Battery Charger Report 3

8/3/2019 Battery Charger Report 3

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Business Plan and Design Proposal:12 Volt Universal Battery Charger

Group 3Final Report

December 17, 2003

Michael EskowitzECE Box # 99

Eric HallECE Box # 133

Chris HammanECE Box # 135


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Table of Contents

Executive Summary 1

Section 1: Introduction 2

1.1 Problem Statement 2

1.2 Planned Approach 3

Section 2: Product Specifications 4

2.1 Market Research 4

2.2 Customer/ Product Requirements 8

2.3 Product Specifications 9

Section 3: Product Plan 11

3.1 Development Schedule 11

3.2 Budget 13

Section 4: Design Approach 14

4.1 Design Options 14

4.1.1 Signal Conditioner 15

4.1.2 Charge Monitor 15

4.1.3 Charge Status Display 16

4.2 Value Analysis 17

4.2.1 Power Supply 17

4.2.2 Charge Monitor 18

4.2.3 Charge Status Display 20

4.3 Competitive Value Analysis 21

4.3.1 Solar Chargers 22

4.3.2 AC Chargers 24

4.2.3 Pedal Chargers 26

4.4 Module Definitions 27


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4.5 Manufacturability 34

4.6 Cost Analysis 35

4.7 Hazard Analysis 37

4.8 Legal Considerations 38

Section 5: Product Results 39

5.1 Product Functionality 39

5.2 Product Form 39

5.3 Expected ROI 40

Section 6: Recommendations 42

Appendix A: Circuit Diagram 44Appendix B: Assistance and Contact Info 45

Appendix C: LM 555 Equation Derivations 46


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Table of Figures

Figure 1: Map of Mali 4

Figure 2: Solar Panel Charger 6

Figure 3: AC-Charger 7

Figure 4: System Block Diagram 14

Figure 5: Solar Charger 22

Figure 6: AC Charger 24

Figure 7: AC Battery Charger 25

Figure 8: Signal Conditioner 28Figure 9: Charger Circuit 30

Figure 10: Charge Status Display 32

Figure 11: Switching Oscillator 33

Figure 12: Kinkajou Charger Casing 40

Figure 13: Battery Charge Display 40

Figure 14: Side View of Charger Case 40

Figure 15: Return on Investment 40


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Table of Tables

Table 1: High-Level Gantt Schedule 11

Table 2: Itemized Task Gantt Schedule 12

Table 3: Power supply value analysis 18

Table 4: Charge monitor value analysis 19

Table 5: Charge status display value analysis 21

Table 6: Competitive Value Analysis 27

Table 7: Component Pricing 36


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Executive Summary

A recent report published by the United Nations1 has indicated that there are

currently 860 million illiterate adults world-wide and 100 million children who have

no access to education. They cite literacy programs as a crucial means of breaking the

poverty cycle.

Design that Matters (DtM), a nonprofit corporation, has developed a low-cost

projection system called the Kinkajou that will deliver teaching materials to

instructors who are desperate for teaching resources. In light of this, our company

has been contracted to design a portable, multi-input battery charging device that willcharge 12 Volt lead-acid car batteries, which are used to power the Kinkajou device.

After a consultation session with the principals, Tim Prestero and Neil Carter, we

were instructed to investigate the viability of introducing the product to a target

market. The country of Mali will be the focus of our feasibility study.

In the following paper, we will present an overview of our prototype

development process, justify our design decisions, make a set of recommendations for

future actions, and propose a business plan that could later be developed for our

product.

1 United Nations, The State of Global Literacy (Online: www.unusa.org)


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Section 1: Introduction

1.1 Problem Statement

You are to design a universal 12 Volt battery charger that can take various

forms of electrical energy and charge a typical 12 Volt lead-acid

(automotive) battery. The charger must be able to handle the following

inputs: a solar panel, a pedal generator, and standard AC power (both

American and European standards). The charger must not overcharge the

battery, and must indicate the state of charge. In addition, the circuit should

not drain the battery. The charger must be affordable in the community it is

used in, and should be suitable for applications such as the Kinkajou

Projector. (http://kinkajou.designthatmatters.org) Prototype cost should

not exceed $50.

1.2 Planned Approach

The process of developing a quality product that meets the demands

of a potential market involves a great deal of forethought and design work.

Our first course of action was to perform market research to anticipate the

needs of our target market and to formulate a set of product specifications and

requirements. After we had gained good insight as to what the productspecifications were we were able to formulate a course of action in which to

carry out the design project. We brainstormed numerous design options and,

based on a value analysis of these options, finalize a design approach.


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Due to the extensive nature of this project and the short time allotted for

completion, we found it necessary to subdivide the various tasks and assign

each group member with a specific set of responsibilities. The assignments

were given depending upon the willingness and ability of each team member.

Additionally, we decided that certain tasks such as writing reports, giving

presentations and doing research were the responsibility of everyone in the

group. By taking a modular approach we were able to design, build, test, and

troubleshoot several subsystems independently and combine them after each

was working as a stand alone device.


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Fi ure 1: Ma of Mali

Section 2: Product Specifications

2.1 Market Research

A. Methods

In developing our market report, we utilized a variety of resources to quantify

our market, research products, and determine design considerations. In addition to

the information session led by the founders of Design that Matters, some of our

research materials included The Stanford Business Journal, Reports from the United

Nations Educational, Scientific and Cultural Organization (UNESCO), the United

States Patent website as well as several product websites.

B.Market Research

From extensive research we were able to

identify and anticipate the needs two markets

both the stated market of Mali and other parts of

the Developing World. A dual market exists in

that the charger could also be sold separately

from the Kinkajou.

Mali is among one of the poorest nations in

the world as 65% of its land is desert or semi-

desert. The yearly per-capita GDP is about U.S.

$2982 and much of the country lacks economic developmentas a result,

constructing a device that is inexpensive to produce and sell is essential. Since

transportation and shipping are expensive endeavors due to the lack of paved

2 International Service for National Agricultural Research, Mali: A Typical Sahelin Country (Online:www.insar.org)


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roads, it is also essential that the device be as light-weight as possible since it will

likely need to be carried over long distances. Our market primarily consists of those

who reside in village communities, which typically lack electricity. Therefore the

charging device would need to accommodate multiple sources of input. Only about

50% of people in Mali can afford the luxury of batteries to power electric devices

and the cost to recharge a battery is up to 700 CFA (Communaute Financiere

Africaine or the African Financial Community) which equates to roughly U.S. $1.24

per battery. This is a substantial cost to people in such an impoverished area.

Therefore producing such a device would result in long term savings to

communities.The Kinkajou Device has world-wide appeal to promote literacy in regions that

lack adequate teaching resources. Organizations such as the World Literacy

Foundation, UNESCO, and the World Literacy Crusade would likely be interested

in purchasing the device for use in their campaigns to fight illiteracy.

There is a world-wide demand in the developing world for a low-cost means

of charging 12 Volt batteries. Power is essential for most modern devices. A

charger with a myriad of inputs could be used for the following:

Adapting charging technology to meet the demands of communities that lack

electricity will likely prove to be a very profitable market. Additionally the

charger could be used in the developed world to accommodate alternative sources

of energy in order to lessen dependence on fossil fuels.

Communication Systems

Refrigeration

Health Services

Disaster Recovery

Residential and Commercial Applications

Utility Applications

Water Pumping

Lighting


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Figure 2: SolarPanel Charger

C. Competing Products

In an effort to evaluate our competitors we performed extensive product

research to determine typical production costs, feature sets, and sales price. Since

a charger that handles multiple power sources does not exist, we examined each

type of charger individually.

Solar Chargers

There are several commercially available solar battery

chargers. Camping and automotive retail stores providedinformation on various models that are currently for sale.

Prices ranged from U.S. $ 29-$50 for low-end battery savers

that provide a low-current, slow charge. There are also a

variety of solar devices that will fully charge a battery with

prices ranging from U.S. $64 - $900 depending on the extra features. Output

wattage of these chargers seemed to be the biggest price differentiator. After

comparing several different chargers, we were able to identify distinguishing

characteristics among competing products.

Distinguishing Features of Solar Chargers:

Rollable-mat solar collectors

Daisy-chain capability for multiple chargers

Built-in diode for reverse current protection

Bypass for charger to Run 12 Volt Device without battery

Pedal Chargers

From our market research, we determined there is not a wide variety of

commercially available pedal chargers. Most of our inquires led us to believe that


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Figure 3: AC-Charger

nearly all pedal chargers are homemade devices that are pieced together from various

parts, typically bicycles and car alternators. There does not appear to be a standard

consensus on how pedal chargers are built; a pedal generator will have various

outputs depending on the RPM being produced, the gear-ratio of the chain drive, and

the actual device being used in the generator to convert mechanical to electrical

energy. Due to the lack of competing products available in the market place, our

company will need to determine a set of requirements for the pedal charging feature.

AC- Outlet Chargers

Our product will need to be able to interface with both European (110 Volt) and US (220 Volt) power

standards. To address this, we researched various products

internationally. Prices for AC-Outlet Chargers ranged from

U.S. $25- $200 depending on the feature set and the output

current, which will determine the rate at which a battery is charged. After comparing

several competing products we were able to synthesize a list of desirable features.

Distinguishing Features for AC-Outlet Chargers:

Reverse Polarity Indicator

Short-Circuit/Surge Protection

Easy-To Read Color Terminals

Charge Rate, Charge Status, Charge Done Indicators


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2.2 Customer/ Product Requirements

From our market research we were able to determine the following set of customer

requirements and product specifications:

Affordability - Our market research shows that to most people, price is the

first thing considered when buying a product. Since the Kinkajou projector is

designed to be used primarily for literacy classes in the developing world, its

components need to be as inexpensive as possible.

Durability - It is reasonable to expect that the device will be bumped and

dropped from time to time, so it is essential that the charger is strong

structurally. Furthermore, our market research shows that Africa is known for

having large power spikes and brownouts, so surge protection is a necessity as

well. It is also essential that the product last as long as possible and need few

repairs over time.

Compact Size/ Light Weight - Many of the users of this product will live in

small communities far from cities where they might purchase such a device.

Thus the product will need to be carried some distance. For this reason, it

needs to be as compact and lightweight as possible so that the average person

can carry it a reasonable distance.

Efficiency - As seen in our customer requirements, the product will need to be

as efficient as possible in its use of power. The device may be powered by a

person using either a hand crank or a bicycle generator and thus it is infeasible

to expect a long duration of supplied power. It is thus critical that all power be

used efficiently.


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Versatility - Our research shows that the population that the product will be

marketed toward has variety of available power sources. Some may have

access to AC power, but many areas will not and thus need to make use of

alternate power sources. It is for this reason that the product needs to be able

to charge a battery with power from three different sources, an AC outlet (both

110 and 220 Volt outlets), solar panels, or a pedal generator.

Simplicity - The product will be used by people who are most likely not

technically educated. Therefore, to appeal the largest market possible, it mustbe simple to operate and switch between the three possible power sources.

2.3 Product Specifications

Once we had developed a good understanding of the needs of our customers, we

were able to merge the findings of our customer requirements and market research

into a general set of product specifications:

110/220 AC power supply input

Solar panel power supply input

Bicycle or hand crank generator power supply input

Non-alpha-numeric output display

Cost per unit of less than U.S. $50

Portable and durable

High Mean Time Before Repair (MTBR)

High efficiency

Charges a 12V lead acid car battery

Does not overcharge the car battery


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We were required to adhere to these underlying product specifications throughout

the course of our design process. By using these product specs as an initial, non-

technical guideline, we were able to hasten the design process and make effective

decisions.

As stated by our contractor, Design That Matters, affordability is a critical aspect

of this device. The target market for this product will be developing nations that will

not be able to absorb a high per unit cost. Specifically, Design That Matters has set a

price target of less than U.S. $50 total for the battery charger and Kinkajou drive

circuitry.

In the course of our market research, we determined that the probable inputvoltage range from the three power sources will range from 6V-22V DC. Due to the

variability of system input, it is necessary to construct a signal conditioning system to

supply a constant input to the charging mechanism. To make this system possible,

low voltage signals will need to be amplified to a constant value just as high voltage

signals will need to be regulated. By ensuring that the charging device receives a

constant input, we can guarantee the operation of the charger.

The charge controller is another module that has several design considerations. In

addition to supplying an efficient and timely charge to the 12 Volt Battery, it will be

essential that the charge controller provide an output of its charge status as well as

stop itself from continuing to charge once the battery has reached full capacity.

Due to the fact that the target market for this device will be in developing

countries with a low literacy rate, an alpha-numeric display is impractical. In order to

make the device as readily understandable as possible, a series of LEDs will be used

to display battery charge status. Additionally, because the Kinkajou system itself will

be primarily used in darkened classrooms, the LEDs will allow the battery charger to

be utilized in such environments as well.


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Section 3: Product Plan

3.1 Development ScheduleDue to the extensive nature of this project we found it necessary to subdivide the

various tasks and assign each group member with a specific set of responsibilities.

The assignments were given depending upon the willingness and ability of each team

member (refer to the R column of Table 2). Additionally, we decided that certain

tasks such as writing reports, giving presentations and doing research were the

responsibility of everyone in the group. We have also divided the project into phases

with dates corresponding to the completion deadline. Please refer to our Gantt charts

below (Tables 1 & 2) for specific task assignments and project phases.

Table 1: High-Level Gantt Schedule

By developing both high-level and itemized task schedules we were able to ensure

that our group was on task and well prepared for future deadlines. The Gantt chart

method was used to plot individual responsibilities and their corresponding due

dates. We made sure to allow a margin for contingency; recognizing that no matter

how much forethought was given, everything would not go as planned.


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Table 2: Itemized Task Gantt Schedule

Key:


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3.2 Budget

One of the most important initial stipulations of the original problem statement

was that .the charger must be affordable in the community it is used in, and should

be suitable for applications such as the Kinkajou Projector. Prototype cost should not

exceed $50. In addition to having a $50 dollar initial prototyping budget, it was also

necessary to ensure that the total production cost when produced in bulk not exceed

roughly $25. This budget constraint played a major role in making design decisions as

economical as possible and also made it obligatory to take calculated risks when trying

potential design methodologies. Throughout the process of devising our product, we

often had to fully consider cost-benefit analysis as well as examine the trade offs

between better specification fulfillment vs. reduction of overall expense.


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Section 4: Design Approach

4.1 Design Options

Given the set of product specifications previously described, we found that

the most effective way to design the device was as a set of several interconnecting

subsystems. The block diagram shown below highlights the three main

subsystems identified during the design process: a signal conditioner, a battery

charge monitor and a charge status display. The signal conditioner in our product

is used to format any applied voltage from the three types of potential inputs (wall

outlet AC, solar panel or pedal generated voltage) and to apply a voltage on the

battery in order to charge it. The charge monitor is needed to regulate the current

flow into the battery so that the battery does not become overcharged or otherwise

damaged during the process of charging. Additionally, the charge status display

is necessary to indicate the level of charge on the battery and, in particular, to alert

when the battery has been fully charged.

Figure 4: System Block Diagram


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4.1.1 Signal Conditioner

The power supply subsystem of our design is responsible for converting an

AC source into DC and accepting two additional DC sources. In brainstorming

this subsystem we determined two ways of handling the AC/DC conversion

process. Converting the 110/220 AC voltage into a DC voltage could either be

done internally through the use of a transformer, bridge rectifier and zener diode

or the conversion could be done externally through the use of an AC adapter rated

for the appropriate voltage range.

4.1.2 Charge MonitorWhile brainstorming the charge monitor we identified several design

strategies for this subsystem. Because the charge monitor must tell the charge

status display what to indicate, we considered using an A/D converter in a

sample-and-hold configuration to quantify the batterys voltage. The digital

output could then be passed through several combinational logic circuits in order

to generate both the appropriate input for the charge status display and the

control signals for the power supply. Another digital approach would be to utilize

a PIC microcontroller with an internal A/D converter. The PIC could then read the

battery voltage and internally generate the output for the charge status display

and control signals for the power supply. This particular design strategy would

eliminate the need for additional combinational logic circuitry.

Having considered digital solutions we next considered an analog strategy

for implementing the charge monitor. One possible analog design consists of

generating a reference voltage (possibly the voltage at which the charger stops

charging) and comparing it to the batterys voltage using a comparator. The

output signal from the comparator would then be sent back to the power supply

in order to control the charge placed on the battery by means of a negative


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feedback loop. Another analog design would be to use the LED array in the

charge status display to measure a specific voltage on the battery and then feed

that voltage back to the power supply in a negative feedback loop. This design

approach has the advantage of merging the charge monitor and charge status

display into a single functional subsystem.

The design approach that we eventually settled on utilizes a UC3906 linear

lead-acid battery charge management IC to implement a three stage charging

algorithm. The IC accomplishes this by controlling both voltage and current

output based upon feedback from the battery. Additionally, this IC will monitor

battery temperature and adjust the output signal accordingly. This componentgreatly simplifies our task of charging the battery in the most efficient way

possible.

4.1.3 Charge Status Display

Several design options exist for the charge status display. An analog

display with an arrow that either ranges between 0 and 100% charge or indicates

the battery voltage (a voltmeter) could be used. A single LED or group of LEDs

could also be used for this task. The single LED design would have the LED lit

when the battery reached full charge, while the LED array design would feature a

progressive update of the charge status. Another option would be to use a 7-

segment LED display to output a numeric charge percentage. Additionally, in

terms of non-visual display systems, a buzzer could be used to generate an

audible signal that the battery has finished charging. The buzzer also need not be

standalone as it could be used in conjunction with one of the other design

strategies.


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4.2 Value Analysis

In order to determine the most feasible implementation we performed

value analysis on the design concepts presented in Section 4.1. We used value

analysis matrices to aid in deciding which options will make our product the most

marketable.

4.2.1 Power Supply

Product Requirements

Handles 110/220V AC as input

Supports solar panels and pedal generator as input

Produces a DC voltage suitable for charging a 12V lead acid car battery

Options Available and Advantages/Disadvantages

External AC/DC conversion using an AC adaptor:

Easy to implement, more expensive.

Internal AC/DC conversion:

Harder to implement, less expensive.

Value Analysis

Cost: Price of subsystem.

Inexpensive 3

Reasonably Priced 2

Expensive 1

Simplicity: Ease of construction.

Easy 3

Moderate 2

Hard 1

Availability: Widely available components

Good 3

Average 2

Poor 1


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Weight Assignments

A completed value analysis for the power supply is shown in Table 3

below.

Table 3: Power supply value analysis

4.2.2 Charge Monitor


Does not overcharge the battery

Outputs to the display

Controls the power supply


Digital with combinational logic:

Harder to implement, easily expandable/robust, high power

consumption.

PIC microcontroller:

Software expandable (handles logic internally), replacement parts

unavailable in developing countries.

Analog with comparator:

Harder to implement, readily available replacement parts.

Integrated with charge status display:


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Efficient design, low power consumption.

UC3906:

Efficient design, replacement parts unavailable in developing

countries.

Value Analysis


Inexpensive 3

Reasonably Priced 2

Expensive 1

Efficiency: Power consumption of the subsystem

Good 3Average 2

Poor 1


Easy 3

Moderate 2

Hard 1

Weight Assignments

A completed value analysis for the charge monitor is shown in Table 4

below.

Table 4: Charge monitor value analysis


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4.2.3 Charge Status Display


Easy to understand

Inexpensive

Low power consumption


Analog display:

Harder to interpret, more expensive.

Buzzer:

Easy to implement, does not indicate charge status.

Seven segment display:

Harder to implement, more expensive, requires literacy.

Single LED:

Inexpensive, low power consumption, easy to implement, does not

indicate charge progress.

LED array:

Inexpensive, low power consumption, harder to implement than

single LED, indicates charge progress.

Value Analysis


Inexpensive 3

Reasonably Priced 2

Expensive 1


Easy 3

Moderate 2

Hard 1


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Understandability: The clarity of the display.

Good 3

Average 2

Poor 1

Weight Assignments

For the display subsystem, we considered understandability to be the most

important criteria and, as a result, it was assigned a weight of 3. Of the remaining

two criteria, cost was assigned a weighting of 2 and simplicity a weighting of 1.

Table 5: Charge status display value analysis

4.3 Competitive Value Analysis

After searching widely, we were able to find many competitors in the

market of recharging batteries. Typical applications for battery charging included

Marine, camping/outdoor, and automotive uses. It was determined after

thorough research that our product would be unique to the marketplace due to the

fact that currently no charging device available is designed to accept multiplepower sources. Despite this, we will evaluate similar products for each type of

input source; AC, Solar, and Pedal Generated. Table 4 shows the competitive

value analysis of our product vs. the four competitors described below.


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4.3.1 Solar Chargers

When solar panels are used to charge storage batteries, their limited output

under low sunlight conditions leads to seriously shortened battery life and

performance. Trying to protect against this creates higher costs, as the typical

solution seems to be increasing the size / number of both the panels and batteries.

In addition, typical solar controllers, although able to protect batteries from

under/over charge, fail to optimize the charge rate capabilities of the solar panels.

They also do not remove sulphate build-up on the batterys storage plates, causing

longer recharge time, boil out and significantly shortened life.

There are a variety of solar devices that will fully charge a battery with pricesranging from U.S. $64 - $900 depending on the extra features. Output wattage and

solar panel size of these chargers seemed to be the biggest price differentiator.

After looking at several models, we what seemed to be two of the better

commercially available solar chargers out there.

PRO-KIT 15-WATT SOLAR BATTERY CHARGER ICP Global Technologies

The Pro-Kit Charger was similar to many other solar products

available. At U.S. $189 the device is far more expensive than

our product, but the photovoltaic cell is what drives the cost of

the charger up and because our charger relies on an external

solar cell, it is reasonable to assume that our product would be

a competitor3.

3BatteryMart, Solar Battery Chargers (Online: http://www.batterymart.com/battery.mv?c=solarchargers)

Figure 5: SolarCharger3


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Specifications:

Wattage: 15 watts Peak Output: 1 amp@15 volts

Approx. Watt-Hrs / Day *: 60 75 Approx. Amp Hrs / Day *: 4 - 5

Dimensions: 38" x 13" x 1" / 965 mm x 330 mm x 25 mm Weight: 9.2 lbs / 4.2 kg

Temperature Range: -40F to 176F / -40C to 80C Warranty: 5 years @ 80% of output

Ratings:

Operating Conditions: 5, Diverse Temperature Range and Weatherproof Design

Display: 2, Very Limited User Display

Extra Features: 1, Has a few added features like overcharge protection

Range: 4, Can operate on many input voltages- dependent upon sunlight

Ease of use: 4, Intuitive to Use

Charge Time: 2, Depends on available sunlight, 15 W Max Output

Modular Design: Unknown- Dont know internal design

Components: Unknown- Dont know internal components

Versatility: 1, Operates on 1 Input

Weight: 3, Light-weight

Price: 0, $189

BATTERYMINDER 12 VOLT 5 WATT SOLAR CHARGER- VDC ELECTRONICS

The BatteryMINDer, produced by VDC Electronics is another typical

product that beats most other competitors price significantly for its output specs.

The device distinguishes itself in particular because it optimizes the solar panels

charge rate, ensuring batteries are charged in the shortest possible time, keeping

them at full-charge indefinitely, without ever overcharging.4

Specifications:

Wattage: 5 watts Peak Output: 333 mAmps@15 volts

Approx. Watt-Hrs / Day *: 20 - 25 Approx. Amp Hrs / Day *: 1.4 - 1.75

Dimensions: 19 5/8" x 13 5/8" x 5/8" Weight: 7 lbs

Temperature Range: 0F to 130F Warranty: 5 years

4 BatteryMart, Solar Battery Chargers (Online: http://www.batterymart.com/battery.mv?c=solarchargers)


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Ratings:

Operating Conditions: 4, Diverse Temperature Range and Weatherproof Design

Display: 0, No User Display

Extra Features: 2, Battery Minder Component Optimizes Charge

Range: 4, Can operate on many input voltages- dependent upon sunlight

Ease of use: 2, Moderate Difficulty

Charge Time: 1, Depends on available sunlight, 5 W Max Output



Versatility: 1, Operates on 1 Input


Price: 0, $99.95

4.3.2 AC Chargers

There were an extensive number of portable, commercially available

battery chargers, with prices ranging from about U.S. $30 - $500. The price was

largely a variable of extra features, number of batteries that could be charged at

one time and the output amperage, which determines the rate at which a battery is

charged. The Competitors also had different ways of implementing what seemed

to be different charging algorithms to achieve optimal charge. There are two

options examined in this section, a typical, fully-finished consumer model and an

exposed AC charger circuit made for industrial/customized applications. Because

most consumer models were essentially the same, we chose the two models that

best represent the needs and specs of our market.

CLIPLIGHT 12 VOLT 10 AMP PORTABLE CHARGER MOBIL LINE

The Mobil Line Deep Cycle Battery charger is typical of most

portable chargers in that it can recover deeply discharged batteries as

well as prevent overcharging. The charger also has overload and

reverse polarity protection as well as an intuitive,

Figure 6: ACCharger5


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simple to understand LED display5. At U. S. $49.95, the device is competitively

priced for the variety of features that it offers in comparison to other models.

Specifications:

Output: 12 Volt Nominal; 10 Amp DC Set Voltage: 14.7 +/- 0.1 Volt

Float Voltage: 14.0 +/- 0.1 Volt Input: 105 VAC - 120 VAC ; 60 Hz

Dimensions: 3-1/2" x 2-1/4" x 4-1/2" Weight: 3 lbs.; 1.36kg

Ratings:

Operating Conditions: Unknown

Display: 2, LED Array

Extra Features: 2, Several Extra features like polarity indicator and surge protection

Range: 0, Only Rated for American Power Standard

Ease of use: 4, Very Easy to Use

Charge Time: 3, 10 Amp Output, uses charging algorithm for optimal time



Versatility: 1, Operates on 1 Input American AC Standard


Price: 1, $49.95

L12-0.5/115AC LEAD ACID CHARGER IBEX INC.

Ibex Inc. offers a wide variety of industrial application

battery chargers that can handle both American and European

AC power sources as well as being manufactured to operate in

harsh and extreme in environments. Their line of devices are

rugged and made to last for many years without failure or need

for repair. The Ibex chargers range in cost from U.S. $45- $806.

4 Battery Mart, 12 Volt AC Chargers (Online: http://www.batterymart.com/battery.mv?c=12voltchargers)

6 Ibex AC Battery Chargers (Online: http://www.ibexmfg.com)

Figure 7: ACBattery Charger6


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Specifications:

Output: 14.8 V 10 Amps Input: 103 252 V AC

Dimensions: 5 x 4 x 3 Weight: 4 lbs

Temperature Range: 0F to 130F

Ratings:

Operating Conditions: 4, Designed to Handle Extreme and Harsh Environments

Display: 0, No User Display

Extra Features: 1, Has some internal extra features

Range: 2, Accommodates American and European Power Standards

Ease of use: 0, Not housed, controls dont come with circuit

Charge Time: 2, Uses 3-Stage Temperature Dependent Charging Algorithm

Modular Design: 1, Circuit is modular

Components: 2, Uses common parts like transformers, diodes and capacitors

Versatility: 2, Operates on 2 Inputs US and European Standards


Price: 1, $45

4.2.3 Pedal Chargers

From our market research, we determined there is not a wide variety of a

commercially available pedal charger. Most of our inquires led us to believe that

nearly all pedal chargers are homemade devices pieced together from various

parts, typically bicycles and car alternators. There does not appear to be a

standard consensus on how pedal chargers are built; a pedal generator will have

various outputs depending on the RPM being produced, the gear-ratio of the

chain drive, and the actual device being used as the generator to convert

mechanical to electrical energy. Due to the lack of competing products available

in the market place, our company will need to determine our own set of

requirements for the pedal charging feature.


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4.4Module Definitions

Signal Conditioner

The Signal conditioning phase is designed ensure that any input signal

above or below the desired operating voltage is regulated before being passed to

the UC 3906. This is accomplished by a boost converter and voltage regulator in

series, which boost or step-down the input signal as necessary.

After evaluating several boost converters, we found the LM2577, a TO-263-

5 package based solution that meets our design requirements. The LM2577 is able

to reliably boost low DC voltages in the range of 3.5 40 volts to a constant output

voltage that can be synthesized by a simple LC configuration.The voltage regulator used for this subsystem is an LM350. This IC will be

used to provide a constant current and smooth voltage signal to the UC3906. As

long as the boost converter raises the any low input signal to above 15 volts, the

Table 6: Com etitive Value Anal sis


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LM350 will be able to ensure that the UC3906 receives a constant supply of 15

volts.

Figure 8: Signal Conditioner

The appropriate components in the boost converter section of the signal

conditioner were chosen using the following equations for VVin 5.3min =

and VVout 17= .

MAX

MAXINMIN

D

DVVL

=

1

)12)(6.0(4.6 min

VVV

VVV

DFOUT

INFOUT

MAX 6.0

min

+

+

=

2

min

2750

IN

OUTLOADC

V

VIR


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OUT

LOADV

VinAI minmax

1.2

OUTIN

LOADCOUT

VV

IRLC

min

max19.

min

2

25.58

INC

OUTOUT

CVR

CVC

1V23.12

1 = OUTV

R

R

The resistors used in the voltage regulator were synthesized using the equation

2

1

2 *125.1 RIR

RV ADJOUT +

+= .

Linear Charger IC

The heart of our design is the UC3906, a linear lead-acid battery charge

management IC which implements a three stage charging algorithm in order to

maximize battery lifespan. (See Figure 9) The IC accomplishes this by controlling

both voltage and current output based upon feedback from the battery.

Additionally, this IC will monitor battery temperature and adjust the output

signal accordingly. This component greatly simplifies our task of charging the

battery in the most efficient way possible.

The UC 3906 accepts an input voltage of 10-40 Volts DC. In our design, the

voltage regulator will provide a regulated voltage in the range of 10-20 Volts DC

to the UC3906. Depending on the input voltage and the charge of the battery, the


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IC will provide a voltage and current as specified by the charging algorithm. In

order to accomplish this the configuration shown in Figure 9 was implemented.

The resistor values used in the circuit were derived from the set of equations

below.

k463.2 ==D

CI

R

k2123.2

1

=

+=

T

XSUM

A

V

RRR

k18== ASUMB RRR

Figure 9. Charger Circuit


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31

k881*3.2

=

=FOC

SUM

DVV

RR

k2303.2=

=

D

FSUMI

VR

A3.010

== MAXOCI

I

k7.43*

=+

=DC

DCX

RR

RRR

1.025.0

==MAX

SI

R

34.0

5.2=

=

T

TIN

T V

VV

R

Additionally, the equations above contained specific voltage and current level that

are specified below.

A50=DI

mA5.1=TI

A5.2=MAXI

V4.14=OCV

V16=INV

V8.13=FV

V2.10=TV

These equations come from the UC3906 datasheet found on Texas Instruments

website.

It should also be noted that standard components may be used for all of the

parts in this diagram except for RS and the transistor. RS must be a 1W resistor and

the pnp transistor must be rated for the maximum current that will be fed to the

battery (2.5A).


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Charge Status Display

We have elected to feature a continuously updated user display. In order

to accomplish this an LM3914 was used to drive an array of ten LEDs. Our design

is shown in Figure 10.

Figure 10. Charge Status Display

In this configuration pin 4 is used to specify the low end of the display

range (10.5V) and pin 6 is used to specify the high end of the range (13.8V). The

input signal (pin 5) is then scaled linearly across the range specified. The resistor

attached to pin 7 is used to determine the luminosity of the LEDs by pulling a

specific amount of current.


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Switching Oscillator

As we have elected to feature a continuously updated user display it is

necessary to repeatedly switch between charging the battery and monitoring the

batterys charge. In order to accomplish this effectively the switch must

disconnect the charger IC from the battery when refreshing the display. An

LM555 configured as an astable oscillator will be utilized to repeatedly switch

between the two systems. Using an LM555 will allow us to specify the refresh rate

of the display (the LM555s frequency) as well as the amount of time available toupdate the display (the duty cycle).

The specific configuration we utilized is shown below in Figure 11. This

configuration implements a duty cycle of approximately 1%. That is, the battery is

being charged 99% of the time.

Figure 11. Switching oscillator

The inclusion of a diode across RB allows for a duty cycle below 50%. During the

charging cycle the current path will bypass RB yielding the following performance

equations.


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( ) ( ) sec69.02ln*k100*F102ln** === AH RCt

( ) ( ) sec3.692ln*M10*F102ln** === BL RCt

sec24.76Period =+= LH tt

mHz13Period

1Frequency ==

It should be noted, however, that these equations are based on the

functioning of an ideal diode and, as such, the actual results in implementation

will vary according to the characteristics of the device.

4.5 Manufacturability

Our product implements both discrete components and common integrated

circuits. All parts are readily available and produced by multiple companies. We

took this into consideration when choosing our parts in the event a company went

out of business, we would still be able to follow our design. One exception is the

UC 3906. This IC is designed specifically designed to charge lead acid batteries,

and will likely be uncommon in typical electronic shops in Mali or other

developing areas.

The battery charger will require a case that is lightweight, attractive, and

durable. The most important aspect of the casing however, is good dissipation of

heat. Our design implements 4 voltage regulators, all of which produce

significant heat when in use. Clearly efficient transfer heat to the outside will be

essential. Durability is also an important aspect of the case design. This product

will undergo frequent use and be transported; therefore it will need to be

structurally sound enough to protect the components from everyday bumping

and jarring. In addition we have made our case design is watertight by caulking

all seems and cracks.


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Our design is modularized on several levels. For example our signal

conditioning subsystem is broken up into two smaller modules, voltage boost and

voltage regulation. This method of using several levels of system subassemblies

makes manufacturing and troubleshooting more simple and efficient.

While our product does have excellent functionality, some improvements

could be made in the manufacturing stage. Firstly, all of the circuitry would

certainly be mounted on a PCB. Another change that should be made in the

manufacturing stage from our prototype design is the use of more standard parts

to reduce part variety. This pertains specifically to resistors and capacitors. In

several instances we connected several components in series or parallel to attain aspecific value which we did not have in a single component. Clearly some

changes need to be made before mass production, but our modular design lends

itself well to manufacturing.

4.6 Cost Analysis

Standard Cost

For the first year, we have projected research and development costs to be

approximately $10,800, as shown in section 5.3. This value is substantially lower

than expected, primarily because we have done a large part of the design and

testing at no charge to Design that Matters. Future development of our design

will likely be conducted by students similar to us who will not be paid either.

However before the product becomes open on the market, we expect that Design

that Matters will hire professional consultants to check our work and perform

safety testing, to ensure the final product is ready for the consumer. For the

second year of production, research and development costs will be approximately

$5,000. This amount is certainly lower than costs for the first year, but still


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necessary because modifications and improvements will undoubtedly occur in the

early stages of product development and implementation.

We expect design that matters will outsource the manufacturing of the

charger. Since at the start of this endeavor, Design that Matters only plans to

produce 800 of these devices. Therefore it does not make sense for them to

purchase the factory and machinery necessary to mass produce a product line

when the market for the device is still untapped and unknown.

The only notable price change between our prototype and the final

manufactured product will be the AC adaptor. For prototyping and testing, we

opted to purchase an inexpensive AC adaptor which could take an input of120VAC and output 17VRMS. This worked fine for testing here in the U.S., but

one of our customer requirements was that the charger needed to accept both

American and European AC power standards. Therefore, in our manufactured

cost analysis we take into account a more expensive adaptor to convert 220VAC to

the proper DC voltage.

COST PER UNIT

QUANTITY1 100 500 1000

UC 3906 $5.36 3.332 3.094 3.0345

LM317 $0.60 0.3375 0.21 0.1995

AC Adaptor $6.95 4.95 4.75 4.5

LM 555 $0.50 0.3525 0.225 0.18

Rocker Switch $0.76 0.46 0.42 0.39

Steel Clips $0.73 0.4526 0.35 0.28

LM 2577 $5.42 3.4314 3.225 3.1992

LED Array $2.10 1.4 1.225 1.12

LM 3910 $2.91 1.598 1.222 1.2032

LM 350 $1.65 0.99 0.891 0.858

Large Heat Sinks $1.25 0.775 0.65 0.5Small Heat Sinks $0.30 0.186 0.12 0.09

Screw Terminals $1.00 0.62 0.48 0.37

Miscellaneous Hardware $3.00 2.24 $2.15 $2.00

LM317 $0.60 0.3375 0.21 0.1995

Large Heat Sinks $1.25 0.775 0.65 0.5

Small Heat Sinks $0.30 0.186 0.12 0.09

Casing $1.50 $1.37 $1.19 $1.05

TOTAL: 36.18 23.79 21.18 19.76

Table 7: Component Pricing


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Retail Pricing

We have estimated the cost of parts to constitute 40% of the total retail price

since Design that Matters is a not for profit organization. In addition,

approximately 15% of the total retail price will be taken by the wholesaler and

distributor. Finally 5% will be allotted to advertising costs since the market is

already defined. This leaves 40% profit after all fixed costs are met. To calculate

the retail price, we simply multiplied the cost of parts by 2.5 to get 100% of the

retail price. Manufacturing in quantities of 1000 yields a retail price of $49.40, or

approximately $50. The above percentages reflect standard fractions of the retail

price.

4.7 Hazard Analysis

Before releasing our product on the unsuspecting people of Mali, it will be

necessary to perform rigorous tests on how well the device will perform under

long-term operation. The casing has not been tested for shock or heat resistance,

leaving a potential hazard with the components becoming overly hot and burning

the user or melting the case. Also the materials have not been tested for toxicity if

ingested or placed in a bodily orifice. In the event that the case might burn or melt

there could be potential hazard associated with the fumes as well. The voltage

regulator and boost converter circuits pose the greatest threat to burning the user.

Were the AC Adapters cord to become unraveled or exposed, it could potentially

pose a great shock risk to the user. At 110 or 220 volts, coming into contact with

the hot wire could be harmful and even fatal.

For the most part though, it can be reasonably concluded that except for a

very small number of possible instances, our product is relatively safe and

contains for the most part, hazard-free parts.


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4.8 Legal Considerations

Patent/ Intellectual Property

All intellectual property, tangible articles of manufacture, and design

methods represented by initial prototypes and design notebooks are the sole and

proprietary work of the members of this design team: Mike Eskowitz, Eric Hall

and Chris Hamman. In the event that, at a later date, something in the design is

determined to be patentable, the group has agreed to abide by the WPI Intellectual

Property Policy. (http://www.wpi.edu/Pubs/Policies/intell.html) Since all

development and design was done using WPI facilities with WPI equipment, the

University would be entitled to ownership rights and would absorb all costs

associated with patenting the invention. WPI would be entitled to no more than

50 percent of any royalties incurred from the patent.

Product Liability

We waive all liability claims to Design that Matters due the fact that time

did not permit extensive safety and reliability testing. The prototype developed

by our group is not guaranteed on any grounds whatsoever. It is the

responsibility of DtM to accept any failures, injury, or loss of life associated with

this design prototype. It is our hope that this section will negate any implied

warranties and sufficiently protect us from involuntary negligence and all

liabilities.


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Section 5: Product Results

5.1 Product FunctionalityAt present, our device is fully functional from end to end. As tested on

prototyping board, each module functions independently as well as with the other

components. To date, our group is still migrating the display circuit module to the

solder board and will have the circuit wired and enclosed by mid-January. By

ordering the components surface mounted and placed on a PCB, the size of the device

could decrease significantly; however, the heat sinks in the boost converter and

voltage regulator must be sufficiently large to dissipate the heat produced when the

circuit is drawing a high current.

5.2 Product Form

In the harsh weather and climate conditions of Mali, it will be necessary for the

products casing to be water resistant, dust-proof, shock and heat resistant, as well as

withstand jarring and drops. For the purposes of our prototype we have enclosed our

circuit in a handmade case, the next design should most likely have a case made of a

strong and resilient composite plastic.

Our user interface is extremely simple to use and understand. The user need only

to plug in the AC Adapter or Input Clips to the proper polarity (red +, black -), attach

the output clips to the battery, and flip the rocker switch into the on position. If the

charger is receiving input voltage, the Green LED will light. The user display

quantizes a range of battery charge in terms of ten different possible battery output

voltages. Our case and interfaces are shown in the following set of pictures:


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Figure 12 and 13: Kinkajou Charger Casing and Battery Charge Display

Figure 14: Side View of Charger Case

5.3 Expected ROI

Our market research has revealed that the market for this type of device is

16,000 units world wide. Assuming that a battery charger will accompany each

kinkajou projector, we feel that our product will be able to capture 5% of this

market, or 800 units. The capital investment required to achieve this production

goal will include costs of research and development, as well as manufacturing.

RDE will be minimal since most of the designing and testing is being conducted


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by unpaid students. Professional consultants will need to be hired to test the final

product for safety and functionality. These calculations are as follows.

(3 engineers) x (15 hours/week) x (4 weeks) x ($60/hour) = $10,800

Manufacturing costs will include contracting production plants as well as

the necessary equipment and machinery. We have estimated initial

manufacturing costs to total $50,000. Therefore, the initial capital needed to begin

production of battery chargers is $60,800.

Since we plan to sell 800 units at a retail price of $50 for the first year, our

first year revenues will be $40,000. Assuming an equal number of chargers are

sold each month during the first year, approximately 67 chargers will be sold eachmonth. Therefore, the monthly revenue will be $3350. Since our calculated retail

price is 40% profit, our monthly expenses will be $2010. At this rate, our break

even point will be at 48 months or 4 years. R0I at 5 years is calculated to be 9.53%.

Clearly this is a substantial amount of time to be in debt. This should most

defiantly be revisited in future project additions. A chart displaying the Return on

investment over time is shown in figure 15.

Fi ure 15: Return on Investment


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Section 6: Recommendations

While our circuit is fully functional, there is still much room for

improvement and modification due to the incredibly short timeframe within

which this design process took place. Obviously seven weeks is hardly enough

time to cautiously and methodically carry out all of the necessary steps when

designing a product that will be potentially used in the real world. Due to the time

constraints that were placed on us, we were forced to cut some corners that would

otherwise have been unacceptable.

First and foremost is the issue of safety; before releasing our product on the

unsuspecting people of Mali, it will be necessary to perform vigilant tests on how

well the device will perform under long-term operation. The casing has not been

tested for shock resistance, there is a potential hazard with the components

becoming overly hot and burning a user or melting the case. Also the materials

have not been tested for toxicity if ingested or placed in a bodily orifice. In the

event that the case might burn or melt there could be potential hazard associated

with the fumes as well.

Another set of tests that will need to be performed are reliability and

extended operation assessments. It is important to examine the behavior of the

circuit over long periods of time: what happens when the charging circuit is used

weekly for two months, or daily for two years? Also can the circuit survive being

constantly on for 3 days unattended? Another issue is whether the device will fail

or will need repair rapidly. By considering issues like this, the circuit could later

be optimized to address the need for a low Mean-Time before Repair and more

importantly Mean-Time before Failure. It is our opinion that the Boost Converter

and Voltage Regulator will be the first components to fail with the Transistor in

the Charging Circuit following sometime after.


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Also because of a lack of both resources and time we were unable to verify

our predictions of system performance when the charger is connected to the Solar

Panel Input. A means of simulating or actually testing the solar panel operation

were not provided for us, so we can only speculate on the behavior our system

with the solar panel. A solar panel can be roughly modeled as a constant current

source; the charge controller is designed to handle input currents of 15 Amps,

given the proper external transistor configuration. Most likely the UC would let

the current pass until the battery reaches full capacity whereupon it would stop

the current flow through the circuit. Later design verification should include a

great deal of testing with a solar power source.Future courses of action should also include investigating the feasibility of

incorporating more common components into the design. While many of our

components like the voltage regulator (LM350), boost converter (LM 2577),

resistors, and capacitors can be found in everyday consumer electronics, other

Integrated Circuits like the display driver (LM3914) and charge controller (UC

3906) are not as widely available in developing nations. On-the-spot repairs are

required in small rural communities, it is important that the device have as many

commonly available components as possible.

Another potential improvement that could be made would be to

incorporate a less-expensive display module. At a total cost of $5.00 the display

could be phased out for the sake of cost by using a single resistor to indicate that

charging has completed. However, making this change would greatly sacrifice the

functionality of the display. Another component change that could be beneficial

would be to implement the regulation system using a switching voltage regulator

as opposed to the linear LM350 and LM317 devices. These linear devices are

inefficient with some power loss being dissipated in the form of external heat.


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Appendix A: Circuit Diagram


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Appendix B: Assistance and Contact Info

If any or all of this design concept is used in the future by DtM,

we would be more than happy to offer our assistance in helping to

further the next design phase. In the event that questions about our

design process arise or if any future consulting is needed, feel free to

contact one of the team members listed below:

Michael Eskowitz

E-mail: [email protected]

Cell: 978.430.2681

Eric Hall


Cell: 207.939.4449

Chris Hamman


Cell: 508.667.7015


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Appendix A: LM555 Equation Derivations

In order to derive equations characterizing the behavior of the LM555 when

configured as an astable oscillator it is best to observe the internal workings of thedevice.

Figure 8: Internal view of LM555

We will now present an analytical overview of the LM555s operation.

1. The most appropriate place to begin analysis in this case is the zero state:

when the capacitor has zero charge placed on it.

2. With zero volts placed across the capacitor comparator 1 will assume a low

state (0) and comparator 2 will assume a high state (1).

3. This will cause the flip flop to set 1=Q and 0=Q .

4. An output of 0 from Q will turn the transistor off.

5. Because the transistor is off the capacitor will become charged. For the

purposes of calculating a time constant it should be noted that the charge

path is through both AR & BR .

6. Once the capacitor reachesCCV

3

1comparator 2 will switch low (0).


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7. When the capacitor reaches CCV3

2comparator 1 will switch high (1).

8. This will cause the flip flop to reset to toggle, assuming the state 0=Q and

1=Q .

9. The logic high output from Q will activate the transistor.10.This will discharge the capacitor through BR .

11.The capacitor voltage will discharge to CCV3

1causing comparator 2 to

switch high (1).

12.This will transition the flip flop into state 1=Q and 0=Q .

13.The process will repeat beginning at step 4.

As we can determine from the qualitative description above, the oscillator is in the

high state ( 1=Q ) when the capacitor is charging up to CCV3

2. It is thus possible to

calculate the duration for which the output is high ( Ht ) using the universal

capacitor equation:

( ) tINITIALFINALFINALCAP eVVVV=

A derivation of Ht is presented below.

Ht :

Ht

CCCCCCCC eVVVV

=

3

1

3

2

Hte=3

21

3

2

Hte=2

1

Ht=

2

1ln

=

21lnHt

( )2ln=Ht

As noted in step 5, the charge path is through both AR & BR , thus the time

constant is equal to:

( )CRRRC BA +==


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( ) ( )2lnCRRt BAH +=

( )CRRt BAH += 693.0

A similar set of steps can be taken in order to determine the time Lt . In this case,

however, the capacitor discharges across BR alone (step 10) yielding a different

time constant and the result:

Lt :

( )2lnCRt BL = CRt BL 693.0=

Having obtained both the high and low times for the oscillator output it is possible

to calculate the output period as:

HLPERIOD ttT +=

The reciprocal of which is its frequency:

HLPERIODHZ ttTf +

==11

Another important attribute is the oscillators duty cycle. The duty cycle is a

percentage measure of time spent in the high state.

( )( ) BA

BA

BAB

BA

HL

H

RR

RR

CRRCR

CRR

tt

t

2693.0693.0

693.0

+

+=

++

+=

+=

Battery Charger Report 3

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Transcript of Battery Charger Report 3