Dynamic Braking Resistor Selection
D-3
Installation Manual for Models ODM-005, ODM-005i, ODM-010, ODM-010i, ODM-020 and ODM-020i
Sample Calculations
The following example uses a 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
parameters, 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 accommodate the peak
Voltage. Adequate information for intermittent duty cycle and surge current applications is seldom pro-
vided 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):
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
=
:
:
:
:
:
R
L
4
R
⋅
=
J
L
10
J
m
⋅
=
ω
o
3000 2
π
⋅ ⋅
60
---------------------------
=
ω
o
314.159
=
:
:
:
t
0 0.01
…
0.5
,
,
=
:
τ
0.866
R
2
R
L
⋅
+
(
)
J
m
J
L
+
(
)
⋅
K
E
K
T
⋅
----------------------------------------------------------------------
=
τ
0.083
=
:
i t
( )
K
E
ω
o
e
t
–
τ
----
⋅
⋅
0.866
R
2
R
L
⋅
+
(
)
------------------------------------------
=
:
0
0.1
0.2
0.3
0.4
0.5
0.6
0
20
40
i( )
t
t
P t
( )
1.154
K
E
K
T
ω
2
o
⋅
⋅
⋅
R
2
+
R
L
⋅
(
)
------------------------------------------------
e
2
–
t
⋅
τ
------------
⋅
=
:
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