How To Limit DC Motor Inrush Current

DC Motor Inrush Current

Choosing An Inrush Current Limiter To Preserve Your DC Motor

So, what does an Inrush Current Limiter have to do with DC motor inrush? More than you may think. DC motor inrush is the maximum, instantaneous input current drawn by the DC motor when first turned on and it is important to know how to limit the inrush current to prevent possible damage to the motor.

A DC motor converts electrical energy into mechanical energy using a Stator which is the static component of the DC motor and a Rotor which causes the mechanical rotations of the motor to occur.

DC motors are used in many industries such as:

  • Industrial
  • Medical
  • Automotive
  • Aerospace

Large DC motors can be found in conveyors, elevators and hoists as well as in the drives for steel rolling mills and in the propulsion of electric vehicles.

Because DC motor inrush current can be as much as 2-3 times its steady state current, employing Inrush Current Limiters to reduce the inrush current will help to extend the life and efficiency of the DC motor.


Watch the video and learn about the impact the Stator and Rotor have on DC motor inrush current.


To learn more about inrush current, visit our FAQ page

Find the right Inrush Current Limiter for your DC Motor inrush in THREE simple steps. The process is simple and straightforward using the calculations below.

The calculations shown are based on a 1HP DC motor. Four other assumptions were also made.

Given Facts:

  • 1 HP DC Motor


  1. Input voltage: 24V.
  2. Inrush Current: 3X steady state current.
  3. Duration of Inrush: 200ms.
  4. Maximum Desired Inrush Current: Reduce inrush current by 50%

STEP ONE: Calculation of Inrush Current

This calculation is performed in three steps because horsepower must be converted to watts before proceeding.

Calculate DC Motor Inrush Current

Calculate DC Motor Inrush Current


STEP TWO: Calculation to determine the energy an Inrush Current Limiter must absorb without failure

This calculation is performed to determine the energy rating that will be needed.

  • Energy equals instantaneous input power multiplied by the duration of inrush.
  • Instantaneous input power equals input voltage multiplied by the inrush current.

Calculate Amount of Energy Needed

Calculate Amount Of Inrush Energy Absorbed by ICL

STEP THREE: Calculation to determine the minimum zero-power resistance

This calculation is performed to determine the minimum resistance needed to keep the motor from failing due to DC inrush current. The goal: Reduce the DC inrush current by 50%.

Calculate Maximum Desired Current

Calculate Maximum Desired Current

The Inrush Current Limiter for this DC motor inrush application

Inrush Current Limiter MS35 1R040

The above calculations recommend the MS35 1R040 for this application. Click the Data Sheet for detailed specifications. Click here to learn more about DC Motors

A recent industry study, conducted by Data and Strategies Group, Inc., Framingham, MA, indicates that Inrush Current Limiters (NTC thermistors) are overwhelmingly the most popular type of device for inrush current suppression for power supplies.

AMETHERM manufactures high quality and cost effective Inrush Current Limiters that are ISO9001 Certified. Learn more about Inrush Current Limiters


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