flexible section between two rigid points takes up that movement, so bolted joints and welded terminals stay unstressed.
Aluminium is well suited to flexible conductors. Its density is about 2.70 g/cm³ against roughly 8.9 g/cm³ for copper, so an aluminium conductor of equal resistance weighs about half as much as the copper one even though it is larger in section. In battery systems where cells have aluminium terminals, an aluminium connector also avoids an aluminium-copper interface and the galvanic and intermetallic problems that come with it.
The trade-off is conductivity: high-purity aluminium reaches about 61 – 62 % IACS, so the cross-section must be larger than a copper part for the same current. Good design also has to deal with the hard, insulating oxide film on aluminium at every contact face. Both are routine engineering problems with well-proven solutions, covered later in this guide.
Ten to fifty thin aluminium foils, typically 0.10 or 0.20 mm each, are stacked and their ends fused into solid contact pads by press (diffusion) welding, ultrasonic welding or laser welding. The free foils in between slide over each other and bend easily. This is the most common type for EV and battery-storage connections because it is compact and carries high current in a low height.
Fine aluminium wires are braided into a flat or round strap and the ends are crimped or welded into terminals. Braids flex in every direction and tolerate continuous vibration better than laminates, but they occupy more volume for the same conductive area.
A short laminated section is welded into a solid aluminium bar or terminal. The rigid part sets the routing and the bolting interface; the flexible part sits only where movement must be absorbed. Used in longer runs between transformers, switchgear and busduct.
Any of the above with heat-shrink sleeving or a dipped PVC coating on the flexible zone, leaving only the contact pads bare. Needed where clearances are small or live parts may be touched.
Wide laminations (100 – 200 mm) of thicker strip, often around 1 mm per layer, used as expansion links in heavy busbar systems and rectifier connections carrying thousands of amperes.
Laminates pre-bent into offset, S, U or V shapes so they fit between terminals at different heights and still allow movement in the planned direction.
Flexible conductors use the purest commercial aluminium grades because conductivity falls quickly with alloying additions. Foils and wires are supplied in the annealed (O) temper for maximum flexibility; terminals and rigid sections can use stronger tempers or a heat-treatable conductor alloy.
| Alloy | Aluminium content | Typical conductivity | Best use in a flexible busbar |
|---|---|---|---|
| 1350 (EC grade) | ≥ 99.50 % | about 61 – 62 % IACS | Electrical conductor grade with controlled impurities; foil, strip and wire for laminates and braids |
| 1070 | ≥ 99.70 % | about 62 % IACS | High-conductivity laminated foil and battery connectors |
| 1060 | ≥ 99.60 % | about 61 – 62 % IACS | Widely available foil for multilayer laminates |
| 1050 | ≥ 99.50 % | about 61 % IACS | General flexible conductors and braided wire |
| 1200 / 1100 | ≥ 99.00 % | about 57 – 59 % IACS | Lower-cost strip and wire where conductivity is less critical |
| 6101 | Al-Mg-Si conductor alloy | about 55 – 59.5 % IACS by temper | Rigid sections and terminals that need more strength than 1xxx |
| 5154 | Al-Mg (about 3.1 – 3.9 % Mg) | about 32 % IACS | Braided straps where strength and fatigue life matter more than conductivity |
Conductivity values are typical published figures for annealed or standard conductor tempers; the certificate for each lot reports measured values where conductivity is specified. 6101 minimum conductivity depends on temper per ASTM B317.
Final values come from current, movement and space requirements on your drawing.
| Property (annealed, approximate) | Aluminium 1350 | Copper (for comparison) |
|---|---|---|
| Density | 2.70 g/cm³ | 8.89 – 8.96 g/cm³ |
| Conductivity | about 61 – 62 % IACS | about 100 % IACS |
| Resistivity at 20 °C | about 0.0280 – 0.0283 Ω·mm²/m | 0.01724 Ω·mm²/m |
| Area for equal resistance | about 1.6 × | 1 × |
| Mass for equal resistance | about 0.5 × | 1 × |
| Thermal expansion | about 23 µm/m·K | about 17 µm/m·K |
Most field failures of aluminium conductors start at the joint, not in the conductor. Aluminium forms a thin, hard oxide film within moments of exposure to air, and it creeps under sustained bolt pressure more than copper. Both are managed with established practice.
Press-welding or ultrasonic welding fuses all foils into a solid block, so current passes through metal rather than across many foil-to-foil contacts. Weld quality is verified by peel or cross-section tests and resistance measurement.
Contact faces should be flat and freshly cleaned or plated just before assembly. A contact compound helps keep oxygen and moisture out of bare aluminium joints.
Tin plating gives a stable, low-resistance contact surface and is the usual choice when mating to copper. Nickel resists higher temperatures and abrasion; silver offers the lowest contact resistance.
Use the torque the terminal and fastener allow, with spring (Belleville) washers or wide flat washers to maintain pressure as aluminium relaxes. Avoid over-tightening thin pads.
Do not bolt bare aluminium directly to bare copper in damp conditions. Use tin plating on one or both faces, or an aluminium-copper bimetal transition piece.
Measure temperature rise or joint resistance after start-up and after the first thermal cycles to catch any joint that has lost pressure.
A typical EV battery module connector, for example, uses about 15 – 20 layers of 0.2 mm 1060 or 1070 foil with welded pads at each end and a gentle offset in the middle to take up module tolerance and swelling. A transformer-to-switchgear link may instead use a wide rigid-flex assembly with thicker laminations and tin-plated bolted ends.
| Application | Typical construction | Main reason for flexibility |
|---|---|---|
| EV battery packs | Laminated 1060/1070 foil, insulated, welded pads | Vibration, cell swelling, module tolerance; Al-Al joints to cell terminals |
| Battery energy storage (ESS) | Laminated foil or rigid-flex, insulated | Rack-to-module tolerances, thermal cycling |
| Inverters and power electronics | Thin laminated foil, plated pads | Compact routing to IGBT modules and DC links |
| Transformers | Rigid-flex or wide laminations | Vibration and expansion at terminals |
| Switchgear and busduct | Expansion links, rigid-flex | Thermal expansion of long bus runs, cabinet alignment |
| Rectifiers and electrolysis | Wide heavy laminates or braids | Very high currents and thermal movement |
| Earthing and bonding | Braided aluminium straps | Movement across doors, hinges and expansion gaps |
Flexible busbars are usually inspected against the customer drawing rather than a product standard. The points below cover what most drawings control:
Material certificates to EN 10204 3.1 report chemistry and, where ordered, conductivity of the foil or strip lot.
Choose 0.1 mm where the connector sees continuous vibration or must bend in a tight space, because thinner foils have lower bending stress and longer fatigue life. 0.2 mm needs fewer layers for the same section, welds more easily and suits connections that only move during assembly or thermal cycling.
Divide the required cross-section by the foil thickness times width. A 50 mm wide connector needing 200 mm² of aluminium uses 20 layers of 0.2 mm or 40 layers of 0.1 mm. Typical designs fall between 10 and 50 layers.
About 1.6 times the area for the same resistance, and often around 1.3 times for the same temperature rise. Even at the larger size the aluminium part weighs roughly half as much.
Yes, if the contact is plated (usually tin) or a bimetal transition piece is used, and the joint is kept dry and correctly torqued. Bare aluminium bolted to bare copper in humid conditions will corrode.
1070, 1060 and 1350 are the usual choices. All are over 99.5 % aluminium with conductivity around 61 – 62 % IACS and excellent formability in the annealed temper.
Yes. Metline supplies conductor-grade aluminium foil, strip, wire and busbar stock, cut, punched, formed and plated to drawing, with EN 10204 3.1 certificates, to customers worldwide.
Share current, movement, space and terminal details. We will recommend foil gauge, alloy and finish and quote material to your drawing.
