Voltage into DTHC

[ddfarmboy]

All, I have had multiple instances where I am getting voltage back into my controller and damaging the DTHC on my CandCNC system. They have been very helpful but I am out of ideas on where the voltage is coming from on my home built table. I am hoping someone will have suggestions.

I have a ground rod under the table connected to a central point on the table that connects to the plasma work lead and water pan.

Wiring is ran through cable chain/guides. This includes home switches, motor cables, and the torch cable, but it is separated in the track.

My limit switches are the typical Omron SS-5GL2. Currently I mounted them by tapping the factory holes (don't remember size, but small) and bolted to the table. Wondering if my tapped holes are possibly allowing voltage into one of the circuits. Doubtful, but I am getting desperate!!

Early symptoms before it gets zapped, I see noise bands on the monitor screen, this has happened even with the powermax 65 (rs485 equipped) powered off. This makes me think it is not an end issue

I checked for resistance between the table ground and the controller and found it was infinite.

My controller, computer, monitor, and communication hub are all mounted in a steel box. My idea was, I can close the lid and protect everything in a small shop. Originally the plasma was also on the same cart, but I moved it off trying to isolate the issue.

I have had my input power checcked by 2 different electricians. The system is hooked to 2 different circuits on the same panel.

Is it possible that the motors are leaking to the table? How could I check?

Sorry for the long rambling post... just really frustrated.

Thanks Dan

[robertspark]

Can you sketch out the wiring schematic (roughly)

[acourtjester]

With you seeing noise bands on the monitor there must be something external that is generating the noise. You said it is a home built table but did not say what the environment was, is there any large electrical equipment in the area? Having electricians check the power may mean yours is wired correctly, does not mean it is clean.

[weldguy]

Any AC tig welding going on the area when this happens?

[ddfarmboy]

There is no large electrical equipment in my shop. I am a 1 one man attempt at a show, so nothing else running. I have not noticed issues with anything else, though not sure what I would see with dirty power. The one thing that just hit me... I have radiant barrier lining my ceiling and 2 layers ofsteel interior/exterior... am I working in a faraday cage? The other thing is my shop has poor cell reception which makes me think if nothing gets in then nothing gets out?

My power is a 100 am sub panel from my main box with a local ground rod.

I will work on a sketch.

Thanks guys

Dan

[ddfarmboy]

Here are a couple of pics of my system.

Control Box (computer, controller, hub, UPS, monitor) for protection from sparks and such in my small shop!

control box.jpg

Here is the wire routing to the cutting head when I was working squaring stuff up. I need to do a better job of separating the home switches (yellow wires) and the motor wires (gray).

Plasma_1.jpg

I believe I was told that the Cat 5 cables can be coiled? The extra length is coiled in the control box.

The extra motor wire lengths are hooked under the table. I have never had any issues with the motors not responding like commanded.

It was suggested that I put Ferrite chokes on the cables. This would be on the end nearest the controller. Is there benefit from putting them on the Cat 5 cables?

Thanks again!

[ddfarmboy]

@acourtjester. Do you have any pics of how you are connecting the shield drain wires? Can they be hooked together with a single wire to the ground lug?

[wmjersey]

I've seen this before and it's because the machine doesn't have a earth ground. 6 foot copper rod driven into the ground with #6 bare ground wire running from the table. This ground is separated from your breaker box ground which should have been grounded in a similar way as described above. Do not trust grounding to your building. CNC equipment can be effected by transient voltage from other equipment. You'll be out about 20 bucks and home depot or Lowes will have everything you need.

[ddfarmboy]

its grounded. Added a ground wire from the z axis to the gantry to the table frame and to the ground rod. Thank you though for the reply

[acourtjester]

Did the ground rod help with your problem? I use 18 ga stranded and shielded cable for my motors, I use 5 pin connectors at my controller to connect the motor cables with the shield through the connector. How ever I don't connect the shield inside the controller, I use the same cable from the connectors to the motor drivers. You are using a CandCNC electronics package, I have used theirs setup twice so I don't think that is your problem. The bands of noise on the monitor still bug me and I keep going back to the environment.
I am not sure I understand this statement "I have radiant barrier lining my ceiling and 2 layers of steel interior/exterior... am I working in a faraday cage" Is this a in floor heating for the room above? I have worked with Faraday cages as I worked installing and maintaining MRI scanners.
There are filters that you could install on the incoming power to the controller similar to this one, the controller may already have one.
https://www.ebay.com/itm/AC-115-250V-6A ... SwgAdekf-x

[ddfarmboy]

I have had a ground rod from the start. I did add a dedicated ground wire from the z axis to the gantry to main ground connection on the table. Single wire connected to each component, but even with that I still damaged the rs485 hub and DTHC card.

The radiant barrier is on the ceiling to create an air gap with the existing insulation and an air barrier. After this was installed it affected cell reception in my shop. One of my friends joked that I had made a large faraday cage out of my shop. I was thinking / wondering if I was trapping my rfi type noise in the building? The building is a pole barn with steel panels on the inside wall and as the exterior wall with spray foam insulation.

I installed the computer in a steel box with the monitor on the lid so I could close and protect stuff when not in use. Originally the controller was also in the box, but it was moved to the bottom of my cart as in the picture.

20200521_200354.jpg

20200521_205249.jpg

[acourtjester]

Now I understand the radiant barrier is really a heat barrier not a true EMI shield.
Do you have a multimeter if so I would disconnect some of the grounds and see if there is a voltage from one to another, ground loops can cause problems too.

[ddfarmboy]

So I tried disconnecting individual grounds, but still had noise on the monitor. Looking back, I didn't check the voltage in the power cord with different ground configurations.

I did check voltage on the controller power cord and found that I have about 8 volts between the neutral and ground with the system powered up and motors enabled. With the system powered and motors disabled it was about 1.2V. Just at the outlet, with nothing plugged in, I had about
0.28 volts.

For kicks I tried them monitor on a different computer and left it up for 20 minutes and it didn't seem to have any issues.

The final thought is I am checking all this with the DC fault light lit (indicates a power issue/potentially a short). So all this may really be misleading me.

[acourtjester]

If I understand what you said
I did check voltage on the controller power cord and found that I have about 8 volts between the neutral and ground with the system powered up and motors enabled.
You may have a problem with the power supply for the motors or how they are hooked up. I use switching power supplies, the inputs are labeled L for line (black wire), N for neutral (white wire), and a ground symbol for the ground wire (green wire).

[ddfarmboy]

I sent the controller in to have it looked at..not sure where to go from there. Tom has been pretty good helping me too and I do appreciate input here. Thanks! Dan

[TJS]

I have Candcnc set up too. I have my plasma unit in a metal box. I have my UBOB unit in a separate metal box. I also have my PC separate from the metal boxes. The DTHC, Hub and voltage probe are mounted separately and away from each other.