Phase Shift or True 3 Terminal Dimmer

greg furey

old lyme ct
Hi all, hope ur doing well. Long time user of this forum. Looking for input on recommended phase shift or true 3 terminal single pole dimmers for wac led208 track heads. I have 5 of these on a track and tried different lutron dimmers led compatabile and still getting flicker
I have emailed the company hope to hear soon. Customer not very happy with the flicker, don't know which other brand might be compatible Thanks all have a Merry Christmas Greg

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Senior Member
181216-2443 EST

A true 3 wire phase shift dimmer in the past was one designed to dim fluorescent lights. It had more than three wires because the ballast required full voltage to heat the fluorescent filaments. Going into the series inductor or transformer the voltage needed to be well behaved and thus the dimmer did not use current to the load to provide AC power for the electronics. Rather this power was obtained directly from the input line to neutral constant sine wave voltage. This also provided good zero crossing information. I also suspect that they did a good job of controlling the average DC current to near 0. This means accurate turn on timing on both + and - cycles.

I have one of these dimmers from many years back, probably a Lutron.



Senior Member
181217-1157 RST

A true 3 wire dimmer will operate with absolutely no external load. When set at a particular angle for turn on this angle will not change as loading on the dimmer is changed. However, with a very inductive load problems will occur because turn off does not occur until a current zero crossing.

You can probably evaluate a dimmer by monitoring output voltage as you vary load with dimmer setting held constant. I have not run this particular experiment.