Re: Controlling Holiday Lights

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, 06 Nov 2006 12:02:52 -0500, Marc_F_Hult
<MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
<nkquk25nuvphhnqm9qj08mhu6hbuksamv1@xxxxxxx>:

>On Sun, 5 Nov 2006 18:58:15 -0700, sylvan butler
><ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx> wrote in message
><slrnekt5ln.fbp.ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxx>:
>
>>On Fri, 03 Nov 2006 23:27:48 -0500, Marc_F_Hult
><MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote:
>>> On Fri, 3 Nov 2006 16:05:12 -0700, sylvan butler
>>><ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxxxxxxxx> wrote in message
>>><slrneknip8.p3a.ZsdbUse1+noZs_0611@xxxxxxxxxxxxxxx>:
>>>>> would be doing is chopping the AC into really small chunks and they
>>>>> would average over the entire wave(s).
>>>>
>>>>that's pretty much how it would work.  But it is a lot easier with D.C.
>>>>You would have to be really motivated to do it with A.C.
>>>
>>> There you go again ;-)
>>>
>>> Powering lamps designed for 120VAC with rectified 170 VDC (= 170 VRMS)
as
>>> you suggest is problematic because if the circuit were to ever stop
>>> chopping, the lamp would burn out right quick.
>>
>>You misunderstand.
>>
>>120vac sine wave == about +/-170v peak.  I was not suggesting creating a
>>filtered 170vdc supply, just rectifying the 120vac sine wave.
>
>Of course you did. sylvan wrote:
>
>	"That gets a bit ugly (and more expensive) if you intend to
>	control 120vac.  (Of course, one could rectify the 120vac to
>	create ca. 170vdc and use MOSFETs...)
>
>So you did in fact clearly and unambiguously  "suggest[] creating a
>filtered 170vdc supply". It was this statement that I responded to. The
>record is crystal clear.


In forty years of designing electronic circuits, I've never seen the
shorthand "ca." to mean "rectified but not filtered".  But I suppose that is
what you did mean. (I misunderstood you and  yes, I can back peddle too ...
;-)

If one "[rectif[ies] the 120VAC to create ca. 170vdc and use MOSFETS", and
don't also "filter" (add capacitance), you get 120Vrms which has a peak
voltage of 170v with 100% ripple.  And depending on how this is coupled and
grounded (or not) it is either DC or AC. In this case, with respect to earth
ground, it is DC sensu stricto (your point).

In the typical 120VAC circuit using MOSFETs for control of AC lamps, the
lamps do see ~120VAC-(2 x 0.65)VAC -- not DC which is what I understood you
to imply.

... Marc
Marc_F_Hult
www.ECOntrol.org