Battery Current

Battery current is the current flowing between the battery and the motor controller. It represents the amount of electrical current being drawn from the battery to power the system.

Battery current is one of the primary factors that determines battery load, electrical power consumption, battery heating, and runtime. Unlike phase current, which primarily determines motor torque, battery current determines how much power is being supplied by the battery.

⚠️ Battery Current is not the same as phase current. A motor controller functions as a power converter and can regulate phase current independently of battery current. As a result, phase current may be considerably higher than battery current, particularly at low motor speeds.

At low motor speeds:

• Phase Current can be several times higher than battery current
• High motor torque can be produced while drawing relatively modest battery current

At higher motor speeds:

• Phase current and battery current become increasingly similar
• Battery current becomes a stronger indicator of overall system load

Battery current limits should be selected based on:

• Battery cell specifications
• Battery pack construction
• BMS current limits
• Connector ratings
• Wiring ratings
• Desired performance and range

Setting battery current too high can result in:

• Excessive battery heating
• Reduced battery lifespan
• BMS over-current protection triggering
• Voltage sag
• Damage to battery cells in extreme cases

Example

A system may be configured with:

• Battery Current Max: 50A
• Motor Current Max: 200A

During low-speed acceleration, the battery may only supply 50A while the controller delivers 200A of phase current to the motor. Although the motor is receiving 200A, the battery is only required to provide 50A.

At higher speeds, battery current and phase current will become more similar as the controller’s ability to multiply current decreases.

⚠️ Battery Current Max is a normal operating limit configured in VESC Tool. The battery, BMS, connectors, and wiring must all be capable of safely handling the selected current.

In simple terms: battery current is the current being drawn from the battery and determines how much electrical power the system is consuming.