# DC SHUNT MOTOR Calculations

#### jonty1986

Dec 17, 2013
2
Hi, I need help with a question. Any help would be appreciated.

A dc shunt motor runs at 1200 rev/min from a 200 V supply when taking an armature current of 20 A. Calculate the speed at which it will run from a 150 V supply when taking an armature current of 18 A. The resistance of the armature circuit is 0.8 Ω. Assume the flux at 150 V to have decreased to 75% of its value at 200 V

Regards

Jonty

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Hi, Welcome to Electronics Point.

Tell us what you've figured out already, and where you're having problems.

#### jonty1986

Dec 17, 2013
2
n = V - IaRa / k PHI symbol phi wouldnt copy across.

Basically i am able to work out the first part. it is the k Phi i do not understand where that figure comes from

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
What do all of those symbols represent?

Which change as the voltage to the motor changes?

If the others remain constant, can you use that information to determine what the speed will be at he new voltage?

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