ECM Voltage Response to a Current Step

1RC Thevenin model — OCV = 3.7 V, R₀ = 0.1 Ω, R₁ = 0.05 Ω, C₁ = 200 F (τ₁ = 10 s)

Current I(t) [A]
Terminal Voltage V(t) [V]
Top — Current I(t)
Step ON at t = 1 s → I = 2 A Step OFF at t = 6 s → I = 0 A
Bottom — Terminal Voltage V(t)
Instant drop = I × R₀ = 0.2 V (at t = 1 s) Slow RC decay (τ₁ = 10 s) → settles ~0.1 V further Instant recovery +I × R₀ (at t = 6 s) Exponential recovery → OCV
Model parameters used:
OCV = 3.70 V  |  R₀ = 0.10 Ω (ohmic / contact resistance)  |  R₁ = 0.05 Ω, C₁ = 200 F → τ₁ = R₁·C₁ = 10 s (diffusion time constant)
Pulse: discharge current I = 2 A applied from t = 1 s to t = 6 s, then removed. Positive current = discharge (voltage drops).
Key insight: R₀ sets the instant drop/recovery; the RC pair sets how fast the voltage drifts during the pulse and recovers after. Real HPPC tests exploit this separation to extract R₀ and τ independently.