Magnetic Stirrer Beta Release V01

8/2/2019 Magnetic Stirrer Beta Release V01

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Product Magnetic Stirrer

DocID D0001 Version 0.1

Author Malcolm Watts Status Pre-release

Editor Tekla Labs Date 7/11/2011

1

Product Overview

Uses:Magneticstirrers(alsoknownasmagneticstirplates)areverycommoninexperimentalchemistryandbiology.

Theyareusedtomixcomponents(solidsandliquids)togethomogeneousliquidmixtures.Commonexamplesinclude

bacterialgrowthmediaandbuffersolutions.

HowTheyWork:Magneticstirrersmixsolutionsusinganexternalmagneticfieldthatrotatesasmallmagneticbarthat

hasbeenplacedinthemixtureofinterest.

Advantages:Magneticstirrersminimizetherisksofcontaminationsinceonlyaninertmagnetbar,whichcaneasilybe

cleaned,isputinsidethesample/fluid.Inaddition,usingamagneticstirrerratherthanmanualstirringiscriticalfor

consistent,reproduciblemixingormixingoverlongtimescales.Proteindialysis,forexample,requiresmulti-houror

overnightsamplemixingandissensitivetobacterialcontamination.

ThisMagneticStirrer:Canrotateaninternalmagnetatvariablespeeds,mixingvolumesuptooneliter.Glasswarewith

astirbarisplaceddirectlyontopofthestirrerunit.Thedeviceisbattery-operatedandlargelyisolatedfromspillsbyits

plasticcaseandgasket.

Figure1.TeklaLabsmagneticstirrerwith500mLsample

Figure2.Internalviewofdesign

Acknowledgements and Creative Commons LicensingDesignedbyM.J.Watts(formerlyofMasseyUniversity).

Designopen-sourcecourtesyofMasseyUniversityNewZealand.

ThisblueprintismadeavailableunderaCreativeCommonsAttribution-NonCommercial-ShareAlike3.0Unported

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


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Navigating the Blueprint Document

ProductOverview .................................................................................................................................................................. 1

AcknowledgementsandCreativeCommonsLicensing ......................................................................................................... 1

WhatSkillsandToolsDoINeed? .......................................................................................................................................... 2

Specifications:Whatcanthismagneticstirrerdo? ............................................................................................................... 3

WhatMaterialsAreNeeded? ................................................................................................................................................ 3

DetailsofMaterials................................................................................................................................................................ 5

Module1:MotorAssembly ................................................................................................................................................... Module2:MotorController(SpeedAdjustment) ............................................................................................................... 10

FinalAssembly..................................................................................................................................................................... 12

HowdoIknowitisworkingcorrectly?................................................................................................................................ 13

NowhowdoIusethis,troubleshootandperformmaintenance? ..................................................................................... 14

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

What Skills and Tools Do I Need?

Safetyconsiderationsduringconstruction

Thesolderingironbecomesextremelyhot.Hotsolderandfluxcangiveoffharmfulfumes.Conductsolderingin

awellventilatedenvironmentandtakestandardprecautionstosecurethehotiron.

Themotorcanbecomehotimmediatelyafteroperation.

Thesesafetyconsiderationsare,ofcourse,inadditiontonormalprecautionsnecessarywhenusingthevarious

toolsneededforthisproject.

Requiredskills

Skill Module(s)

Solderingtoprintedcircuitboard 2Press-fittingshaft 1

Drillingholesinsheetmetal 1

Requiredtools

Tool Module(s)

Screwdriver 1,2,3

Drill(handdrillordrillpress) 1

Solderingiron 2

Methodofcuttingandbendingsheetmetal 1


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Specifications: What can this magnetic stirrer do?

Listofspecifications

1. Magneticstirbarrotatesatanadjustablespeed.Maximumrotationratedependsonthecomponentsused,

includingmotor,magnets,andstirbar.Rotationwillbeoptimalinlowfrictioncontainerssuchasglass

containers.

2. Createsstablevortexinbeakersupto1000mL.Optimizedforusewith250mLbeakers.

3. Stirreroperatesonbatterypower,notplug-inwallpower.

4. Interiorofdeviceisasisolatedfromoutsideenvironmentaspossiblesothatdeviceisresistanttospills.

What Materials Are Needed?

Figure3.Overviewofmaterialsused


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ListofMaterials.Notethatinmanycases,alternatematerialscanbeused,aslongaschangesinpropertiessuchas

dimensionsareaccountedforinthebuildingprocess.Pleaseaddyoucommentstotheonlinedocumentifyoufind

alternativematerialsorsolutions.

Part PartDescription Module PartID Quantity Cost(USD)

Rotorbody Usedtoholdmagnets,cutfromlightwood

orhardboard(fiberboard)5mmthick.

1 M001 40mmdiameter $0.25

Rotormagnets Magnetsthatspinonrotorbody.Circular

orbarmagnetsmaybeused.Seetext,

1 M002 2 $2.60

DCmotor BrushorbrushlessDCmotor,body30-35

mmlong,withmountingscrews

1 M003 1 $2.99

Sheetmetal 16gaugeorsimilar,formotormount.Also

formetalstripconnectingmagnets

1 M004 30x70mm $0.25

Printedcircuit

board(PCB)

Connectselectronics;canalsowirebyhand 2 M005 1 Spare,or

handwire

Plasticcasing Enclosesunit,seeMaterialHints 2 M006 1 $14.90

Batteryclip Holdsandconnectsthebattery 3 M007 1 $0.89

Knob Tosetvariousspeedsettings 2 M008 1 $5.30

Potentiometer Speedregulation,canbeboughtwithknob 2 M009 1

M2.5screws M2.5x10mmmachinescrew 1 M010 2 $0.20

M2.5screws M2.5x20mmmachinescrew 3 M011 4 $0.40

M2.5nut M2.5hexnut 1 M012 2 $0.20

Stirbar Magneticstirbar Final M013 1 $2.00

LEDlight Optional.Lightsupwhenmotorisgetting

power

3 M014 1 $0.40

Battery Dsize Final M015 1 $2.00

Transistors,

capacitors

TeklaLabsisworkingonadetailedlistof

theseparts

2 M017+ $4.00


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Details of Materials

Thisisamoredetailedexplanationofthekeymaterialsusedinthedesign.Ingeneral,equivalentoptionscanbebought

frommanyothersuppliersanddimensionsandotherparameterscanbereadjustedasneeded.

M001Rotorbody

Cutfrombulkmaterial,canusescissorsorhobbyknife.

M002Rotormagnets

Smallrare-earthmagnetsarenecessarytocoupletherotorandstirbarinthiscompactdesign.Theauthorsuggests

removingthemagnetsfrommagneticbatteryconnectors.Magnetscanbecircularorbarmagnets.Theseareavailable

fromScienceLabSupplies,sciencelabsupplies.com,#1921-29($1.30each).Individualmagnetsarealsoavailabledirectly

fromothersuppliers,e.g.http://applied-magnets.amazonwebstore.com/M003DCmotor

AuthorsinitialdesignusedagenerictoymotoravailablefromJayCar(jaycar.com.au),YM2706orYM2707($3.25or

$4.25),1.54.5VDCoperatingvoltage

PrototypecontainsHTIModel32DCmotormarkedHTBRR032021903F-0002

RadioShack273-2331.5to3VDCHobbyMotor($2.99)maybeasuitablereplacement

Motorcaseshouldhavethreadedmountingholesontheshaftside.Thiswillallowittobeattachedtothesheetmetal

mount.

M005Circuitboard

Ifaprintedcircuitboardcannotbeobtained,hand-wiringelectroniccomponentsisstraigthforward.TeklaLabswill

providewiringinstructionsinthefuture.

M006Plasticbox

BudIndustriesPN-1324-DG(DigiKey377-1124-ND)$14.90

TeklaLabsunitisa12cmwidex17cmlongby5.5cmtallcasemadeofABSplastic.Thesedimensionsarenotcritical

butthesurfaceareahastobelargeenoughtoholdthesizeglassbeakeryouwanttouse.

M007Batteryholder

MemoryProtectionDevicesBHDL(DigikeyBHDL-ND)$0.89

M009Potentiometer

TeklaLabswillconfirmresistancerangeanddimensionsofpotentiometer.

M010M2.5ScrewsDCmotorscrewsneedtobeflatheads,otherwiseyouwillhaveexcessiverubbingbetweenthemountingscrewsandtherotating

hardboard.

M013StirbarScienceKitandBorealLaboratories(sciencekit.com)WW46316M14SpinBarMagneticStirBar$2.00

M014LEDlight

PanasonicLN21RPH(DigiKeyP374-ND)$0.40

M016Knob

Optional.StandardknobsareavailablefromDigiKeyforafewdollars.Acylindricalrubberstopperorcorkisacheap

substitute,andcanbepresseddirectlyontothepotentiometer.


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Module 1: Motor Assembly

Approximatetime=1hour

Step-by-stepinstructions

Figure4.Close-upofmotorsetup.

1. Cutsheetmetalintotwopieces:asmallmetalstripforuseontopoftherotorbodyandalargerpiecefor

mountingthemotor.

2. Cutholesinthesmallmetalstripforthe

motorshaftandforthescrewstoholdthe

motor.

Thesmallmetalstripisimportantasit

createsalow-profilehorseshoemagnet,

whichgreatlyenhancesthepullofthe

magnetsascomparedtothecasewhere

nometalstripisused.Ifthemagnetsareputdirectlyontothehardboardwithouta

metalstrip,onehastobecarefulnotto

changethepowersettingtooquicklyon

thefinishedunitorelsethemagneticstir

barwilljumpofftarget.

.

Figure5.Topandsideviewofsmallmetalstrip,magnetsandhardboard


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3. Drillholesformotorscrewsandshaftinthemotor

mountsheet

CAUTION:clampsheetmetaltoworksurfacewhile

drilling.Keephandsfreeofsheetmetalincaseitcomes

freeandrotateswiththedrill.

Positionsofholesformotorscrewsandshaftare

critical.Thesedependontheexactmodelofmotor

thatisused.Formostpreciseplacement,firstmark

holepositioninpencil.Thenindentthesheetmetal

surfacewithanawlornail.Finally,positiontipofdrill

bitintheindentation.

Figure6.Topviewschematicofflatmetalmountsheet,indicatinglocationsofdrillholesandmetalbending.

4. Bendthemotormountsheettoformthemetalmotormountshapedescribedbelow.Themountheight(30

mminthiscase)shouldbehighenoughtofitthemotorwithoutcompressingitssolderleads.Theangleyou

bendthesheetisnotcritical.

Figure7.Sideviewschematicofbend-linesofmetalmountsheet.

5. Attachmotortothemotormountsheetwithscrews.Screwswithshortheadsshouldbeusedsothatthereis

enoughclearancetotherotorbody.


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Figure8.Finalsideviewschematicofmotorandsheetmount.

6. Cutthehardboardtoformtherotorbody

Therotorbodysdiameterisdependentonthesizeofthestirbaryouwillbeusing.Themagnetsontherotorbodyshouldbespacedapproximately80%ofthestirbarlength.Usinglongerbarmagnetsontherotorbody

allowsforawiderrangeofmagneticstirbarsizes.Ourrotoris38mmindiameterand5mmthicktofita

magnetcenter-to-centerdistanceof24mm.

7. Drilltwoscrews(orholes,ifyoureusingmachinescrews)throughthebottombaseofthehardboard.

8. Installthemagneticstriprotoratopthedrilledhardboardusingthecorrespondingnuts

9. Press-fittherotorbodyontothemotorshaft.

Thisisafrictionfit.Themotorshaftcanbecoveredbyapieceofheatshrinkplastictoprovideafirmfittothe

holeinthecenterofthehardboardrotorbody.

10.Solderthetwomotorwirestocontactsontheprintedcircuitboard(onetogroundandonesothatitcanbe

electricallyconnectedtothepotentiometer).

11.Attachthemotormountsheet(withattachedmotor)totheprintedcircuitboardwithscrews.


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12.Gluemagnetsontothemetalstriponthehardboardrotor.Magnetdistanceshouldbeabout80%ofthelength

ofthestirbar.

Figure9.ExplodedviewofModule1components.1)metalsheetformountingmotor2)motor3)hardboard4)smallmetalstrip5)

magnets6)screws,6total


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Module 2: Motor Controller (Speed Adjustment)

Approximatetime=1hour


1. ConstructaPCBaccordingtothecircuitshownbelow.Alternately,ahand-wiredcircuitmaybesimplerto

constructwithavailableparts.(TeklaLabsisworkingonconvertingthiscircuitdiagramintoamoreaccessible

formandphotographingthehand-wiringstep-by-step.)

2. Drillaholethroughtheplasticcasingtoconnectthespeedcontrolknobtothepotentiometer.

3. Attachknobtopotentiometershaftoutsideofcase

Figure10.Schematiccircuitdiatramof

components.

.

Figure11.Wiringdiagramforhardwiringin

theabsenceofaccesstoaprintedcircuit

board

Figure11

npn transistors

pnp transistor

ground

battery

potentiometer

motor

LED light

capacitor

resistor

transistors

KEY


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Module3:BatteryPowerandPowerIndicatorLight

Approximatetime=1hourStep-by-stepinstructions

Batterypower

1. Solderthetwobatterycasingwirestocontactsontheprintedcircuitboard.Onewiremustbeconnectedtogroundandonemustbeconnectedtoacontactsothatthewirecanbeelectricallyconnectedtothe

potentiometer.

2. GluethebatterycasingtothePCB.Hotmelt,ahotglueguncanbeusedforthisstep.

LEDlight(optional)

3. DrillaholeonthesideoftheplasticcasingtofittheLEDlighttoprovideatightfit.

4. SolderthetwoLEDlightwirestocontactsontheprintedcircuitboard(onetogroundandonesothatitcanbe

electricallyconnectedbetweenthepotentiometerandthemotor.

5. CarefullypresstheLEDlightintotheholeusingpliers.

Figure11.Close-upoffinishedbatteryclip. Figure12.Close-upoffinishedLEDlightconnection


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Final Assembly

Approximatetime=30minutes


1. Screwcircuitboardintobottomofplasticcase

2. PlaceD-batteryintobatteryclips

3. Screwtopontoplasticcasebody

a. Donotover-tightenasthiscouldcausetheunevenpressureloadalongtheperimeterandthusbowing

(outwardbending)ofthetopthataffectsthedistancebetweentheglassbeakerandthemagneticrotor.

Figure13.Finished,closedmagneticstirrerwithmagneticstirbarontop.


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How do I know it is working correctly?

Inspection

1. Theunitshouldbecompletelysealed,butwithoutover-tighteningofthescrewsusedtoattachthetopsurface.

Thereshouldbenoentrypointsintotheunitotherthantheholescutfortheindicatorlight(ifused)andforthe

speedcontrolknob.

2. Whenturningtheuniton,withaworkingbatteryinplace,theLEDindicatorlightshouldturnon.

Testing

1. Insertstirbarintooneliterbeakerwithoneliterwater.

2. Stirrodshouldnotrotatewhenknobisturnedtozero.

3. Graduallyturnknobtohighersetting.Stirbarshouldrotatefasterasmotorisoperatedatahigherspeed.

4. Atmaximumspeedsetting,themagneticstirrershouldbeabletoformalargevortexwithinaonelitervolume

beaker(seepicture).

Figure14.Testingthefinishedmagneticstirrer:atfullspeed,alargevortexshouldformin1Lofwater


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

Operatorsafety

1. Whenworkingwithhazardouschemicals,glasswareshouldbecovered.Stirrershouldbekeptinasecondary

containertocatchanyspills

2. Retrievestirbarwitharetriever,notbyhand.Thiscanbemadebytapingamagnettotheendofaplasticrod

orpen.

Maintenance

1. Changebatterywhennecessary(indicatedbyLEDlight).

2. Whenchangingbattery,alsoconfirmthatmagnetrotorstillmakestightfitwithshaft.

Troubleshooting1. Problem

Stirbardoesnotmoveatallwhenknobisturnedup.

Solution

Removecoverandcheckthatmotorandrotorbodyarespinning.Ifnot,checkbatteryandmotorconnections.

Iftheyare,checkthatmagnetsusedarecapableofmovingstirbarandarecloseenoughtotopofplasticcasing.

Ifcurrentisdeliveredtothemotorbutitdoesnotspin,themotormayneedtobereplaced.Ifrotorspinsbut

doesnotcatchstirbar,trymovingrotorfurtherupalongmotorshaft.

2. ProblemStirbarmoveswhenknobisturnedup,butdoesnotrotatefully.

Solution

Double-checkthatthebeakerandstirbararebothcenteredoverthemotorshaft.Graduallyturnuprotation

speeduntilrotorcatchesstirbar.

Feedback

TheTeklaLabscommunitywantstohearfromyou!PleasegivebacktotheTeklaLabscommunitybylettingusknow

ifyou:

- findalternativematerialsorbuildingtoolstouse

- useanotherapproachforbuildingamoduleorpartofamodule

- comeupwithawholenewdesignforthistypeofequipment(oranotherequipmentpiece!)

- hadanyotherproblemsorsolutionstoshare

- needhelpwithspecificpartsofthisTeklaBlueprint.Whatisunclear?Howcanwemakethisbetter?

TogetinvolvedintheTeklaLabscommunity,visitourwebsitewww.teklalabs.org.

Magnetic Stirrer Beta Release V01

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