Measuring effective voltage and current across brushless DC motor

[mawad]

Dear All,
I want to measure the actual power consumption by brushless DC motor. In case of brush DC motor I used voltage divider and current sensor to measure the voltage and current accross the brush DC motor coil and then calculate the electrical power. However in case of brushless DC motor, I have three windings (three cables). How can I measure the effective voltage and current to the motor in order to calculate the electrical power.
Thanks in advance

 

[dogzzz]

Hi !!
In your motor I can imagine that , the DC supply is feed to an inverter out of which 3 phases will come out , thus a resistor (voltage divider ckt) can be placed
as shown in the photo calculate the voltage , and can ammeter be placed in series and thus V* I shall give you power consumed .
I hope this will help.

 

[itsmoked]

Yep.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[GroovyGuy]

Hi Mawad,
Dogzzz is 100% correct, you don't have a "brushless DC" motor, but an asynchronous AC motor with a PWM controller.
Don't forget to factor in the losses thru the controller (which will be at least 5%). Alternately some of the more advanced controllers , with a serial or Ethernet comm port, can provide a ton of data including; speed, torque, power voltage, current, etc.

 

[waross]

an asynchronous AC motor

Actually a synchronous AC motor.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dogzzz]

Motor has permanent magnet rotor , thus will always perform synchronous operation , until somebody adjusts frequency at PWM .

 

[cswilson]

Just so nobody is confused -- a "brushless DC" motor IS an AC synchronous motor.

I wrote this up for engineering.com a couple of years ago:

http://www.engineering.com/Designer...icleID/8131/What-is-a-DC-Brushless-Motor.aspx

Curt Wilson
Omron Delta Tau

 

[mawad]

Many thanks to you all.

@ dogzzz . Do you mean measuring the voltage across the power supply, but the power supply voltage is constant and known? I am wondering if I can measure the effective voltage applied to the brushless DC motor as I don't know any information about the driver efficiency