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List:       soekris-tech
Subject:    Re: [Soekris] power supply question
From:       "Nenhum_de_Nos" <matheus () eternamente ! info>
Date:       2012-02-11 15:19:03
Message-ID: a192edaf876b9fdea823aee2dda29053.squirrel () eternamente ! info
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On Fri, February 10, 2012 08:43, gavrik peterson wrote:
> As I have limited information, I am not sure what is going on here. But I
> assume that the electric shock you refer to happens when you touch the case
> of the 6501 or 5501. I further assume that the Soekris units were not
> otherwise grounded. And that the electric shock occurred when the unit was
> lightly touched with a finger or some other appendage.
>
> If the above is correct, the cause may be something that is referred to as
> "leakage". Leakage is the small AC currents that may flow between the
> primary and secondary of a transformer. While the transformer provides
> galvanic isolation between the primary and secondary there is always some
> capacitance between these windings. Because of this capacitance, it is
> possible for small AC currents to flow in the power supply output. This is
> a common mode current (common to the two output leads) .
>
> All power supplies of the type we are concerned with, provide galvanic
> isolation by emploing a transformer. If the power line connection includes
> a ground (it appears that the Soekris power supplies do not) then it is
> possible eliminate the leakage by placing a grounded shield (a conductive
> foil layer) between the transformer primary and secondary winding. But in
> the case of power supplies that don't have a ground connection, the only
> way to eliminate leakage is to make sure that the correct terminal of the
> plug is connected to the neutral conductor of the power line input. For
> this to work, the plug has to be inserted into the power socket correctly.
> The correct connection can be enforced with a polarized plug. But this will
> not work if the plug is not polarized, or the socket is not be correctly
> wired. If the plug is un-polarized, reversing the connection might help.
>
> Another thing -- if this is just the normal (small) leakage current, it may
> be possible to just to ignore it. If the current is large (the shock is not
> mild), there may be a fault in the power supply and it should be replaced.

Gavrik,

thanks for all the info. I noticed before this behavior, but just as small shocks and they never
bothered me. Just as the person from the DSL company said it would be such a problem (they always
say that anything that may be wrong is the main cause of the problem, it always you ...). Good to
know that it won't affect anything.

and thanks for the tip on reversin the plug, I'll try also :)

thanks,

matheus

> Hope this helps in some way.
>
>   --  Gavrik
>
>
> On Thu, Feb 9, 2012 at 2:17 PM, <lists@neuronenwerk.de> wrote:
>
>>  Mon, 06  20:13 , Nenhum_de_Nos wrote:
>> > hail,
>>
>> ???
>>
>> > I had a problem in my DSL modem this week, and got to notice that the
>> default power supply from
>> > Soekris would make my net6501 and net5501 have grounding issues. Both
>> would cause electric shock.
>> > When I changed the power supply, for another I have that have the ground
>> pin, all went back to
>> > fine.
>>
>> Euro-plugs don't have ground wires, so if your box is statically
>> loaded (or the adapter somehow connects to the housing, which
>> should not go unnoticed) there's no way to get rid of the
>> potential difference.
>>
>> It looks as if your Soekris is loaded out of some reason and
>> there is no chance to conduct it away (except via your body, if
>> you touch it :)
>>
>> Even if you don't encounter that with your new power supply,
>> the problem most probably persists. You just don't sense it
>> anymore because of the ground wire. I suggest you focus on
>> finding the reason instead of fighting the symptoms.
>>
>> It is highly improbable that the leakage originates from the
>> power plug, as you do not have more than a few volts here (given
>> that you didn't open it etc etc). You just wouldn't feel it.
>>
>> Regards,
>> /M
>>
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>>
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-- 
We will call you Cygnus,
The God of balance you shall be

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

http://en.wikipedia.org/wiki/Posting_style
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