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Published 2008
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In this write-up two designs of manpowered battery charger are described. Both designs are very simple as well as cheap in compare with existing man powered battery chargers. All components of these battery chargers are easily available.

Basic principle of a manpowered battery charger is to drive an electrical generator by rotation of the pedals manually and to store the generated electrical energy in a battery. A D.C motor can be utilized as a generator however; high rpm is required to drive a D.C motor worked as D.C generator. A.C generator is not suitable as pedal powered generator for the absence of permanent magnet in it. Stepper motor is the best as it contains permanent magnets and it is designed to produce high torque at low rpm. In one of the designs of this discussion, typical small alternator provided with permanent magnets used in bicycle is suggested. It will be suitable for charging flashlights, radios and cell phones. Power generating capacity of the other design is comparatively higher and stepper motor is preferred in this design.

Research has shown that sustainable power from cycling is around 200W (Bicycling Science, 1982). Normally, most adults can generate steady power ranges from 75 to 150 watts.  Power generated by hand crank is however, less than pedals operation by legs but for simplicity, hand  crank is commonly used for charging of small devices. 

Constructional Details

Constructional features of two types of mechanical charger are described. One charger is designed for light duty purpose and hand crank is used to produce rotational motion of the wheel which drives a 12 Volt bicycle alternator. Another design is pedal operated to generate comparatively more power than the charger with hand cranking system.

Hand Cranking System:

Design. I-

A 3/4th inch thick wooden ply board disc (hot pressed ply board) of approximately 26inch diameter is used as drive unit of bicycle alternator. A full threaded long bolt is fixed at a distance of 6.5inch from the disc centre and a hollow pipe is loosely enclosed the bolt which acts as the crank handle of the disc to impart rotational motion. A pipe is used as the axle of the disc.1/8th inch thick M.S plate of 3inch diameter is welded at axle pipe end and this round M.S plate is fixed with ply board disc as a flange through bolts. Other end of the axle pipe is supported on a rickshaw bearing. The bearing housing is firmly fixed with the supporting stand. One side of a bicycle tyre is cut throughout its rounded portion and then pasted with the one side of ply board disc near the circumference. Small nails may be used in addition at extreme top and bottom portion of the tyre ring throughout the circumference for fixing purpose keeping free the teeth impression portion of tyre ring for driving alternator pinion. Bicycle alternator is located at the base of the arrangement. The supporting frame of the mechanism is fabricated by 3/4thinch M.S angle and thick M.S strips. Output of the alternator is converted to DC current through a rectifier (diode) and stored in a 12volt small motorbike battery. The whole system is shown in the sketches.

<Approximate Cost Estimation

1. 3/4th inch thick hot pressed ply wood piece- 2.25ft x 2.25ft @Rs.35 per sq.ft- Rs.185

2. Rickshaw bearing- 1No- Rs.45

3. Bicycle tyre (cotton tyre)- 1No. costs Rs.80, considering only one tyre Required for making two chargers- Rs.40

    4.   Flanged Axle-                                                                                                     Rs.30                                                                             
    5. M.S angle, M.S strips for supporting stand and alternator bracket- 3kg.
    @ Rs.38 per kg                                                                                                        Rs.114     
    6.   Bolt and pipe for handle-                                                                                    Rs.30
    7. Fabrication cost, i.e. welding work, charge of carpenter etc-                               Rs.150      
    8. Epoxy adhesive, nails, electric wire, diode and other Misc. items-                      Rs.40
    9. Bicycle alternator-                                                                                                Rs.250              
       (Bicycle lighting set includes alternator and headlight and
       total cost of the set is Rs.250)                              
 10. Storage battery, 12Volt, 2.5ampere hour capacity-                                              Rs.550
                                                                                                   Total Rs.1434, say, Rs.1450

Design. II-

In this design, complete front wheel assembly of bicycle, i.e. axle, wheel hub with ball bearing assembly, rim, spokes, tube and tyre is used in place of ply board disc. The system can be more accurately fabricated and a lot of fabrication work is eliminated in this design. In the design, bicycle alternator pinion is driven by inflated tyre teeth as driven in a original bicycle. But two demerits of the design are- time to time air pumping is necessary to inflate the tube and secondly, heavy ply board disc works as flywheel to achieve uniform rotational motion which is not possible by lightweight bicycle wheel unless additional weight is fixed with the wheel.

In this design, one end of the axle is firmly fixed with supporting stand keeping other end free. Two nuts with washers on axle thread rigidly hold the axle with vertical stand of the support by tightening the nuts from both side of the stand. As driving handle, long bolt with pipe as used in ply board design, are fixed with a cluster of rim spokes with the help of M.S plates provided at both side of the spokes. Plates are hold together by the help of nuts bolt system. Handle bolt is welded with plates. However, as the spokes are not straight and are remained in slightly inclined position so, the handle bolt is to be welded in such a manner that the bolt maintains parallel position with wheel axle. The design is shown in the sketches.

Approximate Cost Estimation

1. Hub and axle with bearing assembly- Rs.35

2. Set of spokes- Rs.27

3. Wheel rim- Rs.90

4. Cotton tyre- Rs.80

5. Tube- Rs.40

6. M.S angle, M.S strips for supporting stand and alternator bracket- 3kg.

   @ Rs.38 per kg                                                                                                          Rs.114 

7. Plates, nut bolts and pipe for handle- Rs.35

8. Fabrication cost- Rs.100

9. Misc. items- Rs.40

10. Bicycle alternator- Rs.250

     (Bicycle lighting set includes alternator and headlight and
      total cost of the set is Rs.250)                              

11. Storage battery, 12Volt, 2.5ampere hour capacity- Rs.550

                                                                                                   Total Rs.1361, say, Rs.1360

Pedal Power Operated Charger:

Freewheel pinion of rickshaw is used as wheel hub of the rotating disc of pedal powered machine. Freewheeling arrangement eliminates the requirement of continuous uniform pedaling during operation and makes the mechanism user friendly. Important specifications of a rickshaw freewheel are described here. Teeth height from base circle is approximately 0.28inch; gap in between teeth is 0.28inch at pitch circle, thickness of teeth is 0.2inch, width of the teeth is approximately 0.08inch and distance of base circle from freewheel hub, i.e. height of the solid disc plate below the base circle of teeth is 0.4inch. Width of the hub is 0.6inch.

2.5inch diameter hollow circle is cut around the centre of a 1/8th inch thick M.S disc of 2ft diameter. The hollow circular portion of the disc is mounted on outer circumference of the freewheel through 4 number of 1/4thinch diameter bolts and a retainer ring. The disc is mounted on one side of freewheel teeth and the retainer ring is located on other side of the teeth. Bolts are passed through the gaps in between teeth and firmly hold the disc and ring with teeth. A ring made of M.S strip is welded on the outer circumference of disc. Approximate total weight of the disc assembly is 9kg. Rubber pulley of electrical generator is driven by the outer M.S ring of the disc by frictional effect. Automobile rubber hose or rubber bush may be used as rubber pulley.

Freewheel pinion is mounted on the threaded portion of rickshaw rear axle hub socket as usual. Bicycle sprocket spindle diameter is 0.6inch and it is passed through the hub socket bore and the socket is fixed on spindle by tightening of socket bolts. So, the spindle is worked as the axle of driving disc. Bore of the socket is tapered having maximum diameter is 1inch at one end and then gradually reduced to 0.62inch to the other end. Necessary packing is so inserted inside of hub bore for proper holding of spindle. The spindle is supported by bearings just after the ends of hub socket. Two left side bicycle pedal crank are mounted at both right and left ends of the axle spindle rod.

A seating arrangement is made with a small seat formed by metal sheet with a backrest. 1inch M.S square pipes are used as standpipes. Two standpipes are welded with the seat and the other two standpipes act both as supporting stands of axle rod bearing housings of driving disc and for seating arrangement. Interconnections in between standpipes are also made through 1inch square pipes. Height of the seat from base and height of the driving disc are kept 3ft and 1.5ft respectively. Diagonal distance of minimum 2ft is maintained in between the mid portion of the seat and disc axle. The whole arrangement is shown in sketches.   

Approximate Cost Estimation (Cost of electrical generator and storage battery are not taken into account)

1. 1/8th inch thick M.S sheet for disc, 2ft x 2ft of total weight 8kg @Rs.45 per kg- Rs.360

2. 1/4th inch thick M.S strip for ring- 6ft length, 400gms per running ft @ Rs.38 per kg- Rs.91

3. Rickshaw freewheel pinion- Rs.35

4. Rickshaw rear axle hub socket- Rs.35

5. Bicycle sprocket spindle- Rs.20

6. Left side bicycle pedal crank with pedal, 2 No. - @ Rs.55 per set- Rs.110

7. 1inch M.S sq. pipes for support, 20ft length of weight 8kg, @Rs42 per kg- Rs.336

9. 1/8th inch thick M.S plate as seat and backrest- 1ft x 1ft, 2 pieces,

   of total weight 4kg @ Rs.40 per kg-                                                                           Rs.160

10. Bearings, bearing housing, retainer ring for disc,

     bolts, nuts and other Misc. items-                                                                            Rs.150

11. Cost of fabrication- Rs.200

                                                                                            Total cost Rs.1497, say Rs.1500