need help with multiple ntc/output control circuit

Discussion in 'The Projects Forum' started by jas_stang, Dec 2, 2010.

  1. jas_stang

    Thread Starter New Member

    Dec 1, 2010
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    I am new to the forum and have limited electronics knowledge but am intrigued by it. We have alot of issues at work trying to maintain temperatures of multiple systems tied to the same fan and i want to come up with a control circuit that is cheap and easy to build. open to any ideas as i enjoy learning this stuff. as of now, i am thinking of using multiple (5+)negative coefficient thermistors wired in parallel so that the lowest resistance (highest temperature) will be able to energize an output to bring on a fan and when all ntc's are below a determined temperature, de-energize a fan. I have plenty of room for boards and transformers and will have 208v supply to work with. would an ic chip and pot be able to achieve this? Are there components readily available that will achieve what i want to do? the fan control will only draw about 1-2 amps. any advice or suggestions would be appreciated.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    In electronics, there are always several ways to skin a cat. It would be helpful to have some better understanding of the situation. Is this a lab setup, of some industrial process (the 208 volts suggests this)?

    In general, you can read any number of temperature sensors and make decisions about what to do based on the readings.
     
  3. jas_stang

    Thread Starter New Member

    Dec 1, 2010
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    it is for commercial cooling. there are multiple copper pipes going in one condenser, we try to maintain 90 degree outlet, but when there are multiple systems on one cooling condenser when the weather drops below 30 degrees which is frequent here, then we have issues with some running really hot when one system is not. The current controls are just ambient thermostats for all fans but the lead. The lead fan is either on all the time, or cycles on pressure of the largest capacity system-which isn't always the largest load. i would like to have inputs from all systems and when any of them hit 95-100 degrees, bring on the lead fan until all inputs are below 80 degrees or so. thanks for the help
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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  5. jas_stang

    Thread Starter New Member

    Dec 1, 2010
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    not what i am looking for, thanks for the link though. i have 5 different systems all running at different temperatures. for one to get high enough temperature to bring on the fan, the others are going off on high temperature safety. if i bypass the current fan control to run fan all the time then one goes off on low temperature. i want to monitor all 5 return temps and cycle the fan on if any of them reach a certain point. initially i thought i could achieve this by using 5 nct thermistors as inputs and an ic chip to look at the inputs and control an output of 24volts to energize the fan contactor. i don't have any knowledge of ic chips and what they can and can't do, but i would like to learn more of them, especially if i can program the parameters i want and have this setup work, there are multiple applications across the city that this would save alot of money and repairs on if i can get it working. thanks for the help
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    I may have misunderstood the fan requirement. Your pipe temps are in the range of some compensated devices like the LM35. With some amplification, the signals get large enough to compare using a microprocessor(thermistors need amplification, too, so that's not a biggie). The microprocessor can decide to turn on any number/combination of fans.

    Not having experience with modern micros, I will leave that thought and see is another member won't show up with some further advice.
     
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