[Hallicrafters] Light Dimmers and RFI.

[Charlie]

The typical dimmers operate by varying turn-on of a solid state switch 
(Triac, or 2 SCR's) into the conduction angle of the 60 Hz AC line.  The 
adjustment electrically changes the point in the conduction cycle where the 
switch turns on.    This turn-on is extremely fast and as you know, rapid 
rise times this fast can result in harmonic generation extending well into 
the VHF frequencies.  The method of reducing the interference is to slow 
down that rapid rise by inserting an inductor in the current carrying 
conductor which will oppose any change in current.  The newer dimmers are 
somewhat better in this regard than early designs, but will still rip up the 
lower frequencies, since you can only slow down the rise time so much with a 
tiny inductor that will fit in a wall switch.

Zero-Voltage switches, or control circuits that only turn on the solid state 
AC switch at the zero crossing of the 60Hz waveform,  and therefore have no 
rapid rise waveform, are not practical for use as dimmers since the control 
resolution would cause a noticeable flicker to the light output.    Consider 
the requirement for 20% output.    The 60 Hz AC waveform crosses zero every 
8.333 milliseconds, but in order to maintain a power factor of "1", ZVS's 
normally conduct for a full cycle, or 16.66 milliseconds.  So at 20 %, the 
ZVS would turn on for one cycle, or 16.66 milliseconds and be off for four 
cycles, or about 67 milliseconds which would very noticeable to the eye.  As 
an example, the refresh rate of your TV picture is 30 Hz which is just about 
as slow as you can go before the flicker effect is obvious. (Watch TV in 
Europe which has a refresh rate of 25 Hz and you'll see what I mean.)   The 
Zero Voltage Switches  are however, very practical for controlling heaters.

As for RFI from CFL's , I have at least a dozen running in the house and can 
detect no noise farther than a few inches from them with a portable BC band 
radio.

Curiously, in the typical "shop-light" type fixture, the older magnetic 
ballasts as well as the newest solid state versions also seem to be quiet. 
However, the early non-magnetic (cheap!) types sold, maybe 10 years ago are 
horrific RFI generators.    I had the occasion to replace a couple of these 
recently and was amazed at the efficiency (measured with a "kilowat" 
readout) AND the lack of interference from them.  The ballasts were about 
$25 at the local Home Depot store and for the same light output, drew about 
half the AC power as did the older magnetic devices.

 Likewise, I think the LED as a standard light source will completely take 
over 95% of the lighting requirements in the next 10 years.  I am much more 
concerned about the overall religious conversion to the church of "Global 
Warming" that our dipstick politicians on both sides of the isle seem to be 
falling for.

73' Charlie k3ICH




----- Original Message ----- 
From: "Dennis" <radioart at charter.net>
To: <hallicrafters at mailman.qth.net>; <jeffv at op.net>; <bonddaleena at aol.com>
Sent: Tuesday, December 09, 2008 8:21 AM
Subject: Re: [Hallicrafters] I bet you knew this already.


Its the dimmer switches that cause most of these problems....  Most new 
dimmer switches you get at the hardware store for wall switches generate 
reduced RFI and are usually pretty quiet.  I have one in my shack and I 
don't hear a thing on any band....  The RFI proof switches have a circuit 
that switches the lamp only when the AC cycle is crossing zero so NO 
switching noise (RFI) is generated, works pretty good.

I cant speak to dimmer switches that are a part of lamps.


---- bonddaleena at aol.com wrote:
>
> Hi, if you ever have the opportunity to dissect a dead spiral lamp, you
> will see a 'switching/HV converter' in the base!!!
>
> Give me a filament bulb any day!!
>
> ron
>
> N4UE
>
> -----Original Message-----
> From: jeff <jeffv at op.net>
> To: Jack Dunigan <jack at dunigandesigns.com>;
> Hallicrafters at mailman.qth.net
> Sent: Mon, 8 Dec 2008 7:46 pm
> Subject: Re: [Hallicrafters] I bet you knew this already.
>
>
> Jack Dunigan wrote:
> > My radio bench has one of those magnifying lights in which I put one
> > of those curly, energy saver bulbs. It is bright, runs cool, and
> > supposedly saves money. When I fire up my Hallicrafters S38-C and
> > turn on the light, a terrible buzz obliterates all signals on the
> > lower half of the broadcast band.
>
> I had a similar problem with a cheapo computer power supply. In my
> case, replacing the supply fixed the problem.
>
> Not sure what to suggest about the bulbs, short of going back to the
> `regular' bulbs. I hear they're pretty noisy, although I'm doing ok
> with them so far.
>
> Good luck.
>
> -=-=-
> ... Electronics Rule #2: never solder in shorts
> * TagZilla 0.066 * http://tagzilla.mozdev.org
> ______________________________________________________________
>
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