How to know actual wattage of motors without capacitor?

[motorqs]

Hi all, hope everyone is fine. My question is single phase 220v induction motors related.
Let's say there is an induction motor which draws 370 watts at 225 volts. The motor is approx 1350 rpm, but similar motor of other manufacturer draws 300 watts which i assume is efficiency issue due windings may be?
What actually i want to know how to know actual power or capacity of motor in watts, amperes kw.
Because i noticed that most of manufacturers use wrong size capacitor normally big one for high torque or complete the rpm.
Please reply 2 questions:
1- Is there any way to determine actual motor power without capacitor.?

I believe my question is clear but if someone is not understanding it, To put it other way, my question is : IF I have a motor and there is no rating label and there is no Capacitor, how do I know what's actual power the motor is winded for? The motor is induction motor single phase. How do I determine actual wattage of a motor, how to test etc? This is somehow a root and technical question.

2- This person is running the motors without capacitors, Can I run the motors like this? If my motor only has 1 capacitor, how do I run that like this man doing in these videos:

http://www.youtube.com/watch?v=GFUa7bjNsZk

http://www.youtube.com/watch?v=lQipa_O-4QA

I hope my question is clear.
Thanks in advance to anyone who clarify this for me.

 

[davidbeach]

The motor power will be the power the load requires plus the motor's losses. If the cap is sufficient to allow the motor to run it shouldn't much impact on the wattage. Amps and thus kVA can definitely be impacted, but not watts so much.

 

[motorqs]

@davidbeach Thanks for your time reading and replying, but looks like you haven't understood what I asked, I rephrased my question. Please answer if you know this. Your answer is not what I asked for.
Thanks

 

[Skogsgurra]

Sorry motorqs, but your question didn't get much clearer. At least not so clear that we can give you a straight and useful answer.

If you have a motor that you have no data on, then you have to do several tests to find out what capabilities it has. Tests like checking what voltage and frequency it is wound for, how much load it can tolerate before getting hot, if it is a three-phase or single phase motor, if it is designed for continuous or intermittent operation and other such things.

So, I refrain from answering. There is, in my view, no answer.



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Shaft height or frame size is generally a fair guide to power output if you know how many poles the motor has. That can be determined by inspection of the windings.

 

[theode]

You need some sort of clue to start with.Capacitor sizes can vary over the same wattage range,depending who made the motor.
Also one capacitor size can run different wattages.You can rough guess from the windings (wire size,amount of turns) by seeing how full the slots look,
Example, a 0.25 kw would run from say 3 to 15 mf cap so you're still guessing.
Looking at the clips,the first motor has start and run windings similarly wound.
Join 1 end of start and run together (common) connect to supply Put capacitor across the remaining ends.
Supply one side,motor goes one way.Supply other side,motor reverses.
This is the basic principle.
Take the capacitor out,spin the shaft,it will still go.If you don't spin the shaft,it will just sit there and burn out.
So if you want to stand there spinning all day,feel free.
The second clip looks 3 phase wound,connected delta (dahlander)
Supply 1 phase.Connect capacitor across the other 2 phases,supply either side for direction,
When he put the wire across the 2 phase terminals,it just gives direction due to phase position,
If you listen to the motor,its not too happy and wouldn't last long due to imbalance.

 

[motorqs]

@Skogsgurra: it looks like you have not read my entire question, please reread if you want to help and answer as almost all info is there in my question.

@ScottyUK: Your answer is unclear, how do we inspect windings to know actual power of motor winding?

@theode: Thanks a lot man for taking time to read my questions and seeing videos, so far You are the person read and understood my question and I am again thankful you want to help. Please clarify few things:
1- The videos are not made by me, i found them online and added as ref, Does that mean I can run any induction motor without capacitor for few minutes just by rotating shaft with hand? Can you please explain process of doing so for single and 3 phase motors, like how do I connect wires after removing capacitor? And is it safe?
2- By doing above method, If i check the amperes, will those amperes be motor's actual power of winding? This is actually the thing I need to figure out.
3- What is the other method of knowing actual wound/motor winding power in ampere? Like you mentioned by gauging wire number, then turns etc? Please explain.
4- Is it true and almsot correct rule of thumb for capacitor sizing like 30 to 50 uf for 1kw ?

Thanks again theode, I look forward for your guidance and valuable response.

 

[theode]

Lets try and get this into context.
Due to the numerous types and designs of motors it is virtually impossible to detect wattage accurately.
Cap start/induction run ,Cap start/cap run,Induction start/Induction run,Permanent cap,split phase etc ,to name a few
Also various speeds give various frame sizes as does the duty it is rated for.
So if you don't know what it is,leave it alone and get the one for the job,
Some motors have very fine wire start windings so would burn out if connected for more than a few seconds,
Hence the need for centrifugal switches or relays.
There is no rule of thumb for capacitors as they are factored in when the motor is designed,
I suggest you google motor capacitors and see if you can find out from their many pages.
There are too many variables to answer your specific questions in this forum.

 

[motorqs]

Thanks