50Hz → 25Hz: Does Motor Current Really Drop by Half?

If the frequency is reduced from 50Hz to 25Hz, does the motor current also drop by 50%?

Not necessarily.

Reducing the VFD frequency mainly reduces the motor speed.

Motor current, however, is strongly related to the load torque and operating conditions.

For fans and pumps, when speed decreases, the required torque and power usually decrease significantly. As a result, motor current will generally decrease as well.

But for constant-torque loads, such as:

• Crushers
• Conveyors
• Extruders
• Mixers

reducing the frequency does not necessarily mean the current will decrease proportionally.

25Hz ≠ 50% of the current at 50Hz

This is why VFD selection should not be based on frequency or motor power alone.

You also need to consider:

Motor Power + Load Type + Required Torque + Operating Speed

Understand the load first. Then choose the right VFD.

Don’t select a VFD by frequency alone.
Understand the load first.

ZFENG ELECTRIC
Industrial VFD Solutions