Designing a Temperature-Activated Timer for Grain Storage Fans

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A user seeks assistance in designing a temperature-activated timer for grain storage fans to automate their operation during cold nights. The proposed device would utilize a clock and temperature sensor connected to a microcontroller, which would control a contactor to switch the fans on and off based on temperature readings. The user is unsure about the specific type of contactor needed to handle the electrical load of the fans. Suggestions include using a small timer to activate a relay that could, in turn, control the contactor. The discussion also recommends visiting an electronics hobby site for further guidance and support from experienced enthusiasts.
phlegmy
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Hello knowledgeable ones!

I need your help to make my life easier;

Background.
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.

HELP:
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?
 
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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.
 
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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...
http://www.discovercircuits.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=9580#Post9580


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 don't try to sell you stuff

www.discovercircuits.com

click on 'discover forum' ,, then circuit design

old jim
 
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