we are currently building a motion platform for an airplane simulator and the linear motion actuators will be driven by 6 servo motors of type: Syntron 3KW AC 380V 130HMB-30100.

The datasheet says that the inrush current is 22.1A compared to 7A nominal current, and since the motors will be starting and stopping all the time we wondered if this could cause problems with our supply (63A 3 phase 400V).

Hence I wonder if ac servo motors will draw a significant high current each time they start after stopping, or if the motor only draws high current during the initial power up.

Eventually if anyone knows whether the motor driver (HS0300A-P22S) will help eliminate this in some way.

Motor specs Motor specs continued

  • \$\begingroup\$ of course it will. Can you provide a data sheet for your motor driver? \$\endgroup\$ – Christian Aug 25 '19 at 12:13
  • \$\begingroup\$ You'll need to: either limit the number of motors starting simultaneously, or soft start them (reducing startup torque), or add some surge current capability to your power supply. (Old school : rotary convertor with a big flywheel. Nowadays : electronics.) \$\endgroup\$ – Brian Drummond Aug 25 '19 at 14:14
  • \$\begingroup\$ I have added datasheet for the motor now \$\endgroup\$ – Estin Myrhaug Aug 26 '19 at 10:19

This will come down to how quickly you try and move the motors in your servo loop, the inrush current is caused by the motor seeing full mains applied, and a phase error appearing across the phases as the rotor is stationary at that moment, while mains may be up to 90 degrees out of phase (maximum torque)

when you move a servo slower than its maximum tourque limit, the phase error is smaller, and thus the amount of current is smaller, your motors are in a control loop, meaning they never really stop while powered on, instead you will generally feel a vibration as the loop keeps correcting back to the desired point,

Because of this control loop, the maximum current is only dependent on how much torque you try and have it apply when moving to a new set point, for a constant load scenario this would mostly feed back to acceleration and top speed,

As for your controller, I would rather not go digging through the controllers datasheet, but if it has jerk correction, I would keep it set on the low side.

  • \$\begingroup\$ I have added datasheet for the motor now in chinese, so google translate is required. I have not managed to locate the driver datasheet. \$\endgroup\$ – Estin Myrhaug Aug 26 '19 at 10:20
  • \$\begingroup\$ This still comes down to the phase angle difference between the driver and the motors position, the larger that difference, the closer to the maximum current rating of the motor you can reach, when it is close to 0, you draw the minimum current, usually the no load current, when it is +90 or -90 it draws the maximum, the phase offset is proportional to how much of the motors maximum torque your trying to exert, so the faster you try to move it with a load, the more current it will draw. \$\endgroup\$ – Reroute Aug 26 '19 at 10:26
  • \$\begingroup\$ Ok, thank you for the answers😊 \$\endgroup\$ – Estin Myrhaug Aug 26 '19 at 12:59

The inrush current is due to the capacitor banks being charged when you apply power supply. Once the bank capacitors are charged then it will sink just the nominal current. If you start and stop the servo continuously is just a normal operation for the servo, but you could face lot of regenerative power during braking, in this case a braking resistor is needed.

You didn't provided any datasheet regarding your motor and driver.

If you have 6-axis servo system, then it's better to have a central power supply module with capacitor bank and separate power modules for each axis. You would need only one braking resistor (if needed) and further you could have also regenerative power supply, so the excess of energy is fed back into mains grid.


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