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Motor Choke



General information to chokes can be found on page Chokes.

Why use motor chokes?

The motor choke

  • compensates high capacitive charge/discharge currents typical of shielded motor cables approx. 25 m and longer
  • reduces current alternation noise in the motor
  • reduces current ripple in the motor
  • makes it possible to use longer motor cables
  • reduced load on the amplifier output stages and rectifiers
  • reduced stress on the insulation of the motor windings

For reasons of electromagnetic compatibility, the motor must be supplied with power via a shielded cable. The structure of a cable with 100% shielding and the capacity equivalent circuit diagram (to earth) are shown below.


The digital servo amplifiers' high switching frequencies and steep switching edges give rise to the transfer of capacitive currents to the shield by the three phases (U, V, W). These currents flow from the shield to earth. Depending on the cable length and cable capacity (determined by design), this can lead to the generation of shield currents with peak values of up to 20 A. These shield currents place a load on the servo amplifiers and motor and, on large systems, lead to shifts in potential which can damage other components.

This effect is evident in particular on systems with multiple amplifiers operating in parallel on the same mains filter. The motor chokes slow down the rate of rise of the motor current (reduce edge steepness), thereby reducing the current transferred to the shield. The core material of the choke is magnetized with switching frequency of the servo amplifier. That produces losses in the choke, in the form of heat, so it does warm up.

Why is the cross-section of the motor cable important?

Motor cables longer than 50 m with a small cross-section (e.g. 4 x 1.0 mm²) and therefore a higher equivalent resistance are able to reduce the oscillation tendency of the LCR oscillating circuit (amplifier/choke/cable/motor). This cross-section can also be advantageous for cable lengths shorter than 50 m if the cable capacity and motor inductance are very high. However, the current carrying capacity of the cable must always be within the limits specified by EN 60204.

When is a motor choke required?

Amplifier Length Motor cable
S300 25 ... 50 m
S400 25 ... 50 m
S601-620 25 ... 100 m
S701...724 25 ... 50 m
AKD 25 ... 50 m

Current Kollmorgen motor chokes

CE, UL, and RoHS information can be found on page Approvals.

Type Nominal Current Inductance Frequency CE UL Usable for Drawing
3YL-20 20A 120 µH 8,3 kHz x x S300, S400, S601...620, S701...712 Step
3YL-24 24A 120 µH 8,3 kHz x   S300, S400, S601...620, S701...724 Step
3YLN-06 6A 900 µH 8 kHz x x

S300, S400, S601...606, S701...706, AKD-x003x...AKD-x006x

3YLN-10 10A 900 µH 8 kHz x x S300, S610  
3YLN-14 14A 900 µH 8 kHz x x

S614, S712, AKD-x012x

3YLN-20 20A 450 µH 8 kHz x x


3YLN-24 24A 450 µH 8 kHz x x S724, AKD-x024x Step
3YLN-48 in process            
3YLN-72 in process            
3YLN-96 in process