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Cooling Fan with Thermostat Control

Discussion in 'Electrics UK' started by efiste2, 24 Mar 2018.

  1. efiste2

    efiste2

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    Can someone back me up with this issue, I have what claims to be a N/O Thermostatic Switch that I intend to use to extract warm air from an AV cabinet. The infro from the RS website and the Data plate confirm that it is a N/O type.
    However, when set at 0 degrees C, the contact is CLOSED and as I turn the adjustment upwards it OPENS at what I am assuming is the ambient room temperature.
    My aim is for the cooling fan to operate as the temperature in the cabinet reaches a set level, so therefore I require a N/O Thermostat Switch that will CLOSE at that set level and turn the cooling fan on.
    Am I correct in my thinking, if so it appear the so called N/O switch I have is really a N/C version with the wrong info attached to it.
     
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  3. JohnW2

    JohnW2

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    It certainly sounds as if you have not got what you want/need, but I fear that the terminology is potentially confusing ...

    ... what constitutes 'normal'/'normally' in 'normally open' and 'normally closed' really depends upon the application. When used (probably most commonly) to control heating, 'normal' may well mean 'when heat is not required', whereas for cooling, the situation is the opposite.

    Kind Regards, John
     
  4. Iggifer

    Iggifer

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    A Honeywell T6360B has both NO and NC contacts so will work for your application but I assume you’ve bought something a bit more specific.

    A refridgeration controller would also do what you want with endless amounts of control - overrun, delay, temperature offsets etc. That’s what I’d be looking at and they can be panel mounted should you so choose
     
  5. EFLImpudence

    EFLImpudence

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    ...but I don't think that is what they can be, or are, called in a mechanically operated thermostat?

    As John has said, it depends - for a thermostat on the setting and the temperature.

    NO and NC surely only apply to electrically operated devices and is the position when not powered.
     
  6. JohnW2

    JohnW2

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    ... but they sometimes are! ...
    Indeed - something like a relay or contactor.

    In fact, merely being 'electrically operated' is not enough. In the 'other thread' we have seen that the output terminals of a thermostat are called "N/O" and "N/C" - and, although 'electronically operated' (it is an electronic thermostat), what is actually meant by those two terms is, again, dependent n context (i.e. what is "normal"/"normally"). Indeed, that particular one has a jumper which enables the "N/O" terminal (or the "N/C" one) to have either functional interpretation!!

    Kind Regards, John
     
  7. ericmark

    ericmark

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    I have just found out N/O and N/C contact has nothing to do with if used for heating or cooling, what it means is if the power is removed what the default state will be. I have just bought a Flomasta 6259G thermostat and be it heating or cooling the N/O contact is used, to swap between heating and cooling there is a jumper, before buying this I would have said N/O is heating and N/C is cooling, but clearly that is not always the case.
     
  8. JohnW2

    JohnW2

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    Yes, that makes sense (and is consistent with how one would use those terms for relays and contactors), but it's not particularly helpful to someone trying to work out the functional significance of those two terminals/contacts. As we know, your Flomaster one has a jumper that enables one to reverse the functionality of the terminals.

    Kind Regards, John
     
  9. ban-all-sheds

    ban-all-sheds

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    N/O and N/C are meaningless wrt thermostats, for it is normal for the temperature being monitored and controlled to rise above, and fall below the one the thermostat is set to, therefore it is normal for each set of contacts to be open or closed.
     
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  11. JohnW2

    JohnW2

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    However, as eric has worked out, in the case of electronic thermostats (or other electronic switching devices), it appears that the 'normally' of "N/O" and "N/C" probably relates to the state when no power is applied to the device (as it would for a relay or contactor) - and thus indicates the 'default' state of the contacts when the device is not powered.
     
  12. efiste2

    efiste2

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    I must be missing something, sorry I should have provided more detail....
    The relay I have is a N/O unit with only TWO terminals, the contact is made as the bi-mettalic strip bends etc etc.
    Diag.jpg
    Instruction.jpg
    The instructions state the N/O contact CLOSES with rising temperature , so what I cant figure is why at the min setting of 0 the contact is closed and then as the dial is rotated on the stat the contact opens, which is exactly the opposite to what I need.
    Closed.jpg OPEN.jpg
    Apologies for my nievity ......
     
  13. DetlefSchmitz

    DetlefSchmitz

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    If you bought it from RS then I suggest you phone their technical support department. Likewise wherever else you bought it.
     
  14. EFLImpudence

    EFLImpudence

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    Edited because wrong.
     
    Last edited: 27 Mar 2018
  15. EFLImpudence

    EFLImpudence

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    Ah. I see the instructions are for both types.

    You want what they call a NO Shutter.
     
  16. EFLImpudence

    EFLImpudence

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  17. rsgaz

    rsgaz

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    No, it isn't, you have got what you need.

    Look at it this way, when you set the dial to zero degrees, the temperature in your room is more than that, so the contact is closed and therefore your fan would be running.

    Then, when you set the dial to 27, your room is already cooler than that, so the fan goes off.
     
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