Sample calculations – Rockwell Automation 1398-DDM-xxx ULTRA 100 Series Drives Installation Manual User Manual
Page 285
Publication 1398-5.2 – PDF 1997
Dynamic Braking Resistor Selection
F-3
Sample Calculations
The following example uses an H4075 motor with a 10 times inertia
mismatch and dynamic braking resistors sized at four times the motor
winding resistance. The average power of the motor is 1116 Watts for
the selected paramters, but it is unlikely that a resistor with this
Wattage is required. Pulse type currents, such as this example, require
sufficient thermal mass to absorb the energy and to dissipate or
accomodate the peak Voltage. Adequate information for intermittent
duty cycle and surge current applications is seldom provided by
resistor manufacturers. However, often they will assist in resistor
selection when supplied with the current profile.
Note: The equations using the symbol ":=" are "assigned" in
Mathcad®.
H4075 Motor Parameters in MKS Units:
Load Inertia, Dynamic Braking Resistance and Velocity in MKS
Units:
Time vector:
Time Constant (seconds):
Current Calculation (Amps):
Instantaneous Power Calculation (Watts):
Intro
K
E
90
=
K
T
0.74
=
R
0.9
=
J
m
0.00068
=
K
E
K
E
60
⋅
2
π
1000
⋅ ⋅
---------------------------
=
K
E
0.859
=
:
:
:
:
:
Intro
R
L
4 R
⋅
=
J
L
10 J
m
⋅
=
ω
o
3000 2
π
⋅ ⋅
60
---------------------------
=
ω
o
314.159
=
:
:
:
Intro
t
0 0.01
…
0.5
,
,
=
:
Intro
τ
0.866 R
2 R
L
⋅
+
(
)
J
m
J
L
+
(
)
⋅
K
E
K
T
⋅
-----------------------------------------------------------------------
=
τ
0.083
=
: