Fellow RFI/EMC folks,
I thought I'd provide some update information on two oft-discussed topics on
this reflector: CFLs and LEDs. Here goes.
First, I just purchased a set of 5 CFLs to relamp the light bar in my master
bedroom bath. I had 5 conventional 60 watt "globe" lamps in there that have
worked well for the purpose, but not only do they suck up 300 watts of energy,
they deliver just as much heat. Over the past 3 or 4 years, I have replaced
many standard bulbs with CFLs of varying lumen ratings and been mostly happy
with both performance and CFL life. I have had zero RFI issues. My chief
reason for installing CFLs is to reduce heat load on the A/C system in warm
weather, with reduced power consumption running a close second.
I mention these 5 lamps because of what they are and what the manufacturer says
about them. Please take note: The bulbs are marketed by Feit Electric of Pico
Rivera, CA. They are called "Ecobulb Plus" and are listed as 60 watt
equivalents, drawing 15 watts, delivering 800 lumens, with an estimated life of
8000 hours. (These specs are for each bulb.) The home use warranty is for 2
years, and the cost was $4.88/each. A prominent note on the side of the box
discusses "Proper CFL Usage". I quote: "Globe-shaped covered twist CFLs are
best suited for fixtures that are left on for 15 or more minutes at a time."
The rest of the statement deals with airflow, no use of dimmers, and so forth.
I typically run those bathroom lights for about 30 minutes at a time at least
twice per day. A small print notice on the bottom of the box says that "this
product complies with Part 18 of FCC rules but may cause interference with
radios, televisions, wireless telephones and remote control
s." Note that Part 18 addresses ISM devices, which does include intentional
emitters. I presume that the reference to remote controls is to RF-type
remotes, as opposed to the more common IR ones.
This is the first time, in my CFL-buying experience, that I have seen a
manufacturer actually state the recommended operating conditions on the bulb
packaging. I've checked my other in-stock bulbs, and no, none of them make
that statement. I have saved my sales receipt and the proof of purchase for
each bulb, just in case they don't last 2 years in my application. I might add
that my normal routine with new CFLs is to use a fine-tip marker and place the
date of first use on each bulb (near the base, so that if it dies early, I'll
know. (I have a CFL flood lamp that was installed on 1-31-09 and died on
8/20/10. The 3 others I installed at the same time are still running.) As for
RFI, I don't expect any, but then again, I'm not usually running those lights
while operating.
A final CFL note: I ran a test this morning that I should have run long ago,
but just never found the round-tuit. I have a Teac AM-FM tuner in the family
room as part of my eclectic stereo system. (It's a blend of ancient and modern
components, with the heart being a Dynaco PAS-2 pre-amp fresh from the 60's.)
The AM part of the tuner uses a factory-supplied wire loop antenna (no ferrite
core) that is mounted on a hinge so that the user can pivot the loop (in a
vertical plane) to adjust for best reception. Now that my power line issues
are gone (for the moment, anyway), I can enjoy "armchair" listening to the
major Chicago AM stations that are located about 150 miles or so to the east.
I first tuned in WBBM-AM on 780 kHz and noted usual band noise, but no
significant arcs or buzzes. I then switched on the 2 separate groups of CFLs
(in ceiling fixtures) which light the shared area that includes both the family
room and the kitchen (divided by a breakfast counter). No cha
nge to what I heard. Then I switched on the wall plate dimmer that controls
the set of 4 incandescent bulbs (3 @ 40 watts and 1 @ 60 watts) hanging beneath
the family room ceiling fan. Aaahh - that familiar old buzz-saw sound! I
might add that the dimmer, which was installed by the builder's electrician, is
rated as having an RFI filter! Bottom line: the CFLs are "clean" enough for AM
BC band use.
Quick note on LED lights: I recently received an interesting booklet from
Digi-Key under their "techzone" magazine name. The publication appears to be
partly sponsored by Cree Technology, a major maker of LEDs and related systems.
There are several articles within dealing with the major topics related to LED
lighting technology, including power supplies, thermal issues, and achieving
color balance. I am not quite certain how I got this copy sent to me, I
strongly suggest that anyone interested try contacting Digi-Key to see if you
can get one for yourself.
>From the RFI perspective, one of the more interesting articles was contributed
>by National Semiconductor and is entitled "Driving LEDs: To Cap or Not to
>Cap". Huh? Well, what the title refers to is to use (or not use) capacitors
>on the output side of the switching power supply that is integral to LED lamp
>array operation. Not surprisingly, LEDs work best with constant CURRENT power
>sources, and the article talks about the design of buck-type converters that
>deliver constant current performance AND which offer dimming control! Here is
>the catch: you can not dim the LEDs using the wall plate dimmers as discussed
>above in the CFL discussion. The dimming control signal must go directly to
>the pulse width modulator ("PWM") ship in the power supply. If output caps
>are not used, the limiting factor in the buck converter design becomes the
>series inductor, and that allows more precise control of brightness than if
>there are filter caps after that inductor. So, where are thes
e LED dimmers used? In products, such as displays, not in general lighting.
The article also mentions that typical operating frequencies for these buck
converters are in the range of 50 kHz to 2 MHz.
Hope these comments help. Disclaimer: I have no financial interest in any
product or supplier mentioned.
73, Dale
WA9ENA
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