Template:425inprogress


Project Description

The purpose of this Mech425 project is to design a mechanically powered (Human powered) battery charger that will recharge low voltage batteries used for LED lighting. The reason it charges low voltage batteries is because a LED does not require much voltage to produce light. The lower the rated voltage of the battery that has to be recharged, the less work the human has to do in order to recharge it. The design should be efficient and cost effective to provide a means of charging batteries to those who may not be able to afford electricity and or those who are in areas where electricity is unavailable. The design should also be made of materials that are easily available.

This design utilizes materials that are scavenged from other applications. The proposed design is constructed from an old bicycle rim that is connected to a DC motor from an old printer via a belt that comes from the same printer. When the rim is manually spun it will cause the motor to produce an electric current which is needed to charge a battery. The proposed design is human driven but the overall design could be altered to use a source of power such as the wind to spin the motor, alleviating the need for a human to spin the motor.


Mechanically Powered Battery Charger
The Battery Recharger.JPG
Good Results.JPG

Introduction and Theory

This section is intended to give some insight into the technical background of the project to help understand the overall design.

A W is a device that converts stored chemical energy into electrical energy, and is a source of W. [1] The applications for a battery are endless, but for the purpose of this project they will be theoretically used as a power source for LED lighting. There are two broad categories of batteries: primary and secondary. Primary batteries are not rechargeable; once the chemical energy in the cell is depleted it cannot be restored by electrical means. Secondary batteries can be recharged by applying electrical energy into the cell. [2]

A W is a device used to put energy into a rechargeable (secondary) battery by forcing an electric current through it. [3] A mechanically powered battery charger uses human power to generate the electricity needed to create the necessary electric current to charge the battery.


Rotating Electric Machines

There are three basic classifications of rotating electric machines: Direct-current Machines, Synchronous machines and Induction machines. If a machine converts mechanical energy into electrical energy then the machineis acting as a generator. If the machine converts electrical energy into mechanical energy then the machine is acting as a motor. There are similarities with respect to all rotating electric machines in that the two main components are a stator and a rotor. The rotor rotates inside the stator and is separated by an air gap. The rotor and stator each have a magnetic core and windings to produce a magnetic flux (or use a permanent magnet as is the case of the stator in the DC motor used in this project). The rotor is fastened upon a bearing-supported surface and is either connected to a prime mover (if the rotating electric machine is a generator) or to a mechanical load (if the rotating electrical machine is a motor). The rotor is attached by means of chains, pulleys, belts etc. The speed of the motor is determined by the applied voltage and the torque of the motor is related to the electric current[4].

Producing Electricity with a DC Motor

A DC motor is generally used in applications that require accurate speed control [4]. The motor is connected to a power supply which provides electrical current to the windings in the rotor. When a current is passed through windings, a magnetic field is produced. This magnetic field causes the rotor to spin therefore creating useful mechanical work. These coils may also be used to induce a voltage if the reverse action is taken(rotor is manually spun and the DC motor acts as a generator). This can be explained by Faraday’s Law of Inductionwhich in short states that a voltage is induced by a changing magnetic field [4]. The presence of the magnetic fields makes it possible to produce an electric current and generate power.

A magnet also produces a magnetic field where the strength is quantified by:

Magnetic flux ϕ and magnetic flux density B, units of weber (Wb) and tesla (T) repectively. [1 T = 1 Wb/m2 and Wb=1V/s]

A magnetic field is generally represented by lines, and the strength of the magnet can be visualized by analyzing the density of these lines. By definition the magnetic field lines travel from north to south [4].

Charging a Battery

The motor must be able to produce enough voltage to charge the battery. For example if the rated voltage of the battery is 5 V then the motor must be able to produce at least 5 V. It also must be able to generate enough current so that the time required to charge the battery is lowered. The larger the amperage the shorter time will be required to recharge the battery. Rechargeable battery capacity is rated in mAH (milliampere-hours). The total capacity of a battery is defined as "C", that is it can supply C mA for 1 hour, or 2C for 30 minutes etc.[5] The rate of charge is determined by how much electrical current is allowed into the battery by the battery recharger [6]. The charge current depends upon the technology and capacity of the battery being charged [3]. As a general rule, to arrive at an appropraite charge rate, the capacity of the batter should be divided by 10 (this is called the C/10 rate). There are however charge rates as high as C/3, but this charge rate will only be maintained for a short period of time. [7]. To find the recommended charge rate one should contact the battery manufacturer.

A battery rated at 150 mAh (the one used in this design) can theoretically sustain a 15 mA discharge current for 10 hours (150 mAh/ 15 mA). Some LEDs only require 15 mA to run.

However it is very important to note that the battery is not overcharged, nor should it be charged at a rate that the battery cannt handle. If the battery is overcharged it may explode.make. It is important to understand the parameters involved in charging a battery before making a battery charger.

No battery will last forever as they wear out and will eventually need to be replaced [7], however rechargeable batteries are a great way to reduce cost and waste. [6] One downside to batteries is that when they do need to be replaced they contain toxic materials and should be disposed of properly [7]. To avoid shortening the life of a battery considerable, the battery should not be completely discharged before being recharged. [6]

Construction

This is an outline of the parts, tools and steps required to construct the prototype design. The design consists of a wheel that is rotated by hand that is connected to a DC motor. The motor is connected to the battery and when the wheel spins it provides electricity to the charge battery.

Parts List and Cost

Table 1: Parts List
Part Required Units Total Cost (CAD)
DC Motor

(capable of producing enough V to charge battery)

1 $0.00
Belt 1 $0.00
Old Bicycle Rim 1 $0.00
Nails ~12 #
Scrap Wood (see construction section) #
NiMH Battery (4.8 V, 150 mAh) 1 $13.95 [8]
Copper Wire 6 inches to a Foot #
Diode 1 #
Resistor (120 Ohm) 1 #
Lengths of wire - $0.00
Alligator clips 2 $3.10 [8]
Electrical Tape ~1 foot $2.79 per roll [9]

Note:

The DC motor and corresponding rubber belt were removed from a EPSON Stylus CX3810 printer that no longer functioned properly. There were 3 motors in the printer (2 DC and one stepper). The motor that ran the cartrige feeder was used as it has the gear connection already attached to fit the corresponding rubber belt. The lengths of wire were also extracted from the printer. The bicycle rim was found in a scrap yard, the bearings in the rim were still in good condition and allowed the rim to spin freely. The rim does not have to be in the best condition, as long as it can spin freely on the axle (bearings should be in descent shape). There is no specific lengths/type of wood that need to be used, as long as there is enough material to allow the rim to be properly mounted and rotate freely as discussed below in the mounting the rim section (step 1). Because all of the above materials were salvaged the cost of the project was dramatically reduced. The most significant costs of the project will be due to the battery and the motor. Unfortunatley the DC motor from the printer was unable to be identified. To choose the right motor one should hook up the leads of the motor a voltmeter and manually spin the rotor. The voltage should be able to exceed the rated voltage of the battery that is planned to be used.

Tools

Table 2: Required Tools and Their Use
Tool Use
Digital Multimeter Measuring the V and A in the circuit. Very useful tool. Can also use analog voltmeters and ammeteres.
Hammer Nailing the rim supports to the base and mounting the motor to the base.
Drill Making the holes for the rim axle in the rim supports. If screws are available the hammer and nails can be replaced entirely by the drill and screws.
Utility knife Deconstructing the battery. Can also be used to strip wires.
Wire Strippers Strip the wire for proper connections. Can also very carefully use a utility knife.
Soldering Iron + Solder Connecting the wires in circuit (this was not used but it is a good idea if you plan to make a permanent circuit)

Note: One should be carful when using any of the tools listed above. Be sure to carfully follow the recommended procedures as outline by the tool manufacturers.

Performance and Discussion

The amount of current and voltage through the circuit is proportional to the rotating speed of the rim. The motor easily puts out the required amount of voltage needed to charge the battery and exceeds the amount of required current. This is why a resistor must be incorporated into the electrical circuit design.

The final prototype works althoguh there are many improvements to be made on the design. The most notable design change would be to have a better system to spin the rim such as pedal power or some sort of chrank lever system. A pedal powered design would allow for a significant increase in power to be input into the system and therefore an increase in the amount of electrcicty that can be produced.

Rather than using a voltmeter to regulate the voltage in the system, a simple voltage regultor chip could be implemented. Since the project is intended to be a practical technology this may not be a viable design change.

The most interesting design change would be to have the wheel spin by some other means than human power. If the design could somehow incorporate a waterwheel or small wind turbine blades to spin the rotor, it would grealty improve the overall effectiveness of the system in that someone would not have to waste time turning the rim and could focus on other tasks.

Building the Prototype

Making a New Battery

The reason this battery is being taken apart is because the recharger has to provide at least as much voltage as the battery to charge it. If the battery is 4.8V it would require one to spin the rim faster to produce enough voltage to charge the battery, so the battery will be turned into a 3.6V battery(which is easily capable of being reached at a moderate rotation of the rim). The battery will still have a 150 mAh capacity.

Figure 1: Prototype Battery Construction

Step 1. Original battery Step 2. Cut off outer layer Step 3. After outside layer cutoff
step1 step2 step3
Step 4. Separate two packs of cells Step 5. Remove final plastic layer Step 6. Fasten 3 cells together
step4 step5 step6

Step 1. This is a 4.8V, 150 mAh NiMH battery. NiMH batteries come in 1.2V cells which means that there must be 4 cells in this battery to produce 4.8V (4.8V/1.2V/cell = 4 cells). It cannot be seen in the picture but there is a small white connector on the end of the red and black wires (used for connect the battery to toy cars). This can be removed by cutting it off with wire cutters (or scissors or a utility knife) to expose the ends of the wires. It is important to not let the ends of the red and black wires touch eachother as they will short out the battery.

Step 2. Very carefully apply pressure to the middle of the battery with the utility knife to remove the outer casing of the battery. It is possible to see/feel where there is an air gap between the cells, this is where the outler layer should be cut.

Step 3. This is to show what the outside layer of the battery looks like. It is noted that there is still two casings left. Each case holds 2 NiMH cells (therefore they are 2.4V cases).

Step 4. Separate the two battery casings as well as the protective carboard layer end peices.

Step 5. Remove the final casing layers from the two casings with the utility knife to expose the individual cells. The two packs of individual cells are soldered together. One of the packs must be separated in order to create a 3.6V battery.

Step 6. Three cells are taped together. The battery should now be tested with a digital multimeter to ensure there is a proper connection of the cells.

Note: The red wire was removed in the prototype design although in retrospect it would be much easier to keep this attached to the battery. Also the cell with the black wire attached should have been installed in the pack of three rather than the other cell. This would produce a battery with a wire connection on each side of the battery virtually eliminating the need to make a battery holder

Making a Battery Holder

A battery holder is made to allow for an easy connection of the battery to the circuit.

Note(same as above): The red wire was removed in the prototype design although in retrospect it would be much easier to keep this attached to the battery. Also the cell with the black wire attached should have been installed in the pack of three rather than the other cell. This would produce a battery with a wire connection on each side of the battery virtually eliminating the need to make a battery holder.

Figure 2: Making a Battery Holder

Step 1. Cut Cardboard Step 2. Score Edges Step 3. Cut slits
step1 step2 step3
Step 4. Cut small flaps Step 5. Shows all Materials (other than tape) Step 6. Fold Foil
step4 step5 step6
Step 7. Fold Foil 2 Step 8. Fold Foil 3 Step 9. Fold Carboard
step7 step8 step9
Step 10. Finished Product Test It
step10 test


Step 1. Cut cardboard (use battery packaging if possible) into rectangular shape as shown in step 1. The length of the carboard is the length of the battery plus about a centimeter on each side (2 cm total) but the exact lenghth is not important. The width of the carboard is 3 widths of the battery. Mark the lines as shown in step 1.

Step 2. Score the marked lines with a pair of scissors or the utility knife. This is just a score to make bending the carboard easier, do not cut fully through the cardboard.

Step 3. Cut slits in the carboard as seen in step 3. The slits should be about 1 cm long.

Step 4. Cut about half a centimeter off the ends of the carboard as seen in step 4. This allows for proper dimensions when folded together.

Step 5. All the materials used for the battery holder excluding electrical tape are shown in step 5. This gives the relative dimensions of the materials used to make the battery holder. Strip both ends of two peices of wire to allow for a proper connection to the battery (wires are about 5 cm in length, strip about a centimeter off each end). Cut two rectangluar pieces of aluminum foil about 5 cm in length by 1 cm in width.

Step 6. Fold the foil in half making sure that exposed wire is folded into the aluminum foil.

Step 7. Roll the foil around the wire as shown in step 7. Try to make a 'rectangular' roll.

Step 8. Fold the foil lengthwise. (Repeat steps 5 through 8 for the other piece of wire)

Step 9. Fold the flaps of the cardboard. First fold the middle flap up then fold in the other outside flaps. Tape these in place. It is wise to tape it all together at once with the battery and two wires in place to ensure a tight fit (proper electrical conduction).

Step 10. This is what the battery holder should look like in the end. It is wise to test the final product before continuing to avoid problems with the circuit in the future.

Test It The test reveals the battery is working. The negative sign simply means the leads of the voltmeter were connected to the wrong sides of the battery. To fix this simply flip the leads of the voltmeter, although this is not a problem.

Mounting the Rim

Figure 3: Steps to mounting the rim

Step 1. Ensure Clearance Step 2. Cut Two peices the same length Step 3. Drill Axle Hole
step1 step2 step3
Step 4. Mount and Lock Step 5. Mounted Rim Step 6. DO NOT FORGET
step4 step5 step6

Step 1: It is important to ensure that there will be proper clearance between the wheel and the ground. This step shows the wheel being placed on a rim support to make sure that there is room from the wood to hold the rim up of the ground allowing it rotate freely.

Step 2: Once the length of the rim supports are checked, the two supports should be cut to the same length. It is not absolutely necessary to include this step, but it makes the final product look more appealing.

Step 3: Drill a hole the same diameter of the axle of the rim through both of the supports simultaneously. Be sure to line up the ends of the support that will be touching the ground so that when the holes are drilled and the axle is inserted, it is horizontally alligned with the ground. (refer to the picture in step 5)

Step 4: The rim came with nuts attached to the axle. These should be fastened to the axle to hold the wood supports in place. (If the hole diameter is slightly smaller than the axle diameter then the supports will have to be threaded (screwed) onto the axle alievating the need of attaching the nuts. )

Step 5: The mounted rim should be able to stand freely on the ground although it tips easily without the base secured. The step 5 picture is to show that there is clearance between the rim and the ground (there is about 10 centimeters of clearance from the rim to the ground).

Step 6: Do not forget this step. Be sure to pull the rubber belt under the support on the side of the rim that it will be attahced to. Once the base is secured to the supports there will be no way to fasten the belt to the axle.

Figure 3: Steps to mounting the rim (creating the base)

Step 7a. No base Step 7b. Fitting in the pieces Step 7c. Full Base
step7a step7b step7c

Step 7a,b,c Use scrap wood to create a base upon which the motor can be mounted. Be sure to build the base long enough to hold the motor at a distance that will cause the belt to be taught to increase the efficiency of the system. (The tighter the better, but dont get carried away and snap the belt.) The base provides support for the overall structure. Simply nail the supports to the base. Be sure before you nail the pieces together that the belt it still around the axle in between the support and the rim as once it is nailed together there is no way to attach the belt to the axle.

Mounting The Motor

Figure 4: Steps to mounting the motor

Step 1. Pull belt taught Step 2. Mount the motor Step 3. Side view of mounted motor
step1 step2 step3

Step 1: Pull the belt taught and position the motor on the base. The belt should be positioned to make a 90 degree angle with the axle of the rim.

Step 2,3: The motor is mounted with 4 nails and some copper wire. The four nails were first slightly tapped into the base to be sure the position of the motor was proper. Then the copper wire was wound in the criss cross pattern shown and then the nails were tapped further into the base to secure the copper wire to the top of the motor and hold it firmly in place. It is important that the motor is help firmly in place and does not move at all. The side view of the mounted motor shows what the system will look like up until this point.

Wiring the charger

Firsty the proper current direction must be established. For ease the red wire was chosen to be positive. Hook the voltmeter up to the red (positive) and black wires of the voltmeter and spin the rim to to determine which direction gives a positive voltage. Mark this on the support as shown in figure 5.

Figure 5: Mark the direction on the rim support.


Some calculations need to be done to determine which resistor will be incorporated into the circuit.

This charger will use a charge rate of C/5 to be safe. This means it would take 5 hours to charge a fully discharged battery. Thankfully the battery is not completely depleted so it will not take this long to fully charge the battery.

Ohm's Law is needed to determine the resistor value required to keep the current at an acceptable rate for battery charging.

Ohm's Law -> V=IR

Where V is the voltage in volts, I is the current in amps and R is the resistance in ohms.

Since we are using a charging rate of C/5 this means that for 5 h the charge rate will be 30 mA. If the voltage has to be ~ 3.6V to charge the battery then we can rearrange the equation and solve for R. (watch the units as the current is in mA therefore divide the mA value by 1000 the get A. Rearrange V=IR to R=V/I and sub in the numbers 3.6V/0.030A = 120Ω (ohms).

Go here to find the colour of the proper resistor resistor colour guide

If there is not a resistor for this value you should normally round up to the next standard resistor to add a factor of safety into the design. However since we have already incorporated a factor of safety into the design by charging at a rate of C/5 a 100 ohm resistor will work fine as it gives a charging rate of (3.6V/100Ω = 0.036A = 36mA) which gives a chargig rate of ~C/4.16. This is okay for the prototype although one should contact the battery manufacturer to get the optimum charge rate.

The circuit diagram for this battery recharger is shown in figure 6.

Figure 6: Circuit Diagram from Mechanical Recharger

Future Work

Optimization of the hand cranked system.

Water wheel design.

Pedal powered design.

Relevant Links

Here are some relevant links for pedal powered designs. After building this prototype it was decided that a pedal powered design would be more efficient.

[pedalpower.com] [10]

[Alternative Energy News][11]

[You Tube Clip] [12]

References

  1. Answers.com,"Storage Battery",http://www.answers.com/topic/battery-electricity,Accessed April 10, 2009
  2. Wikipedia, "Battery (electricity)", http://en.wikipedia.org/wiki/Battery_(electricity), Accessed April 10, 2009
  3. 3.0 3.1 Wikipedia, "Battery Charger", http://en.wikipedia.org/wiki/Battery_charger, Accessed April 10, 2009
  4. 4.0 4.1 4.2 4.3 Storey, N. (2006). Electronics A Sytems Approach 3rd Edition. Hampshire: Pearson Education.
  5. Intelligent NiCd/NiMH Battery Charger - Construction Project http://www.angelfire.com/electronic/hayles/charge1.html Accessed: April 09, 2010
  6. 6.0 6.1 6.2 How Stuff Works, "How Batteries Work",http://electronics.howstuffworks.com/battery4.htm Accessed April 08, 2009
  7. 7.0 7.1 7.2 Energy Alternatives Ltd., "Battery Chargers" http://energyalternatives.ca/SystemDesign/chargers1.html Accessed: April 07, 2010
  8. 8.0 8.1 Leading Edge Hobbies, http://www.leadingedgehobbies.com/oscommerce/catalog/default.php, Accessed: Aprile 10,2010
  9. Home Depot, http://www.homedepot.ca/, Accessed: April 10, 2010
  10. Pedal Power.com,http://www.pedalpowergenerator.com/, Accessed: APril 09, 2010
  11. Alternative Energy News,"Pedal Powered Electricity Generator from Windstream",http://www.alternative-energy-news.info/pedal-powered-electricity-generator-windstream/, Accessed: APril 09, 2010
  12. You Tube, "Mobile Pedal-Powered Generator",http://www.youtube.com/watch?v=wcY1ADGcrfs, Accessed: April 09,2010
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