AC servo motor
B&R Industrial Automation 8KS synchronous motors
Large synchronous servo motors up to 140 kW with stall torque up to 555 Nm air-cooled (575 Nm water-cooled 8KSJ9) and speeds to 3,000 rpm, with fan or water cooling.
Key specifications
| Standstill torque (max) | 575 Nm |
|---|---|
| Speed (max) | 3,000 rpm |
| Power (max) | 140,000 W |
| Frame sizes | 240 x 240, 320 x 320 |
| Cooling | radial fan, axial fan or water |
Summarised in our own words from ABB's published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Notes on this data
Page text quotes 'up to 555 Nm'; its table lists 575 Nm stall torque for the water-cooled 8KSJ9.
Specify Motion is not affiliated with ABB. B&R Industrial Automation and 8KS synchronous motors are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a B&R Industrial Automation part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
Kinco's current-generation AC servo motor line, matched to the JD2 and FD5P PRO drives. Small-inertia 40-80 mm frames run at 3000 rpm on 220 V; large-inertia 130 and 180 mm frames are 1500 rpm machines reaching 47.8 Nm rated and 7.5 kW, with 23-bit multi-turn absolute encoders as standard.
| Published maximum | 8KS synchronous motors | SMK Series AC Servo Motors (SMK40S/60S… |
|---|---|---|
| Rated torque | 575 Nm | 47.8 Nm |
| Peak torque | — | 119.5 Nm |
| Speed | 3,000 rpm | 6,000 rpm meets or exceeds |
| Power | 140,000 W | 7,500 W |
Leadshine low-voltage PMSM servo motors from a 25 mm 33 W unit up to a 130 mm 2 kW unit, wound for 24-60 V DC buses. Fully published data covers torque to 6.4 Nm rated / 16 Nm peak, 17-bit absolute or 2500 ppr incremental encoders and IP65. Designed for ELD2, 2ELD2 and ELD3 drives.
| Published maximum | 8KS synchronous motors | ELVM Series Low-Voltage DC Servo Motors |
|---|---|---|
| Rated torque | 575 Nm | 6.4 Nm |
| Peak torque | — | 16 Nm |
| Speed | 3,000 rpm | 6,000 rpm meets or exceeds |
| Power | 140,000 W | 2,000 W |
Leadshine motor-plus-drive units from 200 to 750 W on 24-48 VDC, with 17-bit magnetic encoders, CANopen or Modbus/pulse control and up to 300% overload, published in the Leadshine low-voltage DC catalogue.
| Published maximum | 8KS synchronous motors | iSV2 Integrated Low-Voltage Servo Motors |
|---|---|---|
| Rated torque | 575 Nm | 2.39 Nm |
| Peak torque | — | 7.2 Nm |
| Speed | 3,000 rpm | 4,000 rpm meets or exceeds |
| Power | 140,000 W | 750 W |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What an AC servo motor is
An AC servo motor is a permanent-magnet synchronous motor designed for closed-loop control of position, speed and torque. A wound stator is driven by a servo drive with sinusoidal three-phase current, while magnets on the rotor follow the rotating field. A high-resolution encoder or resolver on the shaft feeds position back to the drive, which adjusts current many thousands of times a second. The result is precise, dynamic motion with high peak torque, typically about three times the continuous rating for short periods.
When engineers choose an AC servo motor
Choose an AC servo for machine axes needing fast, accurate motion under varying loads, such as packaging, robotics, machine tools and printing. Compared with steppers, servos keep torque at high speed and cannot silently lose position. The trade-offs are cost and set-up: a servo needs a matched drive, feedback and tuning. For simple, low-speed indexing with a steady load, a stepper may be cheaper. For very low speeds and high torque, a gearbox or direct-drive motor may be needed.
How to specify the B&R Industrial Automation 8KS synchronous motors
Send these with your enquiry and an engineer can confirm the right 8KS synchronous motors variant or an equivalent:
- Continuous and peak torque (Nm)
- Rated and maximum speed (rpm)
- Load inertia and inertia ratio
- Supply voltage: 230 V single-phase or 400 V three-phase
- Feedback: incremental or absolute encoder, resolution (bits)
- Holding brake, IP code and shaft options
- Flange size and mounting (mm)
Common mistakes to avoid
- Sizing on peak torque without checking RMS torque over the cycle
- Ignoring load-to-motor inertia ratio, which makes tuning hard
- Forgetting the brake is for holding, not dynamic stopping
- Using a motor and drive pair that the supplier has not matched
B&R Industrial Automation 8KS synchronous motors: frequently asked questions
What is the B&R Industrial Automation 8KS synchronous motors?
Large synchronous servo motors up to 140 kW with stall torque up to 555 Nm air-cooled (575 Nm water-cooled 8KSJ9) and speeds to 3,000 rpm, with fan or water cooling. Published series figures include standstill torque 575 Nm, speed 3,000 rpm, power 140,000 W. It is made by ABB; Specify Motion can help source it or propose an equivalent.
Who makes the B&R Industrial Automation 8KS synchronous motors?
The B&R Industrial Automation 8KS synchronous motors is made by B&R Industrial Automation (ABB) and is listed here for engineers comparing options. Specify Motion is not affiliated with ABB; brand names are used only to identify the product.
What is the standstill torque of the B&R Industrial Automation 8KS synchronous motors?
The published series maximum standstill torque is 575 Nm. Individual models and sizes in the 8KS synchronous motors range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the B&R Industrial Automation 8KS synchronous motors?
Yes. On published figures, Kinco SMK Series AC Servo Motors (SMK40S/60S/80S, SMK130G, SMK180G) and Leadshine ELVM Series Low-Voltage DC Servo Motors are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
What is the inertia ratio in servo sizing?
The inertia ratio compares the load inertia reflected to the motor shaft with the motor's rotor inertia. High ratios make the axis harder to tune and slower to settle. Many engineers aim for below about 10:1, and lower for highly dynamic axes, using a gearbox to reduce reflected inertia where needed.
Do AC servo motors need an absolute encoder?
Not always. Incremental encoders need a homing routine after power-up, which is acceptable on many machines. Absolute encoders know their position at power-on, avoiding homing, which saves time and suits robots and multi-axis machines. Multi-turn absolute encoders track turns even when power is off.
Further reading: How to select a servo motor · Servo vs stepper · Servo and stepper motors
Other ac servo motor series
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