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A Portable Warmer/Cooler Regulator

Former Member

I am a volunteer paramedic for a wilderness service, i.e.,we operate in a forest area approximately 40 miles from a nearest

hospital. We need to store our pharmaceuticals between 55-80 degrees Fahrenheit year round. I have been looking for a

commercial Peltier-based system without success. All that I have found require manually switching from heating to cooling.

 

I think the problem may be current demands when switching polarity to achieve heating/cooling. I would like a circuit which

would -

                  - Monitor internal container temperature

                  - Monitor ambient temperatures

                  - Anticipate heating/cooling needs

                          Time of day may be an important feature, i.e., as night falls, anticipate needing heat

                  - Switch between the heating/cooling functions automatically

 

Critical temperature range control is not an issue as long as it can be set for a 5 - 10 degree range, e.g., 60-70 degrees would

be ideal. I would like a temperature readout and indicators for heat/cool functioning.

 

There are a number of portable heater/coolers at reasonable prices (we are an all-volunteer organization) which could be modified.

I have a background in analog electronics (remember mu calculations for vacuum tube-based circuits and nodal analysis?) and

have schematic and construction experience but limited printed circuit board construction skills.

 

Does anyone have any ideas on this? Thank you...

 

Joe

  • 0

    Joe,

     

    This is easy.
    Get any development board you are comfortable.
    Add a thermocouple, themistor, thermometer that can connect with the board.
    Constantly read the temp.
    Have the dev board replace the cooler's control system. (IE: mimic the temperature potentiometer reading.)
     
    If you want to add a heating element (Fish tank heater, for example), go ahead.
    The cooler you want to heat is most likely very insulated, so a small internal heater would work great.
    Same type of setup as above. The same dev board could control the heating element too.
    Write software to handle when the heater should applied, you do not want it turning on and off all the time. (You may destroy what is in the container.)
     
    I would recommend a PIC based development board. It is very versatile with plenty of support from Microchip.
    The PICKit is a good optionThe PICKit is a good option
    Or just a bare board.Or just a bare board.
    Also, take a look at the element14 store for more primary and daughter boards. Everything you need is there.
     
    Cabe
  • 0 in reply to Catwell

    I thank you for your response however I do not wish to 'add a heater' to a cooler. I want to be able to control a Peltier-based

    commercial warmer/cooler to maintain a temperature range between 60-70 degrees Fahrenheit with a control and read out.

    The problem is being able to switch the Peltier device between warming and cooling modes by providing polarity control and

    delay to prevent overcurrent conditions.

     

    I need help in the design of the device, i.e, IC types, schematic, etc...

     

    Joe

  • 0 in reply to Former Member

    Flip the Peltier over and you have yourself a heater.

     

    You have to isolate the who sides from each other anyway. Have one for cooling and one for heating.

     

    Same microcontroller setup as I stated before.

     

    I look forward to what you come up with.

     

    Cabe

  • 0

    Cadac make a12v unit that capableifcolng and heating .be aararthugh that oelterunitscant. Coolmugch below ambient

     

    Sorrifmt selling sux.I'm recoveringfrom a stroke

  • 0 in reply to Catwell

    I researched a commerically available compact cooling/heating unit but was not impressed since it needed to be manually mode switched. It also was limited in that it could not be used in either mode longer than 15 hours continuously.

    I don't understand why a Peltier device needs to be mechanically repositioned to achieve heating or cooling. Doesn't reversing polarity accomplish that? It seems that the active, i.e., working surface inside the cooler, would be changed from heat absorption to radiation much as a heat pump is used for heat transfers in either direction by changing the flow/evaporation portion of the cycle.

  • 0

    I`v watched this thread for a while, as I also have a heater/Cooler (2 of them in fact) in the Lab and both are peltier device base, One I use to store unused Film to keep it cool, the other... well lets just say it comes in handy during the summer and is about 5% Alc.

    these work great as a heater also, but I wouldn`t try doing a Pizza in one, the switch does indeed reverse the polarity to the peltier and is run from a single 12v supply at about 2A.

    the problem I can see is that of an electronic one, but more of Physics, in way of thermal Inertia and Latency.

    this will cause something akin to hysterisis, so you May want to factor this in by taking measurements between On/Off cylces and temp over time achieved, from there you can plot a mean average and compensate for this algorythmicaly.

    the electronics is easy bit, you`ll just need a DPDT relay to switch the polarity (Hot/Cold) and another to engage power when required.

    a pair of transistors to drive these 2 relays, and 2 spare bits/pins on an MCU to do the rest, something like an ATtiny 85 would do the trick nicely.

     

    hope that helps a little image

  • 0

    Hi Joe,

    for switching current to Peltier cooler you can use H-bridge. TCh (in picture) is input for controlling heating/cooling (logic 1/0 from MCU). Peltier module is conected like R3.

    Three-state or PSD controller is good for regulation current to Peltier with use PWM modulation (input PWM in picture).

    For measuring temperature I advice you TMP275AID.TMP275AID. sensor. All is easily implementable in MCU.

     

    TMP275AID.TMP275AID.: http://www.ti.com/product/tmp275

    image

  • 0

    There's a lot of great info in this thread to get you started - I look forward to seeing what you come up with.