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To let users easily calculate the power of external brake resistor, the calculations are described below.
(a) Without external load
If the motor is repeated running forward and reverse, the braking regenerative energy would return to
the aluminum capacitors of servo drive. When the P-N voltage exceeds a particular value, the brake
IGBT switch is turn on and the brake resistor would dissipate the regenerative energy. The following
statement and table provide the calculation of regenerative power.
The Es and Ec of various drive capacity are listed below.
Rotor inertia, J
(x10
-4
kg‧m
2
)
(*1)Regenerative
Energy Es (joule)
(*2)Regenerative
Energy Ec (joule)
Note1: Es is the regenerated energy of a motor without loading that runs a rated speed then stops.
Note2: Ec is the motor deceleration energy that charges into the DC capacitors.
The capacity of brake resistor is calculated as follows:
BR S C
P 2 N+1 E E T( )/
Where:
BR
P : Power of brake resistor
N :The ratio of load inertia to motor shaft
(Defined by users)
If the ratio of load inertia to motor shaft is N, deceleration from the rated speed to stop; the
regenerative energy is (N +1) × Es. The brake resistor consumption is (N +1)× Es - Ec joules. Assuming
the duty cycle is T second, then the recommend power of brake resistor is 2 × ((N +1) × Es-Ec) / T. The
calculation procedure is as follows. J is the motor inertia. (unit: kg‧m2)
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