Re: Singing light bulb on dimmer switch

[mm <NOPSAMmm2005@xxxxxxxxxxx>]

On Wed, 24 May 2006 00:08:24 GMT, "D&SW" <dsweatherwax@xxxxxxxxxxx>
wrote:

>Years ago I tried to use a bridge and two 40mF 450V caps to banish some
>nasty hum coming from two chandeliers, each with five 50W bulbs. Way too
>much load for the caps. The hum remained and the caps were seconds away from
>exploding due to their instant heat buildup. It might have worked with a
>smaller load.

I don't get it.  I thought that if the capacity of a cap was exceeded,
it just filled up on one side, and after that the rest of the current
behaved as if there were no cap.    In fact it occurs to me that in a
DC power supply circuit for a radio or tv, the only reason the cap
ever gets below full charge is that the load is *high* enough to draw
more than is currently, during low parts of the cycle, being provided
through the diodes, so it drains the cap.

During the high points, the peaks of the 120 cycles per second power
(after rectification) there is more than enough power and that's when
the the caps are refilled.

Lowering the load would mean the cap would fill up on one side, and
then just stay filled all the time.

Two 40mF sounds like a lot, but if it wasn't enough, it seems to me
there would have been no current in or out of the caps after the first
charge.

If 80mF was enough to filter, maybe the internal leads couldn't handle
the current in and out without getting hot, even though current in and
out is what caps do.  Maybe that level of heat was within range.

And I would also think that nothing 110 volts could do, even
full-rectified to make it higher than 110, could damage a 450V cap.

I would also wonder if caps are necessary, since an incandescent bulb
with pulsing DC current would remain hot and giving light, despite the
pulsing.  Don't electronic dimmers work by completely turning off the
current parts of the time? And yet all we see is a constant but dimmer
light.  They don't use caps at all except maybe little ones to make
them oscillate.


Posted and mailed because it's been almost 3 days and ahr is so busy,
I'm not sure anyone is reading this thread anymore.  So I wanted the
poster to know I had replied.



>"David D." <daviddiamond.remove-if-not-spam@xxxxxxxxxxx> wrote in message
>news:99qdnalayLQLkezZ4p2dnA@xxxxxxxxxxxxxx
>> "mm" <NOPSAMmm2005@xxxxxxxxxxx> wrote in message
>> news:0mnv62lo2i5da62lklbn66s3tv8e6k5os3@xxxxxxxxxx
>>> On Sat, 20 May 2006 16:35:29 GMT, CJT <abujlehc@xxxxxxxxxxx> wrote:
>>>
>>> >
>>> >I wonder whether a rectifier and capacitor between the dimmer and the
>>> >lamp would work (then the lamp would see DC).  I bet somebody here
>>> >knows whether that would wreak havoc with the dimmer.
>>>
>>> Since the output of the dimmer is still AC, that would dim it further.
>>> by cutting the current in half, unless you used  something like a
>>> bridge rectifier (4 diodes arranged in a square) that is full wave.
>>>
>>> (Sorry, maybe htat is what you mean to begin with.)
>>>
>>>  Then you'd be running yhour lightbulb on DC, and I would be very
>>> intersted in how well that would work.
>>
>> It would probably work, but, as a safety precaution, I would not want to
>> try
>> it.   With AC, one would usually survive a mometary shock.  110-volt DC
>> can
>> burn severely.
>>
>>  - David
>>
>>
>