Previous in Forum: on delay timer   Next in Forum: busbar selection chart
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
5 comments
Rate Comments: Nested
porky2009
Commentator

Join Date: Sep 2009
Posts: 72

Missing Nameplate

09/19/2009 7:06 AM

Hi all,

How can I find out what size (KW rating) a electric motor is when the name plate is missing ? I know that its supply voltage is 380/220 Vac 3 phase... but that is about it..

Thanks
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
2
msamad
Guru

Join Date: Feb 2009
Location: Houston, USA
Posts: 946
Good Answers: 244
#1

Re: Missing Nameplate

09/19/2009 11:40 AM

You can find the approximate KW using the starting current and no load current.

With starting current:

  1. Start the motor with full voltage and try to measure the starting current. It will be difficult to record it because starting current lasts less than 5 seconds. Measure it at least 5 times (with half an hour time gap between each start) and use the average starting current value.
  2. Full load current = Starting current / 6

With no load current:

  1. Start the motor with no load and measure the no load current
  2. Full load current = 3 x No load current

If the Full load current is closer from both of the methods above, the KW may be more accurate. Use the lowest Full load current (FLA) found from these two methods and the approximate KW = 1.732 x FLA x 0.8

As I said this is approximate KW. For safety, you can deduct 10% from this value.

Hope it helps.

-MS

__________________
 "All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
Register to Reply Good Answer (Score 2)
No more Good Answers. Go to first "Almost" Good Answer
saraswata1981
Associate

Join Date: Nov 2009
Posts: 27
#5
In reply to #1

Re: Missing Nameplate

11/11/2009 1:57 AM

kW=root 3 xVxIXcos phai
Register to Reply
vtbgiraud
Commentator

Join Date: Nov 2008
Posts: 80
Good Answers: 4
#2

Re: Missing Nameplate

09/19/2009 11:24 PM

Not sure in what country you are, but at the sawmill I worked at in Canada, there was a chart that listed shaft size, lenght of shaft, height above mounting pad, dimensions of mounting pad, plus a lot of other info. Knowing the RPM and physical size and type of motor (TEFC, open drip, uframe), and the start and run amperages, you should be able to make an educated guess. If all fails talk to a rewind shop, they will have someone that will know.

Vic
Register to Reply Score 1 for Good Answer
Go to Next "Almost" Good Answer
XPRO
Active Contributor

Join Date: Sep 2009
Location: South Africa
Posts: 17
#3

Re: Missing Nameplate

09/20/2009 7:13 AM

My approach as a mechanical guy is to check dimensions of the motor with motor specification as to determine the kW from the specification.

Another way to verify is to measure the amps the motor draws, divide by 2. Use this number to check on a possible kW. Keep in mind this (as far as I know) is reasonable for 380V. Bear in mind that the motor amps vary with load and as such this in not conclusive. I also do not know if this works for 4, 6, 8 pole motors.
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
Anonymous Poster
#4

Re: Missing Nameplate

09/21/2009 4:53 AM

Determine frame size
Register to Reply
Register to Reply
Have a Different Question?
5 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

Anonymous Poster (1); msamad (1); saraswata1981 (1); vtbgiraud (1); XPRO (1)

Previous in Forum: on delay timer   Next in Forum: busbar selection chart

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (62 right now)
Show Members
Advertisement