What reading will I get if I meter a dimmers output?


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Old 07-17-15, 09:32 PM
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What reading will I get if I meter a dimmers output?

Hello everyone

I was reading about dimmer switches and how they work, but I was wondering about the modern voltage chopping dimmers (without resistors), will the output AC voltage reading if the knob is at low setting be a lower AC voltage? like if the knob is at %50, will the AC reading be ~55v instead of 110v
Also, will the voltage chopping technology effect the lifespan of the light bulbs?

Thanks in advance
 
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Old 07-17-15, 10:04 PM
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It's hard to say what you'll see. It depends on the type of dimmer. Some actually vary the output voltage and some turn the output on and off at a variable rate but so fast the eye doesn't notice it.

Running an incandescent bulb at a reduced voltage will extend it's life. I'm not sure if the pulsing has any effect on the bulb life.

I can tell you this......ramping a bulb up slowly is better for it than just applying full power. Many of the better dimmers bring the bulb up to full brightness in a second or so saving the filament from the inrush.
 
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Old 07-18-15, 07:47 AM
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A waveform chopping dimmer theoretically outputs voltage for which a calibrated dial can be constructed where for example 50% setting given 110 volts input yields 55 volts at the output.

Practically, the net chopped waveform can vary depending on load. Also the dial actually supplied might not be accurate.

The waveform chopping in itself does not affect the lifespan of the bulbs compared with other methods of reducing the voltage for dimming purposes.

The waveform after chopping still has an effective pure sine wave equivalent aka root mean square equivalent. That would be the net output voltage.

Starting off with a lower voltage and ramping up to the desired voltage lessens the chance that the temperature of sub-components (such as lamp bulb filaments) will get too high even just for an instant and lessens the chance that voltage applied (notably across semiconductor components such as diodes) will get too high even if just for an instant.
 

Last edited by AllanJ; 07-18-15 at 08:17 AM.
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Old 07-19-15, 09:05 AM
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Thanks guys for the info. Very helpful
 
 

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