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Thread: 300w lighting transformer on Standard Dimmer.

  1. #1
    Join Date
    Apr 2017
    New England

    300w lighting transformer on Standard Dimmer.

    I went on a call and determined that the transformer had gone bad in a tech lighting chandelier. The previous electrician had replaced it with a different manufacturer and after trying to get a replacement for the replacement to no avail I contacted tech and they shipped the original style to my supply house. I noticed that the dimmer was a standard type while I was first on site. The new transformer came and it wants an ELV dimmer. The fixture is made up of 10 or so 12v halogen bulbs (unsure of wattage). Seeing as this will be transformer #3 in said fixture I am going to change the dimmer out to an ELV and hopefully this xformer will last a while longer. I am curious though if I do not change the dimmer out to an ELV is the only downside reduced transformer life?

  2. #2
    Join Date
    Apr 2008
    Ann Arbor, Michigan
    171221-1946 EST

    DC current added to an AC supply and fed to a transformer will unbalance transformer core flux and may cause excessive primary current and burnout of the primary.

    A phase shift dimmer may not (cheap ones won't) supply an equal average current on the positive half cycle compared to the negative and that means some magnitude of DC current.

    Special dimmers are made to minimize the DC component.


  3. #3
    Join Date
    Jun 2010
    Quote Originally Posted by crispysonofa View Post
    I am curious though if I do not change the dimmer out to an ELV is the only downside reduced transformer life?
    Reverse/ELV dimmer on magnetic is the only absolute do not do.

    As for your question, I have no idea. Each dimmer/electronic power supply combination require trial and error. There are many LED lamps that lists traditional as well as reverse/ELV, and many that tolerates either and you can pick whichever that offers the best result.

    ELV dimmer is more expensive and they wouldn't spec it without merit. Traditional dimmer on a unit that asks for ELV/reverse will likely cause reduction in dimming range, developing a sore spot (a range brightness where you can't use due to instability), shimmering and increased buzzing noise from all the parts in the system.

    You'll need this specific SKU which is the model RH703PTUW or another one that specifically says ELV. If they change to a different fixture later that prefers forward phase, this one can be reconfig'd
    Don't mess around with other listings with the title only telling you it's a different color as they're not ELV capable.

    You flip the switch to reverse mode, but after that setup is quirky and the manual is required:

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