Ground loop G251

[Jay C]

Not trying to stir up anything, but I could swear I read on here recently from Marcus that by adding a resistor in series with the G251 (and this is the part I can't exactly recall) it would eliminate the last vestiges of "audible noise" with the G250/251. I could be wrong and it only applies tot he G540 so please set me straight.

Jay

[P.Passuello]

You are right.
I have found the relevant post and copied it here.
The G540 does not have this problem as it is optically isolated.

Cheers
Peter



---IMPORTANT APPLICATION NOTICE---

Problem: Eliminating obnoixious hissing, sizzling and squealing sounds. The G251 drives make unpleasant noises in multiple axis applications. This doesn't hurt the drives and they will not have positioning errors but the sounds are very annoying.

The G251 drive is not a chopper. It is a synchronously clocked pulse width modulated (PWM) drive. It is inherently silent by design, it should make no hissing, squealing, grunting or whistling sounds or any sounds at all.

Cause: The G251 drives are not optoisolated. Signal GND (term 12) from each drive must connect to the parallel port GND (pin 25) to complete the step and direction signal path. Each G251 drive's Signal GND has a slightly different voltage potential because of motor phase currents and wiring resistance back to the power supply.

This small but inevitable (<100mV) potential difference between drive grounds causes significant (>100mA) ground-loop currents to flow between the drives. This high frequency (20kHz) AC current is sufficient to disrupt the operation of the of the motor phase current regulators and make them audibly noisy. The drives are still perfectly accurate but now make annoying noises.

Cure: Install a 100 Ohm 1/4W resistor in series with each drive's Signal GND (term 12) to parallel port GND (pin 25) circuit connection. This completely cures the audible noise problem and renders the drives utterly silent while stopped or turning at slow speeds.

The 100 Ohm resistors are too small to have any effect on performance but are large enough to reduce ground-loop currents 1,000 to 10,000-fold (<<100uA). Such small currents are now completely unable to interfere with the normal, silent operation of the G251 drives.

Mariss

[Jay C]

Thank you Peter.

[Jay C]

Update: this worked perfectly ... the sweet sound of silence

[NiklasJ]

@Jay C

Sorry for this stupid question but do I understand it correctly that you connect the signal ground (term 12 of the G251) to lpt ground, not directly but by/through a 100Ohm resistor?
(English is not my native language)

/Niklas

[Jay C]

Yes , all I did was disconnect the wires I had connected to the COMMON terminal on my C10 BOB and solder on a 100ohm resistor (brown black brown) to the end. Then just inserted and tightened the screw terminals. My C10 is configured so that COMMON is GND.

Jay