Tingles from power supply

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I've recently bought a D-Link DIR-300 wireless router. While
disconnecting its power supply from it, I got a tingling sensation when
I touched the plug (to be clear, I'm talking about the 5V DC plug, not
the mains plug).

An AVO meter shows about 90V AC to earth from either side of the 5V
plug. Short circuit current to earth is about 0.1mA.

Still, I thought these things were meant to be completely isolated. Has
there been a change of approach?

Sylvia.

Re: Tingles from power supply
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Apparently it's normal, and is related to RFI suppression.

Sylvia.

Re: Tingles from power supply
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Sounds like a small cap from mains.

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
We've slightly trimmed the long signature. Click to see the full one.
Re: Tingles from power supply
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Just think, the only thing between you and the great beyond is a thin
layer of ceramic material, possibly contaminated with who-knows-what,
bearing a certification logo of dubious authenticity. It's time to
invest in some rubber-soled slippers.

--
Joe

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It's certainly not a happy thought. I will be treating the low voltage
side of such power supplies with more respect from now on.

BTW, I tried the same tests with the power supply for my cable modem. It
showed higher voltages, but lower current.

But immediately after I'd unplugged it from the mains, I happened to
touch the mains plug pins with the palm of my hand, and got a
significant shock off it. Reverse leakage through the rectifiers? But
why should there even be enough to feel?

Sylvia.


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That is also quite normal !  There is one or more capacitors across the
supply pins.  They can be left in a charged state at the instant you
pull the plug.

The voltage you measured on the output side was simply due to the
leakage capacitance of the transformer or if a switch mode psu the
capacitors on the supply side having a connection to the common rail.

--
Best Regards:
                     Baron.

Re: Tingles from power supply

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100 uA is usually below the threshold of sensation (usually about 1 mA),
but some people can sense current of lower value. If it has a three prong
plug, it may have capacitors to ground. There is also some capacitance from
the primary to secondary windings, especially if they are layer wound. The
shock you got from the plug after disconnecting from the mains may have
been from an RFI filter capacitor that was still charged. If you touched
across two blades of the plug, that might explain it. If you only touched
one blade, then there must have been another return path to ground, such as
the secondary output to a chassis ground, and you would have had to touch
something else grounded, or be wearing very conductive shoes. If it is a
switching supply, there is a fairly large electrolytic charged to about 180
or 360 VDC, and maybe there is reverse leakage through the bridge
rectifier. You might check for DC voltage on the mains plug blades after
disconnection.

Paul



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I did try immediately afterwards (after plugging it in again for a bit).
Couldn't see much. But it may be a time issue - it's possible to get
one's hands onto the pins rather more quickly that a pair of multimeter
probes. Depends how long the capacitor would remain charged with no
output load.

Further experiments using my hand might be informative, but I'm not game.

Sylvia.

Re: Tingles from power supply
On Mon, 09 Mar 2009 02:18:22 +1100, Sylvia Else

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  Please do us all a favor and latch on to the high side of one soon.
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  You're a total retard, and you likely do not even know how to make such
measurements.

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  Damn!  Obviously not significant enough!

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  You're an idiot.  You don't even know what type of circuit the dongle
is constructed with.  You won't know either, until you pull out the
dremel tool, and stop guessing like the twit you are.

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That's another cap ! You're not meant to touch the power pins immediately. It's
all in IEC60065.

Graham


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Try this one.
Run an electric drill, then unplug it.
Get a "friend" to hold the plug in his hand, prongs inward.
Squeeze the trigger.

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
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Well, I just hope that most consumers have read that standard.

It was quite a belt. I'm glad I didn't touch the two pins with separate
hands.

Sylvia.

Re: Tingles from power supply



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It's
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LOL !


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There is a limit on the stored charge and it's meant to be bled away too. Units
with
power switches must NOT do this. (Read it last night).

Graham


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Individuals respond differently. I'm quite tolerant of 'belts' myself.

Now shut up and go away.

Graham


Re: Tingles from power supply
On Mon, 09 Mar 2009 12:20:47 +0000, Eeyore

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 Ceramic caps do NOT "belt" when 'charged' off of a random point in an AC
power line sine wave.

  She is an idiot, as are you.

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YOU are an idiot. You clearly don't understand the term applies to YOU, not
the people here who have explained EXACTLY what is going on.

Graham



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No ?

Suggest we find a big C and try it on YOU.

Graham


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Can I watch?

Sylvia.

Re: Tingles from power supply
On Tue, 10 Mar 2009 03:11:21 +0000, Eeyore

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  After I slice you open, we'll put a 35kV poly cap, fully charged
directly on your pathetic donkey heart.  There would be no 'try' about
it.

Re: Tingles from power supply
On Mon, 09 Mar 2009 12:35:35 +0000, Eeyore

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 You're an idiot.

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