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From: Kevin McMurtrie
Subject: Re: Wall wart with two blade polarized plug,,,Why?
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Sat, 05 Oct 2002 07:01:43 GMT
NNTP-Posting-Date: Sat, 05 Oct 2002 00:01:43 PDT
In article ,
"Phil Allison" wrote:
>"Kevin McMurtrie" wrote in message
>> In article <3D9A856D.99A017C7@110.net>, Jeff Wisnia
>> >I'm trying to think of a realistic reason why my little TV's 120 vac -
>> >12 vdc 1.0 amp simple xformer/bridge rectifier wall wart needs one of
>> >its two input blades wider than the other so that it won't insert into
>> >an duplex outlet in a convenient direction. (i.e. so its body doesn't
>> >interfere with a right angle cord plug already in the other half of the
>> >I've got half a drawer full of wall warts from various now-discarded
>> >devices, and all but one have equal width plug blades and can be
>> >pluggged into a receptical "either way".
>> >Before I file down that wide blade, did I overlook anything? Maybe the
>> >designer of this wall wart has the wide blade connected to the end of
>> >the transformer primary nearest the secondary so that an insulation
>> >breakdown there doesn't connect the hot side of the line to the low
>> >voltage circuitry? That seems a stretch to me.
>> >Anybody know for sure?
>> >Thanks guys,
>> There's likely a resistor between the DC negative and the AC neutral.
> ** Very unlikely in a wall wart. If there it would be several
> . . .. . . . . . . . . . . . Phil
But there are there. You cut off my explanation. TVs throw off
electricity and they must have the resistor to prevent arcing. Even
non-polarized wall warts have a 10M Ohm resistor for general protection
against static discharge which could damage the insulation.
Jeff said he found a 500K Ohm resistor. This makes sense since TVs can
throw off too much current for 10M Ohm and it explains the need for a
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