Green mechatronics project pelton wheel

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GREEN MECHATRONICS PROJECT: PELTON WHEEL DRIVEN MICRO-HYDRO PLANT by William Bolon 2934356 Vasu Sharma 4540214 Manjot Singh 5116484 Submitted to Dr. Riadh Habash for the course Electric Circuits and Machines for Mechanical Engineering (ELG 2331) University of Ottawa March 16, 2010

Transcript of Green mechatronics project pelton wheel

Page 1: Green mechatronics project pelton wheel

GREEN MECHATRONICS PROJECT: PELTON WHEEL DRIVEN MICRO-HYDRO PLANT

by William Bolon

2934356

Vasu Sharma 4540214

Manjot Singh

5116484

Submitted to Dr. Riadh Habash

for the course

Electric Circuits and Machines for Mechanical Engineering (ELG 2331)

University of Ottawa

March 16, 2010

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Part I Design of a Pelton Wheel Driven Micro-Hydro Plant 1.0 Introduction: The purpose of this project is to gain familiarity with combined Electrical and Mechanical applications sometimes known as Mechatronics. The project will consist of the design of a theoretical micro-hydroelectric plant used in off grid applications to generate “Green” power for isolated cottages or farms. Then a working model of the system will be constructed in order to test the design. Finally the maximum load of the system will be measured through experimentation. 2.0 Basic Working Values To provide power to the water turbine, our calculations will be based on residential water pressure to act as the prime mover. Residential pressure can vary depending on several factors, including: distance and elevation difference from the water reservoir, age of the pipes, leakage in the municipal water network, level of impurities present, etc. For a North American home, the average water pressure will be between 45 to 80 psi, with some extreme cases reaching from 30 to 115 psi. For calculation purposes, we will assume the low end of acceptable pressure and use 45 psi. The flow rate will be determined experimentally, but based on the North American residential standard, a ½ inch copper pipe. 2.1 Hydraulic Head In hydroelectric projects, calculations are based on the available hydraulic head. This is a measurement of the difference in elevation between the water source and the turbine. For this project, we will calculate the theoretical hydraulic head based on the available water pressure. Residential Water Pressure 45 psi 1 psi = 6894.757 Pascal Therefore 45 psi = 3.1 x 105 N/m2

In order to calculate the hydraulic head, we use the simplified Bernoulli’s equation of incompressible fluids and assume that the pressure at the surface of the water supply is negligible.

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Head (m) = [Final Pressure (N/m2) – Initial Pressure (N/m2)] / Specific Weight of Water Specific Weight of Water = (10000 kg/m3)(9.81 m/s2) = 9810 N/m3

Therefore Net Head = [(3.1 x 10^5 N/m2) – (0)] / 9810 N/m3

Hn = 31.62m 2.1 Flow Rate q: The second fundamental value to be derived is the amount of water available through the pipe, known as the flow rate. To measure the flow rate, the water supply was opened, and the amount that flowed out in 10 seconds was collected in a large bucket. Once the experimental time had elapsed, the contents of the bucket were measured by pouring it into a measuring cup. The following is a summery of the calculations 3.75 L in 10 seconds 0.375 L/s q = 3.75 x 10-4 m3s-1

2.3 Basic Calculation of Available Power Once the hydraulic head and flow rate have been established for our theoretical micro-hydro project, a ballpark value of power is calculated in order to derive the requirements of the generator. The following formula was used Power (kW) = [Flow Rate (m3s-1)]x[Hydraulic Head (m)]x[Gravity(ms-2)]x[Density of Water (kgm-3)]x[Efficiency (%)]x[1/1000] Or P(kW) =q(m3s-1) x Hn(m) x g(ms-2) x ρ(kgm-3) x η(%) x [1/1000] As this calculation is just designed to give us our upper limit, we will assume an efficiency of 100% P(kW) =3.75 x 10-4(m3s-1) x 31.62(m) x 9.81(ms-2) x 1000(kgm-3) x [1/1000] = 0.116 kW Or 116 Watts

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3.0 Choice of Generator Three main factors where used in choosing a generator for the project: cost, rate of rotation, and available power. The maximum available power was calculated above to be 116 watts. This means that for safety reasons, the generator should be rated for at least a minimum load of 116 watts, or we run the risk of overheating. With the minimum power set as a limiting factor, the following choices were considered. 3.1 Dedicated Electric Generator Specialty electric generators of the scale needed for this project, though available, are far too expensive to be considered, and were rejected based on their price. 3.2 AC Motor repurposed to work as a generator AC induction motors are by fare the most common midsized (1/5 HP) to large (5 HP) electric motors available. Finding an inexpensive second hand unite available for the project would be simple. But induction motors do not use permanent magnets, as such, a large capacitor is often required to “jump start” the induction process if the motor is to work as a generator. Because any information other than what is printed on the motor is almost impossible to find on second hand motors, repurposing a second hand AC motor with a starter capacitor was considered too difficult, and outside the scope of the project. 3.3 Automotive Alternator Car alternators are comparatively simple to use and very affordable when purchased second hand, but they are usually ratted at around 800 watts, which is far too large for our application. 3.4 DC Motor repurposed to work as a generator A permanent magnet DC motor will work perfectly as a generator without any changes to its design. As such, this option was considered perfect for our application. 3.4.1 High Voltage VS Low Voltage permanent magnet DC Motors High voltage permanent magnet DC Motors are highly coveted by wind turbine enthusiasts as generators. The reason has to do with the rate of rotation required to generate electricity. Because wind turbines do not spine very quickly without the use of gearing, low rpm generators are required for these applications. But low rpm permanent magnet DC motors are fairly rare, and as the load increases, the speed at which the

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generator must turn increases faster than it does with high speed/low voltage generators. The following graph produced by pedalpowergenerator.com summarizes this point. Graph #1.1: RPMs required to Maintain 12v VS Load Power for a 12v and 180v Motors

As can be seen from the graph, though the high voltage generator (white line) requires less RPMs at a very low Load, at any reasonable power output it requires many times more RPMs than the low voltage generator (red line). A limited rate of rotation is only a problem for wind turbines, because the rotational rate of a water turbine is a product of the water velocity and the diameter of the wheel. The result is that a relatively low voltage permanent magnet DC motor rated at least 116 watts is required. 3.4.2 Chosen Motor The motor chosen was a second hand 12v Automotive Blower Motor ($10). No other information was available but a survey of similar brand motors reveals that the motors are rated at 120 watts, and between 2000 to 3000 RPMs.

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4.0 Designing the Water Turbine In a very basic sense, water turbines can be separated into two broad categories: reaction turbines that act on a change in pressure in the flow of a fluid, and impulse turbines that are put in motion by the impact of a water jet against a paddle or runner. The precise nature of the application is used to judge which of the many turbine designs is ultimately used. In general, reaction turbines require a very high level of precision between the impeller and its housing, as any gap between the two will result in a much lower efficiency. This requirement for a high precision housing makes the construction of a reaction turbine impractical for this project. The result is that an impulse turbine, specifically a Pelton Wheel was chosen for the turbine design. 4.1 The Pelton Wheel A Pelton wheel is constructed of double cup runners that receive the impact from a high pressure water jet and convert it into rotational movement. The runners are contoured to split the water flow into two halves and reflect both halves backwards, thus maximizing the efficiency of the transfer of energy. Unlike other turbine designs once common in pre-industrial applications, the runners are not meant to hold fluid, rather to expel it, as gravity plays no real part in the collision and subsequent transfer of energy. The design and dimensions of an ideal Pelton wheel can be calculated from the basic specifications already calculated above. The following is a summery of the pertinent information. Hydraulic Head: Hn = 31.62m Flow Rate: q = 3.75 x 10-4 m3s-1 Rotation: 2000 to 3000 RPMs 5.0 Design of the Pelton Wheel The design of the ideal Pelton Wheel can be separated into three categories: calculating the ideal water jet width, calculating the ideal diameter of the wheel, and calculating the dimensions of the runners. In the first two cases, the calculations will be based on the initial characteristics summarized above, while the shape and dimensions of the runners will be determined primarily by the calculated width of the water jet. The calculations used to generate the shape and dimensions of our Pelton Wheel were all based on those found in: MHPG Series, Harnessing Water Power on a Small Scale, Volume 9 Micro Pelton Turbines; published by SKAT, Swiss Centre for Appropriate Technology, 1991.

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5.1 The Ideal Width of the Water Jet The width of the water jet used is an important factor that will help to establish the physical shape of the Pelton Wheel runners. The width of the water jet determines the flow speed of the fluid impacting the runners and is based on the available Hydraulic Head. The following calculations are used to design the water jet width. Calculation 1.1: Absolute Velocity of the Water Jet c1: (ms-1) Absolute Velocity of the Water Jet c1: (ms-1) Nozzle Coefficient; kc (0.96 to 0.98) assume worst case 0.96 Gravitational Constant: g (9.81 ms-2) Hydraulic Head: Hn (m) c1 = kc (2 g Hn)½ = 0.96 ( 2 x 9.81 x 31.62) ½

= 23.67 m/s Calculation 1.2: Optimal Jet Diameter: d (m) Optimal Jet Diameter: d (m) Flow Rate: q (m3s-1) Absolute Velocity of the Water Jet c1: (ms-1) d = (4q/πc1) ½

= [(4 x 3.75 x 10-4)/( π x 23.67)] ½

= 4.5 mm

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5.2 The Ideal Diameter of the Pelton Wheel The Ideal Diameter or Pitch Circle Diameter is the width of a circle calculated from the point of impact of the water jet. The water jet impacts the runners towards the back of the scoops, so the real diameter or Outside Diameter will be slightly larger. The Pitch Circle Diameter along with the width of the water jet will determine the speed of rotation and the torque on the wheel. The reason for this is that the jet width determines the speed at which the water strikes the wheel, while the larger the wheel, the larger the moment arm, but the slower its rotation. Based on the chosen generator and the expected load, the Pitch Circle Diameter will be designed to produce 2500 RPMs. Calculation 2.1: Optimal Peripheral Velocity: u1(ms-1) Optimal Peripheral Velocity: u1(ms-1) Coefficient after Impact: ku (0.45 to 0.49) assume worst case 0.45 Hydraulic Head: Hn (m) Gravitational Constant: g (9.81 ms-2) u1 = ku (2 g Hn)½ = 0.45 ( 2 x 9.81 x 31.62) ½

= 11.097 m/s Calculation 2.2: Pitch Circle Diameter: D (m) Pitch Circle Diameter: D (m) Rotational Speed: n0 (2500 RPM; see above) Transmission Ratio: i (Assume 1:1 ratio of turbine to generator turns) Optimal Peripheral Velocity: u1(ms-1) D = (60 u1 i) / (π n0) = (60 x 11.097 x 1) / (π x 2500) = 0.0847 m Or 8.5 cm

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5.3 The Physical Dimensions of the Runners The dimensions of the runners are calculated based off of the width of the water jet. The following formulas were used based on established standards. The meaning behind these measurements can be obtained from the following diagram.

Figure #1.1 Ideal Dimensions of a Pelton Wheel Runner

Calculation 3.1: Bucket Width: b (mm) b = (3.2)d = (3.2)(4.5) = 14.4 mm Calculation 3.2: Bucket Height: h (mm) h = (2.7)d = (2.7)(4.5) = 12.15 mm

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Calculation 3.3: Cavity Length: h1 (mm) h1 = (0.35)d = (0.35)(4.5) = 1.6 mm Calculation 3.4: Length to Impact Point: h2 (mm) h2 = (1.5)d = (1.5)(4.5) = 6.75 mm Calculation 3.5: Bucket Depth: t (mm) t = (0.9)d = (0.9)(4.5) = 4.05 mm Calculation 3.6: Cavity Width: a (mm) a = (1.2)d = (1.2)(4.5) = 5.4 mm Calculation 3.6: Offset of Bucket: k (mm) k = (0.17)d = (0.17)(4.5) = 3.4 mm

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5.4 Working Values for the Pelton Wheel Once the ideal values had been calculated, a times two safety factor was used to produce the working values. The following table summaries the working values.

Figure #1.2 Working Dimensions of a Pelton Wheel

b = 28.8 mm h = 24.3 mm h1 = 3.2 mm h2 = 13.5 mm t = 8.1 mm a = 10.8 mm k = 6.8 mm D = 85 mm d = 4.5 mm

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Part II Construction of the Prototype Pelton Wheel Runners Creating the Master Pattern: The prototype runner was carved out of balsawood. This model was then used as the master pattern for the mass-produced runners.

The balsawood runner was then water sealed using urethane lacquer to prevent it sticking to the mold material. To allow the balsawood runner to be removed easily from the mold, it was covered in a thin layer of wax.

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Creating the Formwork for the Mold Blanks: A plywood box was bought from the dollar-store, and its bottom and lid were removed making it open at both ends. This box was used as the formwork to enclose the plaster mold. Like the balsawood runner, the plywood formwork was water sealed with urethane lacquer along with a wooden working surface that would act as the bottom. The inside of the box was then covered with a thin blue sponge to make removing the plaster mold simple. To protect the sponge, a layer of wax paper was added.

Making the Lower Molds: Thin pieces of wax were kneaded until they were soft, then they were stuck to the bottom of the master pattern adhering it to the working surface. More wax was used to plug up any holes that existed around the perimeter of the pattern. Excess wax was removed with an X-Acto knife.

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The front opening where the cavity is located (a x h1 on the plans) was plugged with a large contoured wedge. This wedge both plugged up the hole, as well as acted as an alignment mark for the top half of the mold. In addition to the wedge, two half hemisphere balls of wax were added on either side of the flange to act as alignment groves.

A thin piece of wax was added to the bottom of the formwork box that adhered it to the working surface. With the formwork stuck in place, a wax cone was added between the ends of the flange up to the edge of the box. This acted as an opening to pour the epoxy resin into the mold.

Use a paintbrush, a thin layer of petroleum jelly was added to all surfaces within the box, including the wax paper that lined the sides. This layer acted as a parting agent preventing the plaster from sticking to either the mold or the balsawood pattern.

A pre-measured portion of one part water to two parts Plaster of Paris was mixed in a small bowl using a spatula. When mixed, it was poured into the mold.

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In order to remove air bubbles trapped within the mixture, the side of the mold was agitated by hitting it lightly with a small hammer. Once most of the air was out, it was left to dry for 45 minutes.

When it was dried, a drywall spatula was used to peal off the mold from the working surface. The master pattern was then removed from the mold with an X-Acto knife. With the balsawood runner out of the mold, the mold was left to finish drying for one day. The whole process was repeated for three molds just in case one mold was to fail later on in the production. Cleaning up the Lower Mold When the lower mold was dry, many of its edges were rough where they touched the formwork, and the surface of the mold was marked with brushstrokes from the petroleum jelly.

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A file was used to smooth out the sides of the lower mold leaving a small 45 degree wedge along its perimeter. This wedge was used to help separate the two halves of the mold later on. Fine sandpaper was then used to smooth out any rough edges made by brushstrokes left in the petroleum jelly. The sandpaper was then used to make sure that the alignment marks were deep and without jagged groves. Finally, small holes inside the surface of the mold were patched up with plaster.

Making the Upper Mold: The mold formwork was then forced over the upper part of the mold with enough left over at the top to contain the upper portion of the mold. Like with the lower half, petroleum jelly was brushed over all the surfaces. The master pattern was then added to its grove in the lower mold. The wax that was used to make the entry-hole in the bottom half was place back into the mold. Afterwards, petroleum jelly was again brushed over the master pattern and the wax.

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The plaster was mixed and poured over the lower surface of the mold. Again the sides were agitated by hitting them lightly with a small hammer. Once complete, the mixture was dried for 45 minutes. The mold formwork was then forced off, and a drywall spatula was used to separate the two halves of the mold. The master pattern was then removed from the upper half of the mold, and the mold was left to dry for one day. Again the process was repeated for the three molds. Cleaning up the Upper Mold As with the lower half, the brushstrokes left on the inside portion of the mold were carefully sanded away, and any damage or air pockets were fixed with wax. Pouring the Epoxy Resin Air channels were added to the lower mold by cutting thin lines with an X-Acto knife. These lines extended from the end of the scoops to just below the alignment marks. As before, all surfaces were coated with a thin layer of petroleum jelly to prevent the epoxy from sticking to the plaster mold.

The two halves of the mold were connected, and tied closed with masking tape. A measured amount of epoxy resin was then mixed with the hardener in a plastic up. Once mixed, the mixed compound was slowly poured into the three molds through the opening holes at their tops.

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When the hole was filled, it was left to stand for two hours. At this point, the epoxy was dry, but not completely hard. The masking tape was removed, and the two halves of the mold were cracked open. The partially solid epoxy pattern was removed from the mold, and left to harden on a sheet of wax paper.

Preparing the mold for a subsequent pouring Once the epoxy pattern was removed, all remaining smudges of epoxy resin were removed with an X-Acto knife. Any damages made during the opening of the mold were repaired with wax, and a layer of petroleum jelly was reapplied to the surface of the mold. The two halves of the mold were held in place with a new layer of masking tape.

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Cleaning up the Epoxy Patterns When the epoxy patterns were removed from the molds, they were attached to extra material that either formed in errors in the mold that developed as the molds degraded with use, or were from necessary features like the air holes. In either case, these errors were removed through several steps.

The first step was to use an X-Acto Knife to remove the unwanted imperfections, including the area at the end of the flange where it joins the opening hole, and the air holes.

The second step was to sand the surface of the epoxy pattern with fine sand paper. This removed any small bumps caused by air holes left in the plaster mold. The third stage was to polish the epoxy pattern with a Dremel tool. The three stages are illustrated in the following picture.

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Each runner was polished with the Dremel tool, and then washed in soap and water to remove any petroleum jelly still attached to the pattern.

In total, twelve epoxy runners were made, though only the best eight were chosen.

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Part III Construction of the shaft coupling The details of the DC motor used as the generator can be found in part I of the report, but in summary, a used permanent magnet 120 watt 12 volt automotive DC blower motor was chosen.

The particular model chosen was due primarily to its extremely low price. Unfortunately this motor turned out to be from a Japanese or European car, as it had a metric shaft. After an exhaustive search of local Ottawa businesses, no coupling could be found to fit its unusual 7 mm shaft. The result was that an imperial coupling of ¼ inch was machined to a diameter of 9/32 or 7.143 mm.

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Holes were then drilled to attach the coupling to the disc portion of the peloton wheel.

Part IV Construction of the Acrylic Disc (and Redesign) The original design called for each of the Pelton Wheel’s runners to be mounted on a large acrylic disc. An early estimate for the size of the wheel was set at 20 cm in order to keep the speed of rotation bellow 1000 rpms, which at the time was considered a safe speed. As such, two large 20 cm acrylic wheels were constructed to sandwich the epoxy runners.

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Before the wheel was assembled, a test of the motor/generator was run buy attaching the shaft of the motor to a cordless drill and its leads connected to a multi-meter. It was shown that the relatively high running rate of the motor (2000 -3000 rpm), meant that it produced very low voltage at the low speeds produced by the drill. The result was that more investigations into the ideal running speed were made, and ultimately the diameter of the wheel was made smaller, (8.5 cm; see part I of the report for details). With a much smaller diameter, any imperfections in the wheel would be far more damaging to the alignment of the runners than it would have on a larger wheel. The result was that a more accurate method for constructing the wheel was developed. The wheels were first cut out of the acrylic sheet with a saw just as they had been with the larger discs.

They were then mounted on a machine screw roughly the diameter of the motor shaft, and held in place with washers and rubber gaskets.

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The acrylic discs were then spun on a drill press held between a bench-clamp. A file was held against the side of the bench-clamp, and the clamp was slowly tightened so that it acted like a lathe.

In this way, the wheels were sanded to a smooth round finish

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Part V Redesigning the Pelton Wheel Runners As a result of the change in the diameter of the wheel, the flanges attached to the runners are much too large. A systematic method for accurately cutting the flanges was then developed. A wooden rig was constructed to hold the runners by their flange. Saw lines were cut into the rig, allowing each runner to be cut in exactly the same way. In this manner, a close uniformity was maintained among the runners.

The following picture illustrates a cut flange next to one with just score lines.

The following picture illustrates the uniformly cut flanges.

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Part VI Mounting the Runners on the Wheel After the runners were cut, it was clear that with the smaller diameter wheel and its resulting high speed of rotation, any unbalance in the wheel would cause vibrations that might result in damage. As a result, extra care was taken to ensure that the wheel was as balanced as possible. This meant that the original plan of using the acrylics discs to sandwich the runners was considered too inaccurate and a new procedure that could place each runner accurately was conceived. Precision Mounting of the Runners in the Radial Plain: Though the acrylic disc would not be used for structure, it was used to act as a mount for the runners. The hole in the disc would act as a marker for the centre of rotation, while the machine screw attached through the hole would mark the axis perpendicular to the plane of rotation. Before each of the runners was cut, a line was drawn on their flanges to indicate the radial centre line.

In order to line up these center lines on the acrylic disc, radial lines were scratched onto one surface of the disc.

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A stack of washers was then added to the center of the wheel. Unlike the acrylic disc and machine screw, these washers would be glued permanently inside the wheel. The washers served two purposes: to preserve the axis of rotation after the acrylic disc and the machine screw were removed, and to act as a spacer to ensure that each runner was positioned the same distance from the centre of rotation, i.e. the diameter of the washer. Wax was then added between the radial lines so that they could temporarily hold the runners without covering up the guide lines.

Each of the runners was then stuck onto the wax. The first step was to line up the runner’s centre line with the radial lines on the acrylic disc. Because the disc is transparent, this was accomplished by looking through the disc and sliding the runner until its center line completely matched the radial line scratch on the opposite side of the disc. This ensured that each runner was exactly spaced in the radial plane. The second step was to make sure that the ends of each runner was pushed tightly against the washers. This ensured that each runner was exactly the same distance from the shaft.

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Precision Mounting of the Runners in the Vertical Axis: At this stage, steps had been taken to ensure that the wheel was radialy spaced, but for the wheel to act correctly as a Pelton Wheel, the centre ridge of each of the runners must be able to split the water jet. This means that each runner’s ridge must be placed exactly parallel with the plane of rotation. To accomplish this, the acrylic disc holding the runners was held in a drill-press by the machine screw. This setup enabled the disc to be turned through the axis of rotation. A laser level was then clamed in place at the level of the water jet.

The angle of each runner was then adjusted so that its center ridge came in contact with the laser line.

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Gluing the Runners into the Wheel: Once each of the runners was properly positioned in the horizontal, vertical, and radial directions, they were held in place with a layer of epoxy resin. This was accomplished by simply applying a thin layer while the wheel was still held in the drill-press. After the runners were held in place, wax formwork was added to the sides of the acrylic disc, and a structural layer of epoxy resin was pored on the top surface.

Once the top surface had hardened, the machine screw and acrylic disc was removed from the bottom surface.

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The wax was then carefully removed with an X-Acto Knife. To ensure that absolutely no wax remained to interfere with the gluing of the bottom half, the wheel was immersed in hot water to melt off any small specs of wax.

The acrylic disc was then reattached with the machine screw. A strip of cardboard was wound around it to act as formwork for the final poring of epoxy resin.

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Part VII Cleaning and Painting the Wheel At this point, the structure of the wheel had been pored, and 24 hours had passed giving the epoxy resin time to cure. As with the initial molds, a knife was used to remove large imperfections or drip marks, and a buffing wheel was used to clean up the surface for painting.

After the wheel had been cleaned and polished, a primer coat was added. Once dry, any drip marks were sanded away.

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The shaft coupling was then temporarily attached to the wheel by the machine screw. The coupling was oriented so access to the shaft screw could be reached between the runners. Holes where then drilled through the epoxy disc to hold the coupling to the wheel.

The wheel was then painted to provide a protective layer to the finished wheel.

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The shaft coupling was then attached to the finished wheel with 1/8 inch machine screws.

The machine screws were then bolted at the bottom of the finished wheel

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Part VIII Construction of the Generator Mount The basic idea for the generator mount was to design it in such a way as to allow for maximum access to the wheel. As such, the structural part of the machine consists of a single piece of plywood, with the remaining parts: wheel housing, generator, and the legs, simply being bolted to it. The generator mount was constructed from one piece of plywood, with a hole cut in the centre for the generator. Holes were drilled along the perimeter in order to attach the wheel housing. In addition, four small holes were drilled at the corners to be used as pilot holes to attach the legs that would eventually support the completed machine.

In order to waterproof the bottom of the mount, the back of mount has a piece of acrylic sheet glued to it.

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In order to waterproof the outside of the machine, all wooden parts were painted with varnish.

Part IX Mounting the Generator To make sure that the shaft of the generator is mounted at the exact center of the hole, paper was wrapped around the shaft to a thickness just smaller than the hole.

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Bolts were added so the built in flange around the generator lined up with the plywood.

Holes were predrilled, and the generator mounted with three short screws.

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Part X Waterproofing the Generator The electric motor used to create the generator is open at the bottom to help cool the motor during operation. Unfortunately this puts the generator in danger of becoming wet. In order to waterproof the shaft hole, a ring of wax was placed around the hole.

On top of the wax ring was placed a shaft collar with a small sponge ring cut from a dishtowel. The shaft collar will prevent any water from directly hitting the hole. By soaking the sponge in oil, any droplets of water that find there way to the wax-ring/collar interface will hopefully be repelled by the thin layer of oil.

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Part XI Building the Wheel Housing As mentioned above, one of the benefits of the Pelton Wheel is that it does not need to have a precision wheel housing. To design the housing, two things were taken into consideration: it must be easily removable in order to give maximum access to the wheel, and it must make a watertight seal when attached. The wheel housing consists of a large acrylic box open at one end, with a flange running around the perimeter. Holes were drilled in the flange to attach it to the plywood, and to make sure that it could be pressed snugly against the acrylic layer on the bottom surface of the generator mount.

The wheel housing was constructed out of shatterproof acrylic sheet incase an accident was to happen when the wheel was spinning at high speeds. The sides were glued with epoxy, and then metal brackets were screwed in place to add strength. After the glue had dried, silicon was added to waterproof the joints. A hole was drilled in one corner to safely let water out of the housing.

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Part XII Adding the Water Pipes One of the benefits to mounting the Pelton Wheel in a horizontal plane is that multiple water jets may be used at the same time. Adding more jets reduces the force of any one jet only if the flow rate is limited. For a practical application this would not be the case as it would be realistic to assume an endless water supply, but as we are using a residential water pip, it would be reduced. The result is that multiple water jets were added for demonstration purposes, but only one jet would be used for testing. This means that a method for opening and closing water lines was necessary. The pipes were constructed out of prefab CPVC pipe because of its low cost and ease of gluing. Two flow control valves were added to allow a choice of water jets, and they were attached by threaded CPVC fixtures instead of glue.

The pipes were then attached to the top surface of the generator mount by CPVC latches.

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The water jets were also built from CPVC. Brass fittings were used to attach the pipe to special 4mm garden-hose jet nozzles. The pipes were constructed with a “T” joint instead of a 90 degree turn. This allows access to the back of the water jets for later alignment.

Part XIII Aligning the Water Jets One of the most important parts of the assembly was the water jet alignment. The nozzle should be aligned so that the water jet hits the center ridge of the runners, and at a point 3/5 of the way from the front. This positioning is designed to produce the most efficient transfer of energy to a Pelton Wheel. But in order to generate the larges amount of available torque, an impact at 90 degrees at the outermost point of the runners is needed. Because we had two water jets available, and flow control to be able to pick between them, we decided to design one jet with an ideal Pelton Wheel impact, and the second one with maximum torque. The water nozzles were aligned by opening the back of the “T” joint and using a laser pointer to fire a beam out the front of the nozzle, in effect mimicking a water jet. This technique was used to know exactly where the water jet would hit the runners. By knowing this, the alignment of the jet was established.

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Once Complete, The second jet was aligned in the same manner as the first. Holes were then drilled, and the CPVC pipes glued together.

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Part XIV Building the Rectifier Circuit The power produced by a DC motor working as a generator is categorized as direct-current, but the voltage still oscillates between its maximum voltage and zero depending on the position of the windings with respect to the magnets. In order to provide a more steady DC power, a basic rectifier was constructed. The following simple circuit was used to smooth out the DC power.

The rectifier circuit was constructed from leftover bits of acrylic. Holes were drilled for the components on the top plate, with the diode resting on the bottom plate. The individual electrical components were soldered together with bits of house wire.

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Part XV Final Assembly With all the individual parts complete, the completed machine was assembled by attaching the legs with wood glue and four screws, then by attaching the wheel housing along its perimeter with machine screws and wing-nuts. Note: After testing, a PVC pipe was added to the hole at the bottom of the wheel housing to help direct the water to a drain.

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Side view of the completed machine

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Part XVI Testing and Results The machine was tested in the fluids lab using cold water from an available hose. The open terminal voltages were measured for the three possible water jet combinations, and the following data was collected.

• Open Terminal Voltage for 90 Degree Water Jet: 11V

• Open Terminal Voltage for Correctly Positioned Pelton Wheel Jet: 11.6V

• Open Terminal Voltage for Both Water Jets at the same time: 8V It was clear that the correctly positioned Peltoln Wheel water jet was the most successful. During a separate testing day, the rectifier was tested, and a 12v 60W portable television was used as a test load. Though the TV did not get any reception in the basement lab, it did turn on, demonstrating that the machine does function with a load. Conclusion: The Green Micro-Hydro plant was successfully constructed and tested with a real load. Though there was insufficient time to produce a full Voltage/Current graph, the generator system was tested with both an open and short-circuit load. In the second case, the turbine continued to turn, though labored. Construction Tips for Future Students A great many things were learned during the construction of the Green Micro-Hydro Plant that might be of use to future students. Here are a few ideas we picked up.

1. When gluing parts together that require a high level of precision, wax is a surprisingly useful tool. It can hold parts in place, and its oily makeup prevents it from adhering to most glues including epoxy resin.

2. When aligning something, a laser can be very handy. A laser level can be used to

make sure that a part is parallel or perpendicular to another part without interfering with a delicate setup. They are quite inexpensive and can be purchased at Princess Auto for under $10.

3. When taking pictures of your work in-progress, we found that a black piece of

cardboard worked great as a background. It makes the pictures look uniform, and its easer to distinguish the components.