Polarity switching temp. control

Discussion in 'The Projects Forum' started by tcdk, May 5, 2015.

  1. tcdk

    Thread Starter Member

    Jan 7, 2009
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    I have some electrical windows opener, that I wants to fit in my greenhouse, and control them with a temp. controller.

    The window motors are 24V, and I have not been able to find a controller, with seperate heat/cool output for 24V. Only in 110-220v versions.

    So, to avoid having to 24V power supplies, as it requires with the 220v solution, I would like to find a way to do this with my 24V temp. controller.

    [​IMG]


    As you can see, I can't switch polarity this way.

    How can I do that? Guess I need a relay for it?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Is the motor the kind that will run both CW and CCW if you reverse the polarity of the 24Vdc?

    How do you stop motor motion when the window is fully open or fully closed? (You cannot keep motor powered for hours, or can you? Does it have internal limit switches?)
     
  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi tc,
    Do you want to manually reverse the motor or use an automatic system.?
    E
     
  4. tcdk

    Thread Starter Member

    Jan 7, 2009
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    The motors has an inbuildt limiter. So the stop at max/min.
    The motor reverse, by switching polarity.
     
  5. Reloadron

    Active Member

    Jan 15, 2015
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    To make it simple it can be done with your existing Con N/O and N/C relay contacts of your controller. Can limit switches be affixed to the windows? How much current does the motor driving the windows draw? Is the existing temperature controller forward or reverse acting (what does the relay output do above and below set point)? Does the existing controller allow for any hysteresis?

    Uh Oh, I see replies since I started my post. :)

    OK so there are limit switches, that is good. How about my other questions?

    Ron
     
  6. MikeML

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    Oct 2, 2009
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    Use the existing relay closure to control an external DPDT 24Vdc relay. Wire the new relay as a reversing switch

    Like this:

    [​IMG]
     
    Last edited: May 5, 2015
  7. tcdk

    Thread Starter Member

    Jan 7, 2009
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    There is no need for limit switches. The are built into the motor.

    [​IMG]
     
  8. tcdk

    Thread Starter Member

    Jan 7, 2009
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    I'll try a find a relay, and play around with it!

    Thanks
     
  9. tcdk

    Thread Starter Member

    Jan 7, 2009
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  10. Reloadron

    Active Member

    Jan 15, 2015
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    Depends on the needed motor current at start and run. Taken from the actual data sheet.

    Look at the data sheet and remember you have DC Motor Current and make sure the contact ratings can handle the required motor current, including start current and make sure the motor is properly fused so in the event of a stall the relay contacts don't weld shut.

    Ron
     
  11. crutschow

    Expert

    Mar 14, 2008
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    Note that you need to use connections 1 and 3, or 2 and 3 on the controller.
    The connections 1 and 2, as you show in your drawing, never make contact.
     
  12. MikeML

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    It looks to me that terminal 2 is common to 1 and 3.
     
  13. tcdk

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    Jan 7, 2009
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  14. Reloadron

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    Jan 15, 2015
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    Using the relay you linked to and applying it as Mike mentions the schematic would look a little like this:

    Motor Reverse Greenhouse.png

    Your relay pinout is shown at the top of the drawing. However, my earlier questions went unanswered as is the controller forward or reverse acting based on temperature set point and how much current does the motor draw. Thus my schematic is a rough estimate of how things might look. Limit switches were omitted as you mentioned they were in the motor so only polarity reversal to the motor is required based on temperature.

    Ron
     
  15. tcdk

    Thread Starter Member

    Jan 7, 2009
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    My controller has output for both cooling and heating. (3 sockets)
     
  16. Reloadron

    Active Member

    Jan 15, 2015
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    You can work from the above drawing. Your relay may or may not handle the motor load. If the window does the reverse of what you want you can reverse the motor leads. You cal also reverse the relay action of your controller. Anyway, the above shows how your relay would be configured.

    Ron
     
  17. tcdk

    Thread Starter Member

    Jan 7, 2009
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    But the relay, gets no signal for both "heating" and "cooling" ?
     
  18. Reloadron

    Active Member

    Jan 15, 2015
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    No because if it's not heating then it's cooling.

    If I set the temperature set point at 75 F for example I can have the windows either open or close at 75 F. Since the window motor has a limit switch the windows will either open or close, that's as far as they can go. Looking at the controller which is configured as an On/Off controller, Direct (forward) action means that the controller output is On below set point. Indirect (reverse) action means that the controller output is Off below set point. Your drawing shows the relay output of the controller as pins 1, 2, and 3. As drawn it looks like Pin 2 is the Common, Pin 1 is Normally Open and Pin 3 is Normally Closed. So if the controller is set up for Direct (Forward) acting then below set point the output relay is energized and pins 1 and 2 are closed.

    Your initial post makes no mention of what you want above or below set point? The windows only have two states, hey are either open or closed. So they are either open or closed above set point or open or closed below set point. You also don't mention if the temperature controller allows for any hysteresis around set point? You want to reverse the polarity to a motor based on a emperature set point and that is what the relay is configured to do.

    Ron
     
  19. crutschow

    Expert

    Mar 14, 2008
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    You're probably right. At first glance I though the wiper was on pin 3 but, from symmetry considerations, it would appear to be pin 2 as you say.
     
  20. MikeML

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    Oct 2, 2009
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    No it does not. It just has a normally open and a normally closed set of contacts that change state at a single temperature. A Heating/Cooling thermostat has separate outputs with separate temperature settings (two independent channels). You would have to buy two of your controllers for heating and cooling.

    The style of temperature controller that you have does have built-in, adjustable hysteresis. To prevent the shutter from running open-closed multiple times each morning and evening as the ambient temperature slows warms and cools through the set-point, the hysteresis should be adjusted to a several degree spread. That way, the shutter would open as the temperature increases through say 30degC, and then would not close until the temperature drops to say 25degC.

    I worry that the RS relay linked to by tcdk does not have sufficient current rating (2A) for the actuator. We need tcdk to link to the data sheet for the motor/actuator to be sure.
     
    Last edited: May 12, 2015
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