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.
Why do motors draw more current when starting?
At start, the slip of the motor is equal to unity and the induced rotor voltage is equal to the stator voltage. The rotor-induced voltage goes on decreasing as the motor accelerates towards its base speed. It is clear that the induced rotor is maximum at the starting of the motor.
What causes a DC motor to draw higher than normal amps?
Electrical overload or over-current is caused by an excessive current flow within the motor windings, exceeding the design current which the motor is able to carry efficiently and safely. This can be caused by a low supply voltage, resulting in the motor drawing in more current in an attempt to maintain its torque.
What are the damages that can be caused by high starting current in DC motors?
the starting current will be enormously high. Direct-on-line (DOL) starting are not used for large DC motor because the starting current will be enormously high which will cause large voltage drop in the supply mains and armature may get damaged due to excessive heating.
What is the difference between inrush current and starting current?
The inrush current is the current transient that flows in the first cycle or so that establishes the magnetic field in the iron. … The inrush current can be significantly higher than the locked rotor current with 2 – 2.5 times the start current being quoted by some.
What causes inrush current in a motor?
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.
What happens if you give a motor too many amps?
The car will get destroyed because the speed is too high for that road. Too much HP(amps): If you are going with recommended speed of 12 mph then you can have a 50HP engine or a 500HP, your car will be fine.
How do you test a DC motor?
Check to make sure the DC motor’s rotor can turn with no impediments. Switch the voltmeter to “Ohms”. Attach one end of the red lead wires to the DC motor and run the DC motor’s red wire to the battery. Attach the clip of the black lead wire to the DC motor and run the black motor wire to the battery.
What are the disadvantages of DC motor?
Disadvantages of DC motors
- High initial cost.
- Increased operation and maintenance cost due to the presence of commutator and brush gear.
- Cannot operate in explosive and hazard conditions due to sparking occur at brush (risk in commutation failure)
What is used to adjust the speed of a DC shunt motor?
In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field. An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed. This method of speed control is independent of load on the motor.
How do you clean a DC motor?
Care should be taken when cleaning, as sweeping particulates further into the motor unit can worsen the condition. Proper cleaning involves vacuuming dry particulates with a soft bristle brush to loosen the accumulated dust. A cloth, moistened with solvent, helps to remove oily dirt.
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.
How long does an 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.
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.