# Function of a phase angle adjustment in a light dimmer

I'm setting up a light dimmer an have found a adjustable part for setting the "phase angle of light bulbs". That is a literal translation from German. You can see the adjuster in the picture.

My perspective of how the dimmer works is that it just zeroes some parts of the sine shaped voltage therefore reducing the power that reaches the bulb.

What is the purpose of that switch, both functionally (what it does) and conceptually (why and how it's done)?

• Since it says 30 volts ~ 50Hz I'm assuming it is a magnetic low voltage dimmer. With magnetic induction, current always lags the voltage by 90° (cosine), so it's not a balanced sine wave. An aftereffect of this could cause buzzing in the lamps and the phase angle adjuster may help reduce any buzzing. – Kris Sep 15 '15 at 12:07
• Power Factor compensation – Fiasco Labs Sep 15 '15 at 16:49
• I doubt the adjustment has any affect on power factor compensation. The adjustment is likely a type of one-shot triggered at the beginning of each power cycle and does nothing to phase shift the overall load. – user39367 Sep 16 '15 at 13:57

There is a good general description of different types of dimmers here:

As Kris commented, I suspect it is a type of inductive dimmer that you have. If that is correct, then the applicable section in "The Principles of Dimming" would be "Dimming Wire-wound transformers for low voltage halogen lamps." The adjustment of the phase angle of the light bulbs in this context would correspond to the length of time that the thyristor in the dimmer control must be hard-fired to overcome the inductance of a magnetic step down transformer. It is a compensation circuit for the lag time required to drive an inductive load. I do not think it has anything to do with noise control.

• if I understand right, this phase adjuster has to do with he inrush lag, not so much with noise? – Kris Sep 15 '15 at 16:23
• If by "inrush lag" you mean the tendency of an inductive load to oppose changes in current flow, then yes. With this compensation incorrectly set for the load, you could crank the dimmer to the 50% and get no light or conversely the light might remain on even with the dial set to zero, depending on the transformer connected. Since transformer characteristics vary, the compensation needs to be field adjustable. Not so much for noise compensation, correct. – user39367 Sep 15 '15 at 16:35

Actually, there's a 2 missing from the 230V inscription

This dimmer, an Elso T30 p/n 174100 (now Schneider Electric) is an electronic dimmer for LED bulbs.

• Very helpful info, but how does that answer the question. – Kris Sep 16 '15 at 12:06
• 230v and not 30v. That makes sense to me. Still, I suspect this is an "L" type dimmer meant for inductive loads such as transformers or small motors. – user39367 Sep 16 '15 at 14:01
• My German is very poor, but it looks to me like the parts catalog for the EL174100 lists "Trafos" aka "Transformers" as one of the applications for this device. – user39367 Sep 16 '15 at 15:59
• I'm still researching, wanted to make a definitive report on the phasenanschritt control switch, rather than some of the more speculative assertions. – HerrBag Sep 16 '15 at 21:34