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Help with electrical interference
« on: May 19, 2012, 11:58:07 PM »
Good evening all,
I have just completed building a 1300mm X 900mm router table with rack and pinion gantry drive design. I am very happy with the operation of the table and have had great success with the accuracy of it but I am now faced with this frustrating problem.

Subsequent to the initial design I have connected 5 limit/ home switches all wired in series and connected to pin 10 on the breakout board. Also a dedicated Emergency stop switch to pin 12 on the breakout board. Both work exactly as expected, however as soon as I start the spindle motor, it triggers a limit switch activation and the machine stops. If I reset it, the machine will run for about another 10 seconds or so before doing the same. On the diagnostic page, all five limit switch LED's illuminate for about half a second each time the interference occurs. The spindle is a Chinese HY brand 1.5 kw unit and it appears to operate without any issues very smoothly. The spindle is totally electrically isolated from the breakout board. I.e. control is only achieved through the operation of the touch panel on the front of the VFD.

This is what I have tried so far to overcome the problem:

All wiring to the stepper motors, limit switches and spindle motor has been replaced with shielded wire and all shielding taken to a common ground.
The spindle carrier frequency has been changed throughout its entire range with no change.
The config debounce has been set to a figure of up to 2000 ms with no change.

Short of pulling what little hair I have left out, I am stumped with how to fix this.

Any help appreciated

Stuart

Offline dude1

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Re: Help with electrical interference
« Reply #1 on: May 20, 2012, 12:29:18 AM »
how close is the e stop wire and limit wires to the vfd and power wires had same problem just moved e stop wire and separated all power wires from control wires and all problem disappeared
Re: Help with electrical interference
« Reply #2 on: May 20, 2012, 01:14:26 AM »
E stop wire is some distance away but the limit switch wiring runs in the same cable chain as the wiring from the VFD to the spindle. I had been advised this was OK if I used screened cable all around, but I am starting to think otherwise. Was just looking to see if there were any other possible causes or remedies before ripping the wiring out.

Offline Tweakie.CNC

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Re: Help with electrical interference
« Reply #3 on: May 20, 2012, 01:33:55 AM »
Hi Stuart,

This is worth trying before doing any major work....

Connect one 0.1uF capacitor between each used input to you BoB and GND. This will mostly suppress noise spikes which may be triggering you stop condition.

Tweakie.
KEEP SAFE !
Re: Help with electrical interference
« Reply #4 on: May 20, 2012, 02:45:51 AM »
Thanks Tweakie,
This was something I was also thinking about doing but wanted to hear from others first. So I am clear, we are talking about a normal Ceramic Cap (not electrolytic)??

Appreciate your good advice.

Stuart

Offline Hood

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Re: Help with electrical interference
« Reply #5 on: May 20, 2012, 03:22:11 AM »
Have you got the screen connected at one end only and all screens to the same point
Hood

Offline Tweakie.CNC

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Re: Help with electrical interference
« Reply #6 on: May 20, 2012, 03:46:56 AM »
Thanks Tweakie,
This was something I was also thinking about doing but wanted to hear from others first. So I am clear, we are talking about a normal Ceramic Cap (not electrolytic)??

Appreciate your good advice.

Stuart

Hi Stuart,

Yes, the miniature ceramic disc caps are OK (don't forget to sleeve the leads, if necessary, so they cannot short to each other)

Tweakie.
KEEP SAFE !
Re: Help with electrical interference
« Reply #7 on: May 20, 2012, 04:18:21 AM »
Have you got the screen connected at one end only and all screens to the same point
Hood
Hi Hood,
At each Microswitch I have taken the Screen to a lug and connected it to the Aluminium frame of the machine. At the other end of the cables (where they come together at the breakout board) I have joined them all as a common connection and it is connected to the table ground (which is also connected to the supply earth).

Stuart
Re: Help with electrical interference
« Reply #8 on: May 20, 2012, 04:20:34 AM »
Thanks Tweakie,
This was something I was also thinking about doing but wanted to hear from others first. So I am clear, we are talking about a normal Ceramic Cap (not electrolytic)??

Appreciate your good advice.

Stuart
OK. Shall give this a try in the morning when I can get a couple of caps.

Thanks.

Stuart
Hi Stuart,

Yes, the miniature ceramic disc caps are OK (don't forget to sleeve the leads, if necessary, so they cannot short to each other)

Tweakie.

Offline Hood

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Re: Help with electrical interference
« Reply #9 on: May 20, 2012, 04:29:53 AM »
Have you got the screen connected at one end only and all screens to the same point
Hood
Hi Hood,
At each Microswitch I have taken the Screen to a lug and connected it to the Aluminium frame of the machine. At the other end of the cables (where they come together at the breakout board) I have joined them all as a common connection and it is connected to the table ground (which is also connected to the supply earth).

Stuart

 I would try cutting the shield  connection at the switch end, having it earthed at both ends may set up a loop.
Do you also have the VFD and motor wires shielded? If not you may want to also do that.
Hood