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Thread: problem with activating relay

  1. #1
    Join Date
    Dec 2006
    Location
    Scotland
    Posts
    1,408

    Default problem with activating relay

    mmm wonder if any of you guys can offer ideas

    Im running 4 x 5v lasers on a timer

    First im dropping the 240v to 12v with one of these

    http://www.ebay.co.uk/itm/Atrix-18-O...item3a98f95d80


    this supplies 12v into these timers with a relay
    http://www.ebay.co.uk/itm/LED-Home-A...item566c759e91

    kind of irrelvent with the problem im having but the output from above is then
    push through one of these to drop to 5v
    http://www.ebay.co.uk/itm/3A-15W-DC-...item5b06c75f62

    Now heres the problem im having , two are working perfect on a 5m cable run , the other two are at the end
    of a 100m cable run , and although when i meter test it shows just over 12v arriving at the end of the cable run , it seems theres not enough
    voltage to activate the relay in the timer unit ? in theory they should work , but they work perfect on 50m , but at the
    100m end , just not enough juice

    So throw me some bones guys , any quick easy fixes ? bear in mind im not an electronic
    engineer
    In the beginning there was none. Then came the light - #1 UKLEM - 2007
    BUY UK LEGAL LASER POINTER :: NEW - Blue 460nm Laser Pointers

  2. #2
    Join Date
    Oct 2012
    Location
    Germany
    Posts
    1,310

    Default

    ... 100 meters is a pretty big resistor which drops the current, so it won't be enough for triggering your parts.

    This is even more a problem for DC than for AC.

    So either you'll drive with higher voltages or with AC.

    It shouldn't be a problem to feed the 240VAC (or 24V DC) through the 100m and convert it at the end to 12V or 5V ... or you can use much thicker wires to reduce the resistance of the cable.

    For another similar problem with >200m cable lengths I've used glass fibres and LED's instead of voltage to switch/activate the target electronics ...

    Viktor

  3. #3
    Join Date
    Dec 2006
    Location
    Scotland
    Posts
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    Default

    Hi Viktor ,
    many thanks for reply , for safety reasons and positions of cables i simply wont
    ever run 240v down the 100m portion of cable.

    Glass fibre / led , interesting , im going to guess thats a pretty complicated solution , but sounds interesting
    anyways so i would be keen for some links if nothing else for filling the knowledge base :-)

    the two problem units are on their own 12v line coming out of power distribution box .. so i did a search
    for 12v to 15v dc step up transformer .... and came across this .... Any thoughts on if this would work in theory
    bear in mind its a relay that needs the juice , the relay control unit can handle upto 16v according to specs , but
    then its also supposed to handle 10v !
    http://www.ebay.co.uk/itm/Solar-DC-t...item2c841b9ae4
    In the beginning there was none. Then came the light - #1 UKLEM - 2007
    BUY UK LEGAL LASER POINTER :: NEW - Blue 460nm Laser Pointers

  4. #4
    Join Date
    Nov 2014
    Location
    mid michigan
    Posts
    792

    Default

    That should work.
    I have a 24 volt dc buss in my house that is derived from 4 solar panels on the roof. I went with 24 volt because of the loss over the cable, because it's dc and needs a return path your 100m long cable is 200m long to the circuit. Using heavy gauge wire has lower loss per foot or even using 12-24volts AC would work better over that distance
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

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