CFL and dimmer

M

Meat Plow

Guest
Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.
 
On Sat, 27 Dec 2008 02:30:08 -0500, Meat Plow <meat@petitmorte.net>
wrote:

Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.
Click to expand...
Here's one guy who seems to have looked into it more than casually:
http://sound.westhost.com/articles/incandescent.htm#dim2

Shorter version: "To reiterate ... never use a CFL with a dimmer in the
circuit, even if it is set (and kept) at the maximum setting. Doing so
places you at risk of fire, and at the very least will dramatically
shorten the life of the lamp and the dimmer. Remember that these figures
were all measured using a normal dimmer and with a variety of different
CFLs - nothing is guessed, surmised or imagined - this is real data !"

--
Rich Webb Norfolk, VA
 
GE makes CFLs specifically designed to be used with triac dimmers.

I bought one and checked it with my X-10 equipment. It worked well, but only
the top 15 or so levels (rather than the full 255) are available.

In theory, CFLs should work much better with triacs than rheostats, because
the triac's output full line voltage, regardless of the dimming level.
 
Rich Webb <bbew.ar@mapson.nozirev.ten> writes:

On Sat, 27 Dec 2008 02:30:08 -0500, Meat Plow <meat@petitmorte.net
wrote:

Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.

Here's one guy who seems to have looked into it more than casually:
http://sound.westhost.com/articles/incandescent.htm#dim2

Shorter version: "To reiterate ... never use a CFL with a dimmer in the
circuit, even if it is set (and kept) at the maximum setting. Doing so
places you at risk of fire, and at the very least will dramatically
shorten the life of the lamp and the dimmer. Remember that these figures
were all measured using a normal dimmer and with a variety of different
CFLs - nothing is guessed, surmised or imagined - this is real data !"
Click to expand...
The problem is that the CFL is not even a remotely linear load. Incandescent
lamps are far from linear since their resistance changes by a factor of 10
from cold to hot, but in the steady state they look like a resistor.

The input to the typical CFL is a bridge rectifier feeding a filter capacitor
with a time constant of a couple cycles at 60 Hz. This means that to the
source, it looks like an open circuit for a large part of each cycle. That's
not what a dimmer expects and results in the high peak current in short
pulses.

Whether it's as dire a situation as is implied by the quoted text at full
output may be debatable, but it certainly won't be running with anywhere near
normal.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:gq6cl4dmj52umcn6qf4l6aiq48cornk37d@4ax.com...
On Sat, 27 Dec 2008 02:30:08 -0500, Meat Plow <meat@petitmorte.net
wrote:

Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.

Here's one guy who seems to have looked into it more than casually:
http://sound.westhost.com/articles/incandescent.htm#dim2

Shorter version: "To reiterate ... never use a CFL with a dimmer in the
circuit, even if it is set (and kept) at the maximum setting. Doing so
places you at risk of fire, and at the very least will dramatically
shorten the life of the lamp and the dimmer. Remember that these figures
were all measured using a normal dimmer and with a variety of different
CFLs - nothing is guessed, surmised or imagined - this is real data !"

--
Rich Webb Norfolk, VA
Click to expand...

DISCLAIMER: I did not read the entire article at the website referenced in
the post above. Nor do I intend to.

Two factors in the analysis seem to be missing.
One is duty factor and the other is actual temperature rise.
Very short current spikes may be impressive, temperature rise is the
parameter that should be of concern if one is proposing a fire hazard.

I would like to see some empirical data of temperature versus dimmer
settings.

Charlie
 
"Charlie" <left@thestation.com> writes:

"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:gq6cl4dmj52umcn6qf4l6aiq48cornk37d@4ax.com...
On Sat, 27 Dec 2008 02:30:08 -0500, Meat Plow <meat@petitmorte.net
wrote:

Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.

Here's one guy who seems to have looked into it more than casually:
http://sound.westhost.com/articles/incandescent.htm#dim2

Shorter version: "To reiterate ... never use a CFL with a dimmer in the
circuit, even if it is set (and kept) at the maximum setting. Doing so
places you at risk of fire, and at the very least will dramatically
shorten the life of the lamp and the dimmer. Remember that these figures
were all measured using a normal dimmer and with a variety of different
CFLs - nothing is guessed, surmised or imagined - this is real data !"

--
Rich Webb Norfolk, VA


DISCLAIMER: I did not read the entire article at the website referenced in
the post above. Nor do I intend to.

Two factors in the analysis seem to be missing.
One is duty factor and the other is actual temperature rise.
Very short current spikes may be impressive, temperature rise is the
parameter that should be of concern if one is proposing a fire hazard.

I would like to see some empirical data of temperature versus dimmer
settings.
Click to expand...
There are a number of questionable assumptions and conclusions on that
Web site.

Since the very short spikes are confined to the input section - diodes and
filter capacitor - if the diodes can handle the peak current, there really
shouldn't be an issue.

If the average power is essentially unchanged with a dimmer set at full
brightness, it may be fine. What I'd like to see would be waveforms at
the transistors, not the input.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
On Sat, 27 Dec 2008 09:29:56 -0500, Sam Goldwasser
<sam@minus.seas.upenn.edu>wrote:

Rich Webb <bbew.ar@mapson.nozirev.ten> writes:

On Sat, 27 Dec 2008 02:30:08 -0500, Meat Plow <meat@petitmorte.net
wrote:

Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.

Here's one guy who seems to have looked into it more than casually:
http://sound.westhost.com/articles/incandescent.htm#dim2

Shorter version: "To reiterate ... never use a CFL with a dimmer in the
circuit, even if it is set (and kept) at the maximum setting. Doing so
places you at risk of fire, and at the very least will dramatically
shorten the life of the lamp and the dimmer. Remember that these figures
were all measured using a normal dimmer and with a variety of different
CFLs - nothing is guessed, surmised or imagined - this is real data !"

The problem is that the CFL is not even a remotely linear load. Incandescent
lamps are far from linear since their resistance changes by a factor of 10
from cold to hot, but in the steady state they look like a resistor.

The input to the typical CFL is a bridge rectifier feeding a filter capacitor
with a time constant of a couple cycles at 60 Hz. This means that to the
source, it looks like an open circuit for a large part of each cycle. That's
not what a dimmer expects and results in the high peak current in short
pulses.

Whether it's as dire a situation as is implied by the quoted text at full
output may be debatable, but it certainly won't be running with anywhere near
normal.
Click to expand...
That's what I figured. This explains why standard CFLs don't last long
even if they are never dimmed. I suppose all dimmers of the triac type
don't bypass the circuit when the control is fully clockwise.
 
Meat Plow <meat@petitmorte.net> writes:

On Sat, 27 Dec 2008 09:29:56 -0500, Sam Goldwasser
sam@minus.seas.upenn.edu>wrote:

Rich Webb <bbew.ar@mapson.nozirev.ten> writes:

On Sat, 27 Dec 2008 02:30:08 -0500, Meat Plow <meat@petitmorte.net
wrote:

Does the dimmer circuit still affect a CFL adversely even if it's not
dimmed? Not being a dimmer expert I'll assume that the waveform of the
output is still not pure sine even at max.

I had an argument with someone who tried to convince me that it
wouldn't affect the CFL if it wasn't dimmed.

Here's one guy who seems to have looked into it more than casually:
http://sound.westhost.com/articles/incandescent.htm#dim2

Shorter version: "To reiterate ... never use a CFL with a dimmer in the
circuit, even if it is set (and kept) at the maximum setting. Doing so
places you at risk of fire, and at the very least will dramatically
shorten the life of the lamp and the dimmer. Remember that these figures
were all measured using a normal dimmer and with a variety of different
CFLs - nothing is guessed, surmised or imagined - this is real data !"

The problem is that the CFL is not even a remotely linear load. Incandescent
lamps are far from linear since their resistance changes by a factor of 10
from cold to hot, but in the steady state they look like a resistor.

The input to the typical CFL is a bridge rectifier feeding a filter capacitor
with a time constant of a couple cycles at 60 Hz. This means that to the
source, it looks like an open circuit for a large part of each cycle. That's
not what a dimmer expects and results in the high peak current in short
pulses.

Whether it's as dire a situation as is implied by the quoted text at full
output may be debatable, but it certainly won't be running with anywhere near
normal.

That's what I figured. This explains why standard CFLs don't last long
even if they are never dimmed. I suppose all dimmers of the triac type
don't bypass the circuit when the control is fully clockwise.
Click to expand...
There are/were some that do. Only if there is a "click". :)

Having said that, the parts of the CFL ballast that would be running
with absormal waveforms would be largely limited to the front end -
typically a bridge rectifier and filter capacitor with an effective time
constant of 2 or 3 cycles.

So, parts in both the dimmer and CFL will be stressed more than normal
with the much higher peak current. If the rectifiers survive for any
length of time - which is likely - they are probably not going to be
a problem. However, the high ripple current in the capacitor could
increase heating and dramatically shorten its life. Only an actual
analysis would be able to prove that one way or the other.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top