IDIN Build-it: Battery-pwered wd blck phne charger GOALS: TIME: Participants knw hw t build a cell phne charger pwered by a car/mtrcycle battery Participants feel mre cmfrtable with sawing, nailing, making hl es in wd; cutting sheet metal; wiring up a basic circuit. 3.25 hurs (fr grups f 2-3) PREPARATION: Cllect materials and tls Charge the car r mtrcycle battery Make a battery charger yurself t discver what participants might find difficult Review and/r print Build-It: Battery-pwered phne charger instructins Test the battery and travel charger Make sure t have a piece f wd, the expsed battery charger, battery, sheet metal, multimeter, and, if there are enugh, a set f tls fr yur demnstratin Organize the tls int sets t be distributed during the intrductin (ptinal) Pre-cut the wire t 1.5 lengths t facilitate distributin ROOM SET-UP: Sitting n a tarp n the grund wrked well it was clean and had a lt f space free fr peple t walk, sit, and bserve. Hwever, be careful t nt damage the tarp with the sharp tls! MATERIALS NEEDED FOR ONE CHARGER: Wd - 3-4 wide, 8-10 lng, 1.5-2 -thick (Get frm 2x4 wd plank) Plywd f the same width and length as the wd (Get frm plywd sheet) Sheet metal 4 wide, 10 lng, any thickness that is easy t cut (Get frm crrugated rfing sheet) ~25 small nails Wire 3 (1 m) ttal length 1 Fuse rated between 5A and 13A Electrical tape (very little) 1 phne and cell phne travel charger which fits the phne Hwever, d nt cut the wd, plywd, r metal t the lengths indicated abve, but leave them in their raw frm and allw the participants t prepare the materials. The wire can be pre-cut, but nt stripped, in rder t ecnmize wire usage. 12V car r mtrcycle battery (fr testing during a training, ne battery can be shared with all chargers) 2014-04-5 1
TOOLS Wd saw Hammer MATERIALS* Item Amunt Cst 1.5 x 3 wd blck Plywd ~10 lng $0.20 Same size as wd blck $0.10 Metal snips Sheet metal ~10 x 4 $0.20 Needle-nse pliers Wire 3 ttal (abut 1 m) $0.50 Tape measure Fuse 1 (between 5A-13A) $1 Brace and bits (7/8 and 3/8 ) Electrical tape 1 (abut ¼ m) minimal Wire strippers ½ Nails ~30 minimal Ttal cst = $2 ALL ITEMS NEEDED FOR THE CHARGER Wd blck charger $2 Phne crd $4 12V mtrcycle battery $12 System cst = $18 2014-04-5 2
1. What is a Build-It? (5 minutes) A Build-It is a lessn where peple make a small technlgy and learn sme wrkshp skills. Everyne will build tgether, step by step. As yu build the technlgy, yu will learn gd techniques fr handling metal and wd. Each member will have an pprtunity t learn these hands-n skills by using sme tls and materials. At the end f the Build-It, yu will have had sme practice using tls and als have a technlgy fr yu t take hme. 2. What is a wd blck phne charger? (5 minutes) DISCUSS THE CURRENT PROCESS OF CHARGING PHONES Hw d peple charge their phne nw? (pssible answers: friend in twn, lcal generatr, D-cell batteries in series) Hw much des it cst t charge a phne? Where d peple g t charge their phnes? Hw lng des it take smene t charge their phne? INTRODUCE EACH MAJOR PART: BATTERY, WOOD BLOCK, PLUG-IN CHARGER, AND PHONE. Identify the main cmpnents f the wd blck charger (wires, wd, sheet metal, fuse) and infrm participants they will be building the wden sectin first, then attaching the metal prtins f the insides in the secnd half. 2014-04-5 3
INTRODUCE THE IDEA OF USING A CAR/MOTORCYCLE BATTERY TO CHARGE A CELL PHONE The business wner wns a battery and swaps it ut with a lcal mtrcycle- r carwner when the charge gets lw. In return, the mtrcycle- r car-wner culd get free phne-charging. This is gd because it saves peple transprtatin time and csts, creates a lcal business which keeps mney frm flwing utside f the cmmunity, but instead brings in mney frm utside f the cmmunity. The idea came frm building n the ideas frm villagers in Asampu (central Ghana) 3. Setting up the Build-It (5 minutes) ENCOURAGE PARTICIPANTS TO: Ask, Why? Where? What? Hw? at any time during the sessin Share building s that each persn in the grup can bth bserve and participate in all activities Single-gender grups ften wrk best fr allwing all members f the grup t participate evenly. If there are nt enugh tls fr each team t always have a full set, utline the fact that the tls will be shared. Peple shuld let the grup knw when they are dne with the tls in demand. DIVIDE INTO GROUPS OF 2 OR 3. 2014-04-5 4
4. Preparing the wden blck (45 minutes) Tls Materials Steps 1. Cut a 10 lng piece f wd SHOW THE PARTICIPANTS HOW TO PROPERLY MEASURE AND CUT THE 2X4 WOOD PLANK TO 10. Begin by explaining the details f the measuring tape. If there are bth imperial and metric units, clarify which yu are using and what the different-sized lines mean (1, ½, etc.) Then, mark the plank. Situate yurself t begin cutting and explain hw t use a backwards strke n the first cut f the saw. Yu can use yur thumb t help guide and steady the saw. It may be necessary t have teams share planks f wd and/r saws. Walk arund t ensure each participant has used the saw. 2. Mark at every 2 SHOW THE PARTICIPANTS HOW TO MARK THE HOLES FOR THE CHARGERS. Mark every 2 and at the first inch (1, 2, 4, 6, 8 marks) fr the charging prts and fuse hlder and tell them the dimensins several times. Reiterate the dimensins by using the measuring tape as a reference. Cntinue t demnstrate hw t use the measuring tape with precisin as yu explain the dimensins. As yu walk arund, make sure everyne is using the crrect units and marking their wd relatively precisely. The markers are thick and the dimensins fr this particular technlgy are nt critical t its functinality, s sme errr is nt detrimental. 2014-04-5 5
3. Mark 1 away frm the left edge 4. Drill the marks frm step 2 with 7/8 drill and drill the mark frm step 3 with 3/8 drill SHOW THE PARTICIPANTS HOW TO CUT THE HOLES FOR THE CHARGERS USING THE HAND DRILL. The charging prts will be at every 2, made with the 7/8 bit. The fuse hlder will be at the first 1 mark. Line up the pint n the bit with the mark n the wd. The hand n tp des nt mve, but shuld stay directly abve where yu want the hle this keeps the hle vertical and smth. The hand drill needs t be pressed, but nt very hard if it is pressed t hard, it will make it mre difficult 5. Cut a plywd cver the same size as the wd blck EXPLAIN THAT THEY WILL NEED A PLYWOOD COVER FOR THE BOTTOM OF THE CHARGER. The plywd is the same dimensins as the 2x4 wd, s peple can simply trace the shape f the blck nt the plywd. Peple wh are waiting fr the hand drill and bits can make their plywd bttm while they wait fr ther teams t finish up with the bits. The charging prts will be at every 2, made with the 7/8 bit. 2014-04-5 6
5. Understanding the basic circuit (15 minutes) Once everyne is dne preparing the blck f wd and plywd cver, gather peple clse s they can see and hear the explanatin f hw the circuit wrks. EXPLAIN THE BASIC CIRCUIT Peple will build mre carefully when they understand hw the circuit wrks and why shrt circuits shuld be avided Electricity must travel in a circle. The electricity begins its jurney at the psitive end f the battery. It flws thrugh the wire and arrives at the fuse. The fuse has a small wire inside and the electricity flws thrugh it and nt the first metal strip. The electricity then makes its way thrugh the tip f the charger and int the phne. It charges the phne. Nw, the electricity must return t the battery. It travels t the metal strips n the side f the car charger. These strips tuch the metal cylinders inside f the charger hles. These metal cylinders are attached t the secnd metal strip. The electricity mves thrugh the metal strip and int the wire. It travels thrugh the wire and int the negative terminal f the battery, finishing its circular jurney! FUSE DETAILS The fuse is there t prtect the phne. If t much electricity ges thrugh the phne, it will damage it. The wire in the fuse is very thin. If there is an accident and a lt f electricity escapes frm the battery, the thin wire in the fuse will break. This will break the path the electricity ges n and stp the large amunt f electricity frm getting t the phne and damaging it. 2014-04-5 7
A MAJOR SOURCE OF ERROR The tw strips must nt tuch, r even be clse t tuching. The place where the tw strips lay side-by-side and cnnect t the cylinders which cnnect t the charger is mst ften dne incrrectly The tab shuld nly tuch the strip it ges under, but must nt tuch r be clse t tuching the ther strip. The cylinders must nt tuch, r even be clse t tuching the ther strip. POTENTIAL WAYS FOR THE CIRCUIT/CIRCLE TO BREAK (These details are nt necessary t share, but fr yur reference) Shrt circuit the circuit is clsed befre it is suppsed t be. This culd damage the battery and will destry the fuse. Lse cnnectin the circuit has simply been brken. The mst likely places f failure are at bth ends f the fuse. Brken charger check against this by checking fr a cmplete circuit with the multimeter. Dead battery check the vltage f the battery t ensure it is charged * Abve 12.7 V = 100% charged * 12.4 V = 75% charged * 12.2 V = 50% charged * 12.0 V = 25% charged * Belw 11.9 V = fully discharged battery, and the battery may be damage * Belw 10.5 V = battery is severely damaged and needs t be replaced 2014-04-5 8
6. Preparing the metal strips (45 minutes) There are tw cmpnents t the electric circuit: sheet metal and wiring. Yu will start with the sheet metal first. Tls Materials Steps: 1. Cut a 4 x 10 piece f sheet metal and pund ut any bends EACH GROUP WILL CUT THEIR PIECE OF SHEET METAL FROM THE LARGE ROOFING SHEET. Have peple cut a piece f 4 x 10 crrugated rfing sheet. It is easier t cut the piece s that there are many, shrt crrugatins rather than a cuple lng crrugatins. Pund ut the crrugatins. The piece will grw abut 10% alng the crrugatins when flattened; a bit f extra sheet metal is fine. 2. Cut it in half (alng the length) Yu will have tw 2 x 10 pieces DEMONSTRATE HOW TO CUT THE LONG STRIPS Measure and cut tw 2 x 10 strips frm the sheet in rder t shw gd measuring technique as well as prper handling f the snips. Many peple find snips t be cumbersme, s explain that pushing the material all the way back int the muth f the snips when yu have them pen all the way will allw yu t put mre frce int cutting the metal and make the cutting easier t cntrl. Many peple try t cut using the tips f the snips nly, which makes cutting very difficult 2014-04-5 9
3. Cut ne strip in half lengthwise again. Cut the ther half in quarters Yu will have tw 1 x 10 pieces and fur 2 x 2.5 pieces CUT ONE OF THE STRIPS IN HALF, INTO TWO 1 STRIPS. Strips shuld be as straight as pssible, thugh typically peple d a gd jb ensuring it is straight. CUT THE OTHER STRIP INTO SMALL RECTANGLES TO BE MADE INTO CYLINDRICAL INSERTS There is a 2 x 10 strip left. With a marker, make a line acrss the tp f the strip t indicate this is the tp. This will help peple distinguish between the 2 and 2-½ sides, which are difficult t keep track f therwise. (2½ edges will be the nes left with the line) Beginning frm ne side, measure 2-½ and mark and cut until yu have fur pieces. 4. Mark a 1 square in each f tw crners which share a side n the 2 x 2.5 piece 2 side 2.5 side TAKE ONE OF THE CYLINDRICAL INSERT RECTANGLES AND MAKE IT A TABBED AND BENT INSERT. If the explanatin abve desn t make sense, try this ne: With the marked 2-½ side n the tp, measure 1 dwn the 2 side (which are n the right and left sides). Make a hrizntal line between these dts, leaving a ¼ gap (r smaller) in the middle f the line. This is where the tab will stem frm. We fund that, ftentimes, a persn will cut wherever there is a line; even if it desn t make sense t cut the tab ff, they may d s if the line is there. Mark where the tab shuld be cut ut with tw vertical lines which start where the hrizntal lines end at the gap. Cut n these lines t get the T-shaped piece. 5. Cut ut the piece Repeat step 4 fr all fur 2 x 2.5 pieces 2014-04-5 10
6. Trim 1 ff bth f the 1 x 10 strips The strips shuld be 1 shrter than the plank s that the strips are within the edges f the wd (½ n each side). Typically, this means having a 1 x 9 strip. This is t safe-guard against the edges f the terminal being expsed, putting it at risk fr shrt-circuit. 7. Yu will have tw 1 x 9 pieces and fur cut 2 x 2.5 pieces 8. Bend the tabs f each f the 2 x 2.5 pieces t be very smth and rund It is best t be patient and bend a little bit at a time with needle-nse pliers Using needle-nse pliers, begin t gently bend the cylinder int shape. If dne aggressively, the bends will be t sharp and will nt allw the charger t be inserted smthly. Reiterate that it is imprtant t be patient and g slwly t get it smth!! The cylinders shuld be as smth as pssible and be slightly larger than the charging prt hle. The springy nature f the cylinder will allw them t press tight against the sides f the hle. 2014-04-5 11
7. Attaching the metal pieces (20 minutes) Remember that these tw 1 strips shuld never tuch; ne strip is the psitive terminal (attaching t the fuse) and the ther is the negative (attaching t the tabbed cylindrical inserts). If they tuch, the system will be shrt circuited, the battery culd be damaged, and the charger will nt wrk. Tls Materials Steps 1. Insert all cylindrical inserts int the blck All tabs shuld be n the same side. Make sure the cylindrical inserts wrap mst f the way arund the hle Abut a third f the way up away frm the main cylinder bdy, bend the tab. Insert the cylinder int the charging prt hle until the tab is flat against the wd. The pre-bent tab ensures the bttm f the cylinder bdy is kept safely away frm the ppsite terminal. 2. Nail the negative terminal t secure the cylindrical inserts Dn t nail thrugh the tabs the thin nails will bend! Instead, secure the negative terminal by nailing n either side f the tabs 2014-04-5 12
ATTACH THE 1 STRIP - NEGATIVE TERMINAL Lay the 1 strip n tp f the cylinder s tabs. The strip shuld nt be flush with r verhanging the edge. It als shuld nt be t clse t the large hle where the tabbed cylinder is. Otherwise, the metal is expsed and culd create a shrt circuit. Secure the strip by nailing it t the wd n either side f the tab that lies underneath. D nt nail thrugh the strip and tab tgether (2 pieces f sheet metal) nail n the immediate left and right side f the tabs s yu are nly nailing thrugh the strip (1 piece f sheet metal). D nt nail dwn the ends f the terminal clse t the shrt edges f the wd blck. This part will eventually be cnnected t the wire. 3. Nail n the psitive terminal t cver the hles Dn t nail thrugh the hles! ATTACH THE 1 STRIP - POSITIVE TERMINAL Arrange and trim the strip s that 1) the strip cvers ver half f the large hles (the charger tip must cntact this terminal) 2) the strip cmpletely cvers the small hle (the fuse must be securely held in place) 3) the strip des nt cme clse t tuching the ther terminal (this wuld cause a shrt circuit and a nn-functining device) Nail the strip in place (3-5 nails will be enugh) but be careful nt t nail abve a hle! PREPARE TO ATTACH THE WIRES TO THE TERMINALS On the end f the negative terminal (which is cnnected t the cylindrical tabs), yu will attach a wire. On the end that is clser t the fuse, snip a 1 slt int the strip, at abut halfway in the middle. There are a cuple f different ways the wires will cme in. Single wire. If yu have single wire, give each participant a 3 piece t cut int tw 1.5 lengths. Duble- r triple-cre wire. This means that there are tw r three individual wires in the same length f wire. These wires are very cmmn fr ding hmes electric wiring. If yu have duble- r triple-cre wire, cut int 3 pieces and pull all f the wires apart. Make sure the wires are individually insulated and can easily be separated frm each ther. Sme may have the wires insulatin directly attached next t each ther; starting at ne end, carefully pull them apart s as t nt damage the insulatin prtecting the wire inside. Sme may be inside an additinal insulatin which hlds all three wires lse inside; remve the additinal insulatin which hlds all the wires tgether and yu will be left with the individual wires. 2014-04-5 13
8. Wiring the circuit (30 minutes) Tls Materials Steps 1. Cut the wire in half with the wire strippers (r if it is a dualcre wire, pull the wire apart) The gal is t have tw pieces f wire, each abut 1½ lng 2. Strip abut 4 ff ne end f each wire. Strip 1 ff the ther end. Yu shuld have a little mre than 1 left nt stripped Each wire shuld have ne side that is stripped 4 and the ther side with 1 stripped. 3. Wrap the stripped end f ne wire arund the slit cut in the negative terminal Repeat the wrapping shwn in the picture 3 mre times. Nail the tabs dwn nt the bard 2014-04-5 14
ATTACH THE WIRE - NEGATIVE TERMINAL With the first wire, wrap the 4 stripped end thrugh the slit and arund the tabs f the psitive terminal (attached t the cylinders) in a figure eight pattern several times. Nail the tabs dwn t secure the figure eight wrapping. This helps ensure the wire des nt slip ff the negative terminal 4. Wrap the stripped end f the ther wire arund a nail t create a srt f spring ut f the wire Cut the spring ff f the end and put it int the small hle fr the fuse 5. Strip the wire 1 mre and attach it t the fuse Tape the wire nt the fuse cap with electrical tape. ATTACH THE WIRE AND THE FUSE - POSITIVE TERMINAL With the secnd wire, wrap the stripped end arund a medium-t-large nail t create a spring ut f the wire. The spring shuld fit inside f the fuse hle. Cut the spring ff with wire strippers. Strip 1 f the insulatin ff the end f this wire again. Put the spring int the hle where the fuse will g. Wrap the 1 end f the wire arund the metal tp f the fuse and use electrical tape t securely attach the fuse t the wire. It is helpful t wrap the electrical tape in the same directin arund the fuse that yu wrapped the wire arund the fuse. Plug the wire-and-fuse grup int the fuse hle. 6. Insert the fuse int the small fuse hle. Add layers f tape arund the wire-fuse cnnectin t make sure the fuse sits snugly, but nt t much t keep it frm sliding fully int the hle 2014-04-5 15
9. Finishing and checking the charger (15 minutes) Tls Materials (if pssible, multimeter) Steps 1. Ensure the charger is a cmplete circuit but ensure it des nt have shrt circuits CHECK FOR A COMPLETE CIRCUIT Turn the multimeter t circuit mde, where the multimeter beeps if it is cnnected t a clsed circuit. Attach the wires cming frm each side t each ther; tuch the multimeter n the cylinder (negative terminal) and n the metal at the bttm f the hle (psitive terminal). If the multimeter beeps, there is a cmplete circuit (see Trublesht fr shrt circuits belw). If the multimeter des NOT beep, the circuit is nt cmplete and smething is discnnected (see Trublesht fr discnnected circuits ) TROUBLESHOOT FOR SHORT CIRCUITS (THESE ARE BAD!) Discnnect the wires which cnnect t the battery separate while checking fr shrt circuits. At this pint, the psitive terminal and the negative terminal shuld be cmpletely separate. Tuch the psitive terminal and the negative terminal with the multimeter; if it beeps, there is a shrt circuit! Try t find where the tw terminals tuch by tuching different parts f each terminal. The mst cmmn mistake is when the cylinders frm the negative terminal tuch the psitive terminal. 2014-04-5 16
TROUBLESHOOT FOR DISCONNECTED CIRCUITS (THESE ARE BAD!) Tuch the multimeter acrss each cnnectin t ensure the cnnectin is secure The mst cmmn mistake is a miscnnectin at each end f the fuse (The taping at ne end may have mved the wire ff f the metal tip f the fuse OR the tape arund the fuse is t fat and is preventing the bttm f the fuse frm tuching the metal spring which is tuching the psitive terminal strip. 2. Nail n the plywd cver ATTACH THE PLYWOOD COVER Once the circuitry is checked t be crrect, attach the plywd cver t prtect the electrical wrk. Be careful when yu are nailing the plywd t nt nail nt anther nail n the layer belw. 10. Wrap up (10 minutes) Cngratulate them n a jb well-dne! Ask if there are any questins abut the technlgy. 2014-04-5 17
Appendix: Hw t chse the right battery and a gd car plugin Chse a 12V battery This charger design uses a 12V battery because the car plugin charger's circuitry is designed t use the 12V cming frm a car battery. Car/mtrcycle batteries cme in different vltages 6V and 12V are the mst cmmn. If 6V was used, it wuld nt prvide enugh vltage t wrk; if smething mre than 12V was used, it wuld prvide t much pwer and damage the charger and pssibly damage the phne. Chse a "slar battery" (als called "deep cycle battery") Deep cycle batteries are designed t prvide less pwer ver a lng perid f time; this allws the battery t be used fr a lnger time between charges. Slar batteries lk very similar t car batteries and use the same chemicals, but there is ne difference; the plates inside f the battery are slid and thicker. Typical slar batteries can be safely discharged t 50% capacity, then need t be recharged (discharging the battery t 20% is acceptable, but slightly reduces the life f the battery). Discharging t 40%-80% capacity is best. If this battery were used heavily fr phne charging, it is estimated it wuld last abut 6 years. Mst batteries will be labelled deep cycle battery r slar battery, but yu can check the "Depth f Discharge" rating n the battery (DOD). A DOD f 80% means that the battery can be discharged dwn t 20% f its riginal charge; this wuld be a deep cycle battery. Standard lead-acid car batteries are designed t prvide a lt f pwer very quickly and t be immediately recharged; if the battery is used fr a lng time between charges, the battery will be damaged. Hles in the metal plates inside the battery help create a sharp spike f pwer used fr starting a car; nce the car is started, the alternatr immediately recharges the battery t full capacity. Smetimes these batteries are called "Starting batteries." Typical car batteries can be safely discharged t 80% f its capacity, then need t be recharged (20% depth f discharge (DOD)). If this battery were used heavily fr phne charging, it is estimated it wuld last abut 6 mnths. Bth f these batteries will charge phnes, but the slar battery will be able t be discharged mre befre it needs t be recharged. This means mre phnes can be charged befre the battery needs recharging. Chse a battery with enugh strage capacity The strage capacity f the battery is measured in Ah (Amp-Hurs). A 36-Ah battery has half the capacity, s lasts half as lng, at a 72-Ah battery. The physical size f the battery is ften related t its strage capacity. 2014-04-5 18
Chse a gd charger with a micrchip Check with a vltmeter: a gd charger will briefly shw a resistance reading, then revert back t a blank screen. Phne chargers have t cntrl the amunt f current that gets delivered t the phne battery. Gd chargers cntrl the pwer delivered t the phne with a micrchip (and it saves energy!). The micrchip is smart, s des sme switching t avid wasting electricity. With a vltmeter, measure the resistance between the side metal piece and the metal tip f the car charger; it will shw a resistance reading, then g t zer r a blank screen. When yu attach the vltmeter t a gd charger, it initially has a resistance t measure but smehw triggers the switching circuit, and the resistance reading disappears. Cheap chargers cntrl the amunt f current delivered t the phne with a large resistr; pwer is drawn and the resistr wastes the excess energy int heat. With a vltmeter, measure the resistance between the side metal piece and the metal tip f the car charger; it will shw a cnstant resistance r nne at all. Of curse, when in dubt, yu culd buy a charger and carefully split it pen t check befre yu buy mre. Build-Its are published by IDIN. The Internatinal Develpment Innvatin Netwrk (IDIN) is a cnsrtium funded thrugh USAID s Higher Educatin Slutins Netwrk (HESN) that supprts leading universities t catalyze the develpment and applicatin f innvative science, technlgy, and engineering appraches and tls t slve sme f the wrld s mst challenging develpment prblems. The battery pwered wd blck charger featured here was designed by participants f the Internatinal Develpment Design Summit, and has been adapted by IDIN cntributrs. The dcument was created by Benji Mncivaiz in cllabratin with IDIN representatives at UC- Davis and Olin Cllege. 2014-04-5 19