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Reed switches with LED strip lights

Discussion in 'LEDs and Optoelectronics' started by Mark Phillips, Apr 9, 2017.

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  1. Mark Phillips

    Mark Phillips

    4
    1
    Apr 9, 2017
    Hoping for some advice please.
    I have some LED strip lights for a wardrobe. We want to use 3 NC reed switches, one on each sliding door. So if any door is open, the lights come on.
    The reed switches I am seeing have a max current of 0.5A, but the lights collectively draw more than this.
    I've read about using a relay to allow the low current circuit control the higher loaded circuit, but can anyone tell me exactly what relay I need to get to do this, and how to set it up.
    Or any other alternatives please
     
    csxvn likes this.
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    Try this ......Relay is a standard normally open type spst (single pole single throw) or you can use any that have changeover contacts spdt (single pole double throw) ....voltage same as supply to the Leds.
    May have to check on what supply you are using though, could have a bearing on the outcome.
     

    Attached Files:

  3. Mark Phillips

    Mark Phillips

    4
    1
    Apr 9, 2017
    Thanks for the reply. The supply is from a DC mains adapter 12V 2A.
    The LEDs draw about 1.4A all together.
     
  4. Bluejets

    Bluejets

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    Oct 5, 2014
    ok...should be fine as shown then.
    (12v relay)

    Something like this...
    http://www.ebay.com.au/itm/Relay-LY...966620?hash=item1c7e889d1c:g:IKAAAOSwr~lYsA4q

    Relay top shows the pin numbers on the base to connect to but i can't see it clearly in the photo.
    Should be a fairly standard connection though.

    One thing to watch out for is some relays will have a free wheeling diode inside the casing which will make the coil polarity dependant. Looks like it might be that way for the enclosed LED indicator.
     
    Last edited: Apr 10, 2017
  5. Mark Phillips

    Mark Phillips

    4
    1
    Apr 9, 2017
  6. duke37

    duke37

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    Jan 9, 2011
    Reed relays are not very good power switches. I would use them to switch a transistor to either switch the load directly or switch a relay.
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    You mean as shown above????
    20mA is not going to kill a reed switch.
     
  8. duke37

    duke37

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    Jan 9, 2011
    20mA will be OK if the load is not inductive. The best way to ensure this is to use a transistor with a suitable base resistance. I would only use a relay if isolation is required and make sure is has a protection diode.

    I have had reed relays which have been unreliable but on the other hand, I had one measuring the rotation of a shaft at up to 1000rpm which worked without fault for over 2 years. This was supplying a digital counter so a very light load.
     
  9. Mark Phillips

    Mark Phillips

    4
    1
    Apr 9, 2017
    Thanks again, I have tested it and it's all working just as I hoped.
    Just one more thing please.

    I am using 0.5mm 2-core cable for the lighting circuit, which should be fine for the 1.5A current.
    But this wire is a bit thick to use to wire the door contacts, which seems to take about 0.25A when the doors are closed.
    I have some "bell wire", rated to 1A, which is much easier to work with.
    Are there any issues with mixing different wires in this way in the same circuit?

    Might seem like a stupid question. This is my first electronic project and it's been a (very) long since I studied electronics.
     
  10. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    As long as the wire is rated for the applications voltage and current it should be fine.
    Adam
     
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