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Battery Powered Temperature Controlled Thermowell

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rfranzk

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Hello All,
I salvaged a large peltier cooler from an instrument that I want to re-purpose. I work in a consulting field where we monitor ambient temperatures and regular sensor checks and calibrations are performed. Many of the sites are off grid and battery-solar power is used. The temp sensors are checked at 0 degrees C, Ambient, and 50 degrees C.

What I am thinking of (Just researching at this point) is to use a 12 volt 12 ah battery to power this device. It has an insulated well about 1" diameter x 5" long. I would like to have fairly precise control of the cooler and would also like to reverse polarity the device to generate the 50 degrees C needed. It will cool to -5 degrees C in a few minutes and I haven't tried reverse polarity yet. I was thinking PWM with a H bridge controller. The cooler draws 3 amps when connected directly to 12 volts and cooling so I think a controller capable of 6 amps or so is robust enough for the job. Please advise. I would also like to use a thermistor or thermocouple for live readings with a display of some sort, probably back-lit lcd.

I have some experience with both PIC and Arduino and thought that would be the best foundation or platform to achieve my goals.

Any thoughts or recommendations are appreciated.

Thanks in advance.

rfranzk.
 
First off connect your peltier directly to the battery, and confirm that it will give the required performance - no point in getting 'clever' if it won't do the job to start with :D

I also see no need for PWM, not for heating/cooling all you need is simple burst-fire control - the thermal inertia makes PWM of no practical use.
 
Nigel, Thanks for the reply!! I connected the peltier direct to battery with both polarities and achieved 60C+ and -5C temperatures so I think this might be worthwhile. I am not familiar with the burst-fire control method so I did a little research and it appears that it is uses thyristors to control AC current and phase angle?? Is this correct or can you steer me to some information on how it is used with DC since this will be battery operated?

Thanks, Rfranzk
 
I think Nigel is talking about a simple on - off system as opposed to some fancier algorithm. You could try this by had as well. check the temperature of the box and when it gets to 60C turn it off and see how much over 60 it goes.
 
Hello All,
I would also like to use a thermistor or thermocouple for live readings with a display of some sort, probably back-lit lcd.

I have some experience with both PIC and Arduino and thought that would be the best foundation or platform to achieve my goals.

Any thoughts or recommendations are appreciated.
I suggest that you use a digital temperature sensor. That avoids all the analog circuitry, and you get a direct reading into the PIC.

Sensors with SPI are really quite easy to programme for.
 
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