Wattmeter Project Presentation
David Box, Ali Alsuliman, Buck Fife, Matthew Kent, Dylan Brams
Introduction
Presentation Organization:
1.
2.
3.
4.
Introduction
Need, Motivation, Objective, and Alternatives
Requirements and Approach
Design
a) Sensing
b) Power Provision and Enclosure
c) Microcontroller
5. Team Description
6. Conclusion
Problem and Motivation
Reporting Power Consumption
• Monitoring power consumption not currently in broad use.
• Residential consumption tends to be ‘unconscious.’
• Industry moving towards more flexible pricing based on time
of consumption
– Price of electricity, as with power in general, is rising quickly.
• Some appliances have surprisingly high passive power
consumption
Alternatives
There are many existing solutions
• Expensive
• Not consumer-friendly
• Technically packaged
DIY community also active
• Few using circuit boards
• Few go to extreme of surface-mounted hall effect sensors
• All pre-designed circuits found did not export data or have
much flexibility.
Approach
1. Team not strongly divided
–
–
–
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Members self-assigned tasks
Tasks completed with assistance as needed, either by assigned
member or remainder of team
Fluid organizational system
Tasks often completed as a group, with communication between
multiple members to make decisions
2. Relied on class structure
–
Project deadlines used to organize team deadlines
Project
Schedule
Overview
Project
Schedule
Primary Requirements
1.
2.
Able to plug in a standard appliance or device
Read a number representing consumption from an output
LCD and / or USB
3.
Safe :
•
•
•
•
•
Physical barriers around High Voltage Circuit
Always plugged into a GFI strip if not GFI itself
High Resistance Voltage Divider as input for voltage
Fuses
Xener Diodes
Requirements
•
•
•
•
•
•
Indoor use
Compute and Display as a function of Watt
Small enough to transport easily
Two PCB’s that would fit into divisible enclosures
Cheap
At least one working prototype in 8 weeks
Requirements
• Circuit powered:
– Step down 120v to 5V through transformer and bridge rectifier from wall outlet.
– Using power outlet
• Sense Voltage with a voltage divider
• Sensing current
– Current sensor “ACS712”
– Output proportional to AC or DC current
• Microcontroller
– Atmel
Top Level Circuit Block Diagram
AC120V
Voltage Converter
+5V
+5V
Current Sensor
Current Value
Microcontroller Board
LCD Display
USB Board
User
Computer
Sensing Subsystems
Power Calculations
The wattmeter calculates power consumption based on peak to peak
current measurements and nominal voltage values.
Cos(pf)
Measured
Real Power (watts)
Assumes Voltage and
Current are in Phase
Assumes a
sinusoidal waveform
Nominal ignores
 5% variance
Power calculations based on current measurements alone disregards the complex
power component of inductive loads (fans, motors, etc…). Assuming a sinusoidal
current ignores the efficiency of switching power supplies.
Resistive Load
Out of Phase Load
Switching Load
Sensing Subsystems
Current Sensor
Central unit: Hall Effect Sensor
When a current-carrying conductor is
placed into a magnetic field, a voltage
will be generated perpendicular to
both the current and the field.
•
1.2 mOhm internal conductor
resistance
•
2.1 kVRMS minimum isolation
voltage from pins 1-4 to pins 5-8
•
5.0 V, single supply operation
•
66 mV/A output sensitivity,
supported with lab testing of each
component
•
Output offset voltage centered
about the supply voltage
•
Surface Mount Package
A perfect fit!!!
A Sparkfun breakboard allowed for
preconstruction testing and proof of
concept.
Sensing Subsystems
Current Sensor, continued
Capacitors provide power supply noise
rejection and filter sensor noise.
A surface mount component designed
to support up to 15 Amps of current
requires special PCB layout
considerations. Big pads, lots of small
vias.
Lesson Learned:
Small Package +
Large Current =
Potential Disaster
Initial Power Supply Schematic:
Power Supply Circuit
The Power Supply circuit was
added to increase the level of
project complexity and to
allow for an enclosed power
supply.
Design:
• Met with Craig Stewart and
discussed initial design
• Designed to supply enough
power for LCD, uC board
and sensing circuit
•
~ 300mA
• Basic Stages:
• Transform
• Rectify
• Smooth
• Regulate
Power Supply Circuit Testing
Two problems accounted for the
majority of problems:
Problem 1
• The Power Supply would supply 4.98V when
disconnected from the microcontroller but
would dip to 4.6V when the LCD and board
were connected.
Explanation:
• The capacitance of the smoothing section
of the power supply was too low. More
capacitance was needed to smooth the
input to the voltage regulator
Solution:
• A 1000uF electrolytic capacitor was added
in parallel before the rectifier and the
supply successfully powered the board.
• Note: The filtering capacitor was left off the
regulator to remove variables in testing. It
was not needed due to the large
capacitance on the uC board.
Problem 2
• The Power Supply when properly
mounted and connected to the outlet
produced no voltage.
Explanation:
• The board and the mounts of the
transformer were shorting to the box
through the mounting screws
Solution:
• A plastic sheet was added underneath to
isolate the board
• The Transformer mounts were removed
to prevent any connection
Fusing
High Side Fusing:
• Fusing was added to prevent damage to
the device under test and power board
•
•
•
Added in series to the hot of the wall and
the in to the current sensor
Inline package was used to save space on
board
10A, 1¼” x 1/4“, fast-acting , fuse used as
specified in the project requirements
Low Side Fusing:
• Added to prevent damage to the uC board
and LCD
•
Added in series with the positive low side
of the transformer and rectifier
•
Mounted to power board
•
0.5A, 5mm x 20mm, fast-acting, fuse used
to limit current
Final Power Supply Schematic
Enclosure
Steel Boxes:
• Rugged
• Cheap
• Connectable
• Readily Accessible
Faceplates:
• Offset to house transformer
• Plastic microcontroller cover plate
• Cut on the laser cutter
• Mountable for the LCD, Pot
and Switch
Wiring:
• All wires used were greater than
16AWG to meet 10A requirements
• Wire nuts were used to make
proper connections
Green = Ground
Black = Hot
Gray = Neutral
Enclosure Connections
Device Under Test
Enclosure Faceplate
Wall Outlet
Power and Sensing Enclosure
Fuse
Microcontroller
Subsystem
Firmware
LCD Display Controller
USB Controller
Contributions / Team Division
Dave Box
• Microcontroller board design & layout, firmware programming, USB / LCD
daughter board part selection, prototype assembly, part purchasing
Ali Alsuliman
• Power supply design, prototype assembly / test, part purchasing, enclosure design
Buck Fife
• Current sensor board design, documentation, prototype construction, power /
current sensor board layout
Dylan Brams
• Wiki / repository setup, documentation, prototype construction, board / parts
ordering, TA review organization
Matthew Kent
• Power supply design, enclosure design / construction / purchasing
Lessons Learned
Post Mortem Meeting
References
Energy Consumption
•
http://www.energysavers.gov/your_home/appliances/index.cfm/mytopic=10040; Energy consumption of
common appliances
•
http://www.keysenergy.com/appliances.php;Monthly energy consumption of household appliances
Current Sensing
•
http://en.wikipedia.org/wiki/Power_factor;Waveform images
•
http://content.honeywell.com/sensing/prodinfo/solidstate/technical/chapter2.pdf; Background for hall effect
sensors
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http://www.allegromicro.com/Products/Current-Sensor-ICs/Zero-To-Fifty-Amp-Integrated-Conductor-SensorICs/ACS712.aspx; Current Sensor Information
•
http://www.sparkfun.com/products/8882; Current Sensor Breakout Board used for prototyping.
•
http://www.te.com/catalog/bin/TE.Menu?M=MENU&ID=10785&LG=1&I=13; Terminal Block Manufacturer
Website
Power Supply
•
http://www.ehow.com/how_4840923_wire-step-down-transformer.html; Basic Tutorial On wiring a stepdown transformers
•
http://www.eleinmec.com/article.asp?16; Tutorial on building a 5VDC power supply
•
http://www.te.com/catalog/menu/en/17718?BML=10576,17533; List of cable connectors researched
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http://search.digikey.com/us/en/products/64600001003/WK6244-ND/151822; Fuse holder at Digikey
•
http://power-topics.blogspot.com/2011/02/inrush-currents-external-fusing-on.html; Article on Highside
fusing
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http://www.tpub.com/neets/book3/8e.htm; Identification of fuses
People
• Craig Stewart, Electrical Engineer, The Boeing Company - Consulted with to construct the power supply circuit
• Kevin Ting, Electrical Engineering Student, University of Washington - Matt’s lab partner and cowriter of LCD
source code posted on the wiki but unused in the project
• Chris Clark, Computer Engineering Student, Portland State University - Cut the microcontroller cover plates on
the school laser cutter
References
Microcontroller
•
http://www.avrfreaks.net/ - tutotials on ADC conversions, and LCD connections
•
http://www.evilmadscientist.com/article.php/avrserial Source of knowledge on USB communication
and USB source code.
•
http://jump.to/fleury Source of LCD library code
•
ATMEL Atmega datasheet for the ATmega328P
Tools
Software
•
Easily Applicable Graphical Layout Editor (EAGLE) Version 5.11.0 for windows.
•
Ltspice IV Version 4.04q
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Microsoft Office Software Suite
•
Redmine Wiki Site
•
Subversion Document Revision Control and Repository
•
Autocad
Lab Equipment
•
Tektronix MSO 4054 Mixed Signal Oscilloscope
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Tektronix AFG 3252, Dual Channel Arbitrary Function Generator
•
Gwinstek GPS-3303, Laboratory DC-Power Supply
Hardware
•
Soldering tools provided in the PSU ECE Capstone Lab
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Drill Press in the ECE Capstone Lab
•
PSU Laser Cutting Device