Dimmer conspiracy

GoldDigger

Moderator
Staff member
It seems that many (most?) Dimmers only put out about 90% of line side voltage :rant: Does anyone else know about this?
Well, there may be a diode droo or two, and a two terminal phase controlled dimmer has a hard task trying to maintain 100% conduction. It may be a consequence of inexpensive circuitry. Are you measuring with a true RMS meter? An averaging meter will give undue weight to the cutoff sections near the zero crossing.
 

gar

Senior Member
190813-1333 EDT

A scope clearly shows the effect.

A phase shift dimmer essentially detects the time of a zero crossing, and initiates a time delay to triggering of the switch. This minimum time delay becomes a practical problem.

Probably the shortest possible time delay is set by a constant continuous current to the gate, and then the delay is a result of the characteristics of the switch. About a 1 volt switch voltage drop. At 1 V and a 120 V sine wave this is about arc sine of 1/170 = 0.24 degrees.

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electrofelon

Senior Member
Meter is a klein branded true RMS meter so not the highest quality of course, but should be accurate. Dimmer is a lutron Caseta. Client said he heard about this and I was skeptical at first but a believer after I metered it with and without the dimmer.. they do have a high trim adjustment, but he said he had it set to max. I should have verified this but I didn't.
 

gar

Senior Member
190814-2341 EDT

electrofellon:

I expect that you will find that virtually all commercial phase shift dimmers will show less than full voltage when set for maximum brightness.

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GoldDigger

Moderator
Staff member
190814-2341 EDT

electrofellon:

I expect that you will find that virtually all commercial phase shift dimmers will show less than full voltage when set for maximum brightness.

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And not as part of some energy saving conspiracy, but as a necessary consequence of economical design.
 

electrofelon

Senior Member
And not as part of some energy saving conspiracy, but as a necessary consequence of economical design.
I know Obama, the other libs, and big solar are behind this! So you really think it is just a coincidence that as soon as I bring this up, the forum get "upgraded" so everyone is all confused and disheveled so not as many people read this post!?!? Just kidding ;) But seriously, it is interesting that few people seem to know about this.
 
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PaulMmn

Senior Member
Any p-n junction will cause a voltage drop of ~0.7volts. Who knows how many junctions the power in a dimmer has to pass through to get to the other side!
 

mopowr steve

Senior Member
You didn’t know this?
I thought it was more like 95% but it was enough that it could be slightly noticed in light output between hooking direct or installing dimmer.
I've known this since I was knee high to a grass-hopper, just the effects of being controlled by electronics.
But on the up-side, lamp life was extended just by installing a dimmer even if it was kept on high. Probably why many of the 65watt R30 lamps used in my can lighting are still in use today.
 

kwired

Electron manager
I know Obama, the other libs, and big solar are behind this! So you really think it is just a coincidence that as soon as I bring this up, the forum get "upgraded" so everyone is all confused and disheveled so not as many people read this post!?!? Just kidding ;) But seriously, it is interesting that few people seem to know about this.
I could see that some may think it is possible that the solid state portions get bypassed when in full brightness position.
 

GoldDigger

Moderator
Staff member
I could see that some may think it is possible that the solid state portions get bypassed when in full brightness position.
By adding a hardware switch at the max on position that could be done. Or by using a relay. But the users will see a jump from max variable to bypass/full. And it will be more expensive and harder to fit into a single gang format.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
There used to be a dimmer that looked like a standard toggle switch, but the toggle was actually the dimmer control. It had both mechanical-switch off and mechanical-switch fully-on bypass.

If 100% voltage is a requirement at times, parallel the dimmer with a switch.
 
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