Many reactions require a magnetic stirring hot plate. I'm forgetful so I'd like one that can be
programmed with a consistent schedule. Also, I'd like to do a little cooking and test some recipes.
Hey Chris from a couple months ago, can I spend $1400 on a magnetic stirring hotplate?
I don't have the money for that.
Well, guess I'll have to build it myself. Seems straightforward enough.
Are you ready to watch me fail... repeatedly? Because this is Ten Tries.
Magnetic stirrers work by rotating a magnetic field to spin a magnetic stir bar in a
container. I want to break this issue down into parts. In my first attempt, I tackle stirring.
I bought some cheap Teflon coated stir bars, and for the rotating magnetic field,
I designed a setup with a simple dc motor that spins magnets. It is simple, and it sort of works,
but there's no speed control, and the motor wears out the coupler after just a bit of use. Also,
it can't spin too quickly or... The stirrer could use a little work but we'll come back to that.
While it may not be an option on many hot plates i would like some decent temperature control.
For the actual heating element, I picked up this cheap single burner for about twelve dollars. My
control will be a PID temperature controller for another twelve dollars. The thermocouple doesn't
look like it can be submerged in a solution, so I picked up one that can for about three dollars.
It overshot the set temperature quite a bit, but after it settled, the temperature was very stable.
The motor I am using doesn't have much torque, and there's no speed control, so I printed up
a few parts and bought a motor and speed control that is typically used for drones, for 13 dollars.
I designed and printed some parts to mount the motor, measure the speed, and mount the magnets.
While this works fairly well as a magnetic stirrer, there is no way the printed parts
can withstand the heat of the hot plate. Using the lost PLA casting method I showed in my first
two videos, I made these parts out of aluminum. These parts should withstand heat much better.
Also, I used my controller from Try Ten of my lost PLA project
and made a few modifications. So, it's time to put it all together!
I made an enclosure for the control circuitry out of some wood scrap I had laying around
and painted it black. Then, I mounted everything inside with some wood screws. I'll be including
wiring diagrams on the project page for this project on my site, TenTries.com. I added an
accelerometer to help balance the magnet mount, so it doesn't vibrate as much while it spins.
That process was a little involved so I'll have to make a separate video for the balancer, itself.
The device can heat and stir well, so it's time to check the temperature accuracy. To do this,
I compared the readings with the freezing point and boiling point of water. I added ice water
to a bath and heated it until the boiling point while the Python program recorded the temperature.
The idea here is that the temperature should remain at the freezing point of water,
0 degrees Celsius, until the ice melts. Then, the temperature should continue to rise until
it is at the boiling point which should be around 98 degrees Celsius, since I'm doing this test at
about 2000 feet above sea level. The freezing point of water does not change much at different
altitudes, because the water density difference is small when freezing compared to boiling. It seems
the temperature was only about half a degree low for the freezing point and boiling point. That is
pretty accurate. If you'd like to calculate the boiling point of water where you live, I will
include the calculator in the project write-up on my site. I'm going to do something that I've never
done before, follow a recipe. I programmed my hot plate to cook some mac and cheese.
All right, the instructions are right.
I wanted to try cooking something a little more difficult. If you've ever cooked Hollandaise
Sauce, you know it is incredibly easy to mess up. Well, precise temperature helps a lot.
Alright, so for about 40 dollars, the price of some of the cheapest stirring hot plates,
I have one that functions similar to a $1,400 programmable stirring hotplate. How would you
make this hotplate better? Let me know in the comments below. And if you enjoyed this video,
make sure to hit that subscribe button. !t really helps me to make more high quality videos!