Continuous vs Peak Current

Two numbers, two jobs

Continuous current is what the pack delivers indefinitely without exceeding its thermal limits. It is set by the cells, the parallel count, the internal resistance, and how well the enclosure sheds heat.

Peak current is a short burst — typically rated for seconds, not minutes — for starting from rest, accelerating, or a steep pitch. Our 48V catalog quotes 20A continuous against 40A peak; the 36V platform quotes 15A against 30A.

The peak figure is meaningless without the duration it applies for. “40A peak” for 10 seconds and “40A peak” for two minutes describe very different packs.

Where specifications go wrong

Two failure modes, opposite causes.

Sizing on continuous only. The pack meets the average draw and cuts out on the first hard acceleration, because the BMS over-current threshold sits below the controller’s real peak. The customer reports a fault; the pack is behaving exactly as specified.

Sizing on peak only. The pack survives bursts but runs hot in sustained duty — a loaded cargo bike on a long gradient, or a delivery rider at full assist all shift. Heat then shortens cycle life well before the datasheet suggests.

The BMS has its own pair

Confusingly, the BMS carries its own continuous and peak ratings, separate from the cells’. The pack’s real limit is whichever is lower.

This is why fitting a higher-rated BMS to a low parallel-count pack achieves nothing — the cells are already the constraint. And why a high-P pack with an undersized BMS is throttled by electronics rather than chemistry.

The number most buyers have not asked for

The controller’s continuous current, its peak current, and how long the peak lasts. Also the duty cycle: how much of a typical ride is spent near continuous maximum.

That last question is the one most buyers have not asked their own engineering team, and it is the one that decides whether a specification survives contact with real riders.