Back EMF Test

http://cr4.globalspec.com/thread/11147
http://cr4.globalspec.com/thread/41321/About-back-emf

Hello dcpppf,

Thanks for your reply.

But the links explains only what is back emf and i am clear about the concept. But my question is why back emf test is performed in motor testing?

Regards,

sharath

If you truly do understand BEMF, then you should understand why it is part of testing. As with any other design factor, physical measurements are needed to verify calculated design values.

The tests will be performed to verify the design values and practical values. I do agree. But what is the significance of back emf testing? Which parameters are verified? Just i am trying to understand to answer to my friend who is working in production line.

I think you are expert, please answer.

Quality Assurance.

The exact reason and method a particular production line uses a particular test is determined by their engineers.

A simple overview is here --http://dcacmotors.blogspot.com/2010/03/waveform-of-brushless-dc-motor.html

Pantaz,

Thanks for your reply, the link explains back emf waveforms in a better way.

but i got the answer,

Back emf test is performed because the relationship between the back EMF and torque is so predictable.

Explaining:

K_E= e_LL / w_m where 'K_E' - back emf constant , e_LL - peak line voltage & w_m - speed in rad/sec

and e_LL is approximately equal to V_s where V_s is supply voltage.

In similar way Torque constant 'K_T' can be measured as

K_T= T / I where T- Torque in Nm and I - DC supply current to the controller

in the ideal conditions with no saturation, no resistance and no voltage drops in the controller,

K_T = K_E

And P_elec= e_LLI = V_sI = Tw_m

Hence this test predicts torque output of the motor.

This explaination is with respect to 3 phase square wave brushless dc motors.