Rockwell Automation 1336_S_F_T Allen-Bradley Dynamic Braking - Manual (Page 8)

Heavy Duty Dynamic Braking 8
1336-5.64 — July, 2005
Step 1 — Determine the Total Inertia
Step 2 — Calculate the Peak Braking Power
Compare the peak braking power to that of the rated motor power. If the
peak braking power is greater that 1.5 times that of the motor, then the
deceleration time (t
3
- t
2
) needs to be increased so that the drive does not
go into current limit. (This is assuming that 150% of motor power is less
than or equal to 150% drive capacity.)
J
T
= J
m
+ (GR 2 ✕ J
L
) 1.0 lb-ft 2 = 0.04214011 kg-m 2
J
T
= Total inertia reflected to the motor shaft (kg-m 2 )
J
m
= Motor inertia (kg-m 2 )
GR = Gear ratio for any gear between motor and load (dimensionless)
Note: For 2:1 gear ratio, GR = 0.5.
J
L
= Load inertia (kg-m 2 )
J
T
= +( ✕ ) J
T
= __________ kg-m 2
P
b
=
J
T
= Total inertia reflected to the motor shaft (kg-m 2 )
ω
b
= Rated angular rotational speed (Rad / s = 2
πN
b
/ 60)
ω
o
= Angular rotational speed,
less than rated speed down to zero (Rad / s)
N
b
= Rated motor speed (RPM)
t
3
- t
2
= Deceleration time from
ω
b
to
ω
o
(seconds)
P
b
= Peak braking power (watts)
1.0 HP = 746 watts
J
T
✕
ω
b
(
ω
b
-
ω
o
)
t
3
- t
2
P
b
=
✕ ( – )
[ – ]
P
b
= __________watts