DC motor is an electro-mechanical energy conversion device which convert electrical energy to mechanical energy.

1. Working of a DC Motor
• DC motor is an electro-mechanical energy conversion device, in which input is in form of
electrical energy and output is in the form of mechanical energy.

2. Working Principle
The working of DC motor is based on the principle that when a current carrying conductor is placed in a magnetic field, it
experiences a mechanical force.
The direction of the mechanical force is given by Fleming’s Left-hand Rule and its magnitude is given by F = BIL Newton.
Working of a DC Motor
Fleming’s Left-hand Rule
This phenomenon exists in nature invariably everywhere and
never changes, it is documented by many physicist throughout the
world but with scientific approach sir John Ambrose Fleming, in
the late 19th century, gives a simple way of working out the
direction.
According to him When current flows through a conducting wire,
and an external magnetic field is applied across that flow, the
conducting wire experiences a force perpendicular both to that
field and to the direction of the current flow (i.e they are mutually
perpendicular). A left hand can be held, as shown in the
illustration, so as to represent three mutually orthogonal axes on
the thumb, fore finger and middle finger. Each finger is then
assigned to a quantity (mechanical force, magnetic field and
electric current). The right and left hand are used for generators
and motors respectively.

3. Working of a DC Motor
How it Works
An elementary model is shown here in fig (a) to understand the
working in easy way.
• Invariably all dc motors consist of a set of magnetic poles (North and
south) to create magnetic field shown in fig (b).
•All dc motor consist of windings represented by a single loop in this
model for simplicity fig (c).
• Two semi cylindrical shaped commutator segments connected to
each end of the loop fig (d).
•A dc source connected to the commutator segments through two
brushes sliding on the surface of commutator to transfer or collect
current fig (d)
(b)
(c)
(d)
(a)

4. Working of a DC Motor
•A turn of coil along with commutator segments is free to move about the axis shown in fig 1.
• Two stationary carbon brushes slides on two commutaotr segments and pas/collect current through coil loop under magnetic field created by stationary
poles.

5. • This leads to the flow of current in the coil as shown in diagram given below.
Working of a DC Motor

6. • We can see that, because of the action of commutator and brushes, conductor of loop on left side always carries current in one
direction and the conductor on right side always carry current in the opposite direction according to the diagrams given below.
Working of a DC Motor

7. • Therefore conductor on left side always experience force in the upward direction and the conductor on right side always gets
downward force, this is known as commutator action.
• So we can say that, the work of commutator and brushes is to change the direction of current in the conductor when it
passes through geometric neutral axis (GNA).
• Note that, this is not actual construction of DC Motor, this is elementary model which is used here for easy demonstration.
• In actual, the construction of DC Motor is quite typical.
• It consist of number of coils with numbers of turns, commutator segments, sets of brushes and pairs of poles.
In this way DC motor works
Working of a DC Motor
L
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