Posted: 9/20/2011 5:09:04 PM EDT
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Have two pendant halogen lamps on a dimmable circuit in the kitchen above an island, and one went out.
Ok, tried to replace 12 V DC halogen bulb, but no go. So took fixture apart at the ceiling and found an MDL Electronic Transformer part number 316-0011 wired into AC feed. AC wires (black and white) show 120 V AC when the switch is closed (on). No voltage when switch open (off). No DC output voltage regardless of what position the switch and dimmer are in. I took the transformer out and plugged it into a wall receptacle and confirmed no DC voltage output. So far, seems like bad transformer, and I can replace it for $24 online. What I don't understand is how the dimmer aspect of this circuit works. The AC voltage does not change with varying position of the dimmer slider. How does the dimmer work, in this set up? Thanks, in advance. |
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Quoted:
What I don't understand is how the dimmer aspect of this circuit works. The AC voltage does not change with varying position of the dimmer slider. How does the dimmer work, in this set up? Thanks, in advance. Without looking, it's tough to say, but it could be a normal triac-based dimmer. It doesn't alter peak voltage, but rather phase width. The AC pulses have the same peak height, and are still spaced at the same time interval, each one is just skinnier, so to speak. My off-hand guess is that your transformer got hot enough to trip the thermal cutoff that they usually have inside of them. Does the transformer look burned at all? You could peel back the paper or covering from the windings and dig around to see, but since it's bad either way, that would just be for curiosity. Quoted:
You might try re-measuring the transformer output with your meter set to AC volts. ^^^ That too. |
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Quoted:
Quoted:
What I don't understand is how the dimmer aspect of this circuit works. The AC voltage does not change with varying position of the dimmer slider. How does the dimmer work, in this set up? Thanks, in advance. Without looking, it's tough to say, but it could be a normal triac-based dimmer. It doesn't alter peak voltage, but rather phase width. The AC pulses have the same peak height, and are still spaced at the same time interval, each one is just skinnier, so to speak. My off-hand guess is that your transformer got hot enough to trip the thermal cutoff that they usually have inside of them. Does the transformer look burned at all? You could peel back the paper or covering from the windings and dig around to see, but since it's bad either way, that would just be for curiosity. Quoted:
You might try re-measuring the transformer output with your meter set to AC volts. ^^^ That too. Good points, all; it is a transformer, not transformer/rectifier (my mistake in post). The output should be 12 V AC, per the label. So I checked AC voltage, and am only getting ~1 or 2 volts AC. The transformer looks (and smells) fine. It is a solid enclosure, with no paper to peel off. I will let you know what comes of replacing the transformer, when it gets here. |