# Frequent question: How do you limit the inrush current of a DC motor?

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You could also stick an NTC thermistor in series with the motor. These devices start off with a high resistance, until current starts to flow and heat up the thermistor, which lowers it’s resistance to stop limiting the current as much.

## How can we limit the starting current of a DC motor?

In order to avoid high starting current an extra resistance must be connected in series with the armature. This external resistance is known as starter resistance. The series resistance is divided into sections which are cut out one by one as the speed of the motor increases and the back emf builds up.

## How can I reduce my inrush current?

Inrush current can be reduced by increasing the voltage rise time on the load capacitance and slowing down the rate at which the capacitors charge. Three different solutions to reduce inrush current are shown below: voltage regulators, discrete components, and integrated load switches.

## Do DC motors have inrush?

DC motors do not have current inrush. And the DC inrush current should be the DC resistance divided into the applied voltage. Once the motor is spinning it generates a back emf which reduces the current draw.

## What is DC inrush current?

Inrush current is the peak current which flows into the power converter when input voltage is applied or at turn-on. Most system inrush current specifications will be met with VPT’s DC-DC converters alone. Some applications may require limiting the inrush spike into the input capacitors.

## Why is DC motor current so high?

Answer: The starting current is high as there is no back EMF or counter EMF present in the armature circuit because atstarting counter EMF is zero. … It’s armature has very less resistance due to this it need more current at starting time. Hence DC starters are used to limit the starting current ofmotor.

## How does a DC motor start?

So, a DC motor is started by using a starter. There are various types of dc motor starters, such as 3 point starter, 4 point starter, no-load release coil starter, thyristor controller starter etc. The basic concept behind every DC motor starter is adding external resistance to the armature winding during starting.

## Why is inrush current bad?

Often high inrush current drops the source voltage and results in a brownout reset for microcontroller-based circuitry. In few cases the amount of current supplied to the circuit gets beyond the acceptable maximum voltage of the load circuit, causing permanent damage to the load.

## How is inrush current calculated?

Inrush current calculations:

Approximately inrush current I(peak) is equal to the ratio between the root 2 times of maximum applied voltage to DC winding resistance. This calculation gives you the approximate value of the inrush current to understand.

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## What is the difference between inrush current and holding current?

Both inrush current (pull-in current, the amount of current necessary to pull contacts together) and holding current (the amount of current necessary to hold the contacts together after initial pull-in or the sealed position of the contacts) must be calculated for most control-switching devices.

## How inrush current is reduced in motor?

One is to use a soft starter — a device that gradually increases supply voltage to the motor terminals during startup, thus lowering inrush current and controlling startup torque. Similarly, a variable frequency drive reduces inrush current by controlling the voltage supplied to the motor.

## What causes motor inrush current?

Inrush Current and the Motor Components

The difference in the magnetic fields between the stator winding (stationary copper winding group within the motor) and the rotor winding (rotating shaft winding) is the biggest contributor to the initial inrush current experienced at startup.

## Why motor starting current is high?

This high current in the rotor will create its own magnetic field which opposes the main stator magnetic field, this weakens the stator magnetic field so the back EMF in the stator will drop and the supply voltage will be much higher than the stator back EMF and so the supply current increases to a high value.

## How long is inrush current?

These currents can be as high as 20 times the steady state currents. Even though it only lasts for about 10ms it takes between 30 and 40 cycles for the current to stabilize to the normal operating value.

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## How much is motor inrush current?

The inrush current (Amps) is high, at 1,500 Amps. This is about 4 times the idle current of the motor, and almost 50% more than the average current while chipping. Inrush current lasts for approximately 2.5 minutes.

## How long does inrush current last?

The inrush may be as much as 14 times the steady-state current and may persist for a few milliseconds for smaller lamps up to several seconds for lamps of 500 watts or more.