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A Portable Warmer/Cooler Regulator

e14 Contributor

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

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    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

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  • 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

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