42 C by 6 9V batteries

Discussion in 'The Projects Forum' started by whiskeysausage, May 25, 2011.

  1. whiskeysausage

    Thread Starter New Member

    May 25, 2011
    2
    0
    Hi guys and gals!
    This question requires a very specific solution, and I am all thumbs.

    The situation: I need to find a cylindrical resistor that heats up to and stays at 42 C +/- 1 C for 15minutes +/- 1 minute, powered by 4 to 6 9V batteries (wired in any way), and are expected/allowed to be fully drained by the end of the 15minutes.

    What type of resistor would allow this? Is this even possible? Theoretically or practically? How would I keep the temperature constant at 42C?

    Many thanks in advance! Any answers would get me closer to a solution.

    Very Respectively,

    Whiskey Sausage
     
  2. whiskeysausage

    Thread Starter New Member

    May 25, 2011
    2
    0
    Your setup is quick and easy and a great solution to a problem I've been hounding at for quite a while.
    My situation is this (and you might be part of the solution!)
    I need to regulate a cylindrical resistor to get to and stay at 42C for 15minutes, +/- 1C +/- 1minute, powered by 4 to 6 9V batteries.
    How would I, using your thermometer setup, create a chip that would regulate the temperature to STAY at 42C +/- 1 C?

    Any thoughts?

    WS.
     
  3. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    Resistors don't regulate their own temperature. You need to build a thermostat of some sort. Measure the temperature of the resistor and switch the power on if it's too low, switch the power off when the temperature is achieved.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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  5. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    Creating a chip is way beyond my abilities. I would start with a thermistor and a 723 chip, but there are many ways to do this.

    With my method, you place the thermistor on the resistor and let the 723 chip compare the resistance of the thermistor to a set point using a Wheatstone bridge.

    Next advisor?

    ps, I think the LM10 chip is good for this job, too.
     
    Last edited: May 25, 2011
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    The practicality of this depends a lot on the size of the resistor and its thermal isolation from any type of heat sink, and the ambient temperature (unless it's in a vacuum). For example, a tiny resistor (1/8W), with long, small diameter leads, in 25°C air, should be no problem. This may not be true of a 10 watt resistor, attached to a PC board, in 0°C air. What are you going to do with this hot resistor?
    In any case, you probably should use on-off thermostatic control, with low (1°C) hysteresis, in order to conserve battery power.
     
    Last edited: May 25, 2011
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