Diodes in houselighting circuit

Discussion in 'General Electronics Chat' started by drewlas, May 12, 2008.

  1. drewlas

    Thread Starter New Member

    May 12, 2008
    While investigating a bathroom switch (gang of two; one light and one ceiling fan) which was behaving unpredictably, I discovered each switch had a diode (similar to what you would buy from an electronics store), bridging two of the terminals in each switch.
    I removed one from the fan switch and the fan stopped working.
    Why are they there? Are they needed? I hope I am posting in the correct place.
    Any advice happily received.
    drewlas (Australia)
  2. mik3

    Senior Member

    Feb 4, 2008
    Can you post a drawing of how the diodes are connected or explain better?

    Is the light bulb an ordinary 120/240 V AC bulb (i dont know the voltage of the power distribution grid in Australia)?

    Do you know the operating voltage of the fan?
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    I'm sorry, the unsolved mysteries page is two over..

    Are you certain the device was a diode?
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    This suggests your switches have more than two terminals. Unless they have three terminals, with one of those being for the ground wire, the wrong type of switch has been installed in your bathroom.

    Can you provide a more complete description of the switches? And can you describe the connection of the diode?

    I've never heard of a diode being used in this manner, but I'm not an Australian electrician.
  5. hgmjr

    Retired Moderator

    Jan 28, 2005
    Maybe you can take a digital picture of the switch and attach it here.

  6. DC_Kid

    AAC Fanatic!

    Feb 25, 2008
    perhaps the switch is does not switch terminal to terminal. it switches power to the diode and the diode bridges power to the other terminal. perhaps the fan only runs on DC, half wave in this case. i dunno, just a thought. how big is the diode?
  7. pfofit

    AAC Fanatic!

    Nov 29, 2006
    Very odd by your description. Kinda like the animals downunder.
    As noted: some questions to answer.
    Is there a number on the "diode"?
    How many terminals are on the switches? Are you counting ground or is it a three way switch? Are the switches regular/normal house switches? Are they timer switches?
    Can you provide/make a wiring diagram?

    Was the light or fan unpredictable, or both?
    Do you mean intermittent or light being dim or fan slow?

    Originally, did the light switch only control the light and the fan switch only the fan?

    Interesting query you have provided.
    Last edited: May 13, 2008
  8. HarveyH42

    Active Member

    Jul 22, 2007
    Does the fan always come on with the light, and can you switch the fan independent of the light? Basically, if the light is on, the bathroom is in use, and the exhaust fan is probably a good idea (water vapor from shower, nauseous fumes). Sometimes you would like to leave the fan on after turning off the light. Don't know why you would need diodes in an AC system, perhaps it's some other device.
  9. drewlas

    Thread Starter New Member

    May 12, 2008
    Thanks for the interest.
    I will try and get a photo of the wiring. The voltage is 240 and fans of this type (down here anyway) are, naturally, AC, and typically on the lighting circuits (not the power circuits). I have tinkered (or perhaps, tampered) with many switches of this type and have never seen such electronic components of any type being involved before.
    The intermittence, I am certain was a result of a loose connection but I could see no reason for the electronic components, which I assumed must be a diodes.
    The switches are independent and are normal houshold fare. They are the only ones controlling the light and the fan. The active wire comes into one and then is bridged over to the other; they are obviously on the same circuit. The switches each have four terminals, one the earth and one, I believe, is generally only used when there is a double switch control situation. Here my lack of knowledge will probably begin to cloud the issue, so I will stop.
  10. thingmaker3

    Retired Moderator

    May 16, 2005
    If there are four terminals, including one for earth, then you have "three-way" switches. They are SPDT switches.

    The earth terminal should always and forever be connected to the earth conductor - this is for safety. I don't know about Australian codes, but where I live codes require both earth wires (the one coming in and the one going to the fan/light) to be connected with a "pigtail" to the switches. Here they must also be connected with a "pigtail" to the box if it is a metal box.

    I'm curios to know where the diodes - if that's what they are - come into play. Looking forward to your photo!
  11. drewlas

    Thread Starter New Member

    May 12, 2008
    Diode, did I say diode? I think it is a resistor, they are easily confused when you don't know what you are doing. So this could result in longer globe and fan life perhaps, depending on where it was placed. I think that is it.
    Thanks for your interest.
  12. Gadget

    Distinguished Member

    Jan 10, 2006
    Dont dismiss the diode. I have seen a diode used as a nasty Light dimmer, by blocking 1/2 of the ac cycle it effectively dims the lamp...(with a noticable increase in lamp flicker).