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VFD and noise questions
« on: August 31, 2008, 07:19:18 PM »
I have three machines between 2 and 15 HP all running VFD and three phase spindle motors , all have the vfd mounted in the same cabinet with my breakout boards relays , amplifiers etc with no problems.

I am finaly finished with my big MHP 30hp lathe (THANKS HOOD) , the last thing to do was wire the VFD to the breakout board so mach can control speed direction etc.  The VFD on this one is mounted on the wall aprox 6 feet from the machine and everything has been working perfectly before hooking up the control wire . Walk over push the start/stop buttons etc no interference.

I have run a sheilded cable from the VFD to the breakout board consisting of one wire from the analog out on my breakout board , two wires +- from the vfd power supply to the breakout board and three wires from the vfd for direction , common and fw/rv . Both ends of the sheild are grounded , tryed it both grounded and ungrounded.

Now the instant I switch the spindle on with either m3 or m4 it spins breifly and I get an estop and the watchdog triggered message.  In General config the debounce and index (?) settings were set at 200 for the top one and 4 for the lower one. At those settings the spindle will spin up for almost 10 seconds before going into estop . I have adjusted the numbers up and down with out any better results.

If I disable the watchdog in gen config I can power up the spindle but everything on screen freezes , cant move the mouse , hae to hit the physical estop and once the spindle winds down everything is fine , While the spindle is running I can walk over and turn the vfd off by using the stop button on its control panel , it stops as it should but Mach is still frozen until I hit estop .

Any thoughts on how to solve this problem greatly appreciated,  should I possibly not be using the 10v power supply in the VFD for the analog output on my breakout board? on all the others I am using a seperate power supply , this 30 hp vfd had a power supply built in .
« Last Edit: August 31, 2008, 08:50:39 PM by panaceabeachbum »

Offline Hood

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Re: VFD and noise questions
« Reply #1 on: August 31, 2008, 07:23:01 PM »
Best to just have the shielding grounded at the control end I think.
 Try setting the debounce to 2,000 and see if it helps but really thats not a great idea as it slows all responses down.
 Do you have the motor wires shielded? Maybe that is the source of the noise.
Hood
Re: VFD and noise questions
« Reply #2 on: August 31, 2008, 08:17:04 PM »
the motor wires are not sheilded but they never get anywhere near the breakout boards , any wiring or the cabinet that everything is in . They also didnt seem to cause any problems while i was running it this week turning it on manualy with the key pad. i will try detaching the cable sheild from the ground in the VFD and play with a much higher value for the debounce to see if that helps

Offline Hood

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Re: VFD and noise questions
« Reply #3 on: August 31, 2008, 08:21:44 PM »
OK didnt realise it was working from the VFD previously, just thought it was possibly the manufactured 3 phase from the VFD that may have been the issue. Dont know a great deal about grounding but from what I gather its best to have only one end grounded and also to have all of your grounds connected to one single point.
Hood
Re: VFD and noise questions
« Reply #4 on: August 31, 2008, 09:14:32 PM »
It's generally not a good idea to ground a shield at both ends.  That encourage the shield to become a conductor, which is *really* not what you want.  I would connect the shield only at the VFD end, since the VFD is providing the power for the signals.  What BOB are you using, and how is it connected?

Regards,
Ray L.
Regards,
Ray L.
Re: VFD and noise questions
« Reply #5 on: August 31, 2008, 09:16:19 PM »
Thanks Hood , I just set the debounce at 2000 and 3000 with no luck , also just have the control cable grounded on one end . No luck yet . I am going to pull the control wire thru metal conduit instead of plastic in the morning and see if that helps.

The other thing that might be causing a problem is the cable I am using for the control wire has 4 extra wire that are unused , I just folded them back and tie wrapped them to the cable on each end. Is it possible these are acting as an antenna of sorts picking up stray RF ? 

This is the first one I have done where the VFD is outside the main cabinet , all the others are just a foot or so from my breakout board and are all bonded to the same big grounded mounting plate, I wonder if a big bonding strap between the VFD and the body of the machine might help. The machine , the VFD , Rotary Phase converter, motor and Delta to Wye transformer are all well grounded
Re: VFD and noise questions
« Reply #6 on: August 31, 2008, 09:22:46 PM »
"Is it possible these are acting as an antenna of sorts picking up stray RF ?" - Not really. 

Is the *only* difference between the configuration that works and the one that doesn't that you've added the control cable from the VFD to the electronics enclosure?

Regards,
Ray L.
Regards,
Ray L.
Re: VFD and noise questions
« Reply #7 on: August 31, 2008, 09:33:08 PM »
Hi Ray , I have tried it with the sheild grounded at both ends and just one end , at the VFD and in the main cabinet, each in turn , no change.
I am using the C11 board from CNC4PC , same BOB I am using on 3 other machines running VFD .

I have to 10v power supply from the VFD attached to the external power supply input for the analog out on the BOB , The analog out signal 0-10v is attached to the analog input on the VFD . 

There are two dc relays on the c11 BOB , both with NO contacts and a common in , one is triggered by pin 1 the other by pin 16 . The VFD has a 24v power supply for the inputs that choose direction , in the VFD I have the switch set to source inputs and the + from the 24v power supply run to the common in term on the relays and one wire each to the two terminals in the VFD for forward and reverse . I have set the switch to sink and attached the - to the relays, same interference.

M3 is set to output 1, output one is set to trigger pin one , When M3 is called out the relay at pin one is energized and completes the circuit to the VFD to turn clockwise (forward with my rear turret lathe). Which it does until the watchdog trig thing puts the machine in estop.  Reverse is wired similarly to the relay on pin 16 , m4= output2. output2=pin 16 , m4 callout energises the relay at 16 and the spindle turns anti-clockwise until the watch dog triggers estop .

I am pretty sure the BOB to VFD wiring is correct , I have been using the same setup (smaller vfd) on three other machines for quite a while with no problems. I am sure I am just overlooking something simple
Re: VFD and noise questions
« Reply #8 on: August 31, 2008, 09:34:12 PM »
Yes thats the only difference , worked perfectly before the control wire

Offline Kristin D

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Re: VFD and noise questions
« Reply #9 on: August 31, 2008, 09:47:56 PM »
Do you have any ceramic or other non-polarized caps around? Might try connecting one to each signal lead at the BOB and to signal ground.

Kristin