P18463: Water Powered USB Charger

Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

Vision and Progress

Our team's vision for the preliminary detailed design phase was to identify major problems for the rest of our detailed design as well as develop plans to solve these issues, develop plans for testing our device, generate a preliminary Bill of Materials and order parts we will need for testing.

Leading up to the Preliminary Detailed Design Review, the team was able to pinpoint and work towards resolving the problem most crucial to our critical path: creating enough rotation to generate power using a slow-moving body of water. Through CFD analysis, we have concluded a theoretical range of 200-1600 RPMs given the potential flow velocities, with a factored in efficiency of 20% below maximum proficiency due to loses. The key variables in our simulation, such as flow velocity, fin area, blade angle, and efficiency can all be quickly changed to show theoretical performance for multiple designs.

The team has also created test plans and "potential" Bills of Materials for each subsystem, each of which are broken out below. The team is actively reevaluating and prioritizing risks and tasks, and believe we are on track to mitigate them by the Detailed Design Review.

Unfortunately, there are still tasks and risks that still have yet to be fully addressed and resolved by the team due to complexity or priority. We are hoping to begin purchasing our testing materials close to the end of Phase 4, when our Bill of Materials has improved accuracy and justification.

Trello Update

At the beginning of Phase 3, the team transitioned to a different project management tool: Trello. Trello is a web-based project management app that is ideal for individual and small-team projects. It’s relatively flexible and simple interface has helped the team organize and accomplish tasks more systematically than before. Previously, the schedule would be made through Microsoft Project and sit unused on Google Drive. With Trello, everyone always has live access to the tasks at hand.

Trello Boards for Subsystems

Trello Boards for Subsystems

In order to organize our workload, we created boards for each main subsystem or critical component of the device. Inside of each board, there are lists of tasks sorted into different categories based on completeness and/or urgency. Inside of each task card, each team member can create descriptions, add comments, tag others, set due dates, and much more. This has helped the team keep track of references or progress towards each individual goal.

Updated Engineering Requirements

After the System Design Review, the group reviewed and revised certain key Engineering Requirements such as budget, operating range, and cable length. These updates were based around the clarified safe distance from the water, as well as benchmarking and additional feasibility.

The Engineering Requirements document can be found here: Engineering Requirements

Engineering Requirements

Engineering Requirements

Feasibility: Prototyping, Analysis, Simulation

Turbine Design

The graph below shows the expected power output from turbines of different radii at different velocities. The efficiency is assumed at ~40% which our research tells us will be similar to empirically tested efficiency.

Power vs. Velocity Graph

Power vs. Velocity Graph

Posted below is the same graph as above, but the range has been limited to trickle charging range for a clearer view. As can be seen, the minimum water speed of 1 knot (0.5 m/s) produces an incredibly small amount of current at 5V.

Trickle Charging Range

Trickle Charging Range


Any DC motor can be used to generate electricity without the need of excitation current whether be it brush less or with brushes. The best and most efficient solution is to use AC asynchronous motor as the generator, but these require a source of excitation current. The excitation current must flow in the coils to generate the field or else no power would be generated.

EMF equation of a DC generator?

As the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as Er = Eb. The expression for emf is same for both the operations. I.e., for Generator as well as for Motor.

How to derive the EMF equation of a DC Machine - Generator and Motor assuming the following parameters are known?

P – Number of poles of the machine

Phi – Flux per pole in Weber.

Z – Total number of armature conductors.

N – Speed of armature in revolution per minute (r.p.m).

A – Number of parallel paths in the armature winding.

By making use of these parameters, the flux cut by one conductor can be found using the procedure written in the attached Generator Equations Sheet.

The Generator Equation Sheet can be found here: Generator Equation Sheet

Voltage Regulator

Voltage regulation is necessary in order to have safe voltage and current going in to the power bank or else it will get damaged. Depending on the type of generator chosen, the appropriate option would be chosen for power regulation. Options such as:

Integrated circuit chip voltage regulator

Step down converter

Housing & Waterproofing

Magnetic Connection between Generator and Turbine

Magnetic Connection between Generator and Turbine

Close-up of above image showing discs on both the generator side and turbine side of the magnetic connection.

Close-up of above image showing discs on both the generator side and turbine side of the magnetic connection.

To avoid issues with waterproofing a shaft seal, we are currently investigating connecting the turbine and the generator magnetically. This would serve multiple purposes. Firstly and most importantly, the seal that we have needed to create at the rotating shaft location will not be waterproof completely decreasing the risk of the internal components getting damaged by water. Secondly, this decreased the load on the shaft of the generator. Since the housing will be supporting the weight of the entire turbine, it should increase the ruggedness of the entire charger in case of a fall. As for the magnets, we will most likely use neodymium rare earth magnets.

In order to waterproof the electrical cable port on the device, we were going to purchase a special top for the cables called a "TAPP CAPP" kit. However, the full kit seemed overprices and excessive, so we intend on CAD-ing and creating them ourselves. The cap will be lined with an insulative foam, plugged into the outlet on the device, and then fastened with a threaded cap on top of it (think of a hose). A sketch can be found below.

Waterproofing the Electrical Port

Waterproofing the Electrical Port



The device will require both a rigid and electrical cable. After the previous design review, we have been approximating the length of these cables to be about 30 feet each. The rigid cable will need to be slightly shorter so that the electrical cable does not experience a tugging force and is less likely to disconnect.

The rigid cable will anchor the device to a point on land as it generates power in the water. The rigid cable will be made of vinyl-coated twisted steel, and its 340 pound load limit far exceeds our requirements.

The electrical cable will be a durable micro-USB in order to supply power to Android phones in these weather conditions. We will size our waterproofing cap to the size of this cable.

Finally, we will be using a flexible cable sleeve will be used to join the two cables together. This sleeve will not only provide additional protection for the cables, but also help the stability of the device by preventing the cables from separating.


The water-powered USB charger will contain electrical components that can be sensitive at certain high temperatures. Given the extremely hot climate of Kenya and other potential areas of use, it is necessary to protect the device from overheating in hot areas. The device will be effectively cooled by the body of water surrounding it when it is in use. However, when sitting idly on land the charger has no such coolant. It is necessary to create a case consisting of both high thermal and shock resistance to make it rugged enough for the conditions it will be used in.

The intention of the following heat transfer model is to approximate just how much thermal insulation is required to keep the device at acceptable temperatures in hot conditions. There are certain assumptions that are made in this model that may not apply to our application; we are in the process of meeting with subject matter experts to resolve these assumptions and unknowns. However, we do not anticipate this being a high risk issue with our device.

Drawings & Schematics

Turbine Design

From the above graphs (posted in feasibility section), we decided to create a very rough CAD model for visualization purposes. This model has an outer radius of 8.89cm (close to the 9cm point from the above graphs). Model is shown below:

Rough Visualization of 3D Model

Rough Visualization of 3D Model

This CAD model (along with others) were also used to run surface level CFD analysis to confirm any issues that we might not have realized as a group.

Flow through turbine

Flow through turbine

One of the things that was over looked was wobble that would have been created had there only been one ring in use. Therefore, this model was edited to use 3 rings to create stability at a slight loss of efficiency.

We also realized through CFD that if multiple ring elements (blades) are used in our design, they cannot overlap each other (i.e. if turbine is being observed from a cross-sectional view), or else they will create unwanted turbulence and potentially decrease the efficiency.

All CFD above were run at highest water velocity as this is the speed that would have caused the most trouble (if any). CFD analysis was also run on the slowest water velocity but was not posted as they showed no concerns. Ultimately these are just preliminary results and when final analysis with parametric study is posted, all data and diagrams will be posted for proof.

Below are the pressure and velocity mesh results to show that there is minimal turbulence and there isn't too much of a pressure drop around the charger caused by the turbine. These results have also been simulated at the highest velocity specified to display the worst case scenario. Ultimately, these graphs show that the device will be stable.

Pressure Profile

Pressure Profile

Velocity Profile

Velocity Profile

Generator & Voltage Regulator

The electrical wiring diagram shows the connections for the components of the electrical components of the device. This drawing shows the connections needed to successfully connect the generator to the voltage regulator and then to the power bank/phone on shore.

Electrical Wiring Diagram

Electrical Wiring Diagram

Bill of Material (BOM)

Updated Bill of Materials - November 14th, 2017

Updated Bill of Materials - November 14th, 2017

The Electrical Bill of Materials can be found here: Electrical Bill of Materials

Test Plans



1. Background/Summary:

The turbine test will be conducted to compare our theoretical results (through MATLAB and CFD) to empirical data (which will be obtained through this test). The test will most likely include 2-3 different turbine designs with 7-10 different versions of the turbine. These versions might include things such as pitch angle of blades, thickness of blades, different radii, etc. This testing procedure will not include anything up to the point of empirical testing. Any work required to be done before that point in time has been noted on Trello and is already underway.

2. Test Procedure:

a. Choose 2-3 different designs as a group. Use CFD and theoretical data to decide on best options to be empirically tested. One of them will be the ring design that our current feasibility is based on. The other will be one of the impeller designs. The third will most likely be a normal 3 bladed prop as this is the most used designs for such applications, and will give us a good comparison point.

b. Decide on a single radius for all test plans. This radii will be a controlled variable in all the testing. Any results attained at this radius should remain constant for all other radii too.

c. Work 3-4 different angles of blades and 2 different thicknesses of the blades into the CAD files using a parametric setup. This will increase workflow efficiency.

d. 3D print all the parts.

e. CAD and 3D print a waterproof housing to contain the generator and connect generator to tachometer.

f. Start running all turbines through water tank at a constant speed (0.5 m/s minimum, and max speed equipment can go at). Record RPM.

g. Choose propeller which best fits our needs once data is interpolated to our expected water speed.

3. Equipment & Resources:

a. Thermo-fluids Lab water tank

b. Tachometer

c. Generator – with the right RPM required. Consult EE side.

d. The Construct – 3D printing lab

e. Waterproof bearings

f. Possibly a DAQ.

4. Risks

a. Length of water tank does not allow for turbines to reach steady state. Some designs might accelerate to the desired speed faster than others while those others might have a greater top speed (or torque, hence more potential power output).

b. Surface finish of 3D printed turbines might not provide accurate data.

c. Damaging equipment that cannot come in contact with water.

5. Responsibilities

a. Make sure there are always at least 2 people in lab.

b. Make sure all RIT lent equipment is away from water at all times (such as DAQ or computers).


Background & Purpose:

The water-powered USB charger will contain electrical components that can be sensitive at certain high temperatures. Given the extremely hot climate of Kenya and other potential areas of use, it is necessary to protect the device from overheating in hot areas. The device will be effectively cooled by the body of water surrounding it when it is in use. However, when sitting idly on land the charger has no such coolant. It is necessary to create a case consisting of both high thermal and shock resistance to make it rugged enough for the conditions it will be used in. For this test, we will confirm that our material selection is an adequate selection for keeping the device safe from thermal damage.


1. A prototype of the designed case, with an ABS exterior and polyurethane foam interior.

2. Two thermometers, each used to measure the temperature at a different point inside the case.

3. A standard kitchen oven.


1. Place the thermometers at different points in the case. Record the positions at which they are replaced and the initial temperatures that they read.

2. Close the case and place it in an oven at 120 degrees for at least four hours, recording the temperature of each thermometer once per hour. This temperature mark is the anticipated “worst case scenario” for the case being left out in a hot area.

3. If the temperature of the thermometers do not go above the tolerances for the electrical equipment, the test will be considered successful.


1. Never leave the oven unattended while the test is in progress.

2. Use proper protective equipment when removing the case from the oven.

Risks and Contingencies:

1. The case, thermometers, or both get damaged in the process. While it would not be an expensive loss, all items would need to be replaced.

2. Test results will determine if additional thermal insulation will be required.


Now that we have our theoretical calculations, we will be testing these against the actual measured data obtained from putting the assembled device to various tests. These tests will be performed using standard laboratory test equipment as well as other components such as analog DC current sensor for output current measurement.


Two tests will be conducted. First would be testing the generator and the second one would test the polarization of the generator. Theses tests will give verify the theory of generator operation and if the results obtained match the theoretical calculations.

Generator Test: This test will involve increasing and decreasing the generator speed to see how it affects voltage generated.

Polarization Test: If device fails Generator test a then a polarization test is needed: The next time the generator starts up, the residual magnetism creates a small voltage in the Armature windings. Not enough to charge the battery, but enough to allow the Field windings to draw current. As the Field current increases, the pole pieces create even more magnetism. That makes even more voltage in the Armature, and the cycle continues until the generator is capable of producing maximum output.What happens though to a generator which has been stored a long time or is freshly built? The residual magnetism may have decreased to the point where it can no longer get the generator started producing voltage. In the case of a new generator or one which has been mistreated, the residual may even be of the wrong direction (North and South poles reversed).

The Generator Test Plans document can be found here: Generator Test Plans

Voltage Regulator

The voltage regulator’s specified input and output power rating should match with the actual test measurement and that would confirm successful device functionality.

Measure Input Voltage: Check the voltage from input pin to ground. This is to make sure the voltage is in fact being supplied to the regulator. If the regulator is not receiving sufficient voltage then it will not output its rated voltage.This is the only purpose of this test. A multi-meter can be used for this purpose.

Measure Output Voltage: The voltage should output close to 5V and if successful then the voltage regulator is functional and is good.If not, then the voltage regulator is bad.

The Voltage Regulator Test Plans document can be found here: Voltage Regulator Test Plans

Design and Flowcharts

In order to build on the System Architecture designed in Phase 2, we have created a simplified Subsystem Architecture in terms of the inputs and desired outputs of each system, and how we are planning on optimizing these outputs. The System and Subsystem Architectures can be found below:

System Architecture

System Architecture

Subsystem Inputs & Outputs

Subsystem Inputs & Outputs

Risk Assessment

The Risk Assessment Sheet needed to be reevaluated in Phase 3 in order to provide information on the status of certain tasks as well as prioritize our remaining concerns. Multiple new risks have been added and most have been sorted into the following three categories:

Resolved Risks are risks that have either been fully addressed and solved, or have an extremely low probability of occurring due to key information and decisions made.

Resolved Risks

Resolved Risks

Working Risks are risks that are actively being addressed by the team. These risks each specific have plans to address them, but are typically more complicated, require more attention, and have a higher chance of presenting problems.

Working Risks

Working Risks

Unresolved Risks are risks that the team has not been able to full address or resolve yet. While some of these are more important than others, all must be considered in order to meet our customer requirements. These are all areas in which the team is very open to receiving feedback or advice from the guides and customer.

Unresolved Risks

Unresolved Risks

Updated Risk Assessment

Design Review Materials

The Presentation Outline document gives an overview of the Preliminary Detailed Design Review Agenda. The review will cover major resolutions in this phase, tasks that are still in progress, and a summary of how we intend on addressing the items that still need further research and attention. It can be found at the link below:

Presentation Outline - Phase 3

The Project Summary Sheet gives a quick snapshot of many of the important topics that will be covered in the review, in addition to our prioritized questions for the guides. It can be found at the link below:

Project Summary Sheet - Phase 3

Plans for next phase


In order to have a successful Detailed Design Review, the team needs to work diligently to close out MSD I. Ideally, we will be ready to begin testing various subsystems shortly after returning from winter break. This will require a complete, all-encompassing bill of materials, which will account for the costs associated with creating the device, buying the testing equipment, and 3-D printing parts.

The overarching goal of Phase 4 will be based upon resolving our Working and Unresolved Risks. The more risk we mitigate, the less likely we will run into problems during the build. Additionally, mitigating these risks is a productive way of "working backwards" into the right solution.

Finally, we hope to convey all of our findings to the guides in a formal and concise presentation in order to obtain validation of our concept and approach we have been working towards this semester.

Key Action Items

1. CAD device housing

2. Account for all waterproof seals

3. Finalize generator selection

4. Order testing equipment and begin 3-D printing

5. Finish Bill of Materials

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