Today’s post is very important because, in this post we will talk about why there is no cooling fan in the DC motor. But whenever we see the AC motor, a cooling fan is installed on the back side of it. Now this question will come to your mind what does this fan do, and if this fan is installed in an AC motor then why is it not installed in a DC motor?
What is the working of fan in motor?
Friends, when heat is generated in our motor, this fan is used to cool the motor by giving air. In simple words, when our motor is heated, fan keeps the motor cool by giving air. Because if the motor gets to much heat, there is a risk of burning the winding or even damage to the motor.
That’s why we put a cooling fan in the motor. But now the question is why the cooling fan is not installed in the DC motor.
Is there a cooling fan inside a DC motor?
Friends, let us tell you at starting of the post that our AC motor has a cooling fan outside it, which is covered with a cover.
In our DC motor, there is no fan outside it, but there is a fan inside the motor.
Now the question will come why do we put a cooling fan inside the DC motor while the cooling fan is installed outside the AC motor?
Why is cooling fan used outside in AC motor?
Friends, if you want to answer this question in one line, then you can say that in our AC motor, the fan works to cool the stator of the AC motor.
Whereas if you talk about DC motor, the fan works to cool the rotor of DC motor. Friends, if this question is coming to your mind, why are we giving cooling to the rotor of DC motor while in AC motor, we are cooling the stator?
Friends, if you are from electrical background, then you need to understand this concept. Friends, in our AC motor, we give AC supply to winding. If you know the working of AC motor, then we do the winding outside our stator, and we connect this winding with the supply.
Friends, the supply we have connected with this stator is AC supply, and the special thing about AC is that its magnitude changes with time. As you can see in the image below that the current is going upwards for some time. After then it is going down for some time.
Note: whenever current flows through a wire. Then due to the flow of current a magnetic field is generated around that wire. This magnetic field is two types.
(1) changing magnetic field, which is changing with time.
(2) fixed magnetic field means that the magnetic field is fixed. There is no change in it.
Friends, our main question was that why we cool stator of AC motor. Before understanding this you need to understand the working of the AC motor.
Working of AC motor?
The current which is flowing in the stator is AC, which is changing with time. Due to this changing current, our magnetic field produced around the wire is also changing. Now friends, when this changing magnetic field comes in contact with any conductor metal, EMF is induced in that conductor. EMF induced mean voltage is generated.
If you ever hear about Faraday’s law, then Faraday’s law tells us that whenever a changing magnetic field is linked with a conductor, an EMF will be induced in that conductor. Mean voltage will be generated, and Current will start flowing in that conductor. This current is called eddy current.
Example: let’s say we have a coil through which AC current is flowing, so now a magnetic field will be generated around the coil. This magnetic field will change with time and when a conductor such as aluminum or iron is carried around it, then this magnetic field will link to the conductor and an EMF will be induced in that conductor.
When this eddy current flows through conductor, then due to this eddy current conductor start heating.
If we now talk about the case of our AC motor, then AC current flows in the winding of the stator. When this current links with the stator’s conducting metrical, then an EMF is generated in the stator, and eddy current starts flowing through it. The stator starts to heat. To reduce this heating and keep the motor cool, we use a cooling fan outside our AC motor.
But friends, after talking so much, now the question is why do we put fan inside the DC motor instead of the outside fan.
Why is cooling fan used inside in Dc motor?
Friends, the direction of the DC current’s magnitude does not change with time as you can see in the below image that the direction of DC current always remains same. Therefore, the magnetic field generated due to DC current is also not changing with time.
If we talk about our DC motor, then we give DC current to the stator, then a magnetic fled is generated in its winding. This field does not change with time. So when our stator is linked with a magnetic field, no EMF will be generated and no eddy current will flow in it because Faraday’s law states that only if a changing magnetic field link with a conductor, then EMF is induced in it.
But in the case of Dc motor, our magnetic field is not changing, so no EMF will be generated in the stator. so no eddy current flow and no heating issues in stator.
That’s why we don’t even need to cool the stator of a DC motor. But now the question comes that why do we cool the rotor.
Why Rotor is Cooled in DC motor?
Friends, in DC motor, commutator is connected with the rotor. The job of a commutator is to keep changing the direction of the current. Even though, we are giving DC supply to our motor, but this current goes to the rotor through the commutator.
When this current passes through the commutator, its direction changes repeatedly. We can say that the commutator converts the DC current into AC current.
Therefore, due to AC current magnetic field generated also change with time. When a conductor links with this changing field, EMF is generated in it.
So eddy current starts to flow and our rotor start heating that’s why we need cool down our rotor.
Friends, if you want to tell this in one line, then you can say that in our AC motor AC current flows through the winding of the stator. So a magnetic field is produced, and when this magnetic field link with metal of the stator, then EMF will be generated and eddy current starts flowing in stator, due to which our stator of motor heat.
But if we talk about DC motor, then DC current flows in stator winding but the commutator which is connected with its rotor converts DC into AC. Therefore, the magnetic field generated due to this current also changes with time. When a conductor links with this changing field, EMF is generated in it, and eddy current starts to flow. And our rotor starts heating up.
For this reason, we need to cool the stator in the AC motor, we have to install a cooling fan on the outside And to cool the rotor inside the DC motor, a cooling fan has to be installed inside motor.
We hope that you understand. If still any doubt or question remains then feel free to ask in comment section or you can ask this question on Instagram “Electrical Dost”.
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