×
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

DC Motor Voltage Effects

DC Motor Voltage Effects

DC Motor Voltage Effects

(OP)
What are the effects of decreasing the terminal voltage on a DC motor (with brushes).  I cannot find the manufacturer's data sheet on this specific motor.  Is there a certain voltage the motor will no longer work at (assuming it is higher than the back EMF)?  Can I say that for every volt it is dropped, the life of the motor will be decreased by x% ?

Thanks,
JT.

RE: DC Motor Voltage Effects

The DC motor is voltage controlled. The back EMF is proportional to speed. So, when you reduce armature voltage, the speed is reduced. Life can increase, but it can also decrease due to less cooling.

All of the above is true if the excitation is kept constant or if it is a PM motor.

If there is a separate parallel field winding, there are several other things to take into account. Or if it has a series field winding. None of which has been stated.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC Motor Voltage Effects

Yes... Skogsgurra is correct. There are many types of DC motors, so you'll need to clarify what you have and what is the typical load scenario/application if you wish to gather answers which are useful and relevant. Sounds like you have a DCPM machine however.

Other effects you will have to consider is "brush drop" and environmental conditions such as temperature and humidity.
Brush drop is a non-linear voltage drop which is similar to a silicon diode drop in an electronic circuit. The appearance of brush drop is a consequence of the thin layer of cuprous oxide, an insulator that develops on the surface of the commutator. This is a result of a reaction between atmospheric oxygen and the commutator material facilitated by the heat generated by motor operation and arcing. Note conduction through the cuprous oxide layer occurs due to localized dielectric breakdown when current is passed through the brushes. The pros of this cuprous oxide film are that the voltage drop tends to reduce arcing effects, and serves to extend brush life. The con is that the voltage drop reduces the efficiency of lower voltage motors. Moreover the structural integrity of the film can change in very low humidity environments; consequently brush wear may be accelerated under these conditions.

Hope this helps...

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