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  1. #1
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    Default Motion Detector question

    I'm not sure if I know how to ask this correctly.... but here goes.

    Can anyone tell me if motion sensors are more or less all the same voltage wise or do they match the devices they control?
    What I mean is... if the sensor is triggering a standard 120v light fixture, does that mean that the sensor itself is a 120v device? Or am I thinking of it all wrong?

    I'm curious to know if a sensor for a low voltage DC lighting system is different than one for AC... and even further would the sensor for a 6V system be different than one for a 12V system?

    I've seen some motion sensors that require a 9V battery and others that do not and I'm not sure how that figures in.

    I hope the question makes sense.
    Thanks.

  2. #2
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    Default Re: Motion Detector question

    Quote Originally Posted by xyxoxy View Post

    Can anyone tell me if motion sensors are more or less all the same voltage wise or do they match the devices they control??
    You can say they would be different depending on design and application.


    What I mean is... if the sensor is triggering a standard 120v light fixture, does that mean that the sensor itself is a 120v device? Or am I thinking of it all wrong
    Sort of.
    There are two components of a motion senor :
    1. electronic circuit for the "motion" detection
    2. switching - for turning on a device ( example a light) or for change of state signal ( example burglar alarm)
    The electronic circuit portion would usually require a DC voltage and in the case of a 120 volt light ... the AC-DC conversion would be incorporated into the electronic circuit....... So in essence the electronic motion circuit is DC being supplied by an AC source and then converted.

    In the case of a 120 volt light the switching portion is passing 120 volts AC through either a relay contact or from an electronic component.

    So .......with the 120 volt types it's common to wire them to 120 volts for the sensor to function.

    However .....

    There can be the case where a motion sensor can have DC voltage supplied separately to operate the motion sensing circuit and able to perform the switching ( passing) volts AC if it is rated.


    I'm curious to know if a sensor for a low voltage DC lighting system is different than one for AC...
    That would depend on how things would be configured.
    The DC lighting system .... unless it's running off battery power .... would have an AC - DC converter. This may likely be the motion sensor device would be switching the AC supply for the lighting converter .... basically taking the place of the light switch.



    and even further would the sensor for a 6V system be different than one for a 12V system?
    That would depend on the electronic circuit .... if it's designed to operate at 6 volt DC then it wouldn't work with a 12 volt DC source and visa versa.

    As for the switching portion it wouldn't matter ..... depending on it's current rating and whether it's rated for AC current.


    I've seen some motion sensors that require a 9V battery and others that do not and I'm not sure how that figures in.
    This is just a design feature .... instead of having to use a AC - DC converter they are using a battery for the power source.

    BTW .... you could wire up a 9 volt AC - DC adapter and eliminate the battery.

    Hope this makes sense and helps.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
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    Default Re: Motion Detector question

    ***...
    Thanks for a very thorough answer!
    I'm still digesting the details but you answered my main questions.

    I have a 6V device with a motion sensor which I was hoping to convert to 12V to work in conjunction with some other devices... but it looks like that may not be an option.

    I have 2 6V batteries that I've wired in a series as a 12V power source. I may have to run a leg that converts 12V back to 6V just for this device. I assume that's possible though I've never done it.

    Thanks again!

  4. #4
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    Default Re: Motion Detector question

    You can run a 6VDC device on 12VDC by adding a resistor and a voltage clamping device, such as a zenor diode, to clamp the supply voltage to 6VDC fot the device.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  5. #5
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    Default Re: Motion Detector question

    Clamping devices and diodes are a little out of my realm of experience. Are we talking a trip to Radio Shack and breaking out the soldering gun? If so I would need more details.

    Is there an off the shelf option that wouldn't break the bank?

  6. #6
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    Default Re: Motion Detector question

    You said you are already using 2 2 volt batteries in series to get the 12 volt, so you already have 6 vdc available.


    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  7. #7
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    Default Re: Motion Detector question

    Sometimes the most obvious answers are the hardest to see

    Thanks... I think that's all I need !!

  8. #8
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    Default Re: Motion Detector question

    You're welcome. I guess the brain cells are getting a little slow or we're just to use to working on complicated solutions.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

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