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Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
I have a timer a bit like that. The problem I have found is that it draws its power (to run the clock and the control electronics) through the lamp. Obviously, running a milliamp or two through a tungsten lamp does nothing but, when I tried a CFL type it flicked on for a flash every few seconds. I think it was acting like a neon oscillator. As long as at least one of the bulbs you are controlling is a tungsten lamp this shouldn't be a problem. It might be an interesting experiment to disconnect the PARs to see what happens.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Rod Elliott does have some valid concerns, IMO. He showed that a triac could interact with a CFL to cause it to draw very sharp line current spikes, and the resulting increased RMS current could overheat the fusible resistor in the CFL circuit and set it on fire.
In your case, I expect the tungsten lamp load would help the triac to fire properly and there would be no problems. But for other people in this situation, why not use your triac-equipped timer to switch a relay that switches your CFL load.
I have a lot of CFLs at home, but since reading Rod's article I may well rethink how I use them.
BTW, this touchiness has nothing to do with triacs themselves, it's just the cheap drive circuits. With my own hard-fired SCR driver circuit, I've been able to "dim" anything from vacuum cleaners to SSTCs and neon sign transformers.
I'm sure it could successfully lower the DC bus voltage on CFLs too. But it's another matter whether the little HF oscillator thingie inside the CFL keeps running at low voltage, and whether the tube stays lit. The secret to successful dimming of fluorescents is to supply extra filament power at low brightnesses, otherwise the filaments cool off and the arc goes out altogether.
Registered Member #79
Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
Yeah, we had pretty much the same circuit in our shop at one point with florescents. The worst thing we noticed was they didn't come on about 1/2 the time.
We used them for about 6 mo, then got frustrated and took them out. We never noticed any damage to anything. I don't remember a warning or we wouldn't have used it!!! Yikes.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Not knowing the exact design of the schematic I can't say for sure, however I suspect that cheap TRIAC drivers of that type do not compensate for the unbalanced output. I am always surprised that new units can get away without using chokes. With the resistive load it does not matter, however it could result in a slight DC offset for ballasts like the above posters experiments suggested. Just a thought....
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In-Wall light timers + CF lights
