#4 · Continuous vs Peak Current — What’s the Difference?

1. Current names on the spec sheet — "max" is continuous, "instantaneous" is peak

Spec sheets name their currents slightly differently. On POWERCRAFT standard battery pack spec sheets they line up like this.

• Continuous current = "Max Discharge Current" on the spec sheet. The upper limit of current the pack can keep delivering. The continuous current of the DM-PWR-25.6V-100Ah is 150A.
• Peak current = "Instantaneous Discharge Current" on the spec sheet. Current allowed only within a set short time. The DM-PWR-25.6V-100Ah lists "200A @ ≤1.5s" — up to 200A for no more than 1.5 seconds.

The word "max" makes it easy to read as a momentary maximum, but on POWERCRAFT spec sheets max discharge current is a continuous figure. That is also why the "Continuous Max Power" on the same sheet equals nominal voltage multiplied by max discharge current (25.6V × 150A = 3,840W).

Continuous max power (W) = nominal voltage (V) × max discharge current (A)

2. Motor loads — normal current and surge current

Machines driven by motors, such as robots and AGVs, do not draw a steady current. There is the current that flows normally, as in cruising at constant speed, and at the moment a motor switches on (inrush current) or when more force is needed — starting off, accelerating, climbing a ramp — a current far larger than normal is known to flow briefly.

So on the battery side the two figures are matched separately.

• Normal current must be less than or equal to the continuous current (max discharge current).
• Surge current, such as inrush current, must be less than or equal to the peak current (instantaneous discharge current), and the time it lasts must sit within the peak current's time condition.

How large the surge is and how many seconds it lasts depend on the motor, the controller and the way the machine is operated, so a battery manufacturer cannot predict them accurately. They are values to confirm in the machine's datasheet or with the machine manufacturer. Send those values and POWERCRAFT can recommend a standard pack or quote a custom build straight away.

3. Peak current — check size and time together

Peak current should not be compared by the current value alone; the time condition has to be read alongside. Even on POWERCRAFT standard spec sheets, the time condition differs by model.

• DM-PWR-25.6V-100Ah — continuous 150A · peak 200A @ ≤1.5s
• DM-PWR-51.2V-50Ah — continuous 75A · peak 100A @ ≤5s

Worked example 1. A 24V-class AGV drawing 40A normally and 180A for 1 second when starting off, on a DM-PWR-25.6V-100Ah battery pack: 40A is within the continuous 150A, and 180A for 1 second is within the peak 200A for 1.5 seconds, so it is within the spec sheet.

Worked example 2. If the same machine draws 180A for 3 seconds while climbing a ramp, that exceeds the 1.5-second condition. The 180A then exceeds the 150A continuous current of the DM-PWR-25.6V-100Ah battery pack, so a model with a higher continuous current, or a custom build, should be considered.

For continuous current, it is safer to leave headroom than to select a product close to the limit. As with the capacity margin covered in article #3, a margin of 1.2–1.3× is recommended.

4. When you enquire — three values are enough

When choosing a standard pack, confirm three values for the machine — normal current, peak current and how long the peak lasts — and compare them with the max discharge current and instantaneous discharge current on the spec sheet. It is easiest to select voltage first by article #1 and capacity by article #3, then check current. → See all 49 standard battery packs — filter by voltage, capacity and battery type

On the custom build specification request, the same values go in like this. The names differ from the spec sheet, so please take care.

• "Continuous discharge current" field = normal current (continuous current)
• "Peak discharge current / duration" field = peak current and how long the peak lasts