User manual of EL8-EC***F AC Servo
49
Servo drive: EL8-EC750F, Servo Motor: ACM2-08008H2. When T = 2s, rotational velocity
= 3000rpm, load inertia is 5 times of motor inertia.
EL8-EC Drivers
Servo motor
Rotor Inertia
（
× 10
-4
kg.m
2
）
Max. regenerative energy
stored in capacitor Ec(J)
750W
ACM2-08008H2
1.66
22.85
Regenerative energy produced:
E1 =
(N + 1) × J × V
2
182
=
(5 + 1) × 1.66 × 3000
2
182
= 49.3J
If E1<Ec, internal capacitors can’t take in excessive regenerative energy, regenerative
resistor is required.
Required regenerative resistor power rating Pr:
Pr =
(E1 − Ec)
0.5T
=
49.3 − 22.85
0.5 × 2
= 26.45W
Hence, with the internal regenerative resistor Pa = 75W, Pr<Pa, no external regenerative
resistor is required.
Let’s assume if the load inertia is 15 times of motor inertia, Pr = 108.6W, Pr>Pa, external
regenerative resistor is required. And to consider for harsh working environment,
Pr(external)=108.6/(1-40%)=181 W
When selecting the resistance of the regenerative resistor, please be higher than the
minimum value recommended in table 2-3 but lower than Rmax
Rmax =(380
2
-370
2
)/Pr=7500/108.6=69Ω
In conclusion, a regenerative resistor with resistance 40Ω
-
70Ω and power rating 110W to
180W can be chosen.
Please take note that theoretical calculations of the regenerative resistance is not as
accurate as calculations done under normal operation.
