On Sun, 1 Apr 2007 06:57:54 +1000, "Phil Allison"
wrote:


"Arny Krueger"

** Another brain teaser.

The scope trace shows the actual, continuous AC
current draw of a common household item operated on
240 volts/50Hz. Current peaks = +/- 4.4 amps.

RMS value = 0.24 amps.

PF = 0.23

CF = 18.3


You gave the answer in the pic name :-)


** You were not supposed to see that !!

Now, can you say what the problem with this is ?


CFL HF input cap + triac delayed firing optimized for
highest peak current (at top of sinusoid).



** The control on the commercially made, domestic lamp
dimmer is set to max.
With incandescent lamps it traverses the whole, half
cycle range just fine.
At lower settings, the current draw becomes half wave
with much larger peaks.

Now, can you say what the problem with this is ?

Is this CFL designed to be dimmed?



** In common with almost all of them - no.


If the CFL is not designed to be dimmed, my persoanal experience says that
the real question is whether or not the dimmer or the bulb will be the
first to emit smoke and die. The reason for the failure would be the
extremely high current peaks.


** Arny has supplied the correct answer.

The CFL in my test was a single Philips "Genie" rated at 11 watts.

The PROBLEM is that it APPEARS to a user to work more or less OK on a
common triac dimmer.

However, the RMS current draw when used with one is 3 to 6 times the value
normally seen - which will soon over temp an internal 10 ohm resistor in
line with the AC supply. Smoke and fire is the result.

With several CFLs on the same dimmer circuit - the combined current peaks
will likely destroy the triac in a few seconds.

Makers supply either NO warning or a completely inadequate warning of this
serious hazard to purchasers.

With the impending ban on incandescent lamps here in Australia plus Europe
and elsewhere - this is gonna cause a major safety issue.



........ Phil




There will be a huge black market in Mexican incandescent lamps, as
there already is in Cokes (made with real sugar down there!) and of
course narcotics.

John