All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > The Projects Forum

Notices

The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 04-06-2008, 12:34 AM
martgreg martgreg is offline
Junior Member
 
Join Date: Mar 2008
Posts: 17
Default Slowing down a ac motor

Hi I am still working on my fan project ... but am trying a simpler approach and was wondering if it possible to get a regular fan from the store and slow down the rpm by adding a variable resistor "a potentiometer"

Remember this only has to work for a while ..not production,

Or will i end up killing my self and burning down my school.

The motor will be 120 volt ac , 60 htz .35 amps or close


any help will be greatly appreciated.. or any more info needed would be grand

thanks again ..

this is such a helpful forum..
Reply With Quote
  #2  
Old 04-06-2008, 01:18 AM
Audioguru Audioguru is offline
Banned
 
Join Date: Dec 2007
Location: Ontario, Canada
Posts: 9,411
Default

Look in Google for AC Motor Type and you will see some that some types sync with the mains frequency and other types that are "universal" can be slowed by reducing the duty-cycle of the power with pulse-width-modulation.
Which type of motor are you talking about?

A variable resistor in series with a motor must be huge and expensive since it will get very hot. The motor might be the wrong type for a huge variable resistor anyway.
Reply With Quote
  #3  
Old 04-06-2008, 02:22 AM
martgreg martgreg is offline
Junior Member
 
Join Date: Mar 2008
Posts: 17
Default

umm ...

I am basically pulling it from a brand new box fan.... is there any way of me looking at it .. or getting any info from it that would help me find out what type it is ?


thanks for your help



mg
Reply With Quote
  #4  
Old 04-06-2008, 03:32 AM
jpanhalt jpanhalt is online now
E-book Developer
 
Join Date: Jan 2008
Location: Ohio, USA(GMT-5)
Posts: 3,734
Default

Does the motor have carbon brushes? Very few small fan motors have brushes today. Also, a motor like AG is referring to will often be labeled, AC/DC; whereas, the motors that can't be controlled with a resistor we be AC only.

John
Reply With Quote
  #5  
Old 04-06-2008, 03:47 AM
Audioguru Audioguru is offline
Banned
 
Join Date: Dec 2007
Location: Ontario, Canada
Posts: 9,411
Default

I think most fan motors are a cheap induction type which syncs to the mains frequency and need the frequency to be changed (very complicated circuit) to change the speed.

The big ceiling fans switch how many poles are used to change their speed.

I have a 30 years old drill that has sparking brushes. My fans don't have brushes.
Reply With Quote
  #6  
Old 04-06-2008, 03:55 AM
jpanhalt jpanhalt is online now
E-book Developer
 
Join Date: Jan 2008
Location: Ohio, USA(GMT-5)
Posts: 3,734
Default

But, if the fan is shaded pole, it can be contolled with phase. That is, a light dimmer, which I think is easier and cheaper than a big potentiometer. John
Reply With Quote
  #7  
Old 04-06-2008, 04:26 AM
Bill_Marsden's Avatar
Bill_Marsden Bill_Marsden is offline
Super Moderator
 
Join Date: Mar 2008
Location: Dallas, TX (GMT-5 w/ DST)
Posts: 19,045
Blog Entries: 5
Default

Depends on the type of motor. My first thought was a light dimmer (lovely solution to so many problems controlling AC), but those work by reducing RMS power by cutting off part of the sign wave, changing their shape.

If it is a frequency dependent problem than this might work, but I've never built it. It was a solution I put up for another post.

__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
Reply With Quote
  #8  
Old 04-06-2008, 12:09 PM
jpanhalt jpanhalt is online now
E-book Developer
 
Join Date: Jan 2008
Location: Ohio, USA(GMT-5)
Posts: 3,734
Default

Actually, for shaded pole motors (often used in fans), there are commercial speed controllers for about $20. Those controllers are basically just triac light dimmers.

If the OP is willing to open the case of the fan, he can determine if it is shaded pole, either by posting a picture here of the outer laminations or by going to Wikipedia and looking at the picture there. In the alternative, one can often just look though the cooling holes and see the tell- tale single coils of the shaded pole as shown here (from Wikipedia). John

Last edited by jpanhalt; 03-05-2011 at 11:28 PM.
Reply With Quote
  #9  
Old 04-07-2008, 12:20 AM
martgreg martgreg is offline
Junior Member
 
Join Date: Mar 2008
Posts: 17
Default

Hey thanks guys...

Here are a couple of pictures from a motor that I might end up using.....


This one has 6 wires from the motor....

grey and white go to a little black box ( forgot whta this was.. someone told me)

then 4 wires ( white , grey , red ,brown,) go to power cord and 0 1 2 3 speed switch.

I took this apart and connected the white wire to the ribbed wire section of the power cord . Then attached one of the wires ( brown) to the otheer smoothe wire of the power cord... crossed my fingers and plugged it in...

still alive and it spins.. but i dont know what speed ... lol...

a speed control would be great...
Attached Images
File Type: jpg ScreenShot022.jpg (22.6 KB, 23 views)
File Type: jpg ScreenShot023.jpg (35.3 KB, 24 views)
File Type: jpg IMG_0031.JPG (90.8 KB, 23 views)
Reply With Quote
  #10  
Old 04-07-2008, 01:55 AM
jpanhalt jpanhalt is online now
E-book Developer
 
Join Date: Jan 2008
Location: Ohio, USA(GMT-5)
Posts: 3,734
Default

Does not look like a shaded pole motor to me. It looks more like a conventional squirrel cage induction motor where the number of poles and synchronous speed is determined by the way the wires are attached. Apparently, from the labels on the switch, it is a 3-speed motor. With that type of motor, it will be difficult or impossible to get speeds that are in between the three choices without using a variable frequency drive. Even then, the range of useful speeds may be quite limited.

See: Wikipedia for induction motors.. Here is another photo from that source. John

Last edited by jpanhalt; 03-05-2011 at 11:29 PM.
Reply With Quote
Reply   Post New Thread

Tags
,


Related Site Pages
Section Title
Worksheet Performance-based assessments for AC circuit competencies
Worksheet AC motor theory
Worksheet AC generator theory
Textbook Other specialized motors : Ac Motors
Textbook Single-phase induction motors : Ac Motors
Textbook Tesla polyphase induction motors : Ac Motors
Textbook Brushless DC motor : Ac Motors
Textbook Reluctance motor : Ac Motors
Textbook Synchronous Motors : Ac Motors
Worksheet DC motor theory


Similar Threads
Thread Thread Starter Forum Replies Last Post
troubleshooting a treadmill motor controller fritzycat General Electronics Chat 9 06-22-2014 03:09 PM
E69477 115V AC motor: How to wire? asbradford852 The Projects Forum 2 05-20-2014 02:29 PM
Integrating AC motor with DC Logic Harrington82 The Projects Forum 3 04-11-2014 04:09 AM
Two input (selectable) 3 phase breaker/switch for AC Induction Motor rohanmun General Electronics Chat 1 06-15-2011 06:56 PM
AC Motor Reversal kfife The Projects Forum 11 11-13-2009 03:32 AM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 11:25 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin
Copyright ©2000 - 2014, vBulletin Solutions, Inc.