leaking current? shortage? static electricity?

raoulvh
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leaking current? shortage? static electricity?

Post by raoulvh » Wed Jun 25, 2014 10:22 pm

Hi ShapeOko fans!

I recently build a ShapeOko 2. I succesfully milled my first 2 jobs this week, very cool!

Today I connected my laptop to my ShapeOko again, opened up GRBL Controller and it wouldn't connect. I have my Arduino and grbl shield in the gShield Enclosure, bolted to the frame of the machine. When I touch the frame, it feels a bit like static electricity. After jiggling a bit with the cables, the GRBL Controller connected, but I still felt static electricity running through the frame so I started disconnecting cables to look for a possible shortage.

The only thing connected now is the power supply to the grbl shield (which is in the arduino and bolted to the frame with the gshield enclosure) and I still feel the electricity.

Is it normal that you feel a bit of current in the frame? I don't think I felt that earlier, so I guess not, so how could I go from here to solve this?

Thanks in advance!

cvoinescu
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Re: leaking current? shortage? static electricity?

Post by cvoinescu » Wed Jun 25, 2014 11:11 pm

It is common for laptop power supplies and the type of supply used with the Shapeoko to have leakage that can be "felt". It is not static electricity, but rather AC at a low current that you are feeling. This is often enough to destroy equipment if the connection isn't secure (for instance, an unshielded USB cable with a dirty ground contact). Sometimes, this is caused by power supplies designed to be grounded (earthed) being used without ground (earth), which is dangerous and should be avoided. However, many brick-type power supplies are designed to be "floating" (ground/earth not connected), and it's the design of the EMI filter that causes the slight leakage, which is not dangerous to people, but some can feel it. It's also possible that your power supply is defective, and I don't know a good way to test that.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Woodworker
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Re: leaking current? shortage? static electricity?

Post by Woodworker » Wed Jun 25, 2014 11:36 pm

If you have a meter, test from the chassis to ground or between the 2 points where you are feeling it. I would not think that it is safe if you feel it, sounds like either a ground loop or defective power supply.
BRuce - SO2 #4798 - IC's Z axis upgrade, customized Z rail and Z motor mount, spindle Dewalt 611

raoulvh
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Re: leaking current? shortage? static electricity?

Post by raoulvh » Thu Jun 26, 2014 6:46 am

I pulled the thing a little bit further apart to have a better look, when I noticed that one of the bolts, which connects the Arduino to the enclosure, had gone a tiny bit through the solder mask (probably by tightening it to tight).

The enclosure comes with only 4 nylon washers, which go underneath the board according to the manual. So the bolts are directly touching the PCB from the top, by screwing and unscrewing the bolts a couple of times, it will probably wear off the solder mask.

One of the four bolts can't be installed, because the screwhole is to close to the female headers of the board, so I had one spare nylon washer laying around. I now used that nylon washer to insulate the bolt on the top of the board as well. When I bolted everything together again and applied power, the current I felt before when touching the enclosure was gone.

Could it be that I solved it by insulating the bolt, or does it mean that there still is something wrong (leaking/shorting etc) in the board, and I just insulated it from the enclosure but I won't feel the leak anymore?

Thanks for the quick replies!

Woodworker
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Re: leaking current? shortage? static electricity?

Post by Woodworker » Thu Jun 26, 2014 12:15 pm

I will make a guess and say that you have fixed it. If possible I would still try and borrow a meter and verify there is no voltage between the 2 points. Better safe than sorry, also over time the problem may have caused some premature component failures.
BRuce - SO2 #4798 - IC's Z axis upgrade, customized Z rail and Z motor mount, spindle Dewalt 611

WillAdams
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Re: leaking current? shortage? static electricity?

Post by WillAdams » Fri Jun 27, 2014 1:47 pm

Interesting and a bit scary.

Should we suggest using plastic fasteners?
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

Woodworker
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Re: leaking current? shortage? static electricity?

Post by Woodworker » Fri Jun 27, 2014 7:54 pm

That would help but there still seems to be a potential from the ground plane of the Adrino and some other point. I will see if I can find a similar issue with mine. It isn't mounted in a case yet so I have full access to the board.
BRuce - SO2 #4798 - IC's Z axis upgrade, customized Z rail and Z motor mount, spindle Dewalt 611

TheMonkeyStink
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Re: leaking current? shortage? static electricity?

Post by TheMonkeyStink » Sat Jun 28, 2014 3:49 am

Take a look at this:

http://www.shapeoko.com/forum/viewtopic.php?t=3592

I'm thinking the plastic washer suggestion is a good idea. I've seen a few posts now that could very well be attributed to a potential difference. For me the ground loop isolator worked, but I'm going to run out now and check the standoffs for possible contact.
________________________________________
Shapeoko 2 #5177: DW660 with nema 23. Acme Z axis (I believe these come from the same company that Wile E. Coyote gets his stuff)
# of failed cuts (a.k.a. Shapeoko Ohnos): 7
# of successful cuts: 12

WillAdams
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Re: leaking current? shortage? static electricity?

Post by WillAdams » Sat Jun 28, 2014 2:03 pm

Okay, on the electronics page we have a section: http://www.shapeoko.com/wiki/index.php/ ... #Grounding

==Grounding==

Discussion of this in the forums:

* [http://www.shapeoko.com/forum/viewtopic ... 86&p=25493 Re: Connecting shield lead to ground].
* [http://www.shapeoko.com/forum/viewtopic.php?t=3592 USB Ground Loop]
* [http://www.shapeoko.com/forum/viewtopic.php?f=4&t=3707 leaking current? shortage? static electricity?]

If someone wants to write up some text or point me to a link which would explain the underlying concepts we'll see about expanding that --- if someone has a suggestion for a very basic electrical engineering text which I could start w/, I'll try to further my understanding of this beyond the ``Radio Fun.'' course I took in the Air Force.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

TheMonkeyStink
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Re: leaking current? shortage? static electricity?

Post by TheMonkeyStink » Tue Jul 01, 2014 10:10 pm

Heya Will,

I'm writing up a quick summary. I'll post it on this thread for review.
________________________________________
Shapeoko 2 #5177: DW660 with nema 23. Acme Z axis (I believe these come from the same company that Wile E. Coyote gets his stuff)
# of failed cuts (a.k.a. Shapeoko Ohnos): 7
# of successful cuts: 12

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