2015-08-20T22:15:14+05:30
Maximum voltage needed is 15 volt which normal battery has. see the pic below.this is enough for a general dc motor to work
thank u

9.5 is not maximum
2015-08-24T04:03:02+05:30

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(back ) emf  =    phi * Z * N  / 60     * ( P / A)    = k w

phi = magnetic flux through a conductor
Z = number of armature conductors (turns)
N = rotations of the motor per minute. =  60 w/(2 pi)
w = angular speed of the motor
P = number of poles
A = number of parallel paths in the armature.
= 2 for simplex wave winding of the motor/generator
= P  for simplex lap-wound motor /generator

maximum voltage is given by the above equation.

If operating current I and internal resistance R or armature resistance is given, then
back emf = voltage across motor = input voltage V - I R