What makes a quality motor from a poor quality

[beatcan]

Our company is sourcing motors from China for exhaust fans. These are PSC motors, ranging from 1/4HP to 1HP. What is the major determining factor that makes a good quality motor good. Is it the quality in materials (i.e. copper, laminations, slot liners etc.)? Workmanship? Engineering design? Any suggested tests to determine the quality and longevity of the motor.
We have purchased motors in the past that seemed to be good as far as I can tell (they looked and tested the same as our proven motors), however the failure rate was much higher than our standard motors. We always load motors well under the rated heat rise for the class of motor, under worst case conditions. Therefore we can assume that the motors did not fail because of our design.
Any advise?

 

[automatic2]

Field tests are the ultimate. Ask for referrals and follow them up.

 

[electricpete]

It doesn't sound like any easy question to me. There are quite a variety of failure modes and an even wider variety of tests and studies that you could undertake to attempt to answer your question.

 

[fredb]

Hi,

The items that are important in electric motor quality are:
1. Winding insulation (paper stuff)
2. Number winding encapsulant impregnation dips
3. Bearings (should be longest life and sealed)
4. Cast iron bodies are better than sheet metal (less twisting and bending)
5. Get largest frame available in needed horsepower
6. Operating temperature.
7. Get highest service factor available.
8. Get copy of motor tests from factory and compare.
9. Look at your voltage and frequency, for example a 10% drop in voltage will increase full load current by 5-10% and frequency at 105% will increase % slip by 10-15%. Voltage unbalance can also cause problems, because a small voltage unbalance will cause an even greater current unbalance resultant in temp. rise.

I hope all this helps.