i made a good stirrer/hot/cold plate with "Neon® New Mini Black USB Fridge Cooler Beverage Drink Cans Cooler/Warmer Refrigerator'......it is basically a mini usb fridge/hotplate switchable with a little fan on bottom to vent heat sink that magnets could be glued to.....it would be 20$ shipped for a compact hot/cold/stirrer after a little modification and I used a universal ac adapter which i had (but you need one that flips polarity if you want to swich from cold plate to hot plate but with variable power you can control speed of stir and heat/cold......lmk what you think, i am thinking it is a "ok" diy idea for someone going to use it a little but not for real chemist obviously......it even has a led indicator light green cold plate, red hot plate and i use harbor freight magnets that were 2 bucks for ten but only used 2 (they are stong)

http://www.amazon.com/Fridge-Cooler-Beverage-Refrigerator-Computer/dp/B00UYRNODO/ref=sr_1_2?ie=UTF8&qid=1440552091&sr=8-2&keywords=usb+fridge

I see a few problems with this. Firstly, refrigeration and a hot plate work on completely different principals. This has a tiny compressor, which works to cool the air inside. No matter what potentiometer (i play/build guitars; awesome to meet someone on the nexus who also knows this term ) you add, it won't be able to do anything but refrigerate. You would have to add a heating coil which would cost more than the unit itself (I also question how a heating element would ever fit inside of it). Also, magnetic stirrers use electromagnets to operate, so just gluing regular magnets to the device wouldn't suffice. That being said, it's certainly a nifty contraption and would be excellent for storing spice from extractions or even small amounts of brewed aya or dried shrooms.

However, if there's anything I've missed or misinterpreted in the OP, do let me know. I'd hate to be a negative nancy

EDIT: After reading the product description more carefully (I might have to buy one of these!), I realized that it does in fact have a heating function built in. My bad! However, seeing as the cooling range is 8-9 C and the heating range is 40 - 65 C, you'd probably need to find a way to increase the wattage in order to be able to boil and/or freeze water. There's also the issue of it being enclosed, so you'd need to remove the door or better yet remove the components from the housing altogether and build a custom housing so that you can sit beakers or glassware directly onto the heating/cooling surface. But, the unit works via convection and not conduction, so I'm not sure how you would translate that into a hotplate setup. Let us know if you do end up modifying it - if it works out this is a real game changer for sure.

it has a switch that flips it from cooling to heating, it is built in no need for anything in regards to that. So it is a three way switch in other words, off, hot, cold. The potentiometer would just regulate how much power it gets. But you are right about these case i will need to cut and drill for larger beakers. Here is the product description.


Product Description

Color:Black
Features:
1. Mini USB powered fridge with both cooling and heating functions.
2. Built-in green / red LED indicator, magnetic door catch.
3. Keep your beverage cool / warm to drink at your computer side.
4. Can hold a single can, easy installation, no driver required.
5. USB powered - Plug & Play. No batteries required.

Specifications:
1. Overall Size (L x W x H): Approx. 85 x 80 x 185mm
4. Switch Control: "I" for heating, "II" for cooling, O for off
5. Working Voltage: 5V DC
6. Max. Power Consumption: 10W
7. Temperature Range: 8-9 deg C for cooling; 40-65 deg C for heating
8. Material: Plastic

I think the main hurdle then would be that it uses convection rather than conduction. You wouldn't want vapor pressure growing inside of that thing, especially from flammable solvents. I might still buy one and toy around with it though. It seems like a cool little gadget.

EDIT: Lol we keep editing our posts at the same time. I outlined a few potential issues in an edit to my last post. Good old edit tag

I'll throw up a word of caution and remind you that hotplates are designed to be around flammable materials.

1: will solvent vapor destroy the workings?

2: can it heat flammable liquids to a usable temperature without their vapor igniting?

http://m.ebay.com/itm/PC.../351465726775?nav=SEARCH

Just cough up the extra 20 bucks and do it right, rather than gamble $20 and loose your house.

gluing the magnet will work......here is a youtube video showing basic setup

https://www.youtube.com/watch?v=XVLB9c0j1iU

that ebay post is just for hot plate so a stirrer/hotplate is more like 85$ if you are lucky....also in regards to the convention/conduction argument it heats /cools with conduction it is a little plate on inside that heats up and cools down....it cools good because of aluminum can.....and yeah door would be removed so no pressure......I believe it is same way as normal chem style hotplate works.


here is video of fridge/hotplate thing

https://www.youtube.com/watch?v=hrcMGX7kaiw

pretty sure I saw one of those for about 50$. But really is 85$ for a good working reliable piece of equipment that will last almost forever, really that much? Or is penny pinching and ghetto rigging an electrical box full of volatile flammable liquid/gas really that much better?

Not to rain on your idea, I'm just saying that you will be held accountable for whatever consequence comes of this.

I am so used to diy-ing that such things do not bother me......any other suggestions or ideas for design or anything?

ok, I did buy one and seems good for this idea, will take pics and post directions.

posted the tutorial above....first post

Just to clarify, this is a thermoelectric heating/cooling unit which utilises the peltier effect to transfer thermal energy across a dissimilar semiconductor junction. This is done through thermal conduction on either side of the device.

I like the idea, although it does have a few drawbacks. While TECs have a reasonably long life, they do degrade with use. Also, this looks like a rather small unit, which means that (while it may achieve a temperature differential of 50-60 degrees) it likely doesn't have enough TDP to effectively heat even a modest size extraction. Next, the fan only has a tiny motor, as such, it life will be severely shortened by the added load of the magnetic stirring apparatus. Lastly, TECs offer a very low efficiency (in terms of performance coefficient) in comparison to more conventional heating methods.

Another thing to note is that the addition of rate earth magnets to the system may have a detrimental effect on the performance of both the fan and the peltier device (though I'm not certain about this).

Sorry to throw so many negatives. While I really like the concept, I think I'll stick to my $95 lab hotplate/stirrer (it's only a few more NYC pizzas, after all )

yeah this is more for a person that doesn't think they will be doing chemistry stuff long term but yeah with the 12v universal adjustable ac adapter it does get quite hot and cold and fan spins fine if you balanced out magnets.....I actually like the size of the unit and still works fine cooling your soda and heating your coffee if your safe with chemicals.....lol

Have you tried using this with a stirring bar? I have a feeling that the rapidly moving fan with the attached magnets may not transfer enough torque to a stirring bar.

Does the potentiometer also control the fan speed? What's the pot's maximum impedance and power rating?