The three coil D.C motor is one of the most ingenious inventions in the electrical world.
Its construction is so simple and unique that, understanding the working principles behind them will be a real fun.
As usual, to learn about its inner workings, let's have look at the 3D animation.
You an see that, two permanent magnets constitute the stator while the rotor is a three full
time a single coil is used for the complete winding of the rotor you can
understand the winding details by following the current flow
the rotor coil is connected with three commutator rings as shown
each commutator ring sits between the coil pair DC power is supplied to the
commutator rings via a pair of brushes now let's get into it's working the
working of this motor can be easily explained with the help of simple
electromagnetic induction this means that a coil carrying electricity will
become an electromagnet as shown you can easily predict the
direction of this electromagnet with the help of the right-hand thumb rule
let's simplify the coil arrangement to make things a bit clearer and begin with
this position of the rotor assume that DC power is applied let's use the
following notations to represent the three commutator rings and coils at this
position the brushes are in connection with commutator rings one and two with
this arrangement current will flow in all three coils let's hide coil a in
order to understand current flow in a better way
as you follow the coil current will start from terminal to flow through
coils B and C respectively
and finally end up in commutator ring one
if you check the current flow in coil a you can easily predict that there will
be a current flow as shown
now you can easily predict the magnetic polarity of each coil with the help of
the right-hand thumb rule coils B and C become North in polarity while coil a
becomes the South Pole these electromagnets will interact with
a permanent magnet now the North and South Poles will attract while the north
and north poles will repel as shown this will force the rotor to turn as
illustrated however as the rotor turns the brushes come in contact with
different commutator rings this alters the whole rotor current flow and this
simple trick makes the rotor turn again let's see what happens in this
configuration in the new configuration the negative terminal is connected to
the commutator rings 1 & 3 together so rings 1 & 3 possess the same voltage
since coil C is connected between these rings there will not be any current flow
through coil C let's omit this coil current flow occurs
in the remaining two ring coils as shown
here coil a acts as the South Pole whereas coil B acts like the North Pole
due to the forces of attraction and repulsion the rotor will turn as the
rotor turns the brushes come in contact with different commutator rings the
current flow in the coil thus changes again this process is repeated and we
get continuous rotor rotation it is amazing to see just how complex the
operations of seemingly simple engineering devices truly are
would you like to build your own DC motor at home please check out this
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