Am I Looking for NOISE trouble (RF45 Conversion)

[Bird_E]

I have been working on an RF45 style mill conversion for like 3 years! It's getting close and starting to work on the electronics. So this is what am about to do. I have an IGUS cable chain that will carry all the cables and hoses from my control box, up the back of the column and to the head.

In the cable chain I will have the power Wires for the VFD to the motor,
an Airline for power draw bar, Coolant line, 120Volt Power line to controll some air solenoids and a USB cable to connect to a POKEYS board in the head.

I have converted the head to belt drive, so I no longer have any gears in the head. I plan on using the empty head cavity to house the air solenoids and POKey (Usb I/O board) and a few other odds and ends, such as an Tachometer pickup. I also plan on mounting a 4 line lcd module on the front of the head and have the POKeys drive messages to it such as RPM and XYZ position, etc...

So here is the real question.....
I know VFD lines can very noisy and considering that my plan is to have a USB cable run in parrallel with the VFD lines is this totally impossible to get it work considering noise issues? Should I even try this?

do you have any suggestions
Thanks!
Bob

[doorknob]

This is just a guess because I do not have direct, hands-on experience with either a VFD or a pokeys board. So feel free to ignore the following comments.

(comments removed to avoid possible misinformation)

[mike_Kilroy]

doorknob, I'd agree with you, if your basic premise of vfd noise being low freq of at most a few hundred hz was right! please don't get upset with me contradicting you! It is GREAT that everyone gives their ideas!!

That said, I am afraid it may not work at all. The vfd noise comes from the transistors turning on and off to make that low freq 0 to say 200hz sine wave of current into the motor. they turn on and off in nanoseconds nowadays; that is like 100-1000mhz freq and this is what gets into parallel run low voltage signal wires. A rule of thumb is to try to keep any sig wires like USB, serial, analog, etc., at leas 12" away from the vfd motor leads - assuming motor leads are shielded 4 conductor cable with shield tied at both ends. If just 3 wires to motor, you probably cannot get away with analog, usb, serial cables within 3 feet.

I do not know the IGUS track you refer to but if it is available with 2 separate conduit type separated runs that would be better: if you show this post to your IGUS source they will understand and probably offer the proper hardware solution.

So buy shielded motor cable (3 motor leads with motor case ground wire all with an overall shield around them) for best chance of success. If you cannot separate the usb from it at least you have a semipossible chance of success - ok, in my opinion (I apply and sell vfd & servo systems and have to solve this kind of noise problem almost daily)!

[doorknob]

No problem at all - I had modified my initial take on the situation shortly after posting my original comment... But regardless of cable shielding, what do you think about methods for reducing coupling into the pokey inputs themselves?

[mike_Kilroy]

other than good shielding just separation of power and sig lines as far as possible. We generally dont add external filtering on sig lines but we do add filtering on power lines; noise filters to reduce vfd type noise are common on the 3ph input to high end cnc machines, as well as right next to the vfd or servo drives, and even high freq chokes in series with the motor leads on output of drives. usuallly on small or lower cost machines these filters are not used unless a last resort to fix noise issues.

[Bird_E]

The cable chain / conduit is pretty small like 3" X 1", So the USB will run in parrallel within an inch or less of the VFD cables the run is about 4 feet total.

Just curious where can I find sheilded 4 conductor power cable for the motor?
its a 2 HP motor, so what guage of wire should I be looking to use?

Thanks!
Bob

[Al_The_Man]

Belden sell a cable specifically for VFD applications.
But not cheap.
VFD Cables | Belden Industrial Solutions
Al.