Split-Phase Motors

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There is no self starting facility in Single-phase motors and thus it needs something to have the initial torque. Only with the help of rotating flux, the initial torque is possible when rotating torque is generated in the stator. One more important thing to know about this rotating flux as it can be produced only when the difference in the angle of two stationary coils is 90-degree. However, in case there is a larger phase difference between the two fluxes present in the starter, then without thinking much the resultant would be the perfect rotating flux.

The different types of Split Phase Motors are –

  • Split-phase resistance-start induction motor
  • Split-phase capacitor- start induction motor
  • Permanent-split capacitor induction motor
  • Two-value capacitor induction motor
  • Shaded-pole induction motor
  • Reluctance-start induction motor

These all above have different features and working ability. Only after knowing about each of them anyone can easily understand that how to use them.

Split-phase Resistance-Start Induction Motor

In a motor with split-phase induction, the parallel winding are placed by an electrical angle of 90-degree in the space and thus it is less than 90-degree.

In the figure it is clear about the winding diagram. Now, some important points are as follows about a Split-phase Resistance-Start Induction Motor –

  • A few turns along with wound is there in the starting windows. This wound has a very small        diameter copper and as compare to that and this is the main reason of having high resistance and low reactance.
  • The main winding has a heavier wire with many turns and thus it has a high reactance and low resistance. Due to the low impedance, the current that is running in the winding I always have a higher value than the current in the stating window Is.
  • In the provided figure b, it will be clear that how the motor of phase relation of lock at the instant is ready and work in a proper way. The Is lags of the starting winding supply voltage 15 degree. However, 40 degree is there in case of single-phase voltage for current lags in greater running winding. It means there is no equality in the two space-quadrature winding. However, if you look practically, then the components are equal.
  • In case of 90-degree of separation in space and also the 90-degree current displacement in time, then the components are practically similar or equal. And for that a two-phase field rotating is generated and this is the reason of starting and, starting is there that works positively to generate the starting condition of the rotor with an exact acceleration. The rotating field direction is generated by the current.
  • Along with the speed of the motor the acceleration of the torque increases and thus if this goes up to 85% of the speed of synchronization, then it will be clear that the running winding becomes greater than developed winding for both winding. In addition, opening an auxiliary circuit will be advantageous. For variations individually between he switches and the motors, the general opening design gives 75 percent of the synchronized speed. However, this is not very serious case that will affect the operation because winding only generates 200% of torque in the same speed.
  • The switches are connected centrifugally because the starting one is not actually designed to handle the continuous operation. So, after disconnecting of the switches it is not necessary to connect again.

Now, what happened in the hermetically sealed motor? This is de-energized condition, and its switch is operated magnetically.

  • Reversing motor of split phase will get the revered connection just by getting the reverse connection. Nothing will be there if reversal under normal condition takes place.

In case of there is necessity of reversing the motor at the time of rotating then it is very important to slow the motor where the starting- switches come close. It is important in starting as well as placing the winding for supply lines. The timing device is important as this first disconnects and the complete motor and then start reversing one field and the other.

  • Speed control that takes place in speed phase-winding is a very difficult thing because the speed of synchronization of the rotating field is important to determine. It is Ns =120f/p as the number of poles is important in running stator window. Variation of speed may be there by adding the stator winding to change. However, each change in speed is there to accomplish in a proper range and only for that the centrifugal switches are operated.

There are some typical speed of the torque can be seen –

What is the value of the starting torque? This is 1.5 times to 2 times of the full-load starting torque with the ability of starting current 6 – 8 times of the full-load current.

  • The regulation of speed is very good.
  • There is 4-6 percent of percent slip is available.
  • This type of motor may function through a power factor of 0.55-0.65 and efficacy of 60 to 65 percent.
  • The fractional kW ( 1/20 to 1/4 kW ) is used to make this and the ratings is there with speed ranging from 2875 to 700 r.p.m.

Shortcomings and uses

The objections of the motors are –

  • Its starting torque is lower
  • At the time when the motor is loaded heavily as it is able to reduce the e.m.f. and pulsating or elliptical torque produced. Due to this reason the a lot of sound gets produced.

Now, it is clear that grinders, oil burners, washing machines, air compressors are there to produce a lot of sound. 

Split-phase capacitor- start induction motor

Split-phase capacitor- start induction motor is another way of splitting a single phase motor. In this, the capacitor is placed just in a series along with winding of starting auxiliary. In this way, the line voltage is prepared by current in the starting winding.  Due to this winding the displacement of the phase between the two currents is prepared to be 90-degree approx. You must need to know now the circuit capacitor and vector diagram of its voltage and current. Both of these are presented in the figures and for the convenience to use the angles are rounded off. The series capacitor needs to have a lower value when phase-shift is 90 degree to maintain it in a proper way.

  • The phase angle increment is important between running and the stating winding is not only the exact difference between the capacitor-start motor and split-phase, but it is also important to have a low starting-winding turns. So, with the line voltage, the current becomes ill phase. Capacitor provides the propel phase shift at this time. There are many auxiliary starting turns in the motor having capacitor as compared to the         split-phase, and this is perfect in providing ampere-turns in a large manner and thus it becomes very important to have a starting torque.

Only because of a larger angle between the two field currents, the magnitude of the filed currents is similar. In the figure IIS is less ill capacitor-start motor. For a proper line current, the value of starting torque in a capacitor start motor is always higher than split phase induction motor. In capacitor start the value highs up into 3-4.5 times of fully loaded torque, but in case of split phase, it is not more than twice of full loaded torque.


  • There is a proper range of motors of the capacitor start and this follows the range of 1/10 kW to 3/4 kW, however these are also available in larger size.
  • The reversing is possible just by changing any one winding. However, there is some limitations are there and these are completely same as the motor of resistance-start induction.

Use – By using this kind of motors where high starting torque is used, there are many items as a number of the pumps, air-conditioners, refrigeration unit, compressors and a high starting torque under load. Here a proper split phase motor is important to have a high starting torque.

Permanent-split Capacitor Induction Motor

What do you mean by Permanent-split Capacitor Induction Motor? Now for knowing it in a proper way, go through the following points –

  • A Permanent-split Capacitor motor is an induction motor having single phase. This has both the running and starting auxiliary winding with the same capacitor in the series. The reason of this is its continuous running ability just like a split-phase motor which is permanent. There is no need to have any centrifugal switch.
  • The running and starting of the motor depends on two identical windings, which produce quadrature-phase splitting. It means there is no possibility of producing high running torque as either for a capacitor start or a resistance start motor.

So, there is a continuous duty for the capacitor and thus is designed to get the exact resultant in a proper way which is there for an oil-filled type. Its value is based on the optimum running in place of starting characteristic. So, as a result, there is very poor availability of the starting torque and it is 50 – 100 percent of rated torque.

  • The uniqueness is there when equal windings create magnetic fields of uniformly rotated field. The displacement of current arc takes place by 90-degree. In addition, it is very difficult to have the pulsating hum when a number of single phase motors loaded.

Here are some merits of this motor as follows –

  • Higher power factor at full-load
  • Lower full-load line current
  • Higher full-load efficiency
  • Increased pull out torque.

Now, it is clear that the permanent–split capacitor is bit expensive than others as capacitor start and split phase induction motor. The auxiliary winding in this situation also works just like a running winding. Thus the duty rating is continuous and very high.

Uses – The reversing motor response is very quick, and it has an excellent controlling ability of speed and along with that the capacitor motor having permanent split is used for heaters, blowers and intake as well as exhaust fans. It can also be used in unique heaters. The function is suitable in different ways and thus it is important for you to grab the best services from various.

Two-value Capacitor Induction Motor

Two-value Capacitor Induction Motor is the combination of the speed control with exact limitation and the quiet operation. These are advantageous for split capacitor for running permanently.

  • In this figure, there are two different capacitors are employed in the initial stage. One of the two different capacitors is a capacitor of starting electrolytic and the main use of this is intermittent work on the motor of capacitor – start along with split-phase ability. In addition, there is a centrifugal switch that helps in cutting out of the circuit. This has a higher capacity and the cut off is possible at the moment when slip reaches at 25 per cent.
  • The most significant thing is about the two value capacitor is its very high starting torque and along with that quiet operation as well as proper running torque, the leading line gets revered in a genuine manner. When speed is below 25% while reversing, then there is no connection of the centrifugal force with its starting contact and here you will get that when only 15% is the speed of that motor is there, then it can be in its reverse direction.


This can be used in air condition which is small in size. In addition,  small unit where the function can take place just at 15 amp. The starting and lowering current is available over an exact or an improved factor of power is acquired over capacitor start motor running and starting for a compressor with a proper fixed load.

Shaded-pole Induction Motor

Being an induction motor, its one of the cheapest and simplest of all manufactured motors. The poly phase induction motor and the squirrel-cage receive almost same amount of power.But, in case of  the former, the motor revolves perfectly and so has a synchronous speed in the core. In case of the later, it shifts. The tgorque created is non constant as the revolving field has no true value.


In every laminated pole, a slot cut is present which is only one third from the edge of the pole.It is termed as the shading coil. It is placed inside the part called the pole’s shaded part. The remaining part is called the free portion. The exiting coil surrounds the entire coil.

Principle of operation

On supply of proper alternating current, the magnetic axis shifts towards the shaded part of the coil.This effect is almost similar to an actual motion of the pole. As a result, the squirrel cage also shift towards the shaded part. Here, the shifting flux is:

  • The shading coil experiences a short circuit current . According to Lenz’s law, force acts on the opposite direction and created the flux.
  • Flux distribution  is uniform, as depicted  in the figure at point C. As the rate of change of flux is null, the shaded coil experiences on force.
  • Shaded coil experiences greater flux when the direction of flow of current is reversed.
  • Shaded pole motors enjoys power till 40 W.


  • Rugged construction
  • Cheaper in cost
  • Requires little maintenance
  • Normal one is a little lesser than the locked one.
  • Small in size


  • Very low starting torque
  • Low power factor
  • Low efficiency


The uses are as follows:

  • Motion picture projectors
  • Relatively light loads.
  • Small fans and blowers
  • Bending machine
  • turntables or phone motors
  • Rotating store-window display tables

Reversing shaded-pole motor

The reverse shaded pole enjoys a short  circuit current due to the reversing switch. Switches 2 and 4 are is series combination, although they are not active as the arc remains open. Flux does not lag here, voltage does not act in reverse direction and the flux acts vertically downwards.

Reluctance-start Induction Motor

Here, the magnetic field shifts across the poles. There are non-uniform air-gap.When this gap increases, flux nears the phases.Low reluctance means a greater gap between current and flux and vice versa. Both the flux types are created by the same current. Both are displayed in time .And so, flux moves across ploes from a pole with larger air gap to the lower one.

Reluctance start motor.

Use – As torque is very low, its usages also are rare.


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