MV3DB Series DB Units
3. System Design
(07/06)
ALSPA MV3000e Dynamic Braking Units
Page 3-3
Total Start/Stop cycle time (t3)
Repeat
Average
Regenerative
Power
Peak Regenerative Power
time
power
t1
t2
Figure 3-2 DB resistor power dissipation
3.5.2
Calculation Based on Inertia
If the regenerative power is not known, but the inertia of the load is known, the resistance and
power rating may be calculated as follows:
Resistance,
Ω
−
=
)
(
2
.
91
1
2
2
1
2
N
N
JN
t
V
R
DB
where
DB
V
= DB operating voltage (see Table 2-2 in Section 2 “Specifications”)
J
= system inertia (kgm
2
)
1
t
= braking time (seconds)
2
N
= initial speed (r/min)
1
N
= final speed (r/min)
Note:
J
=
)
)
/(
1
(
2
ratio
box
gear
J
J
load
motor
×
+
.
If there is no gear box,
ratio
box
gear
= 1.
Inertia of the motor and load to be determined from the respective suppliers.
Peak power (at start of braking) =
p
P
=
J N
N
N
t
(
)
.
2
1
2
1
912
−
The resistor should have a peak power capability equal to the power during braking and be
able to withstand this power for the braking time
t
1
.
It should also have an average power capability given by:
