Parker EX Series - Thermal Time Constant of the Copper

66 – Pvd3665_Gb_Ex_August 2022
Remarks:
For a DC motor, the mechanical time constant 
mech
represents the duration needed to
reach 63% of the final speed when applying a voltage step without any resistant torque.
However this value makes sense only if the electric time constant 
elec
is much smaller than
the mechanical time constant 
mech
(for the motor EX620EAO taken as illustration, it is not
the case because we obtain 
mech<

elec
.).
An overall summary of motor time constants is given a little further.
3.2.8.3. Thermal time constant of the copper:
coppertherm
CthRth *= 
]/[
][]/[
389*
KkgJ
Kg
copper
KJ
copper
MassCth


=
With:
Rth thermal resistance between copper and ambient temperature [°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]
EX310
3.0
1.1
60.2
EX420
4.6
1.4
71.0
EX430
5.2
1.1
79.8
EX620
8.6
1.3
137
EX630
10.3
1.0
158
EX820
8.5
2.1
135
EX840
11.0
1.5
171
EX860
12.9
1.3
206