Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Dec Fri 13, 2019 4:28 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 6 posts ] 
Author Message
 Post subject: Motor question
PostPosted: Nov Sun 21, 2010 7:45 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 683
Location: Louisiana
This question is for the motor experts on the forum:

Lets say you are working on a single phase 120 volt induction motor with no start or run capacitor.
If you were to apply 120 volts to the stator with the rotor removed, would it draw more or less current that with the rotor in place?

I've been doing some experiments and some of my results are not what i thought they would be.


Top
 Profile  
 
 Post subject:
PostPosted: Nov Sun 21, 2010 8:37 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
I would expect more, because its inductance is lower. But then, if the iron doesn't saturate, its inductance might be higher. It wouldn't saturate without the return magnetic path through the rotor.


Top
 Profile  
 
 Post subject:
PostPosted: Nov Mon 22, 2010 5:55 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3350
Location: Poplar Bluff, MO USA
I would expect more current because the armature is not in place and rotating to cause a counter EMF to be generated in the field coils which opposes the current in the field.

http://en.wikipedia.org/wiki/Counter-el ... tive_force

_________________
However beautiful the strategy, you should occasionally look at the results.
Winston Churchill


Top
 Profile  
 
 Post subject:
PostPosted: Nov Sat 27, 2010 9:08 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 683
Location: Louisiana
Thank you for the replies and the link.
I had initially thought that since the rotor was not installed and this is the focus of the work of the motor then the current draw would be less than rated. In other words no rotor, no load, minimum current.
That's what I thought.
But with your responses and that link I see my error in thinking. I didn't think about the interacting flux.
Now that I have the motor reassembled, the current draw is 0.5 amps at 110v - just as it should be according to the motor rating.
Without the rotor, the current is almost twice that.
Very interesting and a good learning experience - another reason I like restoring things.

Alan


Top
 Profile  
 
 Post subject:
PostPosted: Nov Sat 27, 2010 9:54 pm 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 11814
Location: Powell River BC Canada
With the rotor in and prevented from turning
what is the 'locked rotor' current?

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


Top
 Profile  
 
 Post subject:
PostPosted: Nov Sat 27, 2010 11:47 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
Should be 10 or 20 times the full-load current, essentially limited by the DC winding resistance.


Top
 Profile  
 
Post New Topic Post Reply  [ 6 posts ]  Moderator: Alan Voorhees

All times are UTC [ DST ]


Who is online

Users browsing this forum: decojoe67, jukeboxman, Tim Mullen, Waterski, wyocodak and 13 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB