The Peltier I am using would definitely be underpowered. It takes a while just to cool down the small volume I have in my cooler.

There are much higher power Peltier coolers around (check eBay), one of those might be a better match for your application. The construction of the cooling chamber will be as important as the selection of the Peltier. If the chamber doesn’t thermally insulate the contents very well, the Peltier cooler will need to work much harder to maintain your target temperature. You’ll have to experiment a bit to see what is realistic, unfortunately I don’t have a simple answer for you. You might look at gutting a mini-fridge – the new ones are Peltier while the older ones are compressor style. Either type might be a good start to your project.

Most PID controllers have an auto tune feature to calibrate the PID loop, but since I’m using simple on-off control I didn’t need to mess with that. I don’t think there is an option to calibrate the temperature reading – they come calibrated from the factory.

Different PID controllers work with different sensors. The most common sensor is the type-K thermocouple. Type-K thermocouples are readily available from many sources, such as McMaster-Carr. Some of the better PID controllers support several flavors of thermocouple (each has it’s own optimum temperature range), and some even support RTD’s as well, but I have never used an RTD in a project before. They operate on different principles and are generally more expensive.

I’m pretty confident it can be done – after all many newer mini-fridges use Peltier coolers instead of freon and a compressor.

As far as energy efficiency goes, I’m not sure, but I’d be interested to know if you find out. The number of coolers likely depends on the thermal efficiency of the barrel – how much insulation there is – and how often you intend to open the barrel – too few coolers and it will take forever to get down to temperature again.

I would start small and work up to larger coolers as necessary. The most important thing is to ensure that you can adequately remove heat from the hot side of the Peltier coolers, otherwise the efficiency will drop and the Peltier junctions can overheat and be damaged.

Good luck!
Jeff

Thanks

I’m glad you got your setup prototype working, good luck with the rest of it. If you don’t mind me asking what are you using this for? +-0.2 degrees is a pretty tight window.

Any idea on how to tie the neutral side of the power supply to the controller?

You should be able to tie the ground of your 12V supply to the ground of the 14V control output on the PID and use the MOSFET as shown in the schematic above.

If you want to use MOSFETs as switches, probably the most important thing to remember is that they can’t switch AC, so you can only use them to control things that run on DC voltage. If you need to switch AC you are better off with a SSR (there were a lot of them cheap on ebay the last time I checked).