variable thermostat help

Discussion in 'The Projects Forum' started by wardo5757, Dec 19, 2010.

  1. wardo5757

    Thread Starter New Member

    Dec 19, 2010
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    Hey guys,
    I just built an entertainment center, i have 3 high power amps in it and the amps are behind glass doors. Needless to say the amps got very hot and would go into protection often. I tried drilling several 3 in. holes to get convection air movement but that didnt do the trick. I installed 3, 12 volt fans, 1 for each amp and this kept the amps quite chilled, but these small fans make a LOT of noise. Because of the noise I dropped the voltage on the fans to 5 volts, the fans are virtually quite now and the amps do not go into protection unless im really cranking up the volume.

    Thats where this project comes in, I would like to make a circuit that runs 5v @ 90 dgrees and varies up to 12v at 115 derees. Ive built simple relay circuits in the past nothing this complicated any help would be awesome!

    Thanks
    Eddie
     
  2. wardo5757

    Thread Starter New Member

    Dec 19, 2010
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    0
    thank you Alberto! I didn't think of solving my problem that way, it is simple resolution. I was looking for a circuit that would increase the voltage as the temperature increased and be full on at 115 degrees. What do you think the difficulty level building a circuit like that would be?

    Eddie
     
  3. wardo5757

    Thread Starter New Member

    Dec 19, 2010
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    Last edited: Dec 19, 2010
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    That Mcrochip fan controller ICs are very good for this, there's a lot of them which don't meet my design that are still in supply.
    http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010731
    http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=9002&mid=11&lang=en&pageId=79

    Alternately find a quieter fan, I've found that Scythe fans and a few others can move a lot of air with very little noise. Often the simple addition of a filter assembly on the intake side cuts the noise way down without reducing the CFM a lot.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    3,024
    I agree with this approach, except it can be simplified by eliminating the microcontroller. Just use a dual op-amp to provide the desired offset and slope in response to the LM35 voltage, and use the output (voltage) to control the PWM provided by a 555 circuit. The PWM is fed to a MOSFET to regulate the fan speed. I believe I've seen here a voltage-controlled-PWM circuit, although - full disclosure - I've never built one.

    Another source of info on all this would be the overclockers forums, where you'll find all sorts of insight on fans and cooling. A lot of that will assume you have the computer for control, but it's not required.
     
  6. iONic

    AAC Fanatic!

    Nov 16, 2007
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    The second option by Alberto would be the route I'd take. The relay in the original suggestion would probably be turning on-off too often without some sort of hysteresis.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    I think that circuit would be frowned upon here, as it is directly connected to mains power.

    The ~12v DC approach is better anyway, IMHO. You'll just need to learn about how to control a MOSFET (specialized transistor, kind of like a relay in this application) gate with pulse-width-modulation (PWM, variable duty cycle square wave), probably using a 555 timer IC circuit. And the op amps for the input. Some learning curve, but if you learn this stuff, you can rule the world! Well, a few cool hobby circuits anyway.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Try the quiet fans first and if they're not to your liking then you can go to the trouble of temp controlling something. Simple enough to find a 12V - 2A output Wal-Wart (as they call them here, I call them plug in adapters) at most any thrift shop that can be plugged into one of your switched outlets even if you've got to use a short extension cord in order to plug it in. May as well start the air circulation long before the heat gets out into the general area.

    Most people drive by these thrift shops thinking they only have clothes, fact is most have a ton of stuff they haven't a clue about and end up with a lot of adapters they don't know what fits thus will sell them for 50 cents or a $1 max.

    I'd recommend these fans, they're very high volume yet very quiet and you can of course move down (or up) from there:
    http://www.newegg.com/Product/Product.aspx?Item=N82E16835185060
    http://www.newegg.com/Product/Product.aspx?Item=N82E16835185059
     
  9. wayneh

    Expert

    Sep 9, 2010
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    +1 Simple is better.

    I don't know where to get one, but I've got a 120v AC fan, about 4" square and 1" thick, that's dead silent. It had been used for circulating air in an isothermal cabinet, if that helps.
     
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