gym equipment energy conversion project (2008)
DESCRIPTION
GREEN MACHINEGYM EQUIPMENT ENERGY CONVERSIONTRANSCRIPT
GREEN MACHINE
GYM EQUIPMENT ENERGY CONVERSION
Project Team: Matthew Bruchon Blake Gates Zachary Johnson Erik Peterson Sponsor: Dr. William Edmonson
Spring 2008
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TABLE OF CONTENTS
I. Executive Summary............................................................ 3
II. Newsletter..................….................................................... 5
III. Project Report
1. Introduction.................................................................................................. 6
2. Background.................................................................................................. 7
3. Product Requirements................................................................................. 8
4. Design Alternatives...........……………………………………......................... 9
4.1 Power Generation………………………………………………………... 10
4.2 Power Regulation………………………………………………………... 14
4.3 Power Usage or Storage…………………………………….................. 17
4.4 Monitoring System……………………………………………………….. 19
4.5 Protective Devices……………………………………………………… 21
5. System Design Descriptions
5.1 Design Option 1: Direct Application…………………………………..... 22
5.2 Design Option 2: DC Network………………………………………...… 23
5.3 Design Option 3: Grid Tie................................................................... 25
6. Construction Details …………………………………………………................ 29
7 Future Improvements………………………………….................................... 31
8. Business Considerations.............................................................................. 33
8. Conclusion……………………………………………………………………........ 34
IV. Appendices.........................................................................35
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I. Executive Summary
Project Objective
This project’s objective was to research possible designs for converting the mechanical energy
from gym equipment to electrical energy, and ways to use or store that energy. Various design
options were researched, and the costs and benefits of each option were evaluated.
In addition to this research component, a second objective of the project was to build a working
prototype of one possible design. This prototype was necessary to check assumptions that were
made in our design, learn how it could be improved, and assess its feasibility for use on a larger
scale gyms.
Research & Analysis of Design Options
Research of possible energy conversion systems was divided into five basic aspects of the
design: power generation, power regulation, usage or storage of power, monitoring of the
system’s output, and protection of the system from harmful conditions. Each of these design
aspects had several possible methods of implementation; each possible method was analyzed and
the tradeoffs involved were discussed.
After discussing the design options for each area of the design aspect, we considered how these
options could be combined into a working system. When considering the design at a system
level, we considered three possible uses of the generated energy: direct powering of a load,
application to a DC network, and transferal onto the power grid. Each of these possible uses was
considered and tradeoffs were discussed.
Implemented Design
An exercise bike was used in the prototype that was built. The figure below illustrates our
implemented design.
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DC
Bike/Generator
Source
2N2905
100 5k
0.10.10.1
200
pF1.5k
150
5k
Watt Meter/
Load
LM308
LM338 LM338 LM338
Diode
Design Day Implementation
The wheel of the bike was connected to the shaft of a generator via a rubber wheel. A diode was
used to prevent the backflow of electrical energy into the generator. The diode output was
connected to a voltage regulator. In early testing, a DC to AC converter was used to power AC
loads, but for our final demonstration, only DC loads were connected to the system output. A
watt meter, powered by the system, was used to monitor the system’s output.
Results and Conclusions
The research component of the project evaluated a wide range of possible designs, both at the
level of individual components and at a system level. All three possible system designs were
assessed to feasible; direct application of the power generated is the least costly option, but the
overall benefit depends on the intended use.
The prototype was considered successful, although there were limited resources and several
setbacks. For instance, wear on the generator shaft’s wheel forced a power drill to be used to turn
the generator for demonstrations. However, the fundamental design of the system was sound and
functional, and could provide a basis for further development of a more efficient and marketable
system in the future.
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II. News Release
N.C. State Students Research “Green” Exercise Machines April 30, 2008 - In a time when oil prices and global warming have led the nation to consider
renewable energy more seriously than before, a group of students at N.C. State University
recently researched an untapped energy source: human exercise.
For their Electrical & Computer Engineering Senior
Design Project, a group of four students—Zach
Johnson, Blake Gates, Erik Peterson and Matthew
Bruchon—researched ways to use gym equipment to
produce and store electricity. Their faculty sponsor
in the E.C.E. Department was Dr. William
Edmonson.
The team began by comparing different exercise
machines see what kind would generate the most
energy and be the most marketable; they found an
exercise bike’s popularity and simple design to be ideal.
Next, they looked at three distinct uses for the generated energy: storing it on the power grid to
reduce or eliminate power bills, storing it in a system of batteries, or directly powering a load,
such as a TV screen or a cell phone charger. After doing this, they analyzed how to convert an
exerciser’s effort into electricity most efficiently.
In addition to this research project, the students also implemented a prototype of their design.
The prototype exercise bike, dubbed the “Green Machine”, was able to directly power AC and
DC loads, such as a rotating fan, and the output power could be monitored.
The success of the design, despite limited resources, gave the team high hopes that it could be
feasible for future use at a gym. If it were further developed, it could help boost gym
membership as part of a “green” marketing program. More importantly, it could save money,
reduce energy consumption, and help make the earth a little bit cleaner.
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III. Project Report
1. Introduction
The goal of this project was to analyze the feasibility of using energy generated from exercise
equipment to creating a more self-sustaining gym. To do this, a single piece of exercise
equipment was used as a test subject. The factors considered in choosing what type of machine
to conduct our study with were: ease of connection to a generator, cost, efficiency, and
popularity of the machine type.
After determining what type of equipment was ideal, research was done to find a cost-efficient
way to generate and use the energy. This research included the analysis of methods to generate
power, regulate power, apply it to a load, monitor system output, and prevent damage to the
system. It also included the analysis of three possible system-level design options: to store the
energy converted, to use it to directly power a device of some kind, or to route the power onto a
grid.
Also, a monitoring system was implemented to measure and display the system’s power, voltage,
and current output. By measuring system output at different points, conversion efficiency could
easily be measured.
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2. Background
There are several motivations for creating a system of energy conversion that gyms can use to
generate their own power. Perhaps the most obvious reason is to reduce costs and increase
profits. For the most part, the mechanical energy generated by exercise is completely wasted, so
there is an untapped potential to make the energy useful. If a gym were able to implement such a
system on a large scale, across many or all of its machines, the power generated by the gym’s
customers would offset the gym’s electricity bill. Ideally, enough power would be generated that
it could be returned to the power grid, possibly even turning electricity costs into a net profit.
As public awareness of global warming and carbon neutrality grows, the environment is
becoming a greater reason for implementing such a system at gyms. If a gym were able to
reduce its power consumption, or even produce a net amount of power, its carbon footprint
would be reduced, improving its environmental impact.
The reasons for considering the environment are not only ethical, but also commercial. If a gym
could advertise itself as a “green” gym, its public image would improve and more customers
might be attracted. In fact, the increase in membership could make such a system profitable even
if the electricity savings alone could not offset implementation costs.
Because of these reasons for generating electricity from exercise, there have been several efforts
to research and develop such a system. One case is the California Fitness health club in Hong
Kong, which connected 13 exercise machines to a system of batteries to power some of the
gym’s lights. The system was not found to be profitable, but the environmental benefits were
significant. In the Netherlands, a similar system is being made to power dance floor lights with
energy made from dancers. Research is also being conducted into parasitic generators, which
would use everyday movement such as walking to harvest energy.
These past efforts were well beyond the scope and the budget of this project. Instead of directly
implementing and analyzing large-scale systems, this project’s focus is on optimizing the design
of an individual machine and analyzing whether it would be cost-effective if implemented on a
larger scale.
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3. Product Requirements
R1. The overall cost of the product shall not exceed $250.
R2. A bicycle or gym bike shall be used as the source of the mechanical power.
R3. The generator will output DC.
R4. The power created will have two uses:
a. Power an appliance for display purposes
b. Power the tool used to measure and display system output
R5. The characteristics that will be monitored will at least include:
a. voltage
b. current
c. power
d. kWh
R6. A DC to AC converter will be use to transform created power into a useable source for
appliances and/or power grid.
R7. The output of the generator and CD to AC converter will be monitored and displayed on an
LCD screen.
R8. The device shall be capable of being connected with other power generators to create a
network of sources.
R9. A feasibility study will be done to determine the practicality and plausibility of
implementation in a medium-sized gym.
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4. Design Alternatives
When researching and designing possible design alternatives, we divided down the design into
five major design aspects:
Power generation
Power regulation
Usage or storage of energy
Monitoring of system output
Protection against system damage
Each of these design aspects is, to some extent, are dependent on the implementations of the
other aspects. For example, if the conversion system should power a TV that requires AC
voltage, an AC generator can be used and voltage can be regulated to 120 VAC 60Hz, or we can
select a DC generator and convert our generated VDC into 120 VAC 60Hz.
A more detailed discussion of design alternatives for each aspect of the design follows.
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4.1 Power Generation
The consideration of design alternatives for the generation of power can be further divided into
the areas of exercise equipment, the equipment’s interface with a generator or alternator, and the
generator or alternator.
4.1.1 Exercise Equipment
In order to determine which type of exercise equipment to use, characteristics such as popularity
of machine, cost, and ease of connection were taken into consideration. Based on these
parameters, it was decided that a standard exercise bicycle, Figure 3, will be best qualified for
this specific project. Other choices that were considered were a treadmill, rowing machine, and
an elliptical trainer.
The reason the bicycle was chosen was mainly its simple design, which often incorporates an
open wheel. This open wheel allows for the bike to easily make a strong, high-friction
connection to any standard generator. The type of bicycle used will be one with a wheel in front
of the bike with a diameter no greater than 26”. An ideal bike for this project is pictured below:
Figure 1 - Schwinn IC Elite Indoor Cycling Bike, $1099.00
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4.1.2 Generator/Alternator
The generator is one of the most important components of the entire system. Because of this,
special consideration and calculations must be taken in order to ensure that the correct one is
used. There were several options to choose from for the generator including a DC motor, AC
motor, or an alternator. For each specific motor, there were several advantages and
disadvantages that had to be compared in order to select the best possible generator for a bicycle
generator.
An alternator could have worked for this project but there are a few design flaws that would
interfere with the rest of our system. First, an alternator would only allow a person to pedal the
bike at a one constant speed no matter how hard they tried. This is because an alternator is
designed to always spin at the same rate, so that a constant output is always produced. This
could be a desired characteristic in some cases; however for our purposes this would greatly
prohibit the goal of the project. This is because it would not allow the person who is pedaling
the bike to pedal at their own pace and would hinder a person’s workout.
The next generator that was considered was an AC motor. This has several advantages,
including that it is easier to regulate the output, simpler to produce, and relatively cheap.
However, there was one major concern with the AC motor that had to be considered: AC motors
are hard to operate and relatively useless at low RPMs. This is due to thermal consideration of
the design. Because of this, most AC motors are only used for high power systems, not a bicycle
generator. This was an issue because a person using the exercise bike might be pedaling at a
RPM that was lower than the motor was designed for. If this were to happen, then it would be
difficult to produce or use the power that was generated.
The final motor that was considered was a DC motor. The characteristics of this type of motor
proved to be ideal for our problem. A permanent magnet DC motor was chosen that would
produce 12-24V at 1800RPM and 1/6-1/4 HP. These ratings were chosen since most of our
applications would operate between 12-24V. Also, it was determined through a ratio of the
circumference of the generator shaft to the circumference of the bicycle wheel that 1800RPM
would be the expected input to the generator based on the fact that the user would pedal on
average at 15 mph. Since voltage is proportional to RPMs, if the user pedaled faster or slower
than the desired 1800 RPMs, then, they would see similar results in the voltage. These results
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would be acceptable in our system since a regulator would be used later down the line in order
keep the voltage from going to high.
One problem of choosing a DC motor is that they are a little more expensive than the other
motors to purchase. This will make part procurement slightly more difficult since it must stay
within a budget. The next problem with choosing a DC motor is that the output would need to be
converted to AC for AC loads including a smart charger which would then be used to charge a
battery. During the conversion there will be some energy loses but it was a compromise that is
needed so that a smart charger could be implemented further down the line in our system. Since
this was the only negative characteristic of the DC motor for the bicycle generator application, it
was choice.
4.1.3 Equipment Interface
One of the main issues that needed to be considered in our design was how to connect the
mechanical input produced from the exercise bicycle to the generator shaft so that it could then
be converted into electrical energy. There were several issues that needed to consider here,
including how difficult it would be connect it and the efficiency of a design.
The first idea considered was to use a belt, where one end would wrap around the circumference
of the bike wheel and the other end around the shaft of the motor. In this design, as the bike was
pedaled, the generator shaft would move at a proportional rate. One issue in this case was that
depending on the input provided by the exerciser, the belt could possibly slip. This was
important because there would be several types of user on an exercise bicycle, and the belt would
have to be able to handle different torques.
Another issue was the efficiency of using either a belt or a chain. In mechanical systems, energy
losses due to friction occur due to points of contacts in a system. In the belt system previously
described, there would be a fairly large area of contact, thus producing fairly high energy loses.
The one advantage of this system is that it would be relatively easy to implement. However, the
belt system would make it difficult to keep the system portable and allow it to transfer from one
bicycle to another.
The next design that was considered was to use a system of gears and pulleys that would rotate
the generator shaft as the bike was pedaled. The main problem with this design is that it would
take a lot of mechanical knowledge to implement and would be rather complicated. Efficiency
was a problem here as well. The only thing gears due to a system is cause it to lose energy. This
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design would also make it difficult to transport and move from bike to bike if it needed to be
done.
The design that was most practical was a one-contact-point design. In this set-up a small rubber
wheel would be placed on the shaft of the generator. The size of the wheel would be chosen so
that the generator would produce on average 1800 RPMs, the rating of the motor. This rubber
wheel would then be placed in direct contact with the wheel of the stationary exercise bike so as
the stationary bike wheel spins, the wheel on the generator spins, thus producing electricity. A
strip of rubber would be placed around the wheel of the stationary bike so that slippage would be
kept at a minimum. Like the previous designs, slippage was a major concern that had to be
addressed.
The generator shaft should be placed in a way where the weight from the bicycle itself will help
keep a constant contact between the two wheels. So for this to work it is recommended that the
generator shaft be placed under the bicycle wheel. Also, the material that the wheel that sits on
the generator is made from must be durable enough to withstand wear and tear. These issues and
findings will be discussed in a later section.
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4.2 Power Regulation/Conversion
4.2.1 Regulators
The generator that was used in this project produces a DC voltage from the range of 12V – 24V.
Unfortunately, the inverter that will convert the DC voltage into AC will only allow a range of
10V – 12V before it automatically shuts off due to an installed safety feature. A problem then
remains: how does the voltage maintain a constant output in order to properly operate the
inverter continually, rather than in bursts?
Two options were researched in solving this problem. The first was a DC/DC converter in
which a voltage within a specified range will be input, and then a constant voltage will be output.
However, this still reverts back to the original problem of how to keep the voltage within a range
while someone may be pedaling at either a slow or an extremely high rate of speed. The price of
the DC/DC converter also was found to be close to $200.00.
The second option involved using a LT1083 12V voltage regulator. The voltage output would be
typical for what the project needed; however, the allowed current could not pass 7.5A. The
current output of the generator that we had chosen was anywhere from 8A – 15A. To solve this
problem, we used a parallel connection of three of the LT1083 voltage regulators in order to
keep the voltage constant, but increase the allowable current. The schematic for the voltage
regulator circuit can be seen in the section IV of this report. One component of the regulator
circuit was the use of a variable potentiometer in order to increase or decrease the gain of the
regulator.
4.2.2 Ultracapacitor
The voltage that is supplied by the generator will drastically vary depending on the user of the
bicycle. Some users will produce high voltage for longer periods of time and others will barely
reach a particular voltage level. The voltage will also change depending on what position the
pedals of the bike are in. Because of these varying voltages it is necessary to keep a constant
voltage so that the inverter can then transform the DC voltage to AC. To meet this requirement
it is necessary that an ultra-capacitor is used after the diode and before the inverter in the system.
Ultra-capacitors have become more visible in today’s applications as they have been
implemented in many systems like electric cars and other areas where they are being used to
replace batteries. One of their advantages is that ultra-capacitors have a virtually unlimited life
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cycle unlike batteries, which must be replaced often. The other advantages are that it will reduce
the DC ripple in the input voltage as mentioned earlier, as well as allows for fast charging. Also,
one would not have to worry about over charging or a protective circuit like one that would be
need for a battery.
In the designs listed above, it is recommended that a 58 Farad capacitor be used. This will
provide enough stability to make sure that the varying input voltage will remain as constant to 12
volt DC input that is needed by the inverter. These were priced at roughly $200.
During the original design process, a simple voltage regulator circuit was considered an
implemented to perform the same task as mentioned above with the ultra-capacitor. However, it
was discovered that the input voltage varied too much for the voltage regulator to perform its
function. Further information on this issue will be discussed later in this document.
4.1.3 Inverters
From our proposed design, this was the step from which the first problem arose. The ideal
choice for a generator was DC rather than AC, as stated earlier, but the required input voltage to
the Smart Charger and other AC loads would be AC.
Figure 2 – AC Inverter
Our particular voltage inverter solves this problem by converting the DC voltage from the
generator and outputting an AC voltage for the Smart Charger and other AC loads at an
efficiency rating of up to 90%. The chosen inverter can be seen in Figure 2. In addition to
inverting the voltage, the inverter also regulates the voltage coming from the DC generator.
Although the generator is rated to 12V at 1550 rpm, a higher input from the user will produce a
higher voltage output. The inverter, while classified as a 12V Power Inverter, still will accept
any input voltage between 10V – 15V. As a safety precaution, the inverter will automatically
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shut down any inversion when the input falls out of that range. However, it is important that the
input voltage to the inverter is well regulated due to this feature. This is why an ultra-capacitor
was preferred over a simple voltage regulator.
Once the 12V power inverter receives the voltage, it will convert it to a 120V, 60Hz AC voltage
which has 400 watts of continuous power and 800 watts of start up or peak power. This will be
enough to power the loads connected the design that are discussed later.
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4.3 Power Usage/Storage
The third stage of our design involves the question of how to apply the power that is produced.
4.3.1 Direct Application
There are several choices when it comes to the loads that can be hooked up to the system. The
design makes it possible for both AC and DC loads to be powered at the same time or
individually. This mean the user could power an iPod charger or a portable fan. If direct
application is not needed then the user could output the voltage to a battery or battery bank. The
size of this bank could be customizable by adding various batteries in parallel to the output of the
system. This bank could also be stored in a separate room or closet out of sight from the user of
the system. All that would be required is for cables to be run under the floor from the closet to
the location of the bicycle. These cables would then need to be connected to the DC output
terminals of the system.
The only issue that must be taken into consideration is that there is a limit to how many loads
one can power depending on how fast they are pedaling and how much power the specific load
requires. Otherwise, there are no restrictions to what one could be able to power with the
system.
4.3.2 Battery System/Smart Charger
The DC network design showed in section III.5.2 shows the implementation of a system where a
battery is charged. However, using this idea, it was realized that with a constant charge onto the
battery of certain devices, the battery could potentially be overcharged, causing harm to not only
the battery unit, but the device itself.
To fix this problem, the use of a Smart Charger could be implemented, seen in Figure 3. This
device provides circuitry for the battery to prevent any type of overcharging and opens the
connection once the battery is completely charged and once the battery voltage drops below a
certain threshold, closes the connection and allows for current flow back to the battery.
Typically, deep cycle batteries are better suited for this type of device. The reason for this being
that our design will continually charge and discharge a battery. Batteries such as a laptop battery
degrade over time whenever they are charged and discharged, and therefore will not be sufficient
for our needs.
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Figure 3 – Smart Charger
4.3.3 Grid Tie
Design three is similar to the rest of the designs except for the addition of a grid tie. Grid ties are
commonly used in PV and wind power systems to allow the energy created from these systems
to be put back on the power grid. The grid tie will take the power produced by the AC inverter
and then regulate it and put it in phase with the rest of the power grid so it can be safely added.
The benefit of having a grid tie is that one is able to basically have an unlimited power supply to
store the energy that is created. This power would then be sold back to the energy companies so
that a particular user’s power bill would then be reduced according to how much power was
generated. However, the only downfall of this device is that it is extremely expensive and would
not necessarily be practical for a system where a huge amount of power is not generated.
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4.4 Monitoring System
The ideal system for monitoring the system’s output depends on whether it will be used simply
for test purposes, or whether it will be used as a display for an end user (e.g. at a gym). Three
display systems are considered here: a “Watt’s Up” meter, a Labjack setup, and a custom GUI.
4.4.1 “Watt’s Up” monitoring system
One option is to use a “Watt’s Up” monitoring system, ideal for simple testing and
demonstrations. This device will be able to determine several characteristics of the load input
including voltage, current, power, watt hours, amp hours, peak watts, and peak volts. The Watt’s
up meter, shown in Figure 4, will be placed on the handle bars so the user will be in easy view
of his or her performance. However, the meter is portable enough to be placed anywhere around
the bicycle as long as there is enough wire to still connect it to the rest of the system.
Figure 4 – Watt’s Up Meter, $50
The Watt’s up meter was chosen over other devices like a Labjack because of its simplicity and
the ease of use. No programming or customization involved and the parameters that are
monitored will easily be available to the user. The Watt’s Up meter is also cheaper than other
similar products on the market, with a price of roughly $50.
4.4.2 Labjack
A more robust but costly option is to use a Labjack to monitor the system’s output. The Labjack
allows the system output to be monitored on a computer; it connects to the computer using a
USB cable, which also powers the Labjack. The Labjack is pictured in Figure 5.
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Figure 5 – Labjack U12, $130
The Labjack’s main advantage is its versatility. It has a large number of input ports, and they
can be simultaneously read and displayed on a graph in real-time using Labview software.
However, the cost of this versatility is high; the Labjack costs $130. Also because of this
versatility, a high degree of customization is needed. Existing sample code for graphing inputs
over time are available, but the code would have to be heavily modified to account for power,
which would be the multiplication of the input current and input voltages.
Another disadvantage is the complexity of the circuits required to connect the Labjack to the
energy conversion system. The voltage would need to be stepped down using a voltage divider,
and the current would need to be reduced using a resistive shunt circuit. Of course, reducing
these values would mean the signals input to the PC would have to be scaled by a certain factor
in Labview, and this would introduce an element of inaccuracy.
4.4.2 Custom GUI
Virtually all existing gym machines use a custom GUI, and a similar monitoring system would
be needed on any marketable version of an energy conversion system. A microcontroller could
be used to measure input current and voltage, calculate instantaneous power and the total
generated energy, and display them in a way that would demonstrate to the user how much was
being generated. However, this was beyond the scope of this project, due to the need for
substantial configuration of the microcontroller and custom coding of the GUI.
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4.5 Protective Devices
4.5.1 Diodes
As mentioned earlier, a diode is needed in the circuit to prevent backflow of power to the
generator. Since the output of the system could be connected to batteries or other storage
devices, there is a real possibility that the power generated could then cause the pedals on the
bike to spin if no one is using the equipment, which is a safety hazard. This is certainly not an
acceptable result, so a stud-mounted diode rated at 20 Amps was inserted between the generator
and the capacitor to prevent this from occurring.
4.5.2 Fuses
Another problem that was encountered is the unexpected increase in current that is generated
whenever somebody would get on the bike and pedal extremely fast in a short time. In doing so,
the generator would produce a high current which could in turn cause the voltage regulator to
become overloaded and eventually damaged. To correct this problem, a fuse was inserted into
the circuit. The job of the fuse is to be installed either after the ultracapacitor or before the
voltage regulator. The reason for the change in location is because when an ultracapacitor is
used, it can handle the fluctuation in current, but the watt meter, which is next in the circuit
diagram cannot. The same holds true when a voltage regulator is used. The regulator cannot
handle the increase in current and therefore a fuse must be inserted in order to protect it.
Because the voltage regulator can handle up to 15A, the fuse that would be used would be a 20A
fuse. The idea follows that whenever the current reaches a level higher than this, the fuse will
blow and become an open circuit, therefore blocking any current flow to the next component in
the circuit.
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5. System Design Descriptions
All of the system designs are similar to each other in one way or another. There are only a few
component additions as you progress through each design. An overview of each design can be
found below. With each, we will discuss performance costs and analysis, and the overall
marketability of each design.
5.1 Design Option 1: Direct Application
5.1.1 Design Overview
The idea of the direct connection design is that a device can be powered directly from the design.
Any type of AC or DC load which can be powered on the 12V DC power, or the 120V, 60Hz AC
voltage under 400W can be powered from this design. The use of the ultracapacitor allows for
short time storage of energy which can be discharging whenever the user stops riding for a
period of time. Whenever the capacitor is completely discharged, there will no longer be power
to the loads and therefore they will shutoff.
5.1.2 Performance and Cost Estimates
The direct application design is the next cheapest design in which the only change is the addition
of the ultra-capacitor. As mentioned before, the ultra-capacitor is a much needed component in a
high performance design and was not included in the demonstrated design due to cost factors.
Because of its importance, all other designs do include the addition of this part.
5.1.3 Marketability
Whenever used in a gym setting, this design could be extremely ideal for people who would like
to power some sort of electronic device while they are working out. Modern gyms sometimes
have televisions in front of the equipment with headphone jacks beside of the bike itself. Using
this design, it could possibly be used as a motivational tool for people who would like to power
the television or even an iPod or other MP3 player while they are working out. As long as they
are working, then the device will be powered. However, once they stop pedaling, they will only
have a short time before the capacitor discharges before the device will shutoff.
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5.2 Design Option 3: DC Network
5.2.1 Design Overview
This design takes the basic direct application design and adds onto it a battery and smart charger
system. Unlike the direct application though, a rider is storing up energy into a deep cycle
battery so that even whenever they stop pedaling for an extended amount of time, their devices
will still be charged. A smart charger is put in series with the battery in order to ensure that the
battery is never overcharged, which could in turn cause damage to the entire design. As stated
before, a deep cycle battery would be best used. This battery does not need to be stored directly
beside the machine, but rather could be kept in a storage closet out of the way of the bicycle area
itself. The final component of the design is the ability to add multiple pieces of exercise
equipment together, as seen in Figure 3. The original design of the DC network is kept the same;
however, multiple designs are connected to a single battery or battery bank.
5.2.2 Performance and Cost Estimates
The network design scheme also shows an increase in price due to the fact that a battery system
must be implemented. This could become costly due to the need to replace batteries as well as
the additional parts that must be purchased to ensure the safe storage of the energy generated.
The results that were received as far as the prototype that was built were not overwhelmingly
impressive. It was estimated that if one gym has 10 bicycles utilizing this system for 10 hours a
day for an entire year, only $365 would be saved. This is not a huge number, but if all the gyms
used them, then a somewhat substantial amount could be considered for savings. Due to this fact,
it is estimated that gym savings and profits could be increased by marketing the idea of a “green”
gym and the many benefits that would be created from that concept.
Whenever using the single battery, multiple machine design, the cost is not affected. Because
each bike can be connected with no extra components, there is a direct proportionality to the cost
and the number of bikes a certain gym might have. In fact, the more machines a gym contains,
the more beneficial it is, because they are only having to buy one battery or battery bank
compared to a battery per bike such as the design in Figure 2 suggests.
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5.2.3 Marketability
Because it is not necessarily feasible for a gym to completely produce its own power, this could
possibly be the most cost effective option for the gym. Like the direct application design, it
allows users the ability to power their own devices such as a television or MP3 player. A simple
diode could be implemented in order for the device to cutoff whenever they stop pedaling or
keep being powered by the battery system that is implemented. Even when someone is not using
any of the power they are generating, that power is still being stored in a battery somewhere to
ensure that it is not just wasted immediately as a thermal byproduct. The power that is stored in
the batteries be used to run lights, computers, cash registers, or even other machines whenever
needed. A backup system with regular outlet power would be used to ensure that the devices do
not shut down whenever the batteries are completely discharged.
Finally, the most marketable part of the DC network is that it is the one design that utilizes all of
the pieces of exercise equipment that a gym might contain. By connecting each bike or other
piece to a single battery bank, the gym can store a significantly higher amount of energy used to
power other machines, lights, cash registers and computers.
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5.3 Design Option 3: Grid Tie
5.3.1 Design Overview
The use of a grid tie is an ideal solution for any gym who thinks that they might ever produce an
excess of needed power. Whenever power is generated, it is phase matched with the power grid
installed by the local electric utility company and then power is fed onto those lines. No power
is actually stored locally, but by selling power back to the power company, a gym could reduce
their electrical bill depending on the amount of power they are generating. The overall idea of
this is similar to the use of solar panels on someone’s house whenever they are generating more
power than their house uses.
5.3.2 Performance and Cost Estimates
The grid tie design is by far the most expensive of the four designs described in this document.
This is due to the high costs of the grid tie itself. Grid ties can range anywhere from $3,500 to
$35,000 and could be a huge financial burden for a customer’s implementation. However, this is
the only way to efficiently and safely get the power back on the power grid.
5.3.3 Marketability
As stated before, this design appeals most to a gym that can create an excess of power which can
therefore be sent back to the power company. The benefits of this are obviously that money
would be saved each month, directly on their power bill based upon how much power is actually
generated. While it may be impractical to produce enough power to self-sustain the gym with
the exercise equipment alone, with the combination of solar panels, it can easily be achieved. As
of right now, electric utilities tend to steer away from the idea of buying back power from
individual customers, but with a new wave of green energy sweeping the country, this will soon
change and become much more common than it has been in the past.
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Figure 1 – AC/DC Direct Application
Bike/
GeneratorDiode Capacitor Fuse
Watt
Meter
DC
Adapter
DC/AC
Inverter
AC LoadDC Load
AC
Adapter
Bike/
GeneratorDiode Capacitor Fuse
Watt
Meter
DC
Adapter
Junction
For
Multiple
Bikes/
Generators
Smart
Charger
Diode
Battery
System
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30 April 2008 27 / 37
Figure 2 – DC Network
Figure 3 – Network Configuration
Bike System Bike SystemBike System
DiodeDiode Diode
Battery
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30 April 2008 28 / 37
Figure 4 – Grid Tie Design
Bike/
GeneratorDiode Capacitor Fuse
Watt
Meter
DC/AC
Inverter
Grid
Tie
Power
GridAC
Adapter
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30 April 2008 29 / 37
6. Construction Details
The components for this system could easily fit inside an enclosure that is 22” long by 16” wide.
The only parts that would not fit inside the enclosure would be the battery or battery bank.
These would have to be external to they system and could be stored in a closet or another room
to save space.
Possible Prototype Assembly
The following are illustrations of what a prototype of the system could look like. The design
would allow for the open wheel of the bicycle to sit in the groove in the middle of the design.
The wheel would then be in contact with the gray wheel on the shaft of the generator. This gray
wheel can easily be seen in the top view.
Top View
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Side View
From the side view, the different power outlets are easily in view. On the right is an AC plug, in
the middle are two 12 Volt DC plugs, and on the far left are two miscellaneous DC terminals that
could be connected to a battery bank or for other uses. Not pictured in the illustrations are the
two cords that would run up to the “Watt’s Up” meter. These cords could easily exit from one
side of the device go to the meter, and then enter back into the other side of the device. The legs
of the system would be adjustable so that the system could be raised or lowered depending on the
height of the bicycle. This would also make sure that the bicycle and the generator wheel are in
tight contact with one another. Another feature not pictured in the illustrations could be a strap
or connector that attaches to the front legs of the bicycle. These braces could be used to pull the
system closer to the bicycle wheel, thus ensuring better contact and connection with the
generator shaft.
Again, these are just preliminary designs so that one could get an idea of the system enclosure.
These designs could easily be altered to meet other demands as well.
Front View
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7. Future Improvements
After designing the prototype there are several areas of the design that could be improved upon
and issues that should be considered in the future design of this system.
The first area of improvement is the voltage regulator that is used to steady the input from the
generator. As mentioned earlier, the voltage from the generator was originally regulated in the
design by a simple voltage regulator circuit (See Appendix). This circuit originally consisted of
three voltage regulators in parallel so that they could handle up to 15 Amps. The circuit would
take an input voltage of and regulate it to a voltage between 4.5V and 20V. This value was
determined by a potentiometer that was available for the user to turn. However, when the
voltage regulator was tested in the system, it was apparent that it was not working with the
bicycle. The bicycle that was being tested was extremely old and did not have a smooth spinning
motion to produce a relatively constant voltage. Although this problem was anticipated—thus
the voltage regulator—the solution proved not to be as effective as was hoped. The drastic
changes in voltage as the system transitioned from not having a load to having a load proved to
be too much for the voltage regulator to handle.
As a solution to this problem, it is recommended that an ultra-capacitor be used. This concept
was mentioned earlier in this document and is believed to be the best possible way to solve the
issue. The ultra-capacitor, although more expensive, will be able to handle the sudden change in
voltage and provide the instantaneous power that is demanded once the load is turned on.
Another issue that must be taken into consideration is the connection between the generator on
the shaft of the wheel and the bicycle wheel. It was determined that for an application where it
was necessary for the system to be portable that a single point of contact of design would be best.
However, due to the friction between the two wheels, it is possible for the contact between the
two to become weaker over time. This was experienced during the original prototype testing
when the rubber composite that was on the generator shaft wheel started to wear away over time.
This wear formed a groove in the generator shaft wheel so that when bicycle wheel turned, there
was slippage.
To offset this problem, a stronger material should be used on both the generator shaft wheel and
the bicycle wheel as well. A durable rubber could easily solve this problem and provide the
efficiency in connection that is needed. Overall, a belt system might be the best solution to this
particular problem, but given the demand to be able to easily and quickly set-up the system, a
single point of contact design is still the best.
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The last area of improvement that should be looked at is the type of bicycle that is chosen to be
used with this system. As mentioned earlier, the bicycle that was chosen to test a prototype
design was extremely old and not in the best of condition. When the bicycle was pedaled, the
rotation of the wheel was inconsistent and varying. This proved to be a great problem in
reaching the results that were desired. The bicycle machines that are used today in cycling
classes would be the best design to be used with the system. They still provide the open wheel
design and have a large flywheel that continues to spin for a long period of time once the user
stops pedaling. These bicycles would be better suited to provide a smooth and constant rotation
of the generator shaft and limit problems downstream in the system with instantaneous voltage
changes.
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8. Business Considerations
To a large extent, the ideal design depends on the desired use of the electricity that is generated.
This is a business question, and is largely outside the scope of this project, but a brief discussion
of possible business considerations is included here.
The initial finding of this project is that the power savings that would result from using this
design are not enough alone to break even on the initial investment in a reasonable amount of
time. For this reason, a marketing component would help to make the investment in a “green
machine” a profitable one. One obvious idea is to purchase energy conversion machines and
create a marketing campaign to redefine a new “green”, environmentally friendly image for the
gym. This would help to increase membership at the gym.
One possible use of the energy generated would be to directly power a load, as discussed
previously. If the load were something such as a television or a cell-phone charger, this would
provide an entertaining or at least useful form of motivation for the exerciser, which would
encourage new membership and more frequent use of the gym by members.
However, the general public’s perception of “green” technologies and helping the environment is
centered on benefiting the common good; energy converters that feed the power grid or store
energy in a battery bank would lend themselves to this more easily. In addition to creating a
sense of good stewardship and responsibility among individual users, it would help foster a sense
of community at the gym. This could be done by displaying the gym’s aggregate daily energy
savings, in dollars or in pounds of greenhouse gas offset.
Another business idea some gyms have explored is to create a credit system based on the energy
a member generates. This would be done by keeping track of the kilowatt-hours generated by
the user, who could receive a small discount on his or her monthly dues if a certain amount of
energy were generated. One way to implement this would be by swiping a keycard before the
user starts exercising.
Once this keycard system were created, it could be extended to log other things, such as the
user’s cumulative calories burned and their overall workout patterns; this information would be
of interest to the individual user, and could be given to them periodically. Of course, this would
largely be dependent on exercise machine manufacturers adding this ability to their machines,
and it would not be possible for older machines.
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9. Conclusion
Despite several setbacks and many limitations that resulted from time and budget constraints, the
research and prototyping components of this project were found to be a success.
The research findings provide a wide breadth of information related to a large number of
possible designs. Based on the benefits and disadvantages of each possibility described in this
report, both at the level of individual components and system-level designs, future development
efforts have been given a good foundation to work from. To a large extent, this project found
that the ideal design depends almost completely on the desired application. For example, if the
energy converted would be used to provide instant motivation to work out, a direct load should
be powered, which affects design decisions throughout the system.
There were several setbacks and budget limits that affected the prototyped exercise machine.
Regardless of these, the prototype allowed many of the basic principles of the system to be
analyzed, and verified many of the concepts explored in the research component of the project.
While the design is far from being robust enough for market, it is a good starting point for future
development. Based on the initial findings of this project, it is reasonable to believe this design
could be developed further and eventually become efficient enough to be profitable, especially
when mass production and the economies of scale are considered along with the more intangible
benefits of a “Green Machine” being used at gyms.
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IV. Appendix
Bicycle Used for Prototype
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30 April 2008 36 / 37
DC
Bike/Generator
Source
2N2905
100 5k
0.10.10.1
200
pF1.5k
150
5k
Watt Meter/
Load
LM308
LM338 LM338 LM338
Diode
Circuit Used for Prototype (Voltage Regulator in Dashed Lines)
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30 April 2008 37 / 37
Cost Chart
Parts
Direct
Application Grid Tie Network
Chosen
Design
Bicycle Donated Donated Donated Donated
Generator $80 $80 $80 $880
Diode $10 $10 $10 $10
Capacitor $220 $220 $220 X
Fuse $8 $8 $8 $8
DC Adapter $30 X $30 $30
AC Adapter $25 $25 X $25
Watt Meter $56 $56 $56 $56
Regulator X X X $15
Inverter $34 $34 X Donated
Diode #2 X X $10 $10
Smart Charger X X $70 X
Battery Bank X X $110 X
Grid Tie X $3,000 X X
Misc. $50 $50 $50 $50
Cost $513 $3,483 $644 $284