Understanding Motor Data Sheets

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In summary: The angle of 48.3 degrees should not be used in the calculation of... sorry, i don't understand what you mean by "angle of 48.3 degrees." can you please clarify?
  • #1
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I am trying to understand the motor data sheet and not clear on the data provided
I am trying to understand the Hurst motor data sheet, but i am not clear on the table provided, please help me to understand the data provided
1604417445990.png


System Input: Volts is all in the range of 24V, so it is 24V BLDC motor, i understand.
Amps: It is the current drawn from the DC source i understand.
Watts: I am having slight confusion here, if i take any value say Load2 Volts = 24.05V and the current is 1.07 amps. Then the Watts or the power input should be V*I = 24.05 * 1.07 = 25.7335 but the value specified is 24.90. Why is this difference?
Motor Data: What exactly is the Motor Data? I assume they are the 3 phase signals we apply to the motor. How the values of Volts(RMS), Amps(RMS) Watts(RMS) are derived?
 

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  • #2
PhysicsTest said:
Then the Watts or the power input should be V*I = 24.05 * 1.07 = 25.7335 but the value specified is 24.90. Why is this difference?
Non-unity power factor because the motor has some inductance, even in the case of nonsinusoidal signals.
 
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  • #3
The RMS (root mean square) values and peak values are determined by observation over time under varying conditions ##-## for practical purposes, RMS may be viewed as the normal operating value.
 
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So, my understanding is for the system input they measure the input volts and currents and using a tool they calculate the power factor, based on that they arrive at the System input watts. Am I correct? Similarly for the Motor data, they calculate the ##V_{rms}, I_{rms} ## and calculate the output. So it is all measured data.
 
  • #5
Yes it is probably all measured data. There are many methods of measurement including RMS power meters, and VAR meters.

You can also calculate it if you sample instantaneous voltage and current. At any instant, P=V*I. If you sum many instant samples over a period you can sum them to get average power, avoiding power factor. AC quantities, AC power, reactive power, and power factor are defined for an integer number of whole cycles. But they do not invalidate instantaneous measurements.

To be clear, suppose the signals to the motor are pulses roughly 240 Hertz. If you sample V and I 10000 times per second, calculate P=V*I 10000 times and find the average of those, you get the correct answer for that second.
 
  • #6
Any ideas about the columns Motor Data; Volts, Amps, Watts?

The last line (and many others) show Watts > V x I.
V= 19.86, I= 7.47
19.86 x 7.47 = 148, but Watts is listed as 171.
 
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  • #7
Tom.G said:
Any ideas about the columns Motor Data; Volts, Amps, Watts?

The last line (and many others) show Watts > V x I.
V= 19.86, I= 7.47
19.86 x 7.47 = 148, but Watts is listed as 171.
Could this be down to efficiency, or perhaps calculating the motor supply as three phase power?
 
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  • #8
I surprised myself by getting the answer for the motor data. Top of the table resistance and inductance is mentioned ##R = 0.57 ; L = 0.64 ##. The impedance is then ##Z = 0.57 +j*0.64##. The angle of impedance is
##\theta = tan^{-1}(\frac{0.64} {0.57}) = 48.3 ##Degrees. The formula for the power of the 3 phase is
##P = \sqrt3 *V_L*I_L*\cos(\phi) ; V_L = 19.86; I_L=7.47 ##. Substituting the values I get ##170.9##, it almost matches with what is mentioned ##171.10##. I hope my calculations are correct?
 
  • #9
Now i got one confusion, the reactance of inductance is ##X_L = \omega L, Z = R + jX_L##. But i have considered only inductance, is it correct? Please help.
 
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  • #11
Sorry for the delay, yes i understand that the only reactance is the inductance, but the reactance is given by
##X_L = \omega L## in that case the power calculation does not match with the data sheet, but if i take reactance equal to inductance i.e. ## X_L = L ## then the power data calculation matches with the data sheet. I don't understand what is the mistake.
 
  • #12
PhysicsTest said:
I surprised myself by getting the answer for the motor data. Top of the table resistance and inductance is mentioned ##R = 0.57 ; L = 0.64 ##. The impedance is then ##Z = 0.57 +j*0.64##. The angle of impedance is
##\theta = tan^{-1}(\frac{0.64} {0.57}) = 48.3 ##Degrees. The formula for the power of the 3 phase is
##P = \sqrt3 *V_L*I_L*\cos(\phi) ; V_L = 19.86; I_L=7.47 ##. Substituting the values I get ##170.9##, it almost matches with what is mentioned ##171.10##. I hope my calculations are correct?

the angle of 48.3 degrees should not be used in the calculation of total power, as doing this neglects the existence of back emf of the motor. that 48.3 degrees would be sufficient as power factor in calculating copper losses, but then you'll have to use voltage drop instead of voltage rating in the power calculation.
 
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1. What is a motor data sheet and why is it important?

A motor data sheet is a document that contains important information about a motor, such as its specifications, performance characteristics, and electrical connections. It is important because it provides essential information for selecting, installing, and operating a motor.

2. What are the key components of a motor data sheet?

The key components of a motor data sheet include the motor's model number, type, frame size, horsepower rating, voltage and current ratings, speed-torque curve, efficiency, and physical dimensions. It may also include information on ambient temperature, insulation class, and mounting options.

3. How do I interpret the performance characteristics on a motor data sheet?

The performance characteristics on a motor data sheet can be interpreted by understanding the relationship between speed, torque, and power. The speed-torque curve shows how the motor's speed changes as the load torque increases. The efficiency rating indicates how well the motor converts electrical energy into mechanical energy. It is important to compare these characteristics to the requirements of the application to ensure the motor is suitable.

4. Can I use a motor data sheet to compare different motors?

Yes, a motor data sheet is a useful tool for comparing different motors. It allows you to easily compare specifications such as horsepower, voltage, and efficiency. However, it is important to also consider other factors such as cost, reliability, and compatibility with the application.

5. How do I select the right motor based on the information in a data sheet?

To select the right motor, you should first identify the requirements of your application, such as the speed, torque, and power needed. Then, compare these requirements to the specifications on the motor data sheet. It is also important to consider factors such as cost, reliability, and compatibility with the application. If you are unsure, it is best to consult with a motor expert for assistance.

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