Two DC series motors connected in series draw current I from supply and run at speed N. When the same two motors are connected in parallel taking current I from the supply, the speed of each motor will be

Two DC series motors connected in series draw current I from supply and run at speed N. When the same two motors are connected in parallel taking current I from the supply, the speed of each motor will be

Right Answer is:

4N

SOLUTION

In case of series.

When motors are connected in series and are in running position, Speed ∝ (voltage) ∝(V/2)
(i) (Since the voltage across each motor = V/2 ) and current is Ia.

Ns ∝ V/2I

In case of parallel

When the motor is connected in parallel and are in running position, Speed ∝ (voltage) (V). (Since the voltage across each motor = V ) and current is Ia/2

Np ∝ 2V/I

From both the equation

Ns/Np = V/2I/2V/I

N parallel = 4Nsereis

or

Hence it can be concluded that for the for low-speed operation motor may be connected in series and for high-speed operation motor is connected in parallel.

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