>-----Original Message-----
>From: Randy Ott [mailto:randy@THEOTTS.NET]
>Sent: 28 May 2004 16:12
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: [EE:] Obtaining 5 Volts from live wire
>
>
>On Fri, 28 May 2004 08:52:32 +1000, David Duffy wrote
>> Martin McCormick wrote:
>>
>> >        Some of those electronic light switches that are for
>> >incandescent bulbs only use a SCR instead of a triac so the
>bulb runs
>> >on half-wave pulsating DC.  If they do that in the circuit,
>there is
>> >the other half-cycle of AC that is un-touched and will be at about
>> >the same voltage no matter if the light is on or off.  The
>bulb will
>> >burn at a slightly lower brightness because the over all
>energy level
>> >is .707 times the RMS level, but it will basically work normally.
>> >
>> >
>>
>> "Slightly lower brightness" ?? Try it for yourself one day.
>Running a
>> lamp with half wave is more than slightly reduced! David...
>>
>That's because the lamp sees 1/2 the voltage not .707 as was suggested.
>
>Randy

No, it's running at half *power* (ignoring the reduction in filament
resistance from running cooler).  RMS voltage is indeed reduced to SQR(2)/2
= 0.707

Regards

Mike




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