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Potentiometer direct to mains for lamp

  1. Jul 11, 2007 #1
    Hi guys
    I'm new here and I require some help with a project I'm working on. I'm building a lamp prototype and i need to use a potentiometer to act as a dimmer. The pot needs to fit inside a 25mm ID tube, and is connected directly to the mains. First of all is this possible? I think I have found a suitable pot here (although I would be grateful for help in which one to choose) Sorry If this is appears to be a stupid question, but I have very little knowledge of electronics and nobody to else to ask! If its not going to work, I would be delighted to hear alternative solutions.

    Best regards
  2. jcsd
  3. Jul 11, 2007 #2


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    Gold Member

    Mains!! You need to be very careful with this. Working directly with mains is an absolute no no for people with a lack of experience. Use a transformer to step down the voltage instead.

    But back to your question regarding practicality. It is impractical to use a resistor network, let alone a pot to act as a dimmer. Can you imagine the amount of heat that would be dissipated across the resistor network when connected to mains!
    A feasible dimmer would make use of phase differences to vary the power across the lamp. See my reply here (post #6):
  4. Jul 11, 2007 #3


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    Staff: Mentor

    I echo ranger's cautions about working with the AC mains. Please work with low-voltage projects until you learn a fair amount about electrical safety (both how to work safely with AC mains in your projects, and how to build your projects in compliance with safety regulations, like those of Underwriters Laboratories here in the US).

    And as ranger says, you don't control the dimming of an incandescent lamp with a potentiomenter. You control it with a pulse-width controlled triac or pair of SCRs. That's how existing dimmers work for incandescent lamps. Dimming flourescent lamps is even more complicated.

    So a good project for you would be to use a UL-approved transformer to step the AC mains down to 12VAC, and build an SCR-based dimmer circuit for a 12V lamp. That will get you lots of knowledge and experience with a real dimmer circuit, without the exposure to the shock and fire hazards associated with building an AC mains-based circuit. Sound like a plan?

  5. Jul 11, 2007 #4
    No No No !

    DONT DO IT !!! dont in heavens name connect such a potentiometers in to a mains voltage !!! they will burn with a bright light and you may get killed.

    What kind of bulbs you are using? Most of the lamps work with very low voltages say under 24V, most halogens with 12V, leds even with under 3Volts.
    Those are safe voltages to work with.
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