Magnetic Stirrers here in Brazil often have a very high price.
Based on various projects available on the internet, why not make your own?
Step 1: Materials
We use this case:
- 1 Wooden box
- 1 80mm Fan @ 12Vdc
- 1 Circuit Speed Controller (see next step)
- 1 HD magnet
- 1 power source 12Vdc/500mA - Saved from a older router.
- 1 on / off switch
- 4 screws
- 8 nuts
- Some wires, tools, Gorilla Glue...
Step 2: Speed Controller - PWM
For the speed controller, there are several options, from a simple potentiometer until to a PWM circuit using an 555 IC.
I chose the PWM method for speed control, because the accuracy of rotation required as the substances used.
Usually, the potentiometer is used for adjusting the speed of rotation and the value of this depends on the potentiometer control circuit chosen.
Example of "simple" circuit
Example of PWM circuit
Step 3: Drilling
First step, perform the necessary drilling in the box, taking care to keep the drilling of the fan, centralized.
Step 4: Install Speed Controller
Install the chosen circuit, as well as potentiometer and key in the holes made.
Step 5: Magnet
Glue magnets on the fan, as centered as possible, avoiding the propeller unbalance.
Step 6: Screw Nuts
Connect the fan to the previously installed circuit. To position the fan to the desired height, adjust the screw nuts.
Step 7: Done !
The maximum speed depends primarily of magnet and the viscosity of the substance.
Step 8: First Test
We can test this circuit using a magnetic stir bar and Erlenmeyer.