User's Manual

Geo Direct PWM Amplifier

Connector PinOuts and Wiring 25

Note

The motor thermostats are brought in through connector X3.

Motor Cable, Noise Elimination

The Geo Direct PWM Drives’ voltage output has a fundamental frequency and amplitude that

corresponds to motor speed, torque, and number of poles. The Geo Direct PWM Drive produces higher

frequency voltage components corresponding to the rise, fall and repetition rate of the fast switching

PWM signals. Subsequently, it could naturally couple current noise to nearby conductors. This electrical

coupling can be problematic, especially in noise-sensitive applications such as using high-resolution

sinusoidal encoders, or high rate of communication which could suffer from Electro-Magnetic

Interference EMI. Proper grounding, shielding, and filtering can alleviate most noise issues. Some

applications may require additional measures such as PWM edge filters. The following; are general

guidelines for proper motor cabling:

 Use a motor cable with high quality shield. A combination braid-and-foil is best.

 The motor drain wires and cable shield should be tied together, and attached at both ends

of the motor and Geo Direct PWM Drive chassis. At the motor end, make a 360 degree

connection between the shield and motor frame. If the motor has a metal shell connector, then

you can tie the shield directly to the metal shell of the mating connector. The connection between

the cable shield and the motor frame should be as short as possible). At the Geo Direct PWM

Drive end, make a 360 degree connection between the shield and the provided studs or grounded

chassis (protection earth) at the M4 mounting screws.

 The motor cable should have a separate conductor (drain wire) tying the motor frame to the

Geo Direct PWM drive’s chassis.

 Keep the motor cable as short as possible to maintain lower capacitance (desirable). A

capacitance of up to 50 PicoFarads per foot (0.3048 m), and runs of up to 200 feet (60 m) are

acceptable with 240VAC. Exceeding these lengths requires the installation of a Snubber at the

motor end or an in-series inductor at the Geo Direct PWM Drive end.

 If the grounding/shielding techniques are insufficient, you may install chokes in the motor

phases at the Geo Direct PWM Drive end such as wrapping individual motor leads several

times through a ferrite core ring. DigiKey, Micro-Metals (T400-26D), Fair Rite (2643540002), or

equivalent ferrite cores are recommended. This adds high-frequency impedance to the outgoing

motor cable thereby making it harder for high-frequency noise to leave the control area.

GND

Tie cable shield to

shield stud or chassis ground

Motor Cable