WEATHERIZED COATS

1. WEATHERIZED COATS ADAM ARIFFIN ALVARO GUTIERREZ NIJA JOSHI

2. INRODUCTION MOTIVATION: Winters can get cold and there is nothing better than having a warmer jacket. Something that will save us from having to layer up and feel like a stuffed bear. And hence the invention of our heated jackets.

3. OBJECTIVE • We wanted to build something that will be able to detect changes in the temperature levels and keep the jacket temperature constant at all times. • We also wanted to make sure that we take into account the fact that relative humidity can effect the perception of “heat”.

4. Background Info • Heat is a relative concept • The following effect our perception of heat comfort: • Air temperature • Air speed • Humidity • Mean radiant temperature • Activity Level • Clothing insulation

5. Background Info Comfort Index: • This model uses the idea that relative humidity combined with heat makes you feel a different temperature. • The problem here was that we were dealing with cold and not heat and so we had to update the idea.

6. DESIGN ALTERNATIVES (1) • Alternatives to the Thermion heat pads (flexibility is a requisite): • Wire heating elements • Fluid pipe heating sleeves • Alternatives to direct heating elements: • Blown hot air (same principle as a hairdryer) • Peltier device (Peltier-Seebeck effect, conversion of heat differentials to voltage, and vice versa)

7. DESIGN ALTERNATIVES (2) • Multiple heating loops • A heating loop is an arrangement of heaters controlled by a single ambient temperature sensor • Multiple heating loops allow different parts of the jacket’s temperature to be controlled independently. • Drawbacks include increased complexity and difficulty in debugging.

8. COMPARISONS • The MET5 is a $600 heated jacket manufactured by The North Face. • Benefits over the MET5’s system: • Greater heating potential • Heating elements are not woven into fabric, not prone to wear and tear • Automatic temperature regulation • Humidity taken into account • Jacket insert can be used with any jacket

9. ORIGINAL DESIGN

10. THE PROJECT

11. THE JACKET

13. CONTROLLER • Microcontroller of circuit (PIC16F877A) • Takes in user input, temperature and humidity data and controls heaters

15. FLOWCHART

17. HIH-3610 • Used to detect increases in humidity. • One HIH-3610 in coat located under the right arm. • Usual humidity inside coat is around 30%. • With sweat, humidity increases to around 55%

18. MTS-102 • There are a total of five MTS-102 transistors in our circuit. • Four to monitor the temperature of our heaters. • One to record inner coat temperature. • Linear correlation between temperature and VBE. • As temperature increases VBE decreases, and vice-versa.

19. Calibration of MTS-102 • Each MTS-102 output voltage (VBE) varies slightly according to a certain temperature. • Therefore each MTS-102 has to be calibrated individually. • Steps involved: • Placing each MTS-102 on a heat pad. • Placing a temperature probe next to the MTS • Increasing power to the heat pad in increments of 100mW to gradually increase temperature. • Recording the output voltage (VBE) with the corresponding temperature.

20. Temperature vs. VBE

21. THE THERMION HEATERS • We used 4 Thermion nickel plated carbon-fiber heaters. • Each has a 27 W maximum power rating. • Advantages: • Thin as paper, flexible, durable. • Very uniform heat distribution. • Fast ramp-up and cool-down cycles. • Can operate up to 200 F

22. HEAT DISTRIBUTION • The Thermion heaters are attached to the jacket insert with copper tape. • The copper tape is also used to distribute heat. It has a high thermal conductivity coefficient (390W/mK, close to silver at 430W/mK). • A copper tape network connects all four heaters and spans the entire jacket insert. • Insulating tape is used to create a “heat bubble” directly over the heaters, forcing the heat down the copper tape.

23. POWER • Our project can be divided into two loops: • Heating loop – Thermion heaters and switching circuit require high voltage and current • Control loop – PIC and sensor circuit requires ~5V at low current • These loops are powered separately to: • Protect the control circuit from high currents • Maintain control loop functionality when the heating loop batteries are discharged

24. POWER (HEATERS) • Four Thermion heaters are used in parallel, drawing 2.2A each at 12V. This is ~105W at peak power*! • We chose a high capacity RC helicopter battery with these actual characteristics: 12V, >2.2Ah (more like 3Ah), max current of 15A. • Later: How do we control this power?

25. POWER (CONTROLLER) • A battery pack of four AA cells connected in series is used, generating 6V maximum. • This voltage is stepped down to 5.4V maximum using diodes. The diodes also protect the circuit in case of incorrect battery insertion. • This source is clean and efficient, and lasts through 4-5 main battery cycles.

26. CONTROLLING HEATERS • The heaters are activated by a “logic 1”. • MOSFET switch is used to trigger current flow through the heaters • The voltage from the PIC signal is too low to put the MOSFET into saturation. • We stepped up the voltage using a dual op-amp (single supply). • The op-amp/MOSFET circuit is placed on a compact board, called the “activator circuit”.

28. TESTS • To make sure that our jacket can last for long, we ran battery life tests. • We also ran heating tests, moisture sensitivity tests and for each perfected the design. • I wore the jacket in the rain and hoped that I didn’t get electrocuted. (I trusted our design)

29. SAFETY TEST • We wanted to make the jacket was safe when out in the snow and rain, hence a water-proof jacket. • All the circuits were enclosed in boxes and naked wires were isolated with electrical tape. • We have a circuit breaker in our circuit that cuts when >2.2 A.

30. HEATING TEST • Stood out in the cold with the jacket on and tested the jacket for increase in temperature. • The temperature went up from 70 F to 90 F in about 5 minutes. • Each heating pad was tested to remain within the specified limits (150 F).

31. HUMIDITY TEST • This was a little difficult to simulate because we didn’t want to actually sweat. • So we came up with the innovative method of squirting water on the clothes and seeing how the sensors respond to it.

32. BATTERY LIFE TEST • This was a major concern for us since we wanted to make sure that the person is warm all the time. • We turned the heat on and kept it working till it could supply heat. • Under peak operation, the battery was able to go on for about 1.5 hours.

33. SUCCESSES • Managed to control temperature of each heater by monitoring temperature with MTS-102 transistors. • Detect increase in sweat and shut down heaters accordingly. • Managed to make the system fit into any jacket the user desires. • Fabricated an easy to use user switch.

34. CHALLENGES • Supplying enough heat to the user and still conserve as much power as possible. • Choice of battery • Optimizing circuit power consumption • Distributing the heat in order to avoid heat spots within the inner coat.

35. RECOMMENDATIONS • Have a better heat distribution system. • Add wind speed detection so we can take into account wind chill. • The users should be able to control the heating, something like a thermostat. • Make the system more compact and portable • For future purposes have cooling effects as well.