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  4. About "Motor Performance Chart"

五十嵐電機製作所コラム

About "Motor Performance Chart"

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 What is “Motor Performance Chart”?

 

This performance chart is written in the torque reference system.

Based on torque T [Nm],
you can read the following parameters;

Rotation speed  : N [r / min]

Current   : I [A]

Output   : P [W]

Efficiency   : η [%]

curve_img01.png
Torque is the moment of force around the axis of rotation and represents the rotational force of the motor.

The unit is [Nm].


How to read “Motor Performance Chart”

Torque - Rotation

Horizontal axis  : Torque [Nm]

Vertical axis  : Rotation speed [r / min]

curve_img02.png

No-load rotation speed  N0 [r/min]

Rotation speed when the motor is not loaded

Stall torque Ts [Nm]

Torque when the load of the motor is increased and the rotation of the motor is stopped

Examples from the right figure

N0=4000 [r/min]

Ts =   0.8 [Nm]

 

Torque - Current

Horizontal axis  : Torque [Nm]

Vertical axis  : Current [A]

curve_img03.png

 

No-load current  I0 [A]

Current that flows when a voltage is applied when the motor is not loaded

Stall current Is [A]

Current when the load of the motor is increased and the rotation of the motor is stopped

Examples from the right figure

I0 = 0.2 [A]

Is = 8.0 [A]

 

Torque – Output

 

Horizontal axis  : Torque [Nm]

Vertical axis  : Output [W]

   curve_img04.png
Output

P [W] = N [rad/sec] × T [Nm]

           = N [r/min] × 2π/60  × T [Nm]

The output line can be drawn from the rotation line.

 

Example:  Output at 0.1 [Nm]

 2000[r/min] × 2π/60 × 0.1[Nm] = 21[W]

 

The efficiency line 

 

Horizontal axis  : Torque [Nm]

Vertical axis  : Efficiency [%]

   curve_img05.png
 Efficiency

η [%] = (P [W])/((V × I)  [W])  × 100

The efficiency line can be drawn from the current line and applied voltage.

 

Example :  Efficiency  at 0.1 [Nm]

 21/(24×1.2) ×100 = 73[%]


Changes in each parameter

 

Changing the following four parameters will affect the performance chart.

Voltage of power-supply

  Change in voltage applied to the motor

curve_img06.png

Number of turns

 Change in the number of turns of the winding wound around the core

Diameter of winding wire

 Change in wire diameter of the winding wound around the core

Type of magnet

 Change in magnetic force

Voltage of power-supply

If only the voltage of power-supply changes, the performance is proportional to the change of the voltage of power-supply.

 curve_img11.png
V :Original voltage

V′:Voltage after changed
curve_img07.png
N0′ = N0×V′/V
Is′ = Is×V′/V
Ts′ = Ts×V′/V
 curve_img12.png

Number of turns

When the number of turns is reduced, the no-load rotation speed and stall current increase proportionally.

 curve_img13.png
 

n :original number of turns

n′:number of turns after changed

 curve_img07.png
 N0′ = N0×n/n′ 
 I0′= I0 × n/n′
 Is′ = Is×n/n′ 
 Ts′ = Ts
curve_img14.png

Diameter of winding wire

When the diameter of winding wire is increased, the stall torque and stall current change in proportion to the square of the diameter of winding wire.

curve_img15.png

Φ:original diameter of winding wire

Φ′: diameter of winding wire after changed

 curve_img09.png
N0′ = N0
Is′ = Is×(  Φ′/Φ  )2
Ts′ = Ts ×(  Φ′/Φ  )2
curve_img16.png

 

Type of magnet


Performance changes as the strength of the magnetic force changes.

The dry type is weaker and the wet type is stronger.

 curve_img17.png
 N0′ = N0 × m/m′   curve_img09.png
 Is′ = Is
 Ts′ = Ts ×  m′/m 
 curve_img18.png

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