voltage sensing relay for household lighting

Discussion in 'The Projects Forum' started by circa27, May 3, 2011.

  1. circa27

    Thread Starter Member

    Feb 22, 2011
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    so i have xenon lighting in my house and for some unknown reason they are controlled by a switch that can give them either 8 or 12 volts. Its bad for the lights to attempt to run at 8 volts so i was thinking i could use a relay of sorts to control them

    is there such thing as a voltage sensing relay that would only engage at 12 or more volts, but stay disengaged even when the 8 volt supply is switched on?
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I am assuming that this switch is part of a controller? A controller specifically designed for xenon lights?
     
  3. circa27

    Thread Starter Member

    Feb 22, 2011
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    well it was originally a switch to standard halogen bulbs for dimmer functionality. so the 8v supply would stay dim and the 12v supply would be standard brightness

    I need to somehow add a relay or something to basically ignore any input at or below ~8 volts, so the switch acts as either on or off and has no dimming functionality. Taking out the 2 way dimming switch is out of the question for practicality reasons, but id easily be able to add some sort of voltage sensor/filter if this exists
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    It's not advisable to run a Xenon or any halogen bulb below its rated operating voltage for any long period of time, it needs to see full voltage every now and then as that's what gets the filament hot enough such that the materials emitted are absorbed back by the filament.

    As to your relay you MIGHT be able to find one that won't energize at 8V but will at 12V and also do the same thing in reverse. It would be more desirable to use a comparator IC and a driver transistor for the relay.
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    from what little I know about xenon bulbs (i.e. what I just read on wikipedia) they need a constant current source and a high voltage "kick" to get them going. This requires some kind of simple controller, or what would be referred in flourescent lighting as a ballast. Assuming you aready have a ballast for your lights (I assume that since you measured 8v or 12 v, which doesn't come out of a wall socket) it is probably supplying the proper power to your lights. 8V or 12V may not seem like enough, but were you measuring with the lamp removed? If so, the voltage will change as soon as you put the bulb in, to maintain the proper current. If you were measuring with the bulb in, then maybe 8 or 12v really is the voltage required for your lights to function at their amperage requirement. I can't imagine that a pre-packaged ballast/light combo would be designed to output the incorrect voltage. If you attach a relay to the ballast output, chances are that you will blow up the relay, as the ballast will increase the voltage trying to drive a specified current through the coil. what voltage were you planning to use to energize the lamps via the relay? rmrmber that these lights require DC. I wouldn't try to put 120vac through them.

    EDIT: I didn't see post #3. get a ballast for your lights.
     
  6. circa27

    Thread Starter Member

    Feb 22, 2011
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    I have the wall converted for a halogen bulb that runs fine with the 8-12v as a dimmer, it just happens that the ballast for the xenon need a 12v input.

    @Marshallf3 have you heard of a relay like I explained? I can't find one anywhere. And how would I set up a driver and comparator ic?
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    You've said that this control is a switch. Are you sure of that? Are you saying that it has 3 positions, OFF - Lo - Hi?
     
  8. circa27

    Thread Starter Member

    Feb 22, 2011
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    exactly, off, low (8v) and high (12v)
    A relay that only turns on after 8v is ideal, how would I find one or make something similar?
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    Please post a front and rear photo of this switch or provide a link to the manufacturer's model. It may be possible to simply disconnect the 8V position on the switch. This would provide you with ... OFF - OFF - ON (12V). If it's possible to do that you could also jump the 12V position to the 8V position. This would give you ... OFF - ON (12V) - ON (12V).
     
  10. circa27

    Thread Starter Member

    Feb 22, 2011
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    im actually overseas right now i cant exactly take a picture haha
    but im just assuming that i cant jump the 8v source of the switch

    there has to be some sort of circuit addition i can put after the resisted part (8v) to keep it off until it sees 12v.. is there not? That would take me 5 minutes to do and definitely be the easiest solution, hence why ive been pushing for that
     
  11. CDRIVE

    Senior Member

    Jul 1, 2008
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    Sorry, but I don't see that as the easiest solution. I see it as over engineering a simple circuit.

    Btw, I didn't suggest jumping the 8V source.
     
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