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Thermostat control for fans

Discussion in 'Computers, Cabling & Other Miscellaneous Hardware' started by BoonDogs, Feb 27, 2016.

  1. BoonDogs

    BoonDogs I am self diagnosed with CLAP

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    https://www.ebay.com.au/ulk/itm/331640636931

    I have some fans coming in the mail soon, to put into my enclosures for air flow. I saw these thermostats on eBay, but they're rated at 240vac. Does this mean they can only control 240vac. The fans I have are 12 and 24vdc, and I cannot find a low voltage version of these.

    Thanks
     
  2. smartalec

    smartalec Im a SmartAlec what can i say! Community Project Designer

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    boon i have a circuit board being made as we speak.
    temp sensor fan controller, with wireless so you can monitor it inside.
    i should have it ready by the end of next month for sale.
     
  3. OP
    OP
    BoonDogs

    BoonDogs I am self diagnosed with CLAP

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    I believe we were in contact via Facebook in regards to this. I have 3/4 enclosures I need fans in, with limited room, and I'm already over my budget. I'm interested in your board, but it depends on the price of them as to whether I can afford them or not.
     
  4. tom82

    tom82 New Elf

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    Boondogs - are you looking for something you can set the temperature threshold?


    If so have a look at something like this: http://www.ebay.com.au/itm/12V-1-Channel-Control-Switch-Thermistor-Relay-Sensor-Temperature-Detect-Module-S-/191736124877?hash=item2ca45d15cd:g:xjwAAOSwpRRWmaUH


    You can also get ones with a digital display to set the temperature for about $5.


    That bimetal one you posted sounds like it uses a particular type of metal which moves (opens or closes circuit) when it gets hot. I am not sure if 12/24V would actuate the metal properly.
     
  5. OP
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    BoonDogs

    BoonDogs I am self diagnosed with CLAP

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    The link you posted looks like they would work. Do you have links to the ones with a digital display / 24vdc versions?

    Thanks!
     
  6. i13

    i13 Senior Elf

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    Those can switch 24V. If you can't find a 24V version then a DC-DC converter will do the trick.
    Note that the 24V fans might be noisy. I had to use a resistor to slow mine down to make them quieter. Remember to calculate resistor wattage.
     
  7. OP
    OP
    BoonDogs

    BoonDogs I am self diagnosed with CLAP

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    I'll see whether it's more beneficial to get the relay system linked above, or the ones I linked. I have zero idea how to calculate resistor wattage, so I'll probably be dealing with a noisy fan!
     
  8. i13

    i13 Senior Elf

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    The wattage handled by the resistor is equal to the voltage dropped across it multiplied by the current flowing through it. You'd need to get a resistor capable of handling at least that amount. Unfortunately the resistor will generate heat and a DC-DC converter probably will too.

    It might not be a problem anyway. I've only ever placed/received one order of 24V fans so they may have been a dodgy batch.

    Another option is to connect two 12V fans in series to add up to 24V.
     
  9. tom82

    tom82 New Elf

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  10. AAH

    AAH I love blinky lights :) Community Project Designer

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    The thermal switches will work fine at 24V. The 240V is simply the maximum voltage rating that they can switch. Depending on the fans that you use with them you are better off running them at the full voltage and speed they are designed for. The fans don't need to be very fast as they aren't required to get rid of a lot of heat. A PC power supply type fan (rated at the right voltage) is typically all that most enclosures would require. Depending on how much heat loss there is inside an enclosure the fan is primarily there so that heat isn't building up inside a fully sealed heatproof box.
    As far as dropping the voltage by using a resistor the resultant output will vary depending on the load that the fan is under. As the fan loads up by having to move air into or out of an aperture the current it draws will increase, the voltage across the resistor will increase and the speed of the fan will decrease. For this reason you should try the fan in situ before committing to a given resistor/fan/vent combo.
    Having 2 fans in series (2x 12V to run off 24V) is actually dangerous. If either fan fails short circuit then the other fan will have the full voltage across it. Similarly if 1 fan is loaded up more than the other the voltage ratio across them will vary from the desired safe 1/2 supply voltage.
     
  11. OP
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    BoonDogs

    BoonDogs I am self diagnosed with CLAP

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    Thanks Alan! That was very helpful! I'll debate whether I'm going to use the digital display thermostat or the thermistors that linked. The digital ones seem better because I can adjust the voltage if I find it is too hot.
     
  12. DavidJ247

    DavidJ247 Full Time Elf

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    I find these are a good thing;
    http://www.aliexpress.com/item/Digital-thermostat-50-110-Digital-Temperature-Controller-Switch-Temp-Control-Switch-Plate-W1209/32341233661.html
    The board runs off 12V but the relay is a simple pair of contacts, so I'm sure you could run it at 12v but switch 24V. Nice and small too so it doesn't take up much space inside the enclosure but has a good sized display showing current temp and settings and only about $4.
    Plenty of vids/reviews of these online if you search W1209 thermostat.
     
  13. i13

    i13 Senior Elf

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    Isn't the relay option just going to turn the fan on and off at a single speed making a resistor appropriate? I'm pretty sure that smartalec's option adjusts the fan speed so yes the resistor might not be a good idea with that.

    Any unfused fan failing short circuit could cause problems. Sorry if the second fan in series makes the problem any more dangerous; glad you pointed that out.
     
  14. OP
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    BoonDogs

    BoonDogs I am self diagnosed with CLAP

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    I just went ahead and bought 3 of them. I don't need variable speeds on my fans, just a simple on and off. Thanks for finding these, they're great and inexpensive!
     
  15. damona

    damona Full Time Elf

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    I had a few chats with meanweĺl Australia and they recommend no fan base power supplies for outside. It damages the power supply. I.e. no vents. Use metallic case instead.
     

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