A Loss Mitigation System to Prevent Residential Electrical Fires Caused by High Resistance Connections

1. A Loss Mitigation System to Prevent Residential Electrical Fires Caused by High Resistance Connections Senior Design Lab Fall 2007 Project Team # 8 Aditya Mehta George Nellikunnel Balakumar Sampath

2. Overview • Purpose of Project • Objectives and Required Parameters • Design and Fabrication Stages • a.) Macroscopic view of design • b.) Voltage measurement circuit • c.) Programming of PIC & Wireless Xbee unit • d.) Determining the voltage threshold • e.) Activated Alarm with LED & Relay shutoff • 4. Overall success/challenges • 5. Summary and Future Development • 6. Questions

3. Purpose • Certain household fires are caused by faulty wiring that may have oxidized or worn down due to time and other natural causes • This project aims to detect eminent threats of fire in the home by detecting voltage changes in any one branch of the electrical wiring to an outlet

4. Objectives • Detect voltages at the source and load with 0.1 V Resolution • Drop the voltages proportionally to a window of 0 VDC – 9.9 VDC from a 120 VAC line • Calculate the voltage differences (if any) • Determine if the voltage threshold is reached and if so, trigger the LED and terminate the current going to the load via a relay unit

5. Design and Fabrication • This project has two primary modules: Source Module Load Module • The circuitry is the same for both devices with the exception of additional pieces for the Load module that are used to execute logic

6. Hot Supply Module Load Module Neutral Macroscopic view of Project

7. Supply Module Wireless Transmitter Module From Mains Voltage Divider / Rectifier Analog to Digital Converter PIC Load Module From High Resistance Circuit Wireless Transceiver Module Voltage Divider / Rectifier Analog to Digital Converter PIC LED Relay Unit To home appliance

8. Voltage Measurement Circuit

9. Voltage Waveform Simulations 120 V Input (Output 5.33 V)

10. 115 V Input (Output 5.10 V)

11. 97 V Input (Output 4.25 V)

12. Actual Voltage Measurements 120.5 V Input (Output 6.90 V)

13. 100 V Input (Output 5.60 V)

14. 96.96 V Input (Output 5.40 V)

15. AC Input .vs. DC Output The DC output changes linearly with change in the AC input with an error of approximately 1%.

16. ADC, PIC and Transmission

17. ADC, PIC and Reception

18. Programming the PIC #include <16F877.h> #use delay (clock=2000000) – sets clock speed for delay #use rs232 (baud=9600, xmit=PIN_C6, rcv=PIN_C7) – sets up USART for transmission and reception

19. Transmission Code output_low(PIN_A1); // set ADC R/C pin to 0 delay_ms(WAITMS); // wait for 500ms output_high(PIN_A1); // set ADC R/C pin to 1 ADC_voltage[UPPER] = input_b(); // get the voltage value ADC_voltage[LOWER] = input_d(); // from the ADC delay_ms(WAITMS); // wait for 500ms for (j = 0; j < NUMVOLTAGES; j++) { putc(ADC_voltage[j]); // transmit the voltages delay_ms(SHORTDELAY); // over a 10ms delay }

20. Reception Code for(j = 0; j < NUMVOLTAGES; j++) { while (!kbhit()) {} // wait for data supply_voltage[j] = (int8)getc(); // read from UART } voltage_difference = (supply_voltage // calculate voltage diff. - calibration_voltage) - ADC_voltage; if (voltage_difference < 128) { // non-negative difference if (voltage_difference >= 4600) { // corresponds to 22V output_high(PIN_C3); // red LED on output_low(PIN_C2); // yellow LED off output_high(PIN_C4); // break circuit break; // exit infinite loop } else if (voltage_difference >= 3400) { // corresponds to 16V output_low(PIN_C3); // red LED off output_high(PIN_C2); // YELLOW LED on output_low(PIN_C4); } else { output_low(PIN_C3); // red LED off output_low(PIN_C2); // yellow LED off output_low(PIN_C4); } }

21. Voltage Threshold • Households incorporate 20 amp breakers that utilize 12 gauge wiring • 12 Gauge wiring can withstand a temp. rating of (480-600 degrees Fahrenheit) • Consider 0.5 lbs wire of length 25.30 ft. with safety factors at minimum temp. rating and 15 amps current drawing from any one outlet

22. Calculations • Q = mc( Initial Temp – Final Temp) • Q = 0.5 lbs(.094)(480-75) = 19.035 BTU • Power = Q / (56.89 BTU/1 kW*min) = .3346 kW • P = IV; (I = 15 amps) • Voltage drop = 334.6 W/15 Amps = 22.31 V • Therefore the voltage threshold is: 120-22.31 Voltage Threshold:97.69 V

23. Alarm LED and Relay Shutoff RELAY UNIT Appliance AC Hot Wire AC Neutral Wire LED TTL Logic +5V Load Module

24. Success/Challenges • Success: -Measuring the voltage with specified resolution -Digitizing the signal within a 10 V window -Rectification of the AC signal to DC -Programming the PIC to accept UART signals

25. Challenges: -Getting the wireless modules to talk to each other

26. Summary • Future Development To incorporate a triple output power supply to the circuit (to power components) on a PCB.

27. Summary • Future Development To make the transmission wireless XBee transceiver can be preprogrammed using the RS232 development board and X-CTU software

28. Summary • Future Development To implement multiple load modules to interface with one source (broadcast mode) Load 1 Source Load 2 Load 3

29. Thank You Special Thanks To: State Farm Insurance Co. Prof. Scott Carney Prof. Philip Krein T.A Wayne Weaver