Author Topic: something strange?? or just needs a little explination  (Read 888 times)

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Offline dmkmedia

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something strange?? or just needs a little explination
« on: January 24, 2017, 05:50:49 pm »
https://goo.gl/photos/WvLmUkrv45Jz3nyw6
above is a video of something i was playing with a led matrix and one of the led's didnt work when testing so i went to de-solder it and put in a new one
and to my shock i found that when my soldering iron touched the LED leg the led lit up.

as the soldering iron was not connected to the led's in any way apart the power supply for the led's and the soldering iron was pluged in to my home mains.

how did it happen  :wtf:
 

Offline mmagin

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Re: something strange?? or just needs a little explination
« Reply #1 on: January 24, 2017, 05:56:52 pm »
  • Is your iron tip connected to the ground pin of the power plug?
  • Is either the positive or negative of the power supply output connected to its ground pin?
  • Are your outlets actually grounded?  If not, the shared ground conductor (and as a result the iron tip, perhaps) can get quite a bit of AC voltage on it through Y capacitors.

Just some things to think about.  When my 'ground' was ungrounded, I was able to light an led between my fingers and 'ground' :P
 

Offline dmkmedia

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Re: something strange?? or just needs a little explination
« Reply #2 on: January 24, 2017, 07:56:41 pm »
i am in the uk and everything i plug in has a ground wire on the plug. everything is sharing a single power stack to protect against power surges. could this cause it some how?
 

Offline mmagin

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Re: something strange?? or just needs a little explination
« Reply #3 on: January 24, 2017, 08:12:56 pm »
I would certainly start by unplugging the soldering iron and the power supply and use a DMM to verify what, if anything, is earthed.
 

Offline sleemanj

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Re: something strange?? or just needs a little explination
« Reply #4 on: January 24, 2017, 08:57:28 pm »
It is pretty common.  A modern led will emit visible light with *incredibly* little current, normal earth leakage and capacitive coupling more than sufficient.  It's not uncommon in fact to have led light bulbs that glow when the switch is off, indeed many designs include measures to prevent it (because people prefer that a light switched off, is off :-)

Personally, I wouldn't worry about it too much.
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