A Locally Produced Low Cost Magnetic Stirrer

Ram S. Lamba and Ramón A. De La Cuétara, Low Cost Equipment Project - Puerto Rico

Parts List

The numbers below correspond to the ones in the photo.

1. "Wall wart" adjustable 12 volt DC power supply, sometimes called a "battery eliminator". Best stirring speeds are obtained in the 3-8 volt range at a load of about 100 miliamperes. Any power supply with output in this range will be adequate.

2. Any large magnet, the photo shows one from Radio Shack (part number 640-1877 about US$1).

3. Any socket that will match the power supply, the photo shows a transistor radio battery clip. We do not recommend direct wiring, if the transformer is dropped by accident, it will cause the cable to break most of the time.

4. A suitable enclosure, the photo shows an 8 in. x 6 in. x 3 1/2 in. (20cm x 15cm x 9cm) aluminium box by LMB (part number 783 about US$12)

5. A discarded 5 1/4 inch full height disk drive. The photo shows one by Tandon, from an original IBM-PC. Some half-height drives are suitable but most have the speed control in a printed circuit board that forms part of the motor. These are not easy to modify. Knowledge of electronics is a must to be able to figure these out and find out where to "cut".

6. Epoxy glue and insulating tape (not shown in the photo).

Construction Procedure

Step 1 - remove all parts from the disk drive, leaving only the motor, spindle, and the pulley connecting them. Find two screws that will fit the mounting threads on the side and keep this also. In most drives the motor has 4 wires two of them are for power and the other two are a tachometer winding. Most we have seen use red-blue for power and green-yellow for tach. If you're not shure apply 12 volts DC to a pair at a time (there's only 6 combinations) until the motor spins.

Step 2 - Glue the magnet to the spindle using epoxy glue. Center the magnet on the spindle as best as you can. if the magnet is too short you may need to add a spacer to get it to the proper height. The photo shows a spacer made from a piece of plastic removed from the disk drive.

Step 3 - Drill the case on one side for mounting the motor-magnet assembly and also drill a hole for the connector. Mount the assembly to the case. The photo shows the assembly held on one side with two screws. Solder the connector wires to the motor power wires and cover the exposed joint with insulating tape if there is a possibility of the wires making contact.

Step 4 - Connect the power supply to test the stirrer. If everything works, close the case. The stirrer is finished.