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Drive Died (arcing between pins on the PCBA)

  1. Mar 13, 2015 #1
    Hello:

    I have a problem with a drive located in a small production area. It has failed three times due to arcing between two inputs to a control board. These inputs are about 5mm apart and the manufacturer is saying that this could be from material collecting on these terminals or from gases. Now I can understand material conducting between the inputs, but gases seems rather far fetched. The drive is not sealed and it is at regular atmospheric pressure and cooled with a small muffin fan. The drive does not use any high voltage conversion and the input voltage is only 480V. I remember that it usually takes about 3000V/mm for a spark to develop in air, but I can't find any thing in that range in the drive.

    My question is it possible for an arc to develop spontaneously between to points 5mm apart? And if it is what are some examples of voltage or gases that may be present to facilitate such an event.

    BTW: Please forgive my ignorance on some of this, I know enough only to get things wrong.
     
  2. jcsd
  3. Mar 13, 2015 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    If the atmosphere is wet and dusty, there could be an accumulation of gunk that helps the arc to happen. Do you see evidence of contamination in other areas of that PCB assembly? Have you considered cleaning and conformally coating the PCBA in that area?
     
  4. Mar 13, 2015 #3
    The area is pretty clean and not wet. Specifically the area is a show area for customers that does small production runs, so they keep up with standards very well. Also the drive has been installed for 6 months, and recently the original failed and then two replacements failed as well, within 2 weeks from start to finish. So contamination could have caused the first but the succeeding two, ???????
     
  5. Mar 13, 2015 #4
    Also we have conducted a study on the incoming power feed, which had nothing of note within a ten day study. My gut is telling me this could be manufacturing issue, but I don't want to take a stand on this without a better understanding of the science and how arc's can form.
     
  6. Mar 13, 2015 #5

    berkeman

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    Staff: Mentor

    How can you be sure that it was arcing between those 2 pins that caused the failures? Was anything else changed in the environment around the drive shortly before the first one failed? Like a new piece of equipment being used/installed nearby?

    Can you post a picture of the pins you are talking about?
     
  7. Mar 16, 2015 #6

    jim hardy

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    Science Advisor
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    2016 Award

    Lead free solder is notorious for "whiskers". Search on "tin whiskers"

    http://nepp.nasa.gov/whisker/


    Is the arc-over right at a soldered joint?
    If so,
    Try applying a dab of "Glyptol" insulating paint, or ordinary polyurethane woodworker's varnish (oil based) over the solder pads on the next board.

    I'd guess 480 makes quite a flash when it goes. Current limiting fuses like Shawmut 101 might help preserve some clues.
     
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