Busbar (Multi-Branch Collection) Calculator
Collects several branch currents onto one main busbar: from the total current and design margin it gives cross-section, current density, full-length resistance, voltage drop, conductor and joint losses, estimated temperature rise, and a short-circuit thermal check.
Key points
Busbar (Multi-Branch Collection) Calculator: Collects several branch currents onto one main busbar: from the total current and design margin it gives cross-section, current density, full-length resistance, voltage drop, conductor and joint losses, estimated temperature rise, and a short-circuit thermal check. Formula: R = ρ(T)·L/A ｜ P = I²·(R + R_contact) ｜ ΔT = P/(h·2(W+T)·L) ｜ A_min = I_sc·√t/k. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. Total current = branches × per-branch current × (1 + design margin). Real parallel branches have unequal impedance and therefore unequal sharing, so keep the margin at 10% or more. Temperature rise uses a lumped heat balance: total loss = h × outer surface × ΔT. Joint losses are actually concentrated at the lap joints, so local temperature is higher than the average — leave extra margin at the terminals.
Inputs
R = ρ(T)·L/A ｜ P = I²·(R + R_contact) ｜ ΔT = P/(h·2(W+T)·L) ｜ A_min = I_sc·√t/kCalculation model (updates with parameters)
| Total current I_total | 200 A | 4 × 50 A branches in total |
| Design current (with margin) | 220 A | margin 10% |
| Cross-section A | 120.0 mm² | 30.0 × 4.0 mm |
| Current density J | 1.83 A/mm² | For naturally cooled busbars use 2–4 A/mm² as a reference |
| Resistance per metre R | 170.4 µΩ/m | bar temperature 67 °C |
| Full-length conductor resistance | 85.2 µΩ | L = 0.50 m |
| Voltage drop ΔV | 27.55 mV | ΔV = I·(R + R_contact), R_contact = 40 µΩ |
| Drop ratio | 0.06% | ΔV ÷ Vs (48.0 V) |
| Conductor loss | 4.125 W | P = I²·R |
| Joint loss | 1.936 W | P = I²·R_contact, total 40 µΩ |
| Total loss | 6.061 W | conductor + joints |
| Estimated temperature rise ΔT | 27.4 K | P/(h·A_surf), h = 6.5 W/(m²·K) |
| Busbar temperature | 67 °C | Ta = 40 °C |
| Current capacity (ΔT = 40 K) | 262 A | same section and length, joint resistance included |
| Busbar weight | 0.54 kg | Copper (T2), density 8960 kg/m³ |
Engineering notes
- Total current = branches × per-branch current × (1 + design margin). Real parallel branches have unequal impedance and therefore unequal sharing, so keep the margin at 10% or more.
- Temperature rise uses a lumped heat balance: total loss = h × outer surface × ΔT. Joint losses are actually concentrated at the lap joints, so local temperature is higher than the average — leave extra margin at the terminals.
- The drop includes joint contact resistance; battery packs and DC busbars are usually kept within 2–3%, while power busbars may allow up to 5%.
- Short-circuit withstand uses the adiabatic assumption A_min = I_sc·√t/k (copper k=143, aluminium k=94 for the 90→250°C basis). Bare bars and other insulation/final temperatures use different coefficients — check the standard tables for final design.
- Also check short-circuit electrodynamic (peak) forces and insulator spacing, plus terminal current rating and thermal-cycling reliability.
- For single rectangular bars use the “Copper busbar ampacity (heat-balance)” tool; for a current-density-based quick pick use “Busbar / copper bar selection”.
FAQ
- What is Busbar (Multi-Branch Collection) Calculator for?
- Collects several branch currents onto one main busbar: from the total current and design margin it gives cross-section, current density, full-length resistance, voltage drop, conductor and joint losses, estimated temperature rise, and a short-circuit thermal check.
- What is the formula for Busbar (Multi-Branch Collection) Calculator?
- Core formula: R = ρ(T)·L/A ｜ P = I²·(R + R_contact) ｜ ΔT = P/(h·2(W+T)·L) ｜ A_min = I_sc·√t/k. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Busbar (Multi-Branch Collection) Calculator?
- Total current = branches × per-branch current × (1 + design margin). Real parallel branches have unequal impedance and therefore unequal sharing, so keep the margin at 10% or more. Temperature rise uses a lumped heat balance: total loss = h × outer surface × ΔT. Joint losses are actually concentrated at the lap joints, so local temperature is higher than the average — leave extra margin at the terminals. The drop includes joint contact resistance; battery packs and DC busbar…
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