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Author: Subject: Chinese Hotplate/Stirrers
semiconductive
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Registered: 12-2-2017
Location: Scappoose Oregon, USA.
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[*] posted on 8-1-2018 at 07:13


Quote: Originally posted by JJay  
If it's the 85-2 stirrer, I wouldn't recommend it for chemistry, although it's not so bad if you just want to stir a fermentation mixture, work with ether, or keep an electrolytic cell at a certain temperature. I could see it as being useful to brewers or perhaps in medical or bio laboratories. If it had a ceramic top, a more powerful heating element, and better documentation, as well as a thermostat that goes to 350 C, I could see it as being a lot more useful. There are a lot of things I like about it, but I just can't recommend a hotplate that won't boil water to chemists.

I haven't tried the 85-2A stirrer, but I am curious about it.


I second this opinion. I bought the 85-2, and converted it to run on 110VAC instead of 220VAC by installing an American doorbell transformer in it. But the controller only goes to 99.9C ... I bought the system for it's mechanical box and magnets, because I had the intention of getting rid of the built in controller and replacing it with a circuit board to run it using my own TI MSP430 temerature board that is meant for running kilns up to 1100C. It can also be controlled by a raspberry pi. But for Chemists looking for an out of the box solution, these stirrers don't allow setpoints high enough and don't get hot enough at 110Volts. If you plug them in to 220VAC, (Dryer outlets), they can INDEED get hot enough.

As a note, the controller *IS* able to boil water. It's just not able to set the temperature boiling point above 99.8C before becoming open loop. (Their controller looses temperature regulation when set to 99.9C and it will often spike up to 150C at 110VAC wall voltage.).

The rubber temperature probe holder is also not very useful as it can't hold the thermometer firmly. Which is why I welded a metal plate on the end of the holding rod, so that I could use a u-bolt on the thermometer -- or to hold a glass vial/test tube instead. I also removed the thermometer from the stainless steel jacket because the metal sleeve is actually more reactive with acids than the plastic cord is. ( besides, the jacket makes temperature measurement slow. )

Not having a ceramic top isn't very important ... as stainless steel can be covered with aluminum foil or a glass/sand mixture which can be thrown away. Even more expensive controllers made in the USA with ceramic tops get ruined by chemicals. Check out second hand American hotplate stirrers on ebay, and look at the tops. They are generally in bad shape. No matter what you buy, you'll almost certainly ruin the finish on it if you use it regularly. Besides, stainless steel can be sanded with fine grit sandpaper and you will get a clean finish again just patinaed. It doesn't look bad after cleaning up like ceramic does.

I'm refluxing H2O2 with my stirrer plate, right now. I'm doing it to condensing 3% store bought peroxide into 10 to 30% strength peroxide. Today's the last day of Christmass (day 12) and with help from St. Nick's hat, the water will boil just fine in an hour or so. (I'll upload second picture with hat later. ) You might wonder if it's a Christmas miracle that water steams and boils at 95.5Celsius when I'm only 75ft above sea level ... until you notice where the electronic thermometer is. It's the black cord at the top of the Vigereux column.

Still, the 85-2 is a very low cost stirrer frame for me to build a good system in using my electronics know how. I'll likely show my modified version sometime this coming summer.
The main points I plan to upgrade are 1) the thermometer needs to be chemically passivated with glass, 2) the motor needs a speed controller so that it doesn't stall when stirring very slowly 3) The temperature controller needs a much wider range and 4 digit LED display instead of three digit.

vigereux.jpg - 154kB vigeruxboil.jpg - 1.6MB

[Edited on 8-1-2018 by semiconductive]
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