Wattmeter Project Presentation

1. Wattmeter Project Presentation David Box, Ali Alsuliman, Buck Fife, Matthew Kent, Dylan Brams

2. Introduction Presentation Organization: • Introduction • Need, Motivation, Objective, and Alternatives • Requirements and Approach • Design • Sensing • Power Provision and Enclosure • Microcontroller • Team Description • Conclusion

3. 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

4. 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.

5. Approach • Team not strongly divided • 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 • Relied on class structure • Project deadlines used to organize team deadlines

6. ProjectScheduleOverview

7. ProjectSchedule

8. Primary Requirements • 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

9. 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

10. 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

11. Top Level Circuit Block Diagram AC120V +5V Voltage Converter Current Sensor Current Value +5V Microcontroller Board LCD Display USB Board User Computer

12. Sensing Subsystems Apparent Power (VA) Cos(pf) Power Calculations The wattmeter calculates power consumption based on peak to peak current measurements and nominal voltage values. Real Power (watts) Measured 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. Out of Phase Load Switching Load Resistive Load Assumes Voltage and Current are in Phase Nominal ignores  5% variance Assumes a sinusoidal waveform

13. 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 Sparkfunbreakboard allowed for preconstruction testing and proof of concept.

14. 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

15. Power Supply Circuit Initial Power Supply Schematic: 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

16. Power Supply Circuit TestingTwo problems accounted for the majority of problems: 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 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.

17. 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

18. Final Power Supply Schematic

19. 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

20. Enclosure Connections Green = Ground Black = Hot Gray = Neutral

21. Microcontroller Subsystem Firmware LCD Display Controller USB Controller

22. 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

23. Lessons Learned Post Mortem Meeting

24. 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 http://www.allegromicro.com/Products/Current-Sensor-ICs/Zero-To-Fifty-Amp-Integrated-Conductor-Sensor-ICs/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 step-down 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 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 Highsidefusing 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

25. 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

26. Tools Software Easily Applicable Graphical Layout Editor (EAGLE) Version 5.11.0 for windows. Ltspice IV Version 4.04q Microsoft Office Software Suite Redmine Wiki Site Subversion Document Revision Control and Repository Autocad Lab Equipment Tektronix MSO 4054 Mixed Signal Oscilloscope 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 Drill Press in the ECE Capstone Lab PSU Laser Cutting Device