# Reversing DC Motor with Relay and a Limit Switch

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I thank you for your time. I am new and I have been working on this problem for a while. Hopefully, I can explain it clearly.

Motor I am using is a 12Vdc 1.7amp geared motor.

Summery--I am trying to hook the motor up to a thermostat so that a window will be opened when tempature is above 80deg. And the window will be closed when the tempature is below 80 degrees.

What I think I need to do: The thermostat can switch a relay on or off. So, use a relay and two limit switch on either side of the window, I should be able to have the window move one direction when the relay is on until it hit the limit switch.

Then when the relay close it will move the window back to the other side and hit the limit switch.

My problem is how do I wire this? Also I think I might need to use more than one relay? Any help would be great?

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It might be simpler to use a crank with two stop positions 180 degrees apart. A micro switch at each side of a disc mounted on the crank drive shaft, the disc acts as a cam and hits or releases the switch at window open, window closed positions. The micro switches are momentarily bypassed (by relay from control circuit ) and the cam disc releases the actuator which closes that switch and supplies power to the motor until the second micro switch is hit by the cam disc ( micro switches in series with each other and motor supply ).

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I dont know what sort of output your thermometer gives, but have you considered using an Analogue method similar to Fuzzy Logic?

based on transistors using a differential amp, that way its not just open or closed, it can be anywhere in between to govorn the temp more acurately.

your method will still need some form of hysterisis compensation, the analogue way will bypass that and provide a better over temperature regulation.

basicly it consists of matching a preset potentiameter to the center of your temp, with upper and lower limiting resistors, using this center ref point, the window is free to open and close in fractions according to temp reading.

just a thought

damn this keyboards gunna go up the wall in a minute!

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Sorry you said thermostat and I have thermistor on the brain. This will work.http://www.scienceforums.net/forums/attachment.php?attachmentid=634&stc=1

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• 3 weeks later...
I thank you for your time. I am new and I have been working on this problem for a while. Hopefully' date=' I can explain it clearly.

Motor I am using is a 12Vdc 1.7amp geared motor.

[b']Summery[/b]--I am trying to hook the motor up to a thermostat so that a window will be opened when tempature is above 80deg. And the window will be closed when the tempature is below 80 degrees.

What I think I need to do: The thermostat can switch a relay on or off. So, use a relay and two limit switch on either side of the window, I should be able to have the window move one direction when the relay is on until it hit the limit switch.

Then when the relay close it will move the window back to the other side and hit the limit switch.

My problem is how do I wire this? Also I think I might need to use more than one relay? Any help would be great?

One DPDT relay should do the job for reversing the polarity. Depending on the type of window, you may consider using magnetic switches as your limit switches.

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