31 - PVD3627-August 2011
For a DC motor, the mechanical time constant
σ
mech
represents the duration needed
to reach 63% of the final speed when applying a voltage step without any resistant
torque, if the electrical time constant is much smaller than the mechanical time
constant.
Remarks:
An overall summary of motor time constants is given a little further.
3.1.9.3. Thermal time constant of the copper:
copper
iron
copper
therm
Cth
Rth
*
_
=
τ
]
/
[
]
[
]
/
[
389
*
K
kg
J
Kg
copper
K
J
copper
Mass
Cth
°
°
=
With:
Rth
copper_iron
thermal resistance between copper and iron [°K/W]
Cth
copper
thermal capacity of the copper [J/°K]
Mass
copper
mass of the copper (winding) [kg]
Hereunder is given an overall summary of motor time constants:
Type
Electric time
constant [ms]
Mechanical time
constant [ms]
Thermal time
constant of
copper [s]
MGV420B
9,7
9,7
25
MGV430B
11,5
7,3
23
MGV620C
8,1
10,4
43
MGV635C
10,2
8,0
34
MGV820C
13,4
15,9
61
MGV840C
18,7
6,5
42
MGV930C
34,4
4,4
50
MGV950C
39,9
3,3
45
MGVA30D
27,6
6,5
62
MGVA50D
30,9
5,5
55
