555 timer to control two relays alternately

Discussion in 'The Projects Forum' started by farmerben, Jan 14, 2013.

  1. farmerben

    Thread Starter New Member

    Jan 14, 2013
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    I am completely electronically illiterate so please bear with me! I'm working on a project and I want to alternately control two separate relays. The system will be powered with 12v dc. And I'm not quite sure of how fast I want them to pulse, but they need to be alternated- one relay on the other off than switched. Hope that makes sense. Thanks in advance.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Do you mean one relay is always in the opposite position as the other?

    It's important how fast you want these switching. What speed - roughly - are you thinking of?

    Why are you using relays, have you considered other switching options?
     
  3. farmerben

    Thread Starter New Member

    Jan 14, 2013
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    0
    I guess that's what I mean. Basically, I'm trying to power two units with 12v. But I want unit 1 to be on while unit 2 is off, than switching the voltage to unit 2 and shutting off unit 1. Hope that makes a little sense!
    I'm not quite sure of the speed. Maybe switching 4 or 5 times a second. I'll just start there and make adjustments if necessary.
    I guess I'm just using relays because I don't know of anything else! I'm open for any suggestions though.
    Thanks for the reply
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Switching relays that often will wear them out fairly quickly, not to mention wasting a lot of power. Assuming that your "units" are DC powered, MOSFET switches would be a better choice. What is current required for each "unit" and, if you don't mind, what are these units? Do you want this switching to continue uninterrupted from power-on to power-off, or do you want to control it with a switch? More details on what your objective is would get better suggestions.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Why not just use one SPDT (form C) relay? Connect +12V to C, and your loads to A and B. This won't work if you ever want to turn off both loads.
    As Tracecom suggests, MOSFETs might be a better choice.

    [​IMG]
     
    Last edited: Jan 14, 2013
  6. ScottWang

    Moderator

    Aug 23, 2012
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    You should say some more infos, as what's the purpose and load, current, etc, more details will make you easy to reach to the target.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,034
    That's too fast for mechanical relays, so you should look at a MOSFET switch for DC loads or a SSR (solid state relay) for either DC or AC loads. They can do the same switching chores as a relay but have no moving, mechanical parts to wear out and make no emf pulse when they turn off.

    There's not much more anyone can say without knowing more about your load.
     
    Last edited: Jan 14, 2013
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