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A timed Switch for a motor.

  1. Oct 6, 2011 #1
    Hello knowledgeable ones!

    I need your help to make my life easier;

    I need to turn on fans every cold night during winter in a grain storage shed
    to keep the grain from heating/rotting! This involves treking to the shed in the cold after
    midnight (cheap electricity) and flipping 2 circuit breakers on the wall to activate the fans...
    The fans are just single phase induction motors (around 1.7kw) which plug directly into a standard electrical outlet (240v). The Motors on the fans each have a black box with all the bits nescessary for them to start up etc.

    The Idea.
    I want to build a device containing a clock and a temprature sensor, which will close a contact after midnight if the temprature is less than 6 deg c. and open the contact
    at 7am
    The idea is that you would plug this device into the wall outlet and plug the fan into the device.

    I've figured what i need to make and break the circuit is something called a CONTACTOR, but i'm stumped as to what one i need. The Clock and temprature sensor would be implemented on a microcontroller which would give the signal to the contactor to start the fans. So basically i need a device that would take a low voltage DC input (prob 9V or less) and close a switch to carry about 7A at 240Vac.

    Any ideas?
  2. jcsd
  3. Oct 6, 2011 #2
    There are many small timers that switch 120 VAC on and off at specified times. Could you use one of those to to activate a relay. The relay in turn could activate the contactor.
  4. Oct 6, 2011 #3

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    not an advertisement, merely a suggestion

    i used to frequent an electronics hobby site

    this project is just the type of thing those folks specialize in
    in fact i helped a fellow with a nearly identical project a year ago or so, for his wine cellar
    oops - found the link and it was for his brewery.....

    you'll get enthusiastic help there from hobbyists of all skill levels

    the guy who runs it is darn good at RF questions

    it's free and they dont try to sell you stuff


    click on 'discover forum' ,, then circuit design

    old jim
    Last edited: Oct 6, 2011
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