Potentiometer direct to mains for lamp

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Discussion Overview

The discussion revolves around the feasibility and safety of using a potentiometer directly connected to mains voltage for dimming a lamp. Participants explore the implications of such a setup, including safety concerns and alternative approaches for dimming lamps, particularly incandescent and low-voltage options.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant, freddie, inquires about using a potentiometer as a dimmer directly connected to mains voltage for a lamp prototype, expressing a lack of knowledge in electronics.
  • Another participant warns against working directly with mains voltage due to safety risks and suggests using a transformer to step down the voltage instead.
  • It is noted that using a potentiometer for dimming incandescent lamps is impractical due to heat dissipation concerns, and that phase control methods are more suitable.
  • A suggestion is made to use a UL-approved transformer to reduce mains voltage to 12VAC and to build an SCR-based dimmer circuit for safer operation.
  • One participant strongly advises against connecting a potentiometer to mains voltage, highlighting the risk of burning and potential fatality, and questions the type of bulbs being used.

Areas of Agreement / Disagreement

Participants generally agree on the dangers of connecting a potentiometer directly to mains voltage and the need for safer alternatives, but there is no consensus on the specific approaches or solutions to be used.

Contextual Notes

Participants express concerns about safety regulations and the complexity of dimming circuits, particularly for different types of lamps. There is an emphasis on the importance of understanding electrical safety before attempting projects involving mains voltage.

freddiev
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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 http://ie.farnell.com/jsp/search/browse.jsp?N=411+1000165&Ntk=gensearch_001&Ntt=MDSP&Ntx="(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
freddie
 
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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):
https://www.physicsforums.com/showthread.php?p=1351969
 
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?

http://en.wikipedia.org/wiki/Dimmer
 
No No No !

DONT DO IT ! don't in heavens name connect such a potentiometers into 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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