1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Just starting out on DC motors and hit a snag

  1. Nov 11, 2015 #1
    • Poster has been reminded to post schoolwork in the HH forum and use the HH Template
    Hi Guys
    I'm hoping someone can help me out with a problem??
    I have just started learning about DC motors and I have hit a wall on how to solve the following problem-

    Q.The output of a series d.c. motor when connected to a 230V supply and running at 1320rev/min is 3.8kW. The supply current for this loading is 20.5A.
    Calculate the torque developed and the opperating efficiency??

    Can anyone explain the equations i need to be looking at, as I thought you needed the armature current and field current to be able to solve this??

    Any advice or help is much appreciated

    Cas
     
  2. jcsd
  3. Nov 11, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    You can solve this with conservation of energy. Find the input power (easy for DC), find a way to express output power with angular frequency and torque.
     
  4. Nov 11, 2015 #3

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Power = torque * angular velocity...............................(1)

    The problem gives you the output power and enough info to calculate the angular velocity. Just take care with the units.

    If you have difficulty remembering that equation perhaps remind yourself of the similar equations for linear motion..

    Work = force * displacement
    Power = work/time
    so
    power = force * displacement/time
    but
    displacement/time = velocity
    so
    Power = force * velocity..............................................(2)

    see the similarity between (1) and (2)?

    The problem statement gives enough info to calculate the input power (electrical) and the output power is stated. Efficiency is one divided by the other expressed as a percentage.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Just starting out on DC motors and hit a snag
  1. Dc motor (Replies: 0)

  2. DC Motor (Replies: 3)

  3. DC Motor (Replies: 0)

  4. DC Motors Problem (Replies: 1)

Loading...