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:
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.
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
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.
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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.
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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.
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:
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.
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