×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Motor Current Draw

Motor Current Draw

Motor Current Draw

(OP)
Hi,

Is there a way (sure there is) to calculate the new current draw from an existing motor, if i increase the pulley size on a fan?

Thanks,

 

RE: Motor Current Draw

If you increase pulley diameter by factor f, the fan speed will go up by factor f.  Demanded torque will go up by roughly factor of f^2. Demanded power will go up by factor of roughly f^3.  Motor current should go up by roughly f^3 assuming you are relatively high in the motor current range (let's say above 50% FLA to begin with) so that you can neglect effect of magnetizing current.

There is a big assumption that the system remains fixed (no flow control valves that will adjust themselves toward closed in response to the change), that the system flow characteristic is roughly DP~ flow squared.  Also it assumes efficiency is constant. Finally I think this only holds when the dp is small relative to the total absolute pressure so the density is roughly constant.

=====================================
(2B)+(2B)'  ?

RE: Motor Current Draw

Very well explained, electricpete -- as always.

Iken:  If you're talking about a not-too-big fan, what I've done in the past to avoid overloading the motor is to purchase an adjustable-sheave type pulley, then increase the fan speeds by little bits while monitoring motor amps.

Of course, stop the fan and lock out the disconnect when adjusting...

Good on ya,

Goober Dave  

RE: Motor Current Draw

(OP)
Thanks electricpete, i have just spent a bit of time sufing the net and found more equations for this also.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources