Humming Dimmers

Discussion in 'Electrical Forum discussion & Blog' started by ScottTENN, Dec 4, 2008.

  1. ScottTENN

    ScottTENN New Member

    Messages:
    19
    I got 3 dimmers from HD in the $10-15 range. (Really all they had in a 3way dimmer.)

    Two of them have been installed and they, not the lights, produce a slight hum as the lights are dimmed. The dimmer the more hum. If there was background noise in the room, tv or radio you would probably never notice it. Normal?

    Also while turning one off, since i dont have cover plates on yet, I could feel heat from the housing. They are not dimmed while I'm working in the room. Are they supposed to get warm, noticably warm?
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Cheap dimmers ( under $40) could be susceptible to hum, and to getting warm. Are you dimming fluorescent bulbs?
  3. TheElectricalGuru

    TheElectricalGuru National Electrical Code Expert/Speaker/Educator

    Messages:
    11
    I could not resist......what song are they exactly humming?

    Anyway.....check the dimmers, verify the wattage allowance of the dimmers and if they are designed for the application you are using them for. ( ie: floures and so on )
  4. ScottTENN

    ScottTENN New Member

    Messages:
    19
    They are for incondecent bulbs, 600w. The most I have is 360w, 6x60w.
    I have read about the bulbs humming, but this is the dimmer. I guess they are still to cheap. They say that have an RFI filter, but it must be filtering something else.

    My worry is really the heat.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,132
    Location:
    New England
    While on, few dimmers pass all of the voltage to the bulbs attached - they act sort of like a like a small resister - almost like the filament in the bulb...they'll get warm. Well, not exactly true, but it works as an example (the details are more complicated than that depending on the exact type). Shouldn't get really hot, but maybe warmer than you're used to. Some rheostat type dimmers have a bypass switch to connect the line directly, so when full on, they normally don't get hot, but all of the other types do to some degree or another. You'll notice on many that there are aluminum tabs on the sides. These are heat sinks - small radiators to dissipate heat. The instructions say if you remove them (you might have to to get them to fit a multi-gang box), you need to derate the dimmer so it won't handle as much current.

    When the switch is on, if you took a multimeter and measured from the hot in across the dimmer to the output to the light, you'll measure a little voltage. The higher the voltage (across the switch when it is full bright is an idea of how good the electronics are inside of the switch...the higher the voltage, the hotter the switch will become. Note, this only is valid when it is full bright, it should increase as you dim the lights.
    Last edited: Dec 4, 2008
  6. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    You get what you pay for. You paid crap, you got crap and now you have a problem. Go to a real electrical supply house and tell them what you need and what problem you are having. Take some cash.
  7. I've had humming dimmers too, and I didn't like it. They also got hot.

    I've asked around a lot about it. I've been told stories about rheostats and silicon controlled rectifiers and more. It basically comes down to this: Home Depot sold you 20th century technology, not current (21st century) technology.

    I have often taken merchandise back to HD much later than just weeks or months after purchase. They have always taken it back without much of a struggle. I get a little card and buy more stuff before leaving. Stuff I know I will keep.

    David
  8. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    The problem is that there are very few choices in that small of a package.

    Methods of dimming a light.

    1. Cheep SCR based dimmer. This type switches at 120 Hz

    2. Cycle dropping SCR dimmer. This type changes the pattern of on-off to better drive motors. (I designed one of these for a company project 10 years ago)

    3. Dual FET based dimmer. This type can switch at higher frequency's and can drive motors.

    4. "true sine wave" switching supply. The size of this type of circuit is getting smaller every year and someday could fit inside of a switch package.

    5. Variac. These are large and heavy.
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