Product Magnetic Stirrer DocID D0001 Version 0.1 Author Malcolm Watts Status Pre-release

Editor Tekla Labs Date 7/11/2011

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Product Overview Uses: Magnetic stirrers (also known as magnetic stir plates) are very common in experimental chemistry and biology. They are used to mix components (solids and liquids) to get homogeneous liquid mixtures. Common examples include

bacterial growth media and buffer solutions.

How They Work: Magnetic stirrers mix solutions using an external magnetic field that rotates a small magnetic bar that has been placed in the mixture of interest.

Advantages: Magnetic stirrers minimize the risks of contamination since only an inert magnet bar, which can easily be cleaned, is put inside the sample/fluid. In addition, using a magnetic stirrer rather than manual stirring is critical for

consistent, reproducible mixing or mixing over long time scales. Protein dialysis, for example, requires multi-hour or overnight sample mixing and is sensitive to bacterial contamination.

This Magnetic Stirrer: Can rotate an internal magnet at variable speeds, mixing volumes up to one liter. Glassware with a stir bar is placed directly on top of the stirrer unit. The device is battery-operated and largely isolated from spills by its

plastic case and gasket.

Figure 1. Tekla Labs magnetic stirrer with 500 mL sample Figure 2. Internal view of design

Acknowledgements and Creative Commons Licensing Designed by M.J. Watts (formerly of Massey University). Design open-source courtesy of Massey University New Zealand.

This blueprint is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported

licence. http://creativecommons.org/licenses/by-nc-sa/3.0/

Product Magnetic Stirrer DocID D0001 Version 0.1 Author Malcolm Watts Status Pre-release

Editor Tekla Labs Date 7/11/2011

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Navigating the Blueprint Document

Product Overview .................................................................................................................................................................. 1

Acknowledgements and Creative Commons Licensing ......................................................................................................... 1

What Skills and Tools Do I Need? .......................................................................................................................................... 2

Specifications: What can this magnetic stirrer do? ............................................................................................................... 3

What Materials Are Needed? ................................................................................................................................................ 3

Details of Materials................................................................................................................................................................ 5

Module 1: Motor Assembly ................................................................................................................................................... 6

Module 2: Motor Controller (Speed Adjustment) ............................................................................................................... 10

Final Assembly ..................................................................................................................................................................... 12

How do I know it is working correctly?................................................................................................................................ 13

Now how do I use this, troubleshoot and perform maintenance? ..................................................................................... 14

Feedback.............................................................................................................................................................................. 14

What Skills and Tools Do I Need?

Safety considerations during construction The soldering iron becomes extremely hot. Hot solder and flux can give off harmful fumes. Conduct soldering in

a well ventilated environment and take standard precautions to secure the hot iron.

The motor can become hot immediately after operation. These safety considerations are, of course, in addition to normal precautions necessary when using the various

tools needed for this project.

Required skills Skill Module(s)

Soldering to printed circuit board 2 Press-fitting shaft 1 Drilling holes in sheet metal 1

Required tools Tool Module(s)

Screw driver 1,2,3 Drill (hand drill or drill press) 1 Soldering iron 2 Method of cutting and bending sheet metal 1

Product Magnetic Stirrer DocID D0001 Version 0.1 Author Malcolm Watts Status Pre-release

Editor Tekla Labs Date 7/11/2011

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Specifications: What can this magnetic stirrer do?

List of specifications 1. Magnetic stir bar rotates at an adjustable speed. Maximum rotation rate depends on the components used,

including motor, magnets, and stir bar. Rotation will be optimal in low friction containers such as glass containers.

2. Creates stable vortex in beakers up to 1000 mL. Optimized for use with 250 mL beakers. 3. Stirrer operates on battery power, not plug-in wall power. 4. Interior of device is as isolated from outside environment as possible so that device is resistant to spills.

What Materials Are Needed?

Figure 3. Overview of materials used

Product Magnetic Stirrer DocID D0001 Version 0.1 Author Malcolm Watts Status Pre-release

Editor Tekla Labs Date 7/11/2011

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List of Materials. Note that in many cases, alternate materials can be used, as long as changes in properties such as dimensions are accounted for in the building process. Please add you comments to the online document if you find alternative materials or solutions.

Part Part Description Module PartID Quantity Cost (USD)

Rotor body Used to hold magnets, cut from light wood or hardboard (fiber board) 5mm thick.

1 M001 40 mm diameter $0.25

Rotor magnets Magnets that spin on rotor body. Circular or bar magnets may be used. See text,

1 M002 2 $2.60

DC motor Brush or brushless DC motor, body 30-35 mm long, with mounting screws

1 M003 1 $2.99

Sheet metal 16 gauge or similar, for motor mount. Also for metal strip connecting magnets

1 M004 30 x 70 mm $0.25

Printed circuit board (PCB)

Connects electronics; can also wire by hand 2 M005 1 Spare, or handwire

Plastic casing Encloses unit, see Material Hints 2 M006 1 $14.90 Battery clip Holds and connects the battery 3 M007 1 $0.89 Knob To set various speed settings 2 M008 1 $5.30 Potentiometer Speed regulation, can be bought with knob 2 M009 1 M2.5 screws M2.5 x 10 mm machine screw 1 M010 2 $0.20 M2.5 screws M2.5 x 20 mm machine screw 3 M011 4 $0.40 M2.5 nut M2.5 hex nut 1 M012 2 $0.20 Stir bar Magnetic stir bar Final M013 1 $2.00 LED light Optional. Lights up when motor is getting

power 3 M014 1 $0.40

Battery D size Final M015 1 $2.00 Transistors, capacitors

Tekla Labs is working on a detailed list of these parts

2 M017+ $4.00

Product Magnetic Stirrer DocID D0001 Version 0.1 Author Malcolm Watts Status Pre-release

Editor Tekla Labs Date 7/11/2011

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Details of Materials This is a more detailed explanation of the key materials used in the design. In general, equivalent options can be bought from many other suppliers and dimensions and other parameters can be readjusted as needed.

M001 Rotor body Cut from bulk material, can use scissors or hobby knife. M002 Rotor magnets Small rare-earth magnets are necessary to couple the rotor and stir bar in this compact design. The author suggests removing the magnets from magnetic battery connectors. Magnets can be circular or bar magnets.These are available from Science Lab Supplies, sciencelabsupplies.com, #1921-29 ($1.30 each). Individual magnets are also available directly from other suppliers, e.g. http://applied-magnets.amazonwebstore.com/ M003 DC motor Authors initial design used a generic toy motor available from JayCar (jaycar.com.au), YM2706 or YM2707 ($3.25 or $4.25), 1.5 4.5 VDC operating voltage Prototype contains HTI Model 32 DC motor marked HTBRR032021903F-0002 Radio Shack 273-233 1.5 to 3VDC Hobby Motor ($2.99) may be a suitable replacement Motor case should have threaded mounting holes on the shaft side. This will allow it to be attached to the sheet metal mount. M005 Circuit board If a printed circuit board cannot be obtained, hand-wiring electronic components is straigthforward. Tekla Labs will provide wiring instructions in the future. M006 Plastic box Bud Industries PN-1324-DG (DigiKey 377-1124-ND) $14.90 Tekla Labs unit is a 12 cm wide x 17 cm long by 5.5 cm tall case made of ABS plastic. These dimensions are not critical but the surface area has to be large enough to hold the size glass beaker you want to use. M007 Battery holder Memory Protection Devices BHDL (Digikey BHDL-ND) $0.89 M009 Potentiometer Tekla Labs will confirm resistance range and dimensions of potentiometer. M010 M2.5 Screws DC motor screws need to be flat heads, otherwise you will have excessive rubbing between the mounting screws and the rotating hardboard.

M013 Stir bar Science Kit and Boreal Laboratories (sciencekit.com) WW46316M14 SpinBar Magnetic Stir Bar $2.00 M014 LED light