Universal Battery Charger Team 6 Final Project

Team Members: Vitaliy Gleyzer – ECE Box # 129 Stephen Masullo – ECE Box # 221 Jonathan Mulla – ECE Box # 250

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TABLE OF CONTENTS 1 PROJECT OVERVIEW .................................................................................................................... 1

1.1 PROJECT MISSION ........................................................................................................................ 1 1.2 PROJECT SOLUTION...................................................................................................................... 1

2 PRODUCT SPECIFICATION PROCESS....................................................................................... 3 2.1 MARKET RESEARCH..................................................................................................................... 3

2.1.1 Identifying the Market............................................................................................................. 3 2.1.2 Exploring Other Markets........................................................................................................ 3

2.2 CUSTOMER REQUIREMENTS ......................................................................................................... 5 2.3 PRODUCT REQUIREMENTS............................................................................................................ 6 2.4 INITIAL PRODUCT SPECIFICATIONS .............................................................................................. 6 2.5 MEETING PRODUCT REQUIREMENTS............................................................................................ 7 2.6 MEETING PRODUCT SPECIFICATIONS ........................................................................................... 8

3 PROJECT ORGANIZATION......................................................................................................... 10 3.1 ............................................................................................................................................................ 10 3.2 ............................................................................................................................................................ 10

4 VALUE ANALYSIS ......................................................................................................................... 10 4.1 METRICS FOR VALUE ANALYSIS ................................................................................................ 10 4.2 INDIVIDUAL MODULE ANALYSIS ............................................................................................... 11

4.2.1 Input and Output Connectors Value Criteria ....................................................................... 11 4.2.2 Input Surge Protection.......................................................................................................... 13 4.2.3 Charger Circuit .................................................................................................................... 15

4.3 PREFERRED DESIGN APPROACH ................................................................................................. 17 4.4 OUR COMPETITION..................................................................................................................... 18

4.4.1 Soneil 12 Volt 2.5 amp Constant-Current World Charger ................................................... 18 4.4.2 Cliplight 12V 10 Amp Charger............................................................................................. 19 4.4.3 BatteryMinder....................................................................................................................... 19 4.4.4 SBC-6112 Solar Battery Charger ......................................................................................... 20 4.4.5 Defined Criteria.................................................................................................................... 21 4.4.6 Rate Options Using Criteria................................................................................................. 22 4.4.7 Result of the Value Analysis of the Competition................................................................... 23

4.5 VALUE ANALYSIS CONCLUSIONS............................................................................................... 23 5 INDIVIDUAL MODULE DESIGN................................................................................................. 24

5.1.1 Surge Protection ................................................................................................................... 24 5.1.2 Input Voltage Limiting.......................................................................................................... 24 5.1.3 AC/DC Conversion ............................................................................................................... 25 5.1.4 AC/DC Conversion Options ................................................................................................. 25

5.1.4.1 External AC/DC Converter ........................................................................................................ 25 5.1.4.2 Internal AC/DC Converter ......................................................................................................... 26

5.1.5 Charging Circuit................................................................................................................... 31 5.1.5.1 General Description ................................................................................................................... 31 5.1.5.2 Simulation.................................................................................................................................. 32

5.1.6 Battery Indicator................................................................................................................... 36 6 PROTOTYPE RESULTS/FINAL DESIGN................................................................................... 38

6.1 MODULE STATUS ....................................................................................................................... 38 6.1.1 AC/DC Conversion ............................................................................................................... 38 6.1.2 Current Surge Protection ..................................................................................................... 38 6.1.3 Charging Circuit................................................................................................................... 39 6.1.4 Battery Indicator................................................................................................................... 39

7 TESTING........................................................................................................................................... 40 7.1 AC/DC CONVERSION................................................................................................................. 40 7.2 CHARGING CIRCUIT ................................................................................................................... 40 7.3 BATTERY INDICATOR ................................................................................................................. 40

8 FINAL PROTOTYPE SUMMARY AND FUNCTIONALITY.................................................... 41 8.1 STRENGTHS ................................................................................................................................ 41 8.2 WEAKNESSES ............................................................................................................................. 41 8.3 SUGGESTION FOR IMPROVEMENT ............................................................................................... 41

9 ECONOMIC ANALYSIS................................................................................................................. 42 9.1 UNIT COST ANALYSIS ................................................................................................................ 42 9.2 PRICE SUGGESTION .................................................................................................................... 43 9.3 ECONOMIC FEASIBILITY............................................................................................................. 43

10 CONCLUSIONS ............................................................................................................................... 43 11 APPENDIX A.................................................................................................................................... 45 12 APPENDIX B .................................................................................................................................... 46 13 APPENDIX C.................................................................................................................................... 47 14 APPENDIX D.................................................................................................................................... 48 REFERENCES ........................................................................................................................................... 50

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Table of Tables Table 2: Value Analysis Input and Output Connectors .................................................... 13 Table 3: Value Analysis of Input Surge Protection .......................................................... 14 Table 4: Value Analysis of Charging Circuits................................................................. 17 Table 5: Scoring for Criteria ............................................................................................. 22 Table 2: AC/DC External Charger Specification Table .................................................. 26 Table 1: Transformer Specification ................................................................................. 27 Table 2: Bridge Rectifier Specifications.......................................................................... 28 Table 3: Filter Capacitor Specifications .......................................................................... 28 Table 9: Voltage Regulator configuration resistors ......................................................... 34 Table 10: AC/DC Module Status..................................................................................... 38 Table 11: Current Surge Protection Module Status ......................................................... 38 Table 12: Charging Circuit Module Status ...................................................................... 39 Table 13: Battery Indicator Module Status...................................................................... 39 Table 14: Parts list with Bulk Prices................................................................................ 42 Table 15: Unit Cost Calculation ....................................................................................... 43

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Table of Figures Figure 1: Artist Rendition .................................................................................................. 2 Figure 2: ICP – 15W, 12 V Solar Powered Battery Charger .............................................. 4 Figure 3: Vector - Marine 2/6 Amp Battery Charger ......................................................... 4 Figure 4: Feature Matrix for Competitors........................................................................ 20 Figure 5: Functional Block Diagram ............................................................................... 24 Figure 6: Voltage Clamp Circuit Schematic.................................................................... 25 Figure 7: External AC/DC Adaptor ................................................................................. 26 Figure 8: AC/DC Converter Schematic ........................................................................... 26 Figure 9: AC/DC Converter Schematic with 5600uF Capacitor ..................................... 29 Figure 10: Transient Analysis with 5600uF Capacitor .................................................... 29 Figure 11: AC/DC Converter Schematic with 6800uF Capacitor ................................... 30 Figure 12: Transient Analysis with 6800uF..................................................................... 30 Figure 13: Transformer 110/220 V AC Switch ............................................................... 31 Figure 14: Complete Charging Circuit Module ............................................................... 32 Figure 15: Regulator configuration for Charging Circuit Module................................... 33 Figure 16: Vout Switching for Charging Circuit Module................................................ 34 Figure 17: Reference Controlled Switch for Charging Circuit Module .......................... 35 Figure 18: Reference Controlled Switch for Charging Circuit Module with added

feedback loop ............................................................................................................ 36 Figure 19: Charging Circuit Module................................................................................ 37 Figure 20: Initial General Project Management Chart..................................................... 45 Figure 21: Initial Module Specific Project Management Chart........................................ 46 Figure 22: End Term Project Management Chart............................................................. 47 Figure 23: Complete Circuit Schematic........................................................................... 48

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1 Project Overview

1.1 Project Mission

With the lack of centralized power grids, car batteries have taken the place of one of the main energy sources available in developing countries. With this in mind, our objective will be to design a cheap, versatile and efficient lead acid car battery charger which will interest and appeal to the “cost-minded” customer. One of our main incentives in developing this product has been a parallel project, Kinkajou portable LED projector, initiated by the Design that Matters team, who has approached us with a need for a low-cost charger to integrate or combine with their device. After doing market research in their target communities, they have been able to devise a list of particular features that would be essential to making their device practical to their specific users:

Universal 12 Volt battery charger Various sources of inputs of electricity - solar panel, pedal

generator, and standard AC power (both American and European standards)

Ability to charge a typical 12 Volt lead-acid (automotive) battery Overcharge protection State of charge indicator Affordable

We used these requirements as guidelines to implementing our product as well as include additional features that we thought are important to the functionality.

1.2 Project Solution

We have successfully designed a charger that will be able accept AC input and almost any DC input that can provide enough voltage and current to charge a 12 V lead-acid battery. The charger meets most of the requirements and features requested by DtM.

With the time constraints, we were unable to provide casing and other aesthetic aspect of the design. Figure 1 shows our vision of the final product. Below is a list of features that would be available on a fully complete charger:

• Detachable input plug with adaptors for either American or European standards

• Input terminals for a solar panel or a mechanical pedal generator • Output posts to the battery • Array of LEDs in the shape of a battery to indicate the charge • Easy-to-understand icons to indicate the functionality of each part for the user • 220/110V switch • AC or DC input switch

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Figure 1: Artist Rendition

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2 Product Specification Process

2.1 Market Research

2.1.1 Identifying the Market In conducting our research we realized that we have several different market

possibilities which would have an interest in our product, such as: • Developing countries • Outdoors sporting • Emergency gear • Boating

Our primary concern was, of course, the Kinkajou project and the needs and requirements of their prospective customers. These customers are school teachers and technical educators in underdeveloped countries, such as Mali, which require means of powering the Kinkajou as well as other potential portable teaching tools. With the lack of a central power grid and any sort of energy standard, our versatile and inexpensive charger would be an ideal solution for their needs.

The bulk of our research for this market was provided to us by the Design That Matters team. Since they are our main and the most important cliental, their needs are imperative. They have spent time gathering information and feedback from the users in different schools and technical institutions. Some of the key market targets for the Kinkajou projector are the institutions and groups such as public schools, Doctors without Boarders, other Non Government Organizations, as well as private homes.

2.1.2 Exploring Other Markets Secondary markets are also available for the charger. Looking at the already

available products, there is no comparable device which will combine all the main characteristics that our product will and must have such as, durability, affordability and versatility. With the astounding array of inputs, this charger would be a valuable and handy resourceful tool for any outdoorsman or boatman, who rely on their battery to provide them with music or television entertainment, heat, communication or in fact, any other essential activities that require electricity.

We have found several “competing” devices that would appeal to the same customer base:

The ICP 15W, 12 V Solar power battery charger from Figure 3 is an all around solar panel with already built in 12 Volt charger circuit.

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Figure 2: ICP – 15W, 12 V Solar Powered Battery Charger

This product is available at an average price of $150, and claims to provide battery charging with enough power to run a vehicle full of small appliances. At first, it looks like a perfect one package solution, but with a closer look, there are many disadvantages that are not apparent from the marketing. The most obvious one being, the solar panel will be a useless board without the sun shining in the sky; therefore fruitless during the night, as well as in any densely shaded areas. Second of all, the claim to be able to recharge the battery and run numerous appliances at the same time is somewhat outrages. With a 15W rating and the operating voltage of 15V, the panel can only provide approximately an amp of current at its peak sun condition. This is not very practical, since these conditions are rare, and almost impossible to come by, of course, unless you are living in a desert. These conjectures are confirmed by experienced RV owners who have purchased this product and are dissatisfied with the results. These results were found on a popular forum for RV owners. In addition, this one package deal also excludes the numerous customers who have already invested in solar panel for their or RVs or boats.

Figure 3: Vector - Marine 2/6 Amp Battery Charger

We have also found out that there are three major companies that are involved in the production of chargers for the boating industry: Vector, ICP and Guest. Looking through their inventories, we found a second device, which could possibly compete with our product in terms of price and functionality. It is a standalone charger that is available for $39.99 at the online retailer www.boatersworld.com (Figure 4). The charger seems to

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have most of the desired features plus other “extra” bells and whistles that make it an attractive buy for an outdoorsman. This charger has multiple outputs that “provide for easy trickle charging through aggressive battery charging and jump-starting currents.” Because of the price being certainly on the low end of the spectrum for these kinds of products, this could certainly be a possible competitor in the boating industry.

2.2 Customer Requirements

The market research that we conducted gave us a specific set of requirements for the design of our product. The 12 volt car battery is considered widely available and commonly used in most underdeveloped nations for many applications that usually run off a power grid. One of the larger problems in this implementation of 12 volt car batteries is the cost and difficulty of recharging them. Our product will make the process of recharging the 12 volt battery much easier and cheaper. Since most consumers in underdeveloped nations will not have access to one standard of power input, we must account for various kinds of inputs. These include:

• American 110 V, European and Asian 220V standard wall inputs • Mechanical power generator input (i.e. bicycle or crank) • Solar panel input

Other important customer requirements include: • Portability • User-friendly interface • Reasonable recharge time • Durable design • Low cost

1) Portability - Since this charger will be coupled with the Kinkajou projector the issue of portability comes into play. This means that the battery charger be light weight. Although no battery charger on the market matches our specific specifications, we were able to use this example to get a feel for the weight and dimensions: 8.75cm x 5.63cm x 11.9cm at 3 lbs.

2) User-friendly interface - Since most of the users are not familiar with consumer electronics or have not had the exposure to the modern culture, it becomes evident that our battery charger must be extremely user friendly, making use of intuitive graphic interfaces appose to solely relying on written descriptions.

3) Reasonable recharge time - The recharge time is a crucial concern of the customer, and usually can be the deciding factor between designs. If the battery takes too long to charge, then the customer will not be able to efficiently use the projector.

4) Durable design - The durability of our design will be a major requirement from the customer. A robust design will be more useful to our customers because of lengthened product life.

5) Low cost - Since our market is geared towards developing countries cost is a major factor with our product. Our goal is that the battery charger will cost under $50 and constructed from parts that are readily available in local electronics industries.

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According to the field study preformed by Design That Matters, the electronics industry in Bamako should have sufficient supplies for most of the parts that would be needed to manufacture and repair a battery charger.

2.3 Product Requirements From the market research and customer requirements, we decided on features and

requirements that our design must include. These requirements include important usability safety and marketability factors which we must take into account.

• Must not overcharge battery • Must indicate charge • Must not drain battery • Cheap and readily available parts • Environmental durability • Able to handle spikes from input sources

1) Must not overcharge the battery – The charger must not overcharge the battery for

safety reasons. 2) Must indicate charge – For the most efficient use of our charger, the consumer will

need to know the state of their battery and when it is completely charged. 3) Must not drain battery – Our design will need to be efficient in the way it charges the

battery. We will need to make sure that the charger will not drain the battery when insufficient power is supplied.

4) Cheap and readily available parts – The process of repair is a very important factor to consider in the design and marketing of our product. We must use a design that is easy enough to be fixed by local vendors, with parts that are cheaply available to the area.

5) Environmental durability – The harsh environmental conditions of such 3rd world markets such as Mali, will require our design to be able to withstand heat, humidity and moderately rugged physical use.

6) Able to handle spikes from input sources – Our design must account for inconsistent and even dangerous power sources, such as power surges from lightning strikes. We must make sure that our design will still work in these poor power conditions.

2.4 Initial Product Specifications From the product requirements which we gathered from our market research and

customer requirements, we decided on reasonable constraints for the product specifications.

• Weigh between 2 and 10 pounds • Be at most a cubic 7 inches • Charge the battery completely in 12 hours • Handle peak current surges of up to 500 kA • Cost at most $50, with a target cost of $25

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• Be able to work in temperatures up to 120˚F • 3 different types of input • Removable input and output plugs

1) Weigh between 2 and 10 pounds – Since our design is intended to be highly portable,

the size and weight of our product will need to be small enough for realistic use. We found most chargers on the market to be from 2 to 10 pounds and around 7 cubic inches in dimension.

2) Be at most a cubic 7 inches – Battery recharge time is a crucial factor in our design. We decided that a maximum charge time of 12 hours for any given input is required.

3) Charge the battery completely in 12 hours – The unstable power grid, along with frequent lightning strikes and other power surges requires that we implement safety measures in our design to combat these problems.

4) Cost at most $50, with a target cost of $25 – Although the maximum cost of our design was set to $50, we would like our target cost to be around $25. This lower price will help the marketability of our design, and will make it more competitive in the market.

5) Be able to work in temperatures up to 120˚F - The harsh environmental conditions of our target market area, Mali have required us to set a maximum operating temperature for our device.

6) 3 different kinds of input – The variety of available sources, and the lack of a standard power source in our target market, has required us to accommodate for 3 different kinds of input.

7) Removable input and output plugs – For the sake of portability and ease of use, we decided that detachable plugs for input and output would be ideal.

2.5 Meeting Product Requirements

Our final prototype was able to meet most of our initial product requirements. The product requirements our prototype meets are:

• Must not overcharge battery • Must indicate charge • Must not drain battery • Cheap and readily available parts • Environmental durability

The product requirements our prototype does not meet are:

• Able to handle spikes from input sources 1) Must not overcharge battery – This product requirement is met with the float charge

feature. 2) Must indicate charge – This product requirement is partial met by our prototype. We

have a separate working 4 state battery indicator, but due to time we were not able to incorporate it into the final prototype.

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3) Must not drain battery – This product requirement is met through the use of a high power diode at the output of our prototype, located directly before the battery connection.

4) Cheap and readily available parts – This product requirement was met by the simplicity of our design and the components used.

5) Environmental durability – With the prototype we have now this product requirement may run into problems. It is an issue that would need to be addressed further if this design was to be taken further.

6) Able to handle spikes from input sources – Due to time constraints we were not able to address this issue, therefore our prototype is not protected against voltage or current surges.

2.6 Meeting Product Specifications Our final prototype was able to meet most of the product specifications, but due to

time constraints some of the specifications were not able to be addressed. The product specifications that were met by our prototype are:

• Charge the battery completely in 12 hours • Cost at most $50, with a target cost of $25 • 3 different types of input • Be able to work in temperatures up to 120˚F • Removable input and output plugs

The product specifications our product does not meet are:

• Weigh between 2 and 10 pounds • Be at most a cubic 7 inches • Handle peak current surges of up to 500 kA

1) Charge the battery completely in 12 hours – We estimate that our prototype will

charge 80% of a battery in 10 hours when it is connected to AC power. 2) Cost at most $50, with a target cost of $25 – We determined our unit price to be

$47.75, so depending on how much Design that Matters would sell it for will determine how well we fit this product specification.

3) Three different types of inputs – Our prototype was successfully able to charge a

battery when connected to 110 VAC, 220 VAC, and a pedal generator. We were not able to test it with a solar cell, but we are confident that it will work with a solar cell that can provide enough voltage and current to charge a 12 volt battery.

4) Be able to work in temperatures up to 120˚F - With the prototype we have now this

product requirement may run into problems. It is an issue that would need to be addressed further if this design was to be taken further.

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5) Removable input and output plugs – Our prototype has a removable AC cord and two posts for a DC connection. The output has two posts which alligator clips could be connected to, which would then be connected to the battery.

6) Weight between 2 and 10 pounds – Due to time constraints we were not able to

incorporate any type of housing for the prototype, so the final weight of it is not able to be determined.

7) Be at most a cubic 7 inches – Like the weight, this requirement was not able to me

determined for the same reasons. 8) Handle peak current surges of up to 500 kA – Due to time constraints we were not

able to address this issue.

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3 Project Organization

3.1 Overall, our initial project time management schedule, which can be found in the

Appendix, was changed from our plan because of various external factors. One of the greatest factors in the schedule change was the delay of the ordering of our parts that resulted from a clerical error with our parts list. This delay has caused us to move the building and testing stages of our products a few days back. Also, after completing the research phase, the DC/DC conversion module was dropped from the design. This allowed more time to be allocated to other more important modules, such as the charging circuit.

3.2 Looking back our organization and timing, we believe we made the right decision about using the modular approach to this project. Building separate modules gave the flexibility and tolerance to absorb setbacks and delays. We were able to spend time on the available parts of the project while waiting for components to come in, and not have dependencies without which we could not continue.

4 Value Analysis The purpose of this section is to analyze our different design options and determine

which ones are the most appropriate to meet our goal of creating a unique and competitive solution. This was done by first comparing the different design approaches for each functional component of the battery charger using Value Analysis Matrices to determine feasible and still affordable designs. Then, we went on to perform Value Analysis of our entire product to comparable devices that are already available on the market. This was done to ensure that our efforts of pursuing to design this new device have merit, and there are no other products that are already on the market that can meet the same specifications for a cheaper or better than anything that can be designed by us.

After strenuous research on the internet, we were unable to find worthy competitors that would accurately fit within our primary customer requirements. The major shortfall of the available solution is their inflexibility to accept different inputs such as solar panels or pedal generators. Since versatility is an absolute must for our customer, none of these can really match up to the demanding specifications of our product.

There were several modules in our initial design that could be implemented in various forms, each with their own specific advantages and disadvantages. The modules were evaluated in terms of cost, ease of repair and portability.

4.1 Metrics for Value Analysis

The most important requirement of all our design requirements would have to be cost since it is the biggest constraint that we have in this project. There are a few design

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options where cost could not be estimated because of the lack of knowledge of all the parts that would be required to build it. For these design options we chose to evaluate them based on other important criteria.

4.2 Individual Module Analysis

4.2.1 Input and Output Connectors Value Criteria Product Requirements

Provide input for 220 and 110 VAC wall inputs Provide input for dc solar panel and pedal generator Provide output to a 12 volt lead acid battery

Options Available and Advantages/Disadvantages Sockets:

This method will involve having a socket for a detachable cord for the AC input, and input posts for the DC input from the pedal generator and solar panel. It will also include posts for output to the 12 volt lead acid battery, the included cord will have banana clips to hook into the posts of the charger output and alligator clips to attack to the terminals of the battery. This method is moderately more expensive but it is very portable and easy to repair.

Cords:

This method will involve having a permanent cord for AC input as well as permanent alligator clip output to the battery. There will still be posts for the input from the DC sources. This method is less expensive but is not as portable and can be difficult to repair if the attached cords break.

Cord with posts:

This method will involve the permanent AC input cord as the only permanent cord. This design will include posts for the DC input as well as posts for the output to the battery. This method is more expensive than the cords method, but less than the sockets method. This method is also less portable than the sockets method, but more portable than the cords method.

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Value Analysis Portability: How portable the design is.

Very good 5 Good 4 Average 3 Sub-average 2 Poor 1

Versatility: How portable the design is.

Very good 5 Good 4 Average 3 Sub-average 2 Poor 1

Durability: How portable the design is.

Very good 5 Good 4 Average 3 Sub-average 2 Poor 1

Ease of repair: The ease of repair for the customer.

Very Easy 5 Easy 4 Moderate 3 Semi-Difficult 2 Difficult 1

Cost: The approximate cost in US dollars.

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Weight Assignments

Market Socket Terminal

Attached Cords

Attached Cords with Terminals

Quality Value weight value point total value point total value point total

portability 2 5 10.00 1.00 2.00 2 4.00versatility 1 5 5.00 0.00 0.00 0 0.00durability 3 4 12.00 1.00 3.00 1 3.00ease of repair 3 2 6.00 4.00 12.00 0 0.00

Total 33.00 17.00 7.00

Market Socket/Terminal 33.00Attached Cords 17.00

Attached Cords with Terminals 7.00

Cost Value weight value point total value point total value point total

I/O 5 9.63 48.15 5.54 27.70 8.5 409.28Total 48.15 27.70 409.28

quality/cost 0.69 0.61 0.02

Table 1: Value Analysis Input and Output Connectors

4.2.2 Input Surge Protection Product Requirements Protect circuit from unstable AC power grid Protect circuit from lightning surge Easy to replace/reset Options Available and Advantages/Disadvantages Fuses:

This method would involve using a fuse to protect the circuit from the input power surges. This method is harder to use, but relatively inexpensive Circuit Breaker:

This method would involve using a circuit breaker to protect the circuit. This method is easy and relatively inexpensive.

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Value Analysis Ease of use: The ease of design for customer use. Very Easy 5 Easy 4 Moderate 3 Semi-Difficult 2

Difficult 1 Ease of repair: The ease of repair for the customer. Very Easy 5 Easy 4 Moderate 3 Semi-Difficult 2 Difficult 1 Effectiveness: How well the design accomplishes its task. Very Effective 5 Effective 4 Moderately 3 Less 2 Not effective 1 Cost: The approximate cost in US dollars. Weight Assignments

Market Fuses Circuit Breaker

Quality value weight

value point Total value point total

Ease of use 2 1 2 5 10 Ease of repair 2 4 8 1 2 Effectiveness 3 5 15 5 15

Total 25 27

Market Fuses 25Circuit Breaker 27

Cost value weight

value point total value point total

input surge 1 1 1 1.98 1.98 Total 1 1.98

Quality/cost 25 13.63636364

Table 2: Value Analysis of Input Surge Protection

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4.2.3 Charger Circuit Product Requirements Must charge battery quickly Must charge battery efficiently Options Available and Advantages/Disadvantages

Charging a lead acid battery is a matter of replenishing the depleted supply of energy that the battery had lost during use. This replenishing process can be accomplished with several different charger implementations: constant voltage charger, constant current charger or a "multistage" constant voltage/current charger. Each of these approaches has its advantages and disadvantages that need to be compared and weighed to see which one would be the most practical and realistic to fit with our requirements. Constant Voltage Charger:

Constant voltage charging is one of the most common charging methods for lead acid batteries. The idea behind this approach is to keep a constant voltage across the terminals of the battery at all times. Initially, a large current will be drawn from the voltage source, but as the battery charges and increases its internal voltage, the current will slowly fold and decays exponentially. When the battery is brought up to a potential full charge, which is usually considered around 13.8V, the charging voltage is dropped down to a lower value that will provide a trickle charge to maintain the battery as long as it is plugged into the charger. The best characteristic of this method is that it provides a way to return a large bulk of the charge into the battery very fast. The draw back, of course, is that to complete a full charge would take a much longer time since the current is exponentially decreased as the battery charges. A prolonged charging time must be considered as one of the issues to this design.

Solar cells are one of our main portable power sources. Inherently, they provide a constant current which is dependent on light intensity and other uncontrollable variability in the environment. This characteristic fits well with a constant voltage charge design, which does not depend on the current provided by the input source, which in turn eliminates the dependence of the charger on external variations like the time of day, weather conditions or temperature. The effects of the changing voltage are also minimized since the voltage is being regulated. Constant Current Source:

Constant current charging is another simple yet effective method for charging lead-acid batteries. A current source is used to drive a uniform current through the battery in a direction opposite of discharge.

This can be analogous to pouring water into a bucket with a constant water flow, no matter how full the bucket is. Constant current sources are not very hard to implement; therefore, the final solution would require a very simple design.

There is a major drawback to this approach. Since the battery is always being pushed at a constant rate, when it is close to being fully charged, the charger would force

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extra current into the battery, causing overcharge. The ability to harness this current is the key to a successful charger. By monitoring the voltage on the battery, the charge level can be determined, and at a certain point, the current source would need to be folded back to only maintain a trickle charge and prevent overcharging.

Multi-stage Constant Voltage/Current Charging Solutions:

Both constant voltage and current approaches have their advantages; that is the reason multistage chargers have been developed which combine the two methods to achieve maximum charge time, with minimum damage to the charging cell. An example of a complex, four-stage charger is the Soneil 12 Volt 2.5 Amp Constant Current World Charger. These specifications and explanations for the different stages were taken directly from their website: http://www.4unique.com/battery/soneil/soneil-12v2-5a.htm .

Stage 1: Deep Discharge Charging Pulse Mode The Charger starts charging at 0.5V and give pulse current up to 5V. This has effect of removing loose sulphation formed during deep discharge state of the battery. Stage 2: Constant Current Mode (CC) The charger changes to constant current 2.5A. When the battery voltage reaches up to 14.4V, the charging stage changes from (CC) Constant Current to CV (Constant Voltage) mode. Stage 3: Constant Voltage Mode (CV) The charger holds the battery at 14.4V and the current slowly reduces. When the current reaches at 0.5 C (C= Battery Capacity), this point called the Switching Point. The Switching Point is one of the great features of this battery charger that it can adjust the current automatically according to the battery capacity. Other chargers without microprocessors are not capable to adjust the Stage 4: Standby Voltage Mode The charger maintains the battery voltage at 13.8V and current slowly reduces to zero. Charger can be left connected indefinitely without harming the battery. Recharging: If the battery voltage drops to 13.8V, the charger changes from any mode to Constant Current mode and restart charging. The charging cycle will go through Stage 2 to Stage 4.

This particular charger has also incorporated some other recharging methods that they have found to optimally charge or treat the battery depending on the level of discharge. As much as multi-stage chargers are enticing in terms of their features, for our purposes, the complexity and the control logic needed to implement this kind of solution would make our project unrealistic given the time and money restraints.

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Value Analysis Simplicity: Very Simple 5 Simple 4 Moderately 3 Less simple 2 Not simple 1 Charge time: Very long 5 Long 4 Fairly long 3 Less long 2 Not long 1 Battery care: Very Good 5 Good 4 Fairly good 3 Less good 2 Not good 1 Weight Assignments

Market multistage C current C voltage

Quality Value weight

value point total

value point total

value point total

Simplicity 3 1 3 5 15 5 15charge time 1 4 4 4 4 3 3battery care 1 5 5 2 2 4 4

Total 12 21 22Quality/cost 12 21 22

Table 3: Value Analysis of Charging Circuits

4.3 Preferred Design Approach The design approach that we decide on, based on our value analysis is as follows.

The input and output connector module will follow the socket / terminal design, because of the increased portability and relatively minimal cost difference between the other designs. The input surge protection module will follow the circuit breaker design even though the fuse design won. This was decided because the circuit breaker approach to the design would be much easier for the customer to handle in the case of a power surge, instead of having to replace a fuse, they would only have to reset the circuit breaker. The decision to go against the value analysis in this case, shows the limitations of such an analysis, even though the inferior choice won technically, it can be proven to be the

18

wrong choice. For the charging module, we decided to go with the constant voltage design. This choice was made not only from the results of the value analysis but also from our research that showed that constant voltage charger design is more compatible with solar panel inputs than the other designs. We obtained this information on the various charging methods from the book Rechargeable Batteries Application Handbook by Technical Marketing staff of Gates Energy Products, Inc. The decision to go with the analog design for the overcharge circuit was decided by the value analysis which showed the lack of feasibility of using a digital approach.

4.4 Our Competition After strenuous research on the internet, we were unable to find competitors that

would accurately fit within our primary customer requirements. The major shortfall of the available solution is their inflexibility to accept different inputs such as solar panels or pedal generators. Since versatility is an absolute must for our customer, none of these can really match up to the demanding specifications of our product.

Among the available chargers, we found four comparable chargers that met some or most of the criteria and were in the desired price range of around $50. These chargers were:

1. Soneil 12 Volt 2.5 amp Constant-Current World Charger 2. Cliplight 12V 10 Amp Charger 3. BatteryMinder 4. SBC-6112 Solar Battery Charger

4.4.1 Soneil 12 Volt 2.5 amp Constant-Current World Charger

The first competitive battery charger we looked at was the Soneil 12 Volt 2.5 Amp Constant Current Charger sold on www.batterystuff.com. This battery charger is being offered at $54.00 and offers a large input voltage range. This charger has a pretty competitive price and some important features such as low weight and size. Below are the specifications that were found at the merchant site:

http://www.4unique.com/battery/soneil/soneil-12v2-5a.htm

• Totally Automatic Switch-Mode Battery Charger • Suitable for Gel, Sealed (AGM) and Wet Lead Acid Batteries • Suitable for use anywhere in the world. • Input 115/230 VAC (range 90 VAC to 264 VAC) (47-63Hz) • Automatic Cut Off and then True Float. Can be left connected indefinitely without harming the

battery. • Two color LED to indicate charge status • UL, CSA, CE, TUV, GS & T-mark (Japan) Listed • Meets: FCC Class B; EN55022 Class B • One year warranty • Size: Length 4.7 (119m) x Width 2.9 (73) x Height 1.6 (41mm) • Weight 14 ounces (400grams) • Zero Current Drain when AC power is off • Mean Time between failures 50,000 hours • Protection provided: Reverse Polarity, Short Circuit, Over-Voltage, Over Current and AC Surge.

19

• Soft Start and Stop: Starts and stops gradually. No sudden in-rush of current. This protects both the batteries and any other circuits connected to the charger.

4.4.2 Cliplight 12V 10 Amp Charger

The second competitive battery charger we looked at was the Cliplight 12V 10 Amp Charger which is sold on www.batterymart.com. This battery charger is being offered for $59.95 and has an input voltage range of 105 – 120 VAC. Below are the specifications that were found at the merchant site:

http://www.batterymart.com/battery.mv?p=ACC-12103

12 VOLT - 10 AMP: Fully Automatic two-stage battery charger, UL and CSA approved. Specially designed for Industrial and OEM applications such as Marine, Utility vehicles and Material Handling among others.

• OUTPUT: 12 Volt Nominal; 10 Amp DC • Set Voltage (cut-off Voltage): 14.7 +/- 0.1 Volt • Float Voltage (come-on Voltage): 14.0 +/- 0.1 Volt • INPUT: 105 VAC - 120 VAC ; 60 Hz • DIMENSIONS: 3-1/2" wide x 2-1/4" tall x 4-1/2" deep • 8.75cm x 5.63cm x 11.9cm • WEIGHT: 3 lbs.; 1.36kg

4.4.3 BatteryMinder

The third battery competitive battery charger we looked at was the BatteryMinder which is sold on www.vdcelectronics.com. This battery charger is being offered for $59.95 and offers a feature that prevents permanent cell damage due to self discharge and sulphation.

Below are the specifications that were found at the merchant site:

http://www.vdcelectronics.com/images/Charger%20with%20brain%20saves.pdf

• 105 – 130 VAC @ 50/60 Hz • Charges/maintains up to 4 batteries at a time • Reverse polarity, short circuit and temperature • Battery condition/polarity indicators • Fully automatic, works with all 12 Volt batteries, a push of a button begins de-

sulphation • Prevents permanent cell damage due to self discharge and sulphation • 4-3/4”L x 3-1/2”W x 3”H • 4 lbs

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4.4.4 SBC-6112 Solar Battery Charger

The fourth competitive battery charger we looked at was a solar battery charger,

model SBC-6112, sold on www.powerstream.com. This charger is offered for $87.50 and

offers a battery level indicator along with a charge status indicator.

Below are the specifications that were found at the merchant site:

http://www.powerstream.com/PV-Control.htm

• Solar • Microprocessor controlled PWM and 3 stage charging algorithms. • Electronic Overcharge Protection & back current blocking to PV panel • Bulk, Absorption & Float Charge LED indications, 5 State LED Indications of

battery levels, 3 - State LED indications of charge status • Automatic dusk detect & On-Off operation at DC output • 6(W) x 3 3/8 (D) x 1 3/4 (H) inches • 0.44kg

Features Sone

il 12

Vol

t 2.5

A

Clip

light

12V

10A

Batte

ryM

inde

r

Sola

r Bat

tery

Ch

arge

r

230/120 VAC N/A

Multiple Battery Charging

Multistage Charging

Direct Wall Plug N/A

LED Indicator

Fault Protection

Overcharge Protection

Battery Recovery

Size 4.7x2.9x1.6’’ 3.5x2.25x4.5" 4.75x3.5x3” 6x3.29x1.75”

Weight .88 lb 2.99lb 4 lb 0.97 lb

Price $54.00 $59.95 $59.95 $87.50

Figure 4: Feature Matrix for Competitors

21

4.4.5 Defined Criteria

As the design group, looking at the customer specification and the product

requirements, we defined important criteria which we thought were important to our

customers: price, size, weight, charge time, versatility, battery care consideration, fault

protection and surge protection.

Price: Price has been one of our main criteria, since this product is

designed to be used in developing countries. Size: Size plays a big role; since our product will be a part of a portable

system, the dimensions are important Weight: Same reason as size – portability Charge Time: The charger must be able to charge within the specified time

restraint specification of 12 hours Versatility: Ability to use the charger with almost any power source available

is important since no standardize power grid will be available in the product environment

Battery Care Considerations:

An implicit criteria. Charger must not damage or significantly shorten the life of the charging battery.

Fault Protection:

Product must be able to handle hazardous, user-inflicted, “accidental” conditions such as: shorted or inverted inputs.

Surge Protection:

The unpredictability and low quality of the AC electrical signal, the product also needs to be fully protected against frequent current and voltage spikes.

22

PRICE ($): 0-50 5 50-60 4 60-70 3 70-100 2

100+ 1

SIZE (IN3): 0-22 5

23-35 4 36-50 3 50+ 2

WEIGHT (LBS) 0-1 5 2-3 4 3-4 3 5-6 2

6+ 1

Charge Time (hours): 0-2 4 3-6 3 7-9 2 10+ 1

Versatility: Excellent 4 Good 3 Fair 2 Bad 1

Battery Care Consideration: Rejuvenation 2 Present 1 Not Present 0

Surge Protections: Present 1 Not Present 0

Fault Protections: Present 1 Not Present 0

Table 4: Scoring for Criteria

Weighting Price – 5 Size – 2 Weight – 4 Charge Time – 3 Versatility – 5 Surge Protection – 4 Fault Protection – 4 Battery Care Consideration – 1

4.4.6 Rate Options Using Criteria

Competitors Pric

e

Size

Wei

ght

Vers

atili

ty

Surg

e Pr

otec

tion

Faul

t Pro

tect

ion

Batte

ry C

are

Weighted Total Soneil 12 Volt 2.5 A 4 5 5 3 1 1 2 75

Cliplight 12V 10A 4 4 4 1 1 1 1 58

BatteryMinder 4 3 3 2 1 1 2 58

Solar Battery Charger 2 4 5 2 n/a 1 1 53

OUR CHARGER 5 4 4 4 1 1 1 78

23

4.4.7 Result of the Value Analysis of the Competition Looking at the value analysis table, our charger is the ultimate choice for the

design solution required by the customer. The Soneil, comes in close second at 75, but

since it still can not handle multiple inputs, that are an absolute must, it fails to meet

customer requirements.

4.5 Value Analysis Conclusions In our design we had to make many choices between various design options based

on the advantages and disadvantages of those options. In the input and output connector

module, our decision to go with the sockets and terminal approach resulted in a highly

portable and versatile but expensive and difficult to repair design. In the input surge

protector module, our decision to go with the circuit breaker resulted in and effective and

easy to use but hard to fix design. In the charging circuit module, our decision to go with

the constant voltage approach resulted in a simple design but which took a longer time to

charge. One major advantage of the constant voltage model, in particular to our design,

is its ability to minimize the affects of environmental variations when used in conjunction

with a solar panel. In the Overcharge circuit module our decision to go with an analog

solution instead of a digital one, resulted in a cheaper, more feasible design, which

unfortunately had less features and was more complicated.

24

5 Individual Module Design

Each individual module was designed and constructed separately. After successful simulation and testing, they were put together to create the finalized version.

ACInput

DCInput

SurgeProtection

InputVoltageLimiting

AC/DCConversion

ChargingCircuit

BatteryIndicator

Battery

Figure 5: Functional Block Diagram

5.1.1 Surge Protection A simple circuit breaker will be used to protect the charger from excessive

current.

5.1.2 Input Voltage Limiting The input voltage limiting capability is necessary to protect the voltage regulator

in the charging circuit from input voltage above the maximum allowable value. This value is determined by the input output differential. It may not exceed 36V.

Figure 8 shows the voltage clamp circuit that was taken out of our prototype at the last minute. The specification of the pass-through transistor added a voltage drop of 4V at the maximum current, which was not acceptable since the charging circuit requires 17V for steady voltage regulation.

This circuit compares the zener diode reference to a fraction of the input voltage. Based on this comparison, the op-amp controls transistor Q2, which either turns off or turns on transistor Q1; therefore disconnecting the charging circuit from the input.

25

1

2

3

5

4U1

LM741

D15.1 V

R13kohm

R247kohm

R36.8ohm

R47.5kohm

R53kohm

D2

5.1 V

R6

1kohm

R71kohm

R81kohm

Q1

Q2

Vin Vout

Figure 6: Voltage Clamp Circuit Schematic

5.1.3 AC/DC Conversion

5.1.4 AC/DC Conversion Options The module will convert the AC input of 115 or 230 Volts, depending on the

mode settings, to a usable DC output greater than 17V for the charger circuit. From our research stage for this module, we came up with two possible implementations to accomplish the task: external and internal AC/DC converters.

5.1.4.1 External AC/DC Converter A complete solution for this module can be bought separately as a pre-made

external AC/DC adapter that provides a clean 18 V DC output from both American and European standard outlets, as well as include built in over voltage and short circuit protection. While potentially more expensive than other possible solutions, this approach provides versatility and portability to the design that our customers will need. This feature is important in our attempt to create an adaptable product. This allows the customer to decide which inputs they would like to have available to control the cost of the product overall. For example, a customer that lives 50 miles from the nearest plug, but has a solar panel nearby, probably does not need AC/DC conversion for their charger.

The external AC/DC converter adapter in Figure 3 is the DTS180330UC-P5P-ET DC, 3.5A adapter made by CUI Inc. The specifications were obtained from the manufacturer’s website, and a quote for the mass production price of $18.25 for 1000 units is included in the appendix.

26

Input Voltage/Frequency Range : 90~264VAC/47~63HZ Inrush Current : 30A max @ 115VAC/50A max @ 230VAC, cold startLine Regulation : +/- 1% Load Regulation : +/- 5% typical +/- 0.4V min Ripple/Noise : 1% typical 100mV min Operating Temperature : 0 ~ 40°C Storage Temperature : -10 to 70°C Dimensions (LxWxH) : 108mm x 66mm x 36mm Approvals : UL/cUL/ITS-GS/CE

Table 5: AC/DC External Charger Specification Table

Figure 7: External AC/DC Adaptor

5.1.4.2 Internal AC/DC Converter The second option for the AC/DC conversion is a custom design. This design

will include an internal transformer, bridge rectifier and a filter capacitor. This option is a relatively less expensive approach, but it limits functionality, portability and versatility in the sense that it would not be an optional component. The reason why we include the standard AC/DC converter option in our design is in contingency of not being able to obtain the external adapter.

T1

16 VCT @ 3.5 A

1

2

4

3

D1

C1

6800uF

110/220 VAC Input +

-VoutC2

6800uF

Figure 8: AC/DC Converter Schematic

27

Operation:

1. Input signal from the outlet lowered to 16Vrms 2. 16Vrms gets rectified going through the full-bridge rectifier, with 2 diode

voltage drop loss (~ 1.4 V) 3. Capacitor is charged to the peak value of the signal 4. Capacitor is discharged by the rest of the circuit until the voltage on the

capacitor is not increased by the rectified AC signal wave

In our search for the proper transformer, we had to consider many factors such as input voltage, output voltage, output current and price. Since the primary function of a transformer is to step down large AC signals to smaller ones, we needed to make sure that our transformer would handle both 115Vac and 230Vac standards. For output we needed to make sure that our transformer would be able to produce 16 Vrms with a current of at least 3Arms. The output requirements of the transformer come directly from the input requirements of the charging circuit. The transformer that we chose was the Jameco #104408CF Quick Connect Power Transformer from the Jameco online catalog. The cost for a single unit is $12.95. We obtained the specifications in Table 1 from the online catalog.

Terminals: Quick Connect, Solder Input voltage: 115/230VAC Output voltage: 16VCT@3.5A VA Cap: 56.0 Terminal size: 0.187" Size: 2.00"L x 2.70"W x 2.30"H Weight: 1.8 lbs.

Table 6: Transformer Specification

Following the transformer output, the next stage in the AC/DC conversion process

involved inverting the negative cycles of the AC input. This process requires the use of a full wave rectifier diode bridge. We determined the required specifications for the bridge rectifier based on the input voltage and current. We determined that our rectifier would have to be able to handle the peak voltage of 22.6V along with voltage spikes from a dirty line, as well as the 3 amps that the charging circuit would be pulling with some head room for current spikes. The rectifier that we chose is the KBPC6005 Bridge Rectifier by International Rectifier. We found this rectifier in the Digikey online catalog with the part number KBPC6005-ND with a single unit cost of $1.80. The specifications in Table 2 were obtained from the online catalog.

28

DIODE/RECTIFIER TYPE: BRIDGEVoltage-Rated: 50V Current Rating: 6A Package / Case: D-72 Packaging: Bulk

Table 7: Bridge Rectifier Specifications

The filter capacitors from the input voltage and the maximum ripple voltage allowed by the charging circuit. The capacitor would have to be able to handle the peak input voltage of 22.6V along with headroom for voltage spikes from a dirty line; it would also have to be able to maintain a ripple voltage that would not dip below 17 volts at any time. The capacitor that we chose is the Jameco #115431 6500uF@50V capacitor from the Jameco online catalog. The cost for the single unit is $3.49. We obtained the specifications below from the online catalog.

OPERATING TEMPERATURE RANGE: 40 DEGREES C TO +85 DEGREES C MAX. leakage current: 0.02CV (uA) or 3mA whichever is smaller Tolerance: +/-20% Capacitance: 6800uF@50V Size (DxL): x 51mm (dimensions and lead spacing may vary)

Table 8: Filter Capacitor Specifications

The simulation of our AC/DC conversion module consisted of a modeled AC

input after the transformer, a bridge rectifier, a filter capacitor and a current source to model the load. The reason why we went with a modeled AC input, was because of the lack of the specific transformer which we would need to step down the 220VAC wall source. Our model for the AC input consisted of 16Vrms at 50Hz, which would be the output of the transformer. We tested for different known values for the capacitor to see how they would affect the output. The current source that we used to model the load was determined to be 3Amps because that is the maximum current that the charging circuit will draw due to the internal current limiting of the voltage regulator. We computed the required capacitor values using the formula:

dtdvCI =

I = 3Amps. This is the maximum load current of the charging circuit, so the worst case would be if the circuit pulled this amount of current. dv = 22.6V- 17V, this is the amplitude of the input signal minus the minimum voltage required by the charging circuit. This gives us the minimum distance that the ripple voltage can be at from the peak. dt = 1/100Hz, because the frequency of the rectified signal is twice the frequency of the input. We chose the 50Hz of the European signal for analysis, because it is the worst case scenario since there would be more time for the capacitor to discharge.

29

C = 53571.4 uF. Since the calculated value is not a common value we chose the next highest value, 5600uF. We chose a higher value because higher capacitor values decrease the ripple voltage.

While searching for parts we found a 6800uF capacitor with a better voltage rating and a lower price than most of the 5600uF capacitors that we found. The simulations below display the outputs of the simulated transient analysis for the circuit with both capacitors. AC/DC Converter Schematic with 5600uF Capacitor

I13A

1

2

4

3

D1

MDA2501

V122.63V16.00V_rms50Hz0Deg

C25600uF

0

1

7

2

Figure 9: AC/DC Converter Schematic with 5600uF Capacitor

Figure 5 shows the 5600uF capacitor, and the corresponding transient analysis

simulation is given by Figure 5.

Figure 10: Transient Analysis with 5600uF Capacitor

30

AC/DC Converter Schematic with 6800uF Capacitor

I13A

1

2

4

3

D1

MDA2501

V122.63V16.00V_rms50Hz0Deg

C26800uF

7

0

2

10

Figure 11: AC/DC Converter Schematic with 6800uF Capacitor

Figure 6 uses the 6800uF capacitor and the output of the simulated transient

analysis from Figure 7. Note the smaller ripple voltage in this graph, compared to the previous simulation.

Figure 12: Transient Analysis with 6800uF

Transformer Configuration

As it can be seen in Figure 13, the transformer switches between 110 and 220 VAC utilizing a double pole double throw toggle switch. The toggle switch works by switching the dual primary transformer from a series configuration, 220 VAC, to a parallel configuration, 110 VAC.

31

Figure 13: Transformer 110/220 V AC Switch

5.1.5 Charging Circuit

5.1.5.1 General Description The full charger feedback control circuit can be seen in Figure 8. This circuit

implements a three stage charger algorithm: constant current state, constant voltage full charge state, and constant voltage float charges state. This circuit will require an input voltage of at least 17 volts to output the 14.7V for charging because of the 2V drop across the regulator.

The comparator is used to provide feedback of the current that the battery is drawing from the circuit: as the battery charges, the current drawn decreases. The current sensing resistor is used to convert that current into voltage, which can be used to compare to a reference within the circuit. This will be the logic needed for the state switching mechanism. The full charge state will provide 14.7V or 2.45V/Cell on the battery and float charge will provide 13.8V or 2.3V/Cell. The battery will try to draw maximum current, in this case:

(14.7V-10.5V)/.1Ohm= 42A (assuming the battery is completely dead) The current limiting of the voltage regulator will force the current to 3A. The

charger will continuously pump this 3A until the battery current falls below the limit of 500 mA. This will bring the voltage of the battery above the reference point, therefore causing the comparator to turn on the transistor switch, pulling the output voltage to the float charging level.

32

Vreg

U1LM350

IN OUT

R110ohm

R2220ohm

R32.3kohm

R4251kohm

R5

1kohmR61kohm

R7

0.1ohm

D1

Schotkey

D2

5.1 V 1

2

3

5

4

U2

LM741

Q1

Vin

To Charge Indicator

Battery+

-

Figure 14: Complete Charging Circuit Module

The circuit is not very tolerant to resistor changes, therefore low tolerance ±1% resistors would probably preferable.

5.1.5.2 Simulation The simulation was slowly built up piece by piece to ensure proper simulation of the complete circuit, as well as catch any simulation problems that might be encountered. Step 1: Testing Voltage Regulation

Our circuit will include an LM350, 3-Amp, adjustable voltage regulator, but since the model for this regulator was not available in Multisim, a comparable adjustable regulator was used for simulation purposes.

33

Vreg

U1LM117HVKSTL/883

IN OUTR1223.3ohm

R22492ohm

V125V

Figure 15: Regulator configuration for Charging Circuit Module

The input to the regulator was chosen to be at least two volts higher above the set output voltage. In Figure 9., the resistor values were chosen so that the voltage regulator is configured to the output 14.5V DC for testing purposes only. An interesting note, the simulator applies a 1.3V potential between the adjustment and the output pins. This somewhat varies from the specification of the LM350, which tries to maintain 1.25V across the same pins. Using the simulator’s voltage across R1, the voltage was calculated to be 14.5V:

Vout = 1.3V + (1.3V/R1)*R2 This was confirmed by the simulation. Step 2: Varying Vout through a Single “Switch” Controlling the output voltage to the battery is an essential part of multi stage charging circuitry.

34

Vreg

U1LM117HVKSTL/883

IN OUT

R21690ohm

V117.2V

R31000ohm

R4

4555ohm Q12N3393

R110ohm

R5240ohm

V20V 5V 1msec 0msec

Figure 16: Vout Switching for Charging Circuit Module

Adding a transistor will act as a switch to ground, and therefore vary the

equivalent resistance of R3 which will provide control over the voltage regulator. When the “switch” is turned on, R4 is connected to ground, putting it in parallel with R3. This lowers the equivalent resistance of both resistors, and therefore lowers the voltage across both of them. Since the voltage is lower, the total output voltage is brought down the same amount. The voltage on the first stage needed to be 14.7V or 2.45 V/Cell and during the float state, 13.8V or 2.3V/Cell.

The current through R1, R5 and R2 is

1.25V/250Ohms=.005 A

The output voltages were calculated to be:

Transistor State R3||R4 VR3 Vout OFF 1000 5.0 14.7 ON 820 4.1 13.8

Table 9: Voltage Regulator configuration resistors

Simulating the circuit, the output voltage was measured to be 14.2V when the transistor was completely on, and 15.1V when it was completely off. This .4V difference is due to the fact that the potential difference between the adjusting terminal and the output pin is 1.3 rather 1.25; therefore producing a larger current, which increasing the output voltage. Another possible source of discrepancy could be the voltage drop across

35

the transistor, which does not completely pull the resistor to ground when it is on, and also has leakage currents.

Step 3: Reference Controlled Switch Providing automatic switching based on voltage level was implemented using a comparator. The logical state change happens when the battery reaches a certain potential below the full charging voltage.

Vreg

U1LM117HVKSTL/883

IN OUT

R21690ohm

V117.2V

R31000ohm

R4

4555.5ohm Q12N3393

R110ohm

R5240ohm

3

2

4

7

6

U2

LM307N

V212V

Figure 17: Reference Controlled Switch for Charging Circuit Module

The current through R1 and R5 was calculated to be 5 mA. Breaking the 250Ohm

resistor into 240Ohm resistor in series with a 10Ohm, provides a 50mV reference below the output voltage. This reference is used as the negative input for the comparator, and the battery voltage as the positive input. Whenever the battery charge is greater than the reference point, the comparator turns on the transistor, and therefore lowers the output voltage to the float charger state.

This phenomenon was observed as predicted in the simulations. Step 4: Providing Feedback through the Current Sensing Resistor This final step was to build the complete circuit. It proved to be a challenging task. Even though logically the circuit seemed to make sense and did not vary significantly from the previous one, we were unable to get the expected output. After numerous hours of trying to appease the simulator, we came to the conclusion that our analysis is probably correct and that the feedback loop through the current sensing

36

resistor R6, added enough complexity to the circuit that the simulator did not provide us with an accurate answer.

Vreg

U1LM117HVKSTL/883

IN OUT

R21690ohm

V117.2V

R31000ohm

R4

4555.5ohm Q12N3393

R110ohm

R5240ohm

3

2

4

7

6

U2

LM307N

V212V

R6_10W

0.1ohm

R7

1kohm

Figure 18: Reference Controlled Switch for Charging Circuit Module with added feedback loop

5.1.6 Battery Indicator We came up with a very simple design for a voltage monitor. Figure 18 depicts a

quad-voltage comparator (LM324) that used to control a simple bar graph meter to indicate the charge condition of the 12-volt lead acid battery. A 5.4-volt reference voltage (D1) is connected to each of the non-inverting inputs of the four comparators and the inverting inputs are connected to successive points along a voltage divider. The LEDs illuminate as the voltage at the inverting terminals exceeds the reference voltage. LED 1 turns on at 11 volts, LED 2 turns on at 13 volts, LED 3 turns on at 14 volts, and LED 4 turns on at 14.3 volts.

37

1

23

U1

1

23

U2

1

23

U3

1

23

U4

D15.4 V

R12kohm

R210kohm

R31.5kohm

R4570ohm

R5160ohm

R67.5kohm

R7

1kohm

R8

1kohm

R9

1kohm

R10

1kohm

LED1

LED2

LED3

LED4

LM324

To Charging Circuit

Figure 19: Charging Circuit Module

38

6 Prototype Results/Final Design Consisting of only a transformer, 6800uF capacitors, bridge rectifier, voltage

regulator and an op-amp, the final implementation came out to be very simple and functional. The final schematic can be found in the Appendix.

6.1 Module Status

6.1.1 AC/DC Conversion

AC/DC ConversionFunctionality Converts AC input into DC Implementation Rectified Dual-prime transformer (115/230 V AC) signal

And External AC/DC Conversion Input 110 or 220 VAC Output 16Vrms DC @ 3A+ Status Built and Implemented

Table 10: AC/DC Module Status

Our AC/DC conversion module worked as expected. It outputs the correct

voltage, and can handle the load simulating a dead battery. We have 2 different options for future implementation, one is an external AC/DC converter design which includes a transformer, bridge rectifier and filter capacitor, the second option is an external AC/DC adapter.

6.1.2 Current Surge Protection

Surge ProtectionFunctionality Provide surge protection from voltage and current spikes on the

AC input line Implementation Re-settable Circuit Breakers Input Unstable AC from outlet 115/230 VAC Output AC signal, without excessive voltage or current spikes Status Built but not Implemented

Table 11: Current Surge Protection Module Status

This module has not been fully implemented into our design yet, because of time

issues. We are confident that if we did implement it, it would work as expected.

39

6.1.3 Charging Circuit

Charging Control Circuit, Overcharge ProtectionFunctionality Provides control of the charger, and implements the three stage

charging algorithm Implementation Voltage regulation with feedback Input 17V-36V DC Output 14.7V, 13.8V (Stage dependent) Status Built and Implemented

Table 12: Charging Circuit Module Status

The charging circuit module works completely as expected, but there is an

inherent design problem. Since the charger is built around a linear regulator, heat dissipation creates a major problem if not addressed properly, especially in warm climates such as Mali’s.

6.1.4 Battery Indicator

Battery IndicatorFunctionality Indicate battery charging level Implementation 5 LED Array (square LEDs) Input Voltage of the battery (10.5V-14V) Output Number of LEDs turned on proportional to the battery charge

level Status Built and Implemented but needs improvement

Table 13: Battery Indicator Module Status

The battery indicator module works independently and indicates the status of the

battery while it’s not charging. Since the battery voltage level during charge does not correspond to the actual voltage of the battery, as we found out during testing, the indicator would not accurately represent the actual charge of the battery. The indicator would need to be modified to indicate the actual status of the battery.

40

7 Testing

7.1 AC/DC Conversion

We tested our AC/DC converter with an oscilloscope in three stages. The first stage was the transformer connected to a load. We measured the output and confirmed that it would meet our voltage requirement. The second stage was the transformer hooked up to the rectifier and to a load. We verified the inversion of the negative cycle of the ac input. The third stage was the transformer with the rectifier and filter capacitor. In this stage we measured the ripple voltage to make sure it met our voltage requirements.

7.2 Charging Circuit

We used several methods to test the charging circuit, using different kinds of loads to simulate a battery. The first method we tried was to use several high power 10 ohm resistors. The second method was a variable resistor which ranged between 0-110 ohms. From these tests we verified the operation of our charger. After using these simulated loads we tested the circuit on an actual battery, and verified the charging algorithm.

7.3 Battery Indicator We used a power supply set to various voltages to test the turning on and off of the

LED’s.

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8 Final Prototype Summary and Functionality We were able to build a working prototype that satisfied all or most of the customer

requirements.

8.1 Strengths

• Charging Circuit o Successful 3 stage charging o Reasonable charging time

~80% of dead battery in 10 hours (wall outlet) o Overcharge protection o Works with 110/220 VAC and DC pedal generator

• Fault protection o Output can be shorted without causing damage to the circuit

• Will not discharge battery • Simple design

o Easy to repair • Will not be heavier than 3 pounds with metal casing • Detachable AC cord for replacement for both 110 and 220 AC plugs

8.2 Weaknesses • Heat Dissipation

o Hot to the touch o Lower lifespan of components o In hotter temperatures (Mali) this becomes more of a problem

• Lack of voltage spike protection • Solar panel input not tested • Charge indicator does not work with charging circuit

8.3 Suggestion for Improvement • Larger heatsinks to dissipate the heat • Include metal casing to improve heat dissipation • Modify design to incorporate switching regulator • Redesign indicator to work with charging circuit. • Indicate the “Bulk” or “Float” charge state to represent the charge state of the

battery • Include power zeners to clamp the input voltage to protect the voltage regulator

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9 Economic Analysis

During various stages of our project we have needed to consider the economic aspects of our design. From the first product specification stage where we set the precedent of a low product cost as a critical requirement, to the various design cuts and revisions based on part pricing, we have kept the cost in serious consideration.

9.1 Unit Cost Analysis

To determine the price of our product we had to come up with a unit cost for our design. This unit cost was based on several factors such as…

• the cost of parts • distribution • manufacturing • assembly

We looked up all the parts that we used in our design and found the bulk price for a target sale of 1000 units. We determined 1000 units as the yearly sales number because of the approximate 800 units that World Education will buy and the projected 16,000 other customers worldwide. This information was given to us by Design that Matters and we used it for the base of our economic analysis.

Part Number Distributer Distributer’s Part

Number1 500/1000 Quantity Unit Cost Mass Producton

LM741 Mouser UA741CD $0.3000 $0.2100 1 $0.3000 $0.2100

LM350K Mouser 511-LM350K $5.7000 $4.8500 1 $5.7000 $4.85002N3904 Mouser 625-2N3904 $0.0500 $0.0360 1 $0.0500 $0.0360

Zener 5.1V Mouser 78-1N5231B $0.0400 $0.0140 2 $0.0800 $0.0280

.1 Ohm Res Digikey 20JR10-ND $1.9600 $1.0800 1 $1.9600 $1.0800

5A Diode Digikey SB520CT-ND $0.3900 $0.2200 1 $0.3900 $0.2200

Transformer Jameco 104408 $12.9500 $10.4900 1 $12.9500 $10.4900

6800 uF Jameco 115431 $3.4900 $2.8900 2 $6.9800 $5.7800

Full Bridge Mouser 583-BR61 $0.8000 $0.4700 1 $0.8000 $0.4700

2.2 C/W Heatsink Digikey HS265-ND $2.4800 $1.3860 1 $2.4800 $1.38601/4 Resistors Mouser N/A $0.0700 $0.0050 14 $0.9800 $0.0700

Case Digikey HM612-ND $6.6600 $4.1600 1 $6.6600 $4.1600

AC Cord Digikey Q100-ND $1.5800 $0.9700 1 $1.5800 $0.9700 Table 14: Parts list with Bulk Prices

For distribution we used a UPS Shipping calculator to find the price for bulk shipping

using estimated weight of a single unit times the bulk number. We assumed that many of the parts. Because the maximum allowable weight per package is 70kg ,roughly 154.3 pounds, our bulk rate is 85 units per package. This calculation gave us a shipping cost of around $29.75 per unit. This shipping number seems extremely high, so we assumed that

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with complete bulk shipping of 1000, and cheaper distribution alternatives such as freight shipping, our estimated distribution cost would be around $10.

We decided that for the final product, we would recommend PCB layout for the board. This solution is ideal because it provides a cheap and easy assembly process for this product. With a PCB board, the entire unit can be assembled locally at a much cheaper cost. Searching online at http://www.pcbpro.com we found a quote for $2.62 a board for 1000 5x3 in. boards after 5 weeks.

We assumed that all the product assembly would be done in Mali by the local electronic component shops. For this we assumed an hourly wage of $5 and estimating about an hour to assemble.

Parts $29.75Manufactur $3.00Distribution $10.00Assembly $5.00Unit Cost $47.75

Table 15: Unit Cost Calculation

9.2 Price Suggestion I would suggest a price of $50 based on the price requirement that DtM estimated for

our project. This price of $50 is very close to the estimated per-unit cost, so the profit margin will be very close. If DtM averages a yearly sale of 1000 units, it will get $2250 annual revenue.

9.3 Economic Feasibility One of our greatest concerns in this project is the feasibility of mass producing this

product. Our sponsor, Design that Matters, determined that a cost of $50 would be reasonable for our target market, Mali West Africa. Throughout our product design development we have felt pressured to keep our solutions within the price range. This has been hard considering the cost of our components. Since our estimated per-unit cost is so close to the suggested price, we believe that this is not a feasible price for sale. If DtM gave a wider price range for this product, it would be much easier to justify.

10 Conclusions

We were able to accomplish our main goal, and that is design a working prototype for a 12V lead-acid battery. In this project we have learned more then just how to make a simple universal battery charger and drawing upon our EE knowledge from our previous classes. We experienced our first taste of design and major project management. Along with these

44

specific skills, we also improved our time management and team work skills. Through our design project we experience many success and failures in the process, and have had to make a lot of important design decisions. With more time we could have taken our rough design and brought it to usable standalone charger.

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11 Appendix A

Figure 20: Initial General Project Management Chart

46

12 Appendix B

Figure 21: Initial Module Specific Project Management Chart

47

13 Appendix C

Figure 22: End Term Project Management Chart

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14 Appendix D

Vreg

U1LM350

IN OUT

R110ohm

R3220ohm

R22.3kohm

R5251kohm

R4

1kohmR71kohm

R6

0.1ohm

D1

Schotkey

D3

5.1 V 1

2

3

5

4

U3

LM741

Q1

Battery+

-1

23

U2

1

23

U4

1

23

U5

1

23

U6

D25.4 V

R82kohm

R910kohm

R101.5kohm

R11570ohm

R12160ohm

R137.5kohm

R14

1kohm

R15

1kohm

R16

1kohm

R17

1kohm

LED1

LED2

LED4

LED3

Bus

T1

16 VCT @ 3.5 A

1

2

4

3

D4

C1

6800uF

C2

6800uF

Switch

Solar Panel / Pedal Generator Input

110/220 VAC Input

Figure 23: Complete Circuit Schematic

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15 Appendix E QQ UU OO TT AA TT II OO NN DTS180330UC-P5P-ET

Design That Matters Attn: Jonathan Mulla November 26, 2003 e-mail: jonmulla@wpi.edu Description: Switching Desktop power supply, 90~264VAC/47~63Hz Universal input. 18VDC@ 3.3A output, with a 6-foot output cord terminating to a 2.1mm x 5.5 mm x 9.5mm center positive DC power plug. Includes AC Power Cord. This unit is UL/cUL/TUV/CE/CB/FCC/BSMI/EK/PSE/NORDIC Approved. Part Number: DTS180330UC-P5P-ET Quantity: 1K pcs Price: $18.25/unit (Minimum Order Quantity) Quantity: 2K pcs Price: $17.87/unit First Delivery: 10~12 weeks via Sea freight, ARO/ or approval of credit. Delivery time may be reduced to 5~6 weeks by Air freight at an additional cost. Standard Terms: 1. Terms: 1%/10 days, Net 30 days on approved credit. 2. FOB: Beaverton, Oregon. 3. Customer’s PO must acknowledge that Orders are non-cancelable and non-returnable. 4. This quotation is in USD, and is valid for 60 days from date of issue unless withdrawn prior to

acceptance. 5. CUI Inc. requires customer approval of a sample unit prior to acceptance of a production order. If you have any questions or comments, call me at any time. Thank you for your interest in CUI products. Sincerely, Heather J. Roley NE Regional Sales Manager

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16 References RV owners’ forum:

http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/683429/gotomsg/683780.cfm

Boaters World:

www.boatersworld.com

Battery Stuff.com: http://www.4unique.com/battery/soneil/soneil-12v2-5a.htm

Battery Mart:

http://www.batterymart.com/battery.mv?p=ACC-12103 Battery Minder:

http://www.vdcelectronics.com/images/Charger%20with%20brain%20saves.pdf

PCB Pro.com: http://www.pcbpro.com

Powerstream.com:

http://www.powerstream.com/PV-Control.htm